1998 BASICS OF THE BASIN ABSTRACTS
alphabetized by presenting author
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Abadie, S. W. , A. C. Jeandron and M. A. Poirrier. Department of Biological Sciences, University of New Orleans, Lakefront, New Orleans, Louisiana 70148:
The Effects of the 1997 Bonnet Carré Spillway Opening on Lake Pontchartrain Benthic Invertebrates
Benthic invertebrates including infaunal species that occur in sediment and epifaunal species that occur on a hard substratum were sampled before, during and after the 1997 Bonnet Carré Spillway opening. Benthic invertebrates are good indicators of the impact of adverse water quality on biological communities because they cannot move when adverse conditions occur. A comparison of the relative abundance of species present before and after the Spillway opening would provide information on any beneficial or adverse effects resulting from the replacement of Lake water with River water and any effects of the blue-green algal blooms. Blue-green algae can produce changes in the food chain because of their toxic properties, and can reduce dissolved oxygen after they die and decompose.
Infaunal invertebrates were sampled from five sites on an east-to-west transect across the middle of Lake Pontchartrain on seven occasions and epifaunal invertebrates were sampled from two sites on the New Orleans Seawall on eleven occasions. Water chemistries were recorded and phytoplankton samples were collected on each sample date.
Dominant infaunal taxa included oligochaetes, the polychaetes Streblospio benedicti and Hobsonia florida, the gastropods Texadina sphinctosoma and Probythinella protera, the pelecypods Congeria leucophaeta and Rangia cuneata and Chironomids. Dominant epifaunal taxa found during this study included nematodes, the bryozoans Victorella pavida and Conopeum sp., the polychaetes Polydora websteri and Neanthes succinea, bivalves Congeria leucophaeta and Ischadium recurvum, the barnacles Balanus subalbadus and B. improvisus, the tanaid Hargeria rapax, amphipods Melita sp. and Corophium lacustre, the mud crab Rhithropanopeus harrisii and Chironomids.
Detailed analysis of all data is still in progress. Based on work currently completed, a benthic invertebrate community composed of brackish-water species persisted during the freshwater conditions and blue-green algal blooms associated with the Spillway opening. Hargeria rapax may be the only organism among the dominant epifaunal taxa that did not occur after the Spillway opening. This agrees with observations from the 1973 and 1975 Spillway openings. Based on preliminary comparisons of the number of taxa and total numbers of individuals, no major impact on infaunal populations are apparent. The number of individuals did decrease at the eastern most infaunal site where the salinity change was greatest.
Abadie, S.W. and M.A. Poirrier, Department of Biological Sciences University of New Orleans, Lakefront, New Orleans, LA 70148:
Increased Abundance of Large rangia Clams as an Indicator of Recovery from 57 Years of Shell Dredging in Lake Pontchartrain
Lake Pontchartrain has been degraded by urban and agricultural runoff, shell dredging, saltwater intrusion, the inflow of Mississippi River water, and industrial discharges. Restoration efforts include the cessation of shell dredging during the summer of 1990 and better management of urban and agricultural runoff.
Rangia cuneata is a relatively large clam that is found in Atlantic and Gulf of Mexico oligohaline estuaries. It is an important component of the food chain serving as a non-selective filter feeder and as a prey item for fish, crabs, and ducks. In Lake Pontchartrain, gamete production starts when clams are two to three years old (23.75mm) and the clams have an average life span of about four to five years. Deposits of its shells in the Lake bottom supported a shell mining industry from 1933 to 1990. Rangia shells were primarily used for construction of roadways, parking lots, levees and in the production of cement.
Large (> 20 mm) Rangia cuneata clams were abundant in Lake Pontchartrain in the early 1950's, but rare in 1970's and 1980's samples. A Lake wide mean density of large clams was reported as 95/m2 by Suttkus and Darnell in the 50's. A study conducted by Tarver and Dugas in the 70's found large clam densities of 44/m2 in Lakes Pontchartrain and Maurepas. In the early 80's Sikora and Sikora found that large clams represented only 0.03% of their total Rangia catch, or < 1 large clam per square meter in Lake Pontchartrain. Poirrier et al. in 1984, studied the effects of outfall canals on the benthic community. They found a mean density of 40/m2 on the south shore of Lake Pontchartrain. Sampling location differences should be considered but it is clear there was a significant decrease in abundance of large Rangia in the open lake. The absence of large clams was attributed to shell dredging. The goal of this study was to determine whether the number of large clams has increased after shell dredging was stopped in 1990.
As part of a study of the current status of benthic invertebrates in Lakes Maurepas, Pontchartrain and Borgne, 56 sites were sampled in 1996 and 1997. At each site three replicate samples were collected with a petite Ponar dredge, washed in a 0.5 mm sieve bucket and fixed in buffered formalin. Clams were measured and put into 5mm increment size classes in the laboratory. Large clams were abundant at all sites except those influenced by the Inner Harbor Navigation Canal (IHNC). This demonstrates that large clams have returned to the mid-lake areas. The termination of shell dredging is the best explanation for the recovery. Large clam densities ranged from 0/ m2 at sites near the IHNC to 722/m 2 in the eastern Lake. The mean density of large Rangia clams in the three lakes was 137/m2 comprising 31% of the total Rangia catch. Previous studies have not reported large clams in the eastern lobe of Lake Pontchartrain or in Lake Borgne but they are present in this study. Large clams are still absent offshore from the IHNC due to low bottom dissolved oxygen from salinity stratification associated with saltwater intrusion. Based on large Rangia distribution, the area affected by saltwater intrusion, is at least 100 square miles and at times may extend 15 miles north of the IHNC.
Baird, Bruce H., U.S. Army Corps of Engineers, New Orleans, LA:
The 1997 Bonnet Carré Spillway Opening: Popular Myth vs. Fact
The Bonnet Carré Spillway is a vital feature of the multi-state Mississippi River and Tributaries (MR&T) system, which uses a variety of measures to provide flood protection to the alluvial Mississippi Valley from Cape Girardeau, Mo., to the mouth of the Mississippi River. The MR&T features include levees and floodwalls to contain flood flows, floodways (such as Bonnet Carré) to redirect high flows out of the Mississippi River, reservoirs, pumping plants, and channel improvement and stabilization features. Bonnet Carré is the southernmost floodway in the MR&T system. Located on the east bank in St. Charles Parish, it can divert a portion of the rivers floodwaters via Lake Pontchartrain into the Gulf of Mexico, thus allowing high water to bypass New Orleans and other nearby river communities. The structure has a design capacity of 250,000 cubic feet per second (cfs), which is conveyed nearly six miles between guide levees to the lake.
A 1927 report of the Chief of Engineers, known as the Jadwin report, determined that a maximum flow of 1.25 million cfs could safely pass New Orleans, and thus the Bonnet Carré Spillway was constructed to divert excess flow from the river. The report stated that the benchmark to trigger the opening of the spillway was when the flood stage at New Orleans was projected to reach 20 feet on the Carrollton Gauge. The benchmark of 20 feet was used as an indicator of river flow. The river reach at New Orleans now holds more water, and thus a given flow corresponds to a lower flood stage. Thus, the benchmark of 20 feet at New Orleans is now obsolete. Therefore, as explained by corps officials in the Times Picayune (March 18 & 20, 1997), the spillways use is based not so much on river stages as on flow.
Heavy rain and snowfall in the Ohio Valley in early 1997 caused rising waters in the Mississippi River, raising the possibility of flooding in southeast Louisiana. The structure was opened from March 17 through April 17, with peak flows of approximately 240,000 cfs. This was the first time the spillway had been opened in 14 years. The Mississippi River flow was greater than 1.25 million cfs when the spillway was opened, and in fact reached 1.48 million cfs on March 26 at Red River Landing.
The 1997 flood was the fifth largest flood this century, and its severity was reflected in several ways; emergency levee raising was required in Baton Rouge and the Marchand-Darrow area, Angola State Penitentiary had to be temporarily evacuated, and some flooding occurred in areas along the Atchafalaya River, such as Stephensville and Morgan City. High velocities caused hazardous conditions for river traffic, and numerous accidents were reported. Opening of the spillway lowered stages in the river both upstream and downstream of the structure.
Before, during, and after the Bonnet Carré Spillway was opened in the spring of 1997, numerous misconceptions about the impacts of the opening have been presented in numerous meetings, news reports, and other venues. Many of these misconceptions concern the ecology of Lake Pontchartrain and the relationship between the Mississippi River and the lake. Some have been repeated often, and have been picked up by the television and print media unchallenged. Some of these misconceptions have apparently been accepted by enough people that they could be considered myths.
Some of these myths are grounded in subjective opinion, and thus can neither be proved nor disproved. Others are presented as statements of fact, and can be directly refuted by scientific data. Myths of this kind are presented and examined in light of published articles and other sources of scientific data. It is hoped that dispensing with such misinformation will lead to a better understanding of the impacts of spillway openings on the lake.
Bart, H.L., Jr., S .L. Taylor and S. Adams. Tulane University Museum of Natural History, Belle Chasse LA and Department of Geology, Tulane University:
Fish Community Composition and Condition under Different Contamination and Flow Regimes in the LaBranche Wetlands
We compared fish community composition and structure, and mean condition coefficients of common fish species, in contaminated and relatively pristine bayous in the LaBranche Wetlands to assess impacts of contamination on the fish community. Bayou Trepagnier, the contaminated bayou, served as a receiving stream for a petrochemical manufacturing complex for 80 years. As a consequence, sediments in the bayou are contaminated with petroleum by-products and heavy metals. In 1995, discharge from the petrochemical complex - which represented a substantial portion of the flow to Bayou Trepagnier - was diverted to the Mississippi River. There were concerns that the diversion would increase the availability of contaminants to the biota. We sampled fishes monthly from fixed stations on Bayou Trepagnier and two relatively pristine neighboring bayous, LaBranche and Traverse. We adjusted catch according to sampling effort and/or used the method of rarefaction to derive estimates of species richness based on a standard sample size. We compared our collection data with that from an earlier fishes survey (Casher et al. 1994), conducted at a time when Bayou Trepagnier was still receiving discharges from the petrochemical complex. Overall fish diversity and abundance in Bayou Trepagnier was comparable to that in neighboring bayous. However, fish diversity and abundance declined significantly along gradients of increasing sediment contamination and decreasing water quality within Bayou Trepagnier. Fish in Bayou Trepagnier were in similar physical condition as fish in cleaner neighboring bayous. Of seven species tested, only two (both sunfishes of genus Lepomis) were in significantly worse physical shape in Bayou Trepagnier than in neighboring bayous. We collected more species in Bayou Trepagnier (32) than were collected in the pre- diversion survey (20), but the difference is partly due to sampling and catch differences between surveys. Most of the fishes collected in the LaBranche Wetlands are adapted to harsh and variable environmental conditions. The life habits of many of the species may limit their exposure to contaminant-laden sediments most of the time.
O'Rourke, Scott Partridge, Charlyn*; Schultz, David*; Mandhare, Keshav; and Beck, James P.O. Box 2022, Department of Physical Sciences and Department of Biological Sciences*, Nicholls State University, Thibodaux, LA 70310. Phone (504) 448-4500, FAX (504) 448-4927, e-mail firstname.lastname@example.org.:
A Survey of Mercury, Copper, Chromium, Lead, and Zinc Concentrations in Soils and Various Species of Fish Taken from Lake Boeuf, Louisiana
Mercury was analyzed in redear sunfish, largemouth bass, bluegill sunfish and black crappie taken from Lake Boeuf in southeastern Louisiana. From each fish, three tissue samples were removed and analyzed by EPA method 7471 using a Coleman (BACHARACH) model 50B mercury analyzer system. Sediment samples were collected using a coring device capable of collecting cores up to 60 inches in length. The cores were sectioned into 2.54 cm lengths, dried, ground a powder, and a 1.0 g sample was digested using microwave digestion techniques ( for Cr, Cu, Pb and Zn). The concentrations were determined using standard atomic absorption spectrometry. Mercury was analyzed using the cold vapor procedure outlined in Standard Methods using a one gram dry sediment sample.
The results to date have shown that the concentrations of mercury in fish vary from 0.001 to 1.15 ppm, with the high values exceeding the LADEQ limits. The concentrations in sediments varied from < 0.03 to 0.08 ppm, with peak concentrations being found at a depth of 20 to 45 cm below the surface. The results for the determination of Cr, Cu, Pb, and Zn in fish tissue have revealed variations from non-detectable to about 2 ppm with little or no variation between the three tissue samples analyzed. Concentrations of these same trace metals in the sediments were found to range from non-detectable to 20 ppm, and showed a decreasing concentration in the first 15 to 20 cm below the surface.
Branch, Bill, Louisiana Cooperative Extension Service, Baton Rouge, Louisiana:
From Point to Nonpoint and Back Again
For many water quality professionals, 1972 was a defining moment. The amendments to the Water Pollution Control Act, usually referred to as the Clean Water Act (CWA), introduced us to the National Pollutant Discharge Elimination System (NPDES). It may even have suggested that we would eliminate waste water discharges in our efforts to achieve "swimmable, fishable" surface waters.
During the past 25 years we have measured, treated, pre-treated and reduced those discharges "from a pipe, ditch or man-made conveyance" into "waters of the state" under a point source discharge permit system. EPA and the state regulatory agencies started work on the large discharges and over the years worked their way down to the smaller ones. A few years ago, DEQ included car washes, laundromats, milking parlors and alligator barns in their general permit system, and last year, they began to add household sewage systems discharging less than 2,500 gallons per day.
Millions of federal tax dollars were consumed in the first half of that quarter century to build municipal sewage treatment plants and to train thousands of sanitary engineers, microbiologists, hydrologists and technicians who conducted research, and developed and implemented waste water treatment technologies. Business and industry and consumers provided funds for similar investments in treating industrial waste water. With the advent of the "no new taxes" era, however, federal grants have been replaced by revolving loan funds and bond issues.
Farmers were brought into the national point source water quality picture for the first time with the 1972 Amendments. Confined Animal Feeding Operations (CAFO) were defined and required point source discharge permits. A separate section required permits of discharges from aquacultural operations. Section 208 referred to diffused nonpoint source discharges which did not require discharge permits and were to be addressed with Best Management Practices (BMPs).
In 1987, EPA told Congress that enough progress had been made on point source discharges that we needed to focus more of our attention on nonpoint sources. The states developed nonpoint water quality inventories and management plans. Agriculture and forestry occupy most of our land and have received most of the attention since nonpoint source pollution results from rainfall runoff from the land. Nonpoint sources were to be addressed with voluntary implementation of BMPs.
The U.S. Department of Agriculture (USDA) has addressed the major nonpoint source pollution, soil erosion, since at least 1935. The Soil Erosion Service was created in response to wind erosion of soil in the "Dust Bowl" days. It later became the Soil Conservation Service and then the Natural Resources Conservation Service. Its Field Office Technical Guide lists conservation practices which are the basis for most of the BMPs recommended for use by farmers and foresters. These practices have reduced the amount of soil eroded off fields each year. Inadvertently, the U.S. Army Corps of Engineers (USACOE) reduced the amount of soil coming down the Mississippi River by installing dams for flood control and navigation. Many tons of rich Midwestern topsoil are stored behind USACOE dams.
During this same period of time, the EPA and the states wrestled with storm water discharges. These resulted from rainfall contaminated by contact with production processes or materials and discharging through a "pipe or a ditch" and required treatment prior to discharge into surface waters. Under Phase 1, municipalities with more than 100,000 population, construction sites larger than 5 acres and certain SIC code industries had to be covered by Pollution Prevention Plans detailing management of storm water. New Orleans, Baton Rouge and Shreveport were covered by Phase 1. Phase 2 includes smaller cities and construction sites and other businesses and industries.
We have thus gone from point sources which require permits to nonpoint sources which do not require permits except for those nonpoint sources covered by storm water which makes them point sources. If, however, your land is in the Coastal Zone, or drains into the Coastal Zone, you may be required to implement mandatory Management Measures under the 1990 Amendments to the Coastal Zone Act in order to reduce Coastal Zone nonpoint sources.
We have made great progress in treating waste water coming out of a pipe during the last 25 years developing the technology as we went and consuming millions of taxpayer and consumer dollars in the process. Ten years ago we began to focus on water not coming out of a pipe, but running off the land after a rain storm. Louisiana sources include six million acres in farms, thirteen million acres in trees, and another six million acres in city parks, golf courses, front yards, back yards, gardens, school play grounds, roads and bridges and swamps. This time however, we said "no new taxes", to investigate and address a much more widespread and more difficult problem.
Regardless of whether we call it call it a storm water point source or a nonpoint source, we must recognize that soil erosion was here long before we were. Our Louisiana land mass was partially formed by soil eroding off of land in 31 states in the U.S. and in several provinces in Canada and carried into the shallows of what we now call the Gulf of Mexico. We cant stop soil erosion. We can and must continue to reduce it because, in addition to losing a valuable resource, every inch of top soil we lose brings us that much closer to mean sea level. We do not have as much soil coming down the Mississippi River to replenish our losses as we did years ago. Most of that which does come down the river is discharged into deeper waters of the Gulf and doesnt build new land.
Reducing storm water point source and nonpoint source water pollution is going to be a long-term process. It will require all of us working together to find new methods and the funds to implement them. It is essential to sustain Louisianas natural resources.
Brantley, Christopher G. Department of Oceanography and Coastal Sciences, Louisiana State University and U.S. Army Corps of Engineers, New Orleans District, P.O. Box 60267, New Orleans, Louisiana 70160-0267:
Recent History and Status of the Brown Pelican in Lake Pontchartrain
Brown pelicans (Pelecanus occidentalis) were considered abundant across the entire Louisiana coastal region during historic times. Population estimates between 1918 and 1933 ranged from 12,000 to 85,000 birds (King et al. 1977). However, a sharp decline in nesting was observed between 1958 and 1961. By 1962, no nesting brown pelicans were found in Louisiana and by the mid-1960s, brown pelicans had been extirpated from Louisiana (Lowery 1974, McNease et al. 1984). This sudden and dramatic decline has been attributed to pesticide poisoning which caused reproductive failure and a direct die-off of adults (Lowery 1974, King et al. 1977, Blus et al. 1979).
That population decline, along with the restoration and subsequent recovery of the brown pelican in not only Louisiana but also region-wide has been well documented in the literature. Between 1968 and 1980, the Louisiana Department of Wildlife and Fisheries and the Florida Game and Freshwater Fish Commission released 1,276 brown pelicans from Florida on three sites in coastal Louisiana (McNease et al. 1984). One of these release sites was North Island in the Chandeleur Island chain, where after 90 birds survived the initial release in 1977, nesting first occurred on this re-established colony in 1979 (McNease et al. 1984, 1992). Since then, this population of brown pelicans has increased considerably where by 1990, estimates of 500 adults had fledged 1000 young out of 700 nests (McNease et al. 1984, 1992; Martin and Lester 1991). This colony became the probable source population for expansion of nesting areas on nearby North Grand Gosier and South Grand Gosier Islands as well as a wintering population in Lake Pontchartrain.
I used several data sets to describe the re-establishment of brown pelicans to Lake Pontchartrain. One of the few sources for long-term evaluation of the early winter abundance and distribution of many North American bird species is the National Audubon Societys Christmas Bird Count (CBC). CBCs date back to 1900 and are conducted annually at selected locations on a single day within a 2-week period centered around Christmas Day (December 25). Birds are censused within a 24.1 km (15 mile) diameter circle at the particular CBC location.
CBC records from Louisiana were examined for every reporting locality over a 50-year period from the 47th count (1946-1947) to the 97th count (1996-1997). For each CBC locality, the total number of brown pelicans reported as well as the number of hours spent observing by each party were noted. Regional reports for each CBC year were checked to substantiate the data. The CBCs in the Lake Pontchartrain estuary, primarily New Orleans, Reserve-Bonnet Carre, and St. Tammany Parish, Louisiana, were analyzed further for determining population distribution and trends. To standardize the counts, data were converted into number of pelicans observed/number of hours observing (Schreiber and Schreiber 1973).
In addition, beginning in October 1991 and continuing through February 1998, vehicular surveys of brown pelicans were taken along the Lake Pontchartrain Causeway, a 38.6 km bridge that bisects Lake Pontchartrain north-to-south. Usual drive times were between 0600-0630 and 1550-1620 hours local time, and usually included a driver and one observer. Total number of pelicans were tallied on each trip, and as with the CBC records described above, data were converted into number of pelicans sighted/number of hours observing.
Data collected by Louisiana Department of Wildlife and Fisheries on the number of nests and number of pelicans fledged in the state were also analyzed. This information was used mostly to provide substantiation or relation to the number of birds sighted during that same time period in Lake Pontchartrain utilizing CBC and vehicular surveys.
Aside from a 1980 sighting of a pelican along the Causeway, the recent progression of brown pelican sightings from the vicinity of Lake Pontchartrain began during the winter of 1987-1988 (LSU Museum of Natural Sciences bird record files). Brown pelicans were officially tallied again on the New Orleans CBC during the 89th count (1988-1989). The birds were absent from this count circle for a period of 31 years. Based on this 50-year data set, it appears that sightings of brown pelicans on the New Orleans CBC may reflect a nesting population level on North Island. Brown pelicans were first tallied on the St. Tammany CBC during the 95th count as birds began moving into the upper estuary. As of the 97th count, brown pelicans have failed to appear on the Reserve-Bonnet Carré CBC, however, there was a sighting of one in that count circle prior to the 98th count (LSU bird record files). Spearman rank correlation analysis indicates a positive trend for brown pelicans in this estuary over time and linear regression of log transformed data reveal a significant positive slope.
Causeway transects first detected pelicans in February 1993 and has shown yearly increases to date. The past two years indicate that increasing numbers of pelicans are using the lake in both a spatial and temporal context.
Pelicans appear to be occupying the end of a major trophic sequence for Lake Pontchartrain, which can be described as a "telescoping of the food chain" (Hiatt 1944). Macroplant detritus, benthic macroalgae, and cyanobacteria (Anabaena and Microcyctis) constitute the primary producers, phytophagous fish (Mugil cephalus and Brevoortia patronus) replace zooplankton as the herbivore and pelicans are the upper level consumer (Odum 1970, Brantley unpubl. data).
Deegan (1993) has shown that for estuaries where menhaden (B. patronus) are present, greater quantities of N and P relative to C are exported out of estuaries. According to Deegan (1993), the N and P export by menhaden was about the same as passive waterborne export but of a higher quality. Future research into the role that brown pelicans may have in mass, energy and nutrient fluxes across this estuary is needed.
Butterworth, V. C., College of Urban and Public Affairs, UNO, New Orleans, La.; Wilson, J., Department of Geology and Geophysics, UNO, New Orleans, La.; Koch, J., Department of Geology and Geophysics, UNO, New Orleans, La.; Stone, C., Department of Geography, UNO, New Orleans, La.; Kachler, K., Department of Geology and Geophysics, UNO, New Orleans, La.,; Broom, L., UNO, New Orleans, La.; Suckow, M., UNO, New Orleans, La.; Cross, M., UNO, New Orleans, La.,; Kennedy, N., Department of Geology and Geophysics, UNO, New Orleans, La.; and Penland, S.P., Professor of Geology, Department of Geology and Geophysics, UNO, New Orleans, La.:
The New Orleans Lakefront Project: From Lake Bottom to Subdivision
While land reclamation in Southeastern Louisiana has frequently met with failure, the New Orleans Lakefront Project is one of the most successful ventures exemplifying the collaborative planning of the state, the parish levee board and the city of New Orleans. When the project was completed in 1930, the Orleans Levee Board had successfully engineered the creation of 2000 acres of land, spanning 5.5 miles from the West End to the Industrial Canal. It was the fulfillment of an idea dating back to 1873, when New Orleans city surveyor W.H. Bell formulated the first proposal for developing the southern shore of Lake Pontchartrain. While threats from river flooding were consistently addressed upon the founding of the city, the "back door" threat of flooding from Lake Pontchartrain had been neglected. The marshy swamp lands that comprised the natural shoreline of the lake were dotted with "seedy" fishing camps and shanties as well as being subject to frequent flooding during periods of high tide, seasonal frontal systems or hurricane winds. Recognizing this threat Bell prepared the first plan for protection of the city coupled with the creation of more habitable land for future growth. After more than fifty years of debate, discussion and planning by the state Legislature actual work by the Orleans Levee Board began in 1926. The existing shoreline was divided into zones, around which wooden bulkheads were erected from 2500 to 3500 feet outward into the lake. Upon completion of the project, billions of cubic yards of lake bottom material had been hydraulically deposited behind the bulkhead to elevations of 2 to 8 feet above sea level with the bulkhead being replaced by a concrete seawall. The new land along Lake Pontchartrain now contains five residential areas, a state university, a municipal airport, public parks and a scenic parkway.
Carnelos, Susanne and Dr. J.A. McCorquodale University of New Orleans, New Orleans, LA:
A 2-D Model of the Behavior of Surface Buoyant Discharges into Lake Pontchartrain
In Orleans and Jefferson parishes, Louisiana, the urban runoff is collected and pumped into outfall canals discharging into Lake Pontchartrain. Many of these discharge plumes leave the outfall canals at an insufficient velocity and, subsequently, remain in the nearshore region where they are significantly affected by ambient cross-currents. The result is extremely poor spreading and dilution in plumes that travel along the shoreline causing nearshore contamination. Plume behavior models can be used to predict the extent of mixing and lateral and longitudinal spreading that would occur with the existing urban outfall canals. The model may also be useful to improve the outlet designs so that in the long-term it may be possible to re-establish certain nearshore areas of Lake Pontchartrain as suitable recreational sites.
Two models, PLUMES and CORMIX have been reviewed in terms of their applicability to this situation. The EPA PLUMES model was abandoned since it can only be applied to diffuser discharges. CORMIX3 may be used for surface buoyant discharges (the discharge is mainly freshwater and the receiving water is saline) into large uniform-density water bodies, but it imposes a limitation on the canal outlet geometry. It will only accept a width to depth ratio of 5:1 at the outlet while most of these outfall canals are very wide and shallow having width to depth ratios in the range of 25:1 to 30: 1. Thus, it was decided to develop a two-dimensional numerical model based on the theory that the fundamental laws governing the diffusion of these buoyant jets are the conservation of mass, momentum and buoyancy. Throughout the development results from the model are compared with results obtained from CORMIX3 for suitable channel geometry conditions as well as with actual observational data such as results from drifter experiments.
The following assumptions were made in developing the equations used for predicting the plume width, depth, density, velocity and dilution in a stagnant receiving body: the outfall canal outlet and the discharge velocity profile was approximated by a rectangular shape (the velocity is constant throughout a cross-section of the plume); the behavior of the jet is symmetric about the jet axis (i.e. the time-averaged velocity and buoyancy distributions are similar in shape on an arbitrary section of the jet.); the mean velocity is independent of time and the flow is fully turbulent; the outfall discharge spreads linearly in both the x-y plane and the x-z plane; the Boussinesq approximation is valid (i.e. density variation affects only the gravity term); the ambient water pressure is hydrostatic and the ambient density is uniform throughout the water body; the receiving water region extends infinitely into the offshore region.
Current development focuses on the effect on the plume trajectory in the presence of ambient crosscurrents as well as the prediction of achievable dilution of contaminants, such as fecal coliform.
Cashner, R. C., J. M. Humphries, C. Schieble, University of New Orleans, New Orleans, LA, and J. G. Stewart, Southern Illinois University, Carbondale, IL:
An Inventory and Monitoring Program for Lake Pontchartrain Nekton
Biotic inventories are the surveying, sorting, cataloging, quantifying and mapping of entities such as populations, species, habitats, ecotopes, even ecosystems, and the synthesis of the resulting information for the analysis of processes (Stork and Samways, 1997). Inventories involve the application of both applied and theoretical aspects of systematics, ecology, biogeography and management and provide a baseline for the understanding of changes in ecosystem structure and function. Monitoring is the intermittent surveying of the biota to record deviation from the expected status of the system. The current study of the Lake Pontchartrain nekton community is intended to provide data and methodological updates on both activities. Nearly 50 years of sampling of the Lake will provide a baseline understanding of community structure within the basin and the current two years of repeated, regular sampling will form the core of a management plan for long term monitoring of the health of the Lake ecosystem. The fundamental premise behind this sampling effort is that because of their varying life histories, feeding habits and habitat requirements, an assessment of the health of the fish community provides a reliable approximation of the health of the entire ecosystem. In addition, because fishes are widely recognized for their economic and aesthetic value, the societal costs of any discovered degradation can be evaluated.
The temporally and spatially heterogeneous nature of Lake Pontchartrain presents challenges, but offers considerable opportunity to enhance our understanding of community structure in complex estuarine environments. For example, although most estuarine systems are known to exhibit considerable inter-annual variability in hydrological and environmental characteristics, we know surprisingly little about the ecological consequences of this variation. This ignorance is especially apparent in terms of our understanding of nekton population dynamics in estuarine systems. We have few long-term population time-series that might reveal the patterns and scale of variation in abundance. Also, many fish populations have complex life histories in which the interaction of density-independent and density-dependent mortality factors may come into play in different environmental settings and at different spatial scales. The current nekton study and comparison with earlier surveys provides considerable evidence for stability in some components of the biota, but strong habitat fidelity and consequence change in abundance in many other species.
The current study, funded by a grant from Freeport-McMoran, was designed to assess the health of the Lake based, in part, on an ongoing survey of nekton populations and comparison to earlier surveys, primarily those conducted in the early 1950's and late 1970's. A total of fifteen lake based sites and four marsh based sites comprise the sampling regime for the current monitoring effort. These sites were chosen both to maximize congruence with earlier surveys and to assure adequate coverage of all habitats and regions within the Lake. Quarterly sampling for a total of eight quarters has been carried out to date. The primary methods of collecting has been by 16 foot trawl and 15 foot seines. Each method was carried out for a standardized length of time and with standardized techniques. Water quality measurements are made with all collections. All data are being archived in a state of the art database system, with all samples geocoded for GIS analysis. At the end of two years, the regular monitoring will cease. Because certain habitats and types of fish are missed by the regular monitoring scheme, we will concentrate future collecting on other methods utilized in earlier surveys including gill nets and beach seines.
Cothren, Gianna, Alim Hannoura, Alex McCorquodale, University of New Orleans, Civil & Environmental Engineering, New Orleans LA 70148; Srikanth Patibandh, University of New Orleans, Computer Science, New Orleans LA 70148:
Lake Pontchartrain Basin Geographic Information System
The development of a Geographic Information System for the management of the Lake Pontchartrain basin is underway. The Colleges of Engineering and Sciences at the University of New Orleans have taken this initiative in recognition of the need for a long-term database on the water quality and biota of the Pontchartrain Ecosystem. The development of a computerized database to study biotic resources and water quality dynamics in the Lake is the focus of this GIS. The long-term objective is a management model which integrates land-use and hydrological processes, atmospheric fallout, resources development, biological processes, and food chain dynamics as a measure of Lake productivity.
The tools used to develop this GIS are Integraph's MGE and GeoMedia GIS software using Oracle for the relational database. The relational database, developed with Oracle 2000 tools, is designed for graphical access through the GIS or as a distinct product with user friendly forms. Within this relational database, users can track environmental/water resources data and easily access stations of interest within particular subsegments; of the basin for any period. The database provides the structure necessary for the expansion of additional data as well as additional agencies as sources of data.
Some of the data that are incorporated in the GIS are the Louisiana Department of Environmental Quality (LADEQ) monthly water quality monitoring data dating back to 1958, the National Climatic Data Center (NCDC) weather data, USGS daily flow data, and STORET water quality data. The graphical layers of the basin prepared thus far are the base map and boundaries of the Pontchartrain Basin in Louisiana and Mississippi from 100K Digital Line Graphs, Orleans and Jefferson Parish ortho photos and infrastructure, Landsat TM-SPOT Merge Satellite imagery of Louisiana, and Land use/Landcover of Louisiana and Mississippi.
Future improvements to the GIS include auto buttons to run the relational database separately using the Oracle user interface to retrieve or query data located in each basin. These improvements will also be used to develop input files to run rural and urban runoff models as well as supply the data needed for the Lake circulation model.
Inas Ismail, Gianna Cothren, Alim Hannoura, Alex McCorquodale, University of New Orleans, Civil & Environmental Engineering, New Orleans LA 70148:
Water Quality Assessment in the Lake Pontchartrain Basin
Lake Pontchartrain, located in southeastern Louisiana, is one of the largest lakes in the southern part of the United States. Five major rivers discharge into the Lake directly or indirectly: Amite, Tickfaw, Tangipahoa, Tchefuncte, and Pearl. This basin has experienced a phase of declining water quality accompanied by decreased productivity, and limitations on its use for recreational activities. In the recent past, erosion of shorelines, drainage of adjacent marshes, and appearance of dead zones have all been observed in Lake Pontchartrain (Calvert and Emmer, 1992). These factors influence economic development and cast a negative outlook on the quality of life in this history-rich urban center of the State. An alarming sign is the recurrence of algal blooms. Excessive algae may be harmful and obnoxious and are an indication of an increase in the degree of eutrophication.
This research is part of a larger vision of developing a watershed management tool integrated with a Geographic Information System (GIS) that allows resource managers to do impact assessment, ..what if scenarios", and future forecasting on the Pontchartrain Basin. The objective is to develop a water quality assessment of Lake Pontchartrain. This assessment is achieved by: 1) realizing the temporal and spatial trends of water quality parameters (nitrogen, phosphorus, turbidity, water temperature, and dissolved oxygen) in the Lake basin; 2) evaluating the nutrient loads and dissolved oxygen contributed by the major rivers, Amite, Pearl, Tangipahoa, Tchefuncte, and Tickfaw; 3) analyzing data during a reported algal bloom incident in the early summer of 1993, and 4) establishing the correlation between water quality parameters and Chlorophyll-a (Chl-a) measurements.
Monthly water quality monitoring data from the Louisiana Department of Environmental Quality (LADEQ) are available in the GIS. Preliminary results based on these data have been achieved and further research is underway to attain detailed results. Temporal trends indicate a 70% to 80% reduction in nutrients contributed to the lake from the rivers. Spatial analysis reveals higher nutrient concentrations and turbidity values on the south shore of the lake compared to the north shore and the center of the Lake. Analyses of dissolved oxygen indicate that downstream stations on the Amite and Tchefuncte rivers experience episodes of summer DO concentrations less than 5 mg/l. The DO concentrations in the Lake drop to 6.5 mg/I in summer from 10.5 mg/I in winter. Analysis of coincident water quality data at the time of the reported 1993 algal bloom, and analysis of chl-a and other water quality parameters are underway.
Management of the water quality of Lake Pontchartrain will require a comprehensive understanding of the factors affecting the contributing rivers's water quality. Intensive monitoring along the south shore is recommended since the water quality at the south shore station is significantly lower than the water quality at the north shore. Results of the analysis at the time of the algal bloom in 1993 indicate correlation between the bloom incident and nitrogen, phosphorus, turbidity, and temperature reported at the Lake stations. Although Chl-a correlation with nutrient data is still at a preliminary stage, these results will likely be useful in predicting algal bloom incidents based on the prevailing water quality conditions.
Dortch, Q., Peterson, T., Louisiana Universities Marine Consortium, Chauvin, LA and Turner, R.E., Louisiana State University, Baton Rouge, LA.:
Algal Bloom Resulting from the Opening of the Bonnet Carré Spillway in 1997
The Bonnet Carré Spillway was opened from March 18 to April 17, 1997 for flood control purposes, allowing nutrient-rich, turbid Mississippi River water to flow into Lake Pontchartrain. Beginning on March 13, 1997 and continuing to the present, phytoplankton samples were collected at weekly to monthly intervals, depending on the time of year, from seven stations on the Causeway Bridge in the center of the Lake, stations in or near all the major nutrient sources, and near the exit. Other hydrographic and water quality measurements were also made. The purpose was to determine if an algal bloom would occur, and, if so, what the causes and impacts of the bloom would be.
All phytoplankton samples were filtered on 8 mm polycarbonate filters, stained with proflavine and bloom organisms were counted with epifluorescence microscopy. Samples from a station in the middle of the Causeway Bridge were size-fractionated by filtering onto 0.2, 3, and 8 mm polycarbonate filters, stained with proflavine, and all autotrophic organisms were counted with epifluorescence microscopy. Additional taxonomic tools were applied to these samples in order to identify some of the organisms. At all stations salinity, chlorophyll, nutrient, suspended matter concentrations and Secchi disk depths were measured.
By the end of March, nutrient levels in the middle of the lake had increased from <10 mM Dissolved Inorganic Nitrogen (DIN) and <1 mM Dissolved Inorganic Phosphorus (DIP) to values which approached 90 mm DIN and 5 mm DIP in some locations. A visually obvious bloom of cyanobacteria (blue-green algae) became apparent over large parts of the Lake by the end of May, peaking in mid-June. The bloom consisted of two species of Anabena and one species of Microcystis. Both genera are capable of positive buoyancy, which allows them to avoid light limitation in turbid waters, and are known to be stimulated by excess nutrients. Exposure or ingestion of water with high numbers of these organisms can cause severe allergic reactions and sometimes produce heptatoxins and neurotoxins. High levels of heptatotoxins were measured during the peak of the blooms with traces persisting into the fall. An advisory against recreational use of the Lake was issued by the Louisiana Department of Health and Hospitals. Although the bloom was stimulated by the simultaneous increase in DIN and DIP and declined as both reached low levels, the increased number of heterocysts in Anabena (indicating N2 fixation), the lack of akinetes in Anabena (stimulated by phosphate limitation), and the low DIN/DIP ratios indicate that the bloom ended as a result of N depletion.
A total of 71 autotrophic taxa were observed at Station 4, where complete counts were made. Many of these organisms were quite small and difficult to identify to the species level in the sediment matrix in which they were embedded. The purpose of the complete counts was to determine if other organisms also bloomed. The single most abundant group were small (~1 mm), coccoid cyanobacteria. Except during the peak of the Anabena/Microcystis bloom, they dominated numerically and their abundance increased from early spring to fall. Similar numbers of small, coccoid cyanobacteria and the same seasonal pattern of increasing abundance with increasing water temperature are found in other Louisiana estuaries. Approximate calculations of biomass, based on cell volume, indicate they dominated the biomass as well. Cryptomonads, Diatoms, and Chlorophytes were the next most abundant groups. Their relative abundance was extremely low, but highest in the spring before the Anabena/Microcystis bloom. No organisms other than Anabena spp. and Microcystis sp. bloomed during 1997. Overall the average relative abundance by cyanobacteria was 96%. Such extreme dominance by cyanobacteria is indicative of a highly eutrophic system. Until similar studies are conducted during a year without an opening of the Bonnet Carré Spillway, it is not possible to determine how different 1997 was from other years.
Francis, J. C., and M.A. Poirrier. Department of Biological Sciences, University of New Orleans, Lakefront, New Orleans, Louisiana 70148:
Recent Trends in Water Clarity of Lake Pontchartrain
An analysis of Secchi disc transparency observations from three sites on the Lake Pontchartrain causeway indicates that water clarity has increased since 1990 at the north shore and mid-lake sites, but has not changed at the south shore site. Louisiana Department of Environmental Quality data from 1986 through 1995 were used in the analysis.
Higher transparencies usually are associated with higher salinities and lower wind speeds because salinity has a statistically significant positive effect on transparency, and wind speed has a statistically significant negative effect on transparency. Our analysis indicates, however, that the higher transparencies observed at the north shore in the 1991-95 period were not associated with higher salinities or lower wind speeds, but rather with lower salinities than those measured at the mid-lake and south shore sampling sites and with wind speeds that were the same at the three sites.
The higher transparencies at the north shore during the 1991-95 period may be explained by the positive effect on transparency realized through cessation of shell dredging in 1990. Sediment disruption produced by shell dredging probably had a greater negative effect on transparency in the lower-salinity waters of the north shore because of the tendency for lower-salinity waters to retain particles in suspension longer.
Higher transparency peaks were apparent at the north shore and mid-lake sampling sites by the fall of 1991. This observation is consistent with expectation because an immediate increase in transparency was not anticipated. Unconsolidated sediments that are more susceptible to re-suspension by wind would persist for a period of time following dredging and have a longer-term effect on turbidity. In addition, an earlier expression of higher transparency may have been mitigated by lower lake-wide salinities in 1990 and early 1991 that would have lowered transparency.
Transparency remained essentially unchanged at the south shore after shell dredging was stopped. Several factors may have contributed to this outcome. Dredging was prohibited within three miles of the south shore extending from the Lake Pontchartrain Causeway east to Paris Road in Orleans Parish, and near oil and gas facilities in Jefferson Parish west of the Causeway. Consequently, dredging and its effects on transparency may have been less intense near the south shore site. The south shore is subject to urban runoff from metropolitan New Orleans, and it has a highly modified shore line with no exchange with natural streams and wetlands. Runoff introduces nutrients that can promote algal growth with the result that turbidity from phytoplankton growth may have replaced turbidity from re-suspended sediments.
Shell dredging began in 1933 and probably affected transparency prior to the first transparency measurements in 1953. The cessation of shell dredging in 1990 reestablished conditions favoring higher transparencies in some regions of the lake. The change to higher transparencies cannot be attributed to changes in salinity or wind speed.
Poirrier, M.A., C.D. Franze, Department of Biological Sciences, University of New Orleans, Lakefront, New Orleans, Louisiana, 70148.
Bayou St. John: Practical Water Management for an Urban Scenic Stream
Bayou St. John, in its natural state, was a tidal stream that discharged runoff from former wetlands into Lake Pontchartrain. As a low-gradient stream, tidal exchange of brackish water from Lake Pontchartrain occurred. Before being highly modified by man, it was similar to streams such as Bayou Trepagnier and Bayou LaBranche, which drain the southwestern wetlands of the Lake. These bayous are low salinity systems that support a mixture of marine and freshwater organisms.
The Bayou has been highly modified with the development of New Orleans. Water from the Bayou no longer discharges into the Lake. Exchange from the Lake into the Bayou generally occurs through the sluice gates in the new flood control structure when the water level in Lake Pontchartrain is high enough to permit gravity flow. The gates on the old control structure are not fully operational and are kept in an open position. Lake water flows upstream through the Bayou into the City Park pond system. Water movement in the Bayou is slight and the current direction is reverse of a natural stream. Bayou St. John is an important source of water for the City Park pond system. Water enters the ponds through a 14-inch gravity flow pipe north of Mirabeau Avenue and is pumped into the ponds at two other locations south of Harrison Avenue. Water from the Bayou maintains brackish water conditions in the ponds.
Water quality on the south shore of Lake Pontchartrain can at times be extremely poor and at other times relatively good. The input of plant nutrients and other pollutants into Bayou St. John and the City Park pond system can be controlled by allowing water flow into the system only when water quality is at desired conditions. Water should not be allowed to enter the system during periods of high outfall canal discharge, or during periods when the Bonnet Carré Spillway is open, or leaking into Lake Pontchartrain.
Management of the flood control structures on Bayou St. John only considers flood protection and water level control. Design of the new flood control structure between Lake Pontchartrain and the old flood control structure provides a unique opportunity for more control of water flow into the Bayou from the Lake. Carefully coordinated water management practices of salinity, plant nutrients and the movement of marine organisms into Bayou St. John can potentially improve fishing, control the growth of aquatic plants and improve the general environmental quality of the Bayou and the City Park pond system.
Salinity levels can be managed so that they are low enough to ensure successful spawning of important freshwater species such as bass and bluegill. Salinity can also be maintained at high enough levels to allow marine fish that move in from Lake Pontchartrain to grow in the Bayou. This could provide a sport fishery for species such as speckled trout, red drum, sheepshead, flounder and blue crabs. Marine organisms could also be stocked into the system to encourage this development. In addition, marine fish and invertebrates might also control unwanted aquatic vegetation. Control of unwanted freshwater aquatic plants can also be achieved by maintaining salinity above vegetation tolerance. Both, Bayou St. John and the ponds in City Park have the potential to become a unique and truly outstanding urban, marine, sport fishery. Interestingly, the state record for sheepshead, weighing 21 pounds, was caught from Bayou St. John by Wayne Desselle.
Proper water management can prevent fish kills and algal blooms caused by poor water quality. During July 1995, a major fish kill occurred from the mouth of the Bayou south to Filmore Avenue. Environmental conditions that caused this fish kill did not originate in the Bayou, but were the result of blue-green algal blooms in Lake Pontchartrain. The fish kill and foul odors associated with it could have been prevented by closing the sluice gates and not allowing water with a high concentration of algae to enter the Bayou. In 1997, under the advice from the senior author, the gates were closed and nutrient rich Mississippi River water was prevented from entering the Bayou. A fish kill occurred on the Lake side of the control structure, but not in the Bayou. Phytoplankton blooms and floating mats of filamentous green algae, which have covered the Bayou in the past, were also prevented. A regularly managed water quality plan should be implemented to protect the Bayou St. John and City Park ecosystems.
Gurney, David R., Southeastern Louisiana University and Citizens For A Clean Tangipahoa, Hammond, LA,:
Fecal Coliform Levels in Tributaries to Lake Pontchartrain
Since the late 1970s, the Louisiana Department of Health and Hospitals (DHH) in conjunction with the Louisiana Department of Environmental Quality (DEQ) have regularly been measuring fecal coliform levels from a number of sites on rivers and bayous in the Lake Pontchartrain Basin since the late 1970s. In 1988, because of continuing high levels of fecal coliform bacteria, the DHH and DEQ posted signs on the Tangipahoa River stating that the water was unsafe for primary contact activities, such as swimming, and even unsafe for secondary contact activities, such as boating. As a result, the recreation industry on the Tangipahoa, which supported an estimated 200,000 visitors per year, virtually disappeared taking with it some $4 million dollars in business revenue for Tangipahoa Parish. This paper will examine fecal coliform data collected by DHH\DEQ over the last twenty years from sites on the Tangipahoa and also on other tributaries to Lake Pontchartrain. The aim will be to characterize the situation on individual waterways, demonstrate trends where possible, and to make across the board comparisons for all of the waterways.
Pittman, L. P., Gammill, S., Haase, L. B., Good, B., Ph. D., Louisiana Department of Natural Resources, Baton Rouge, LA:
Coast 2050 and Strategic Coastal Planning in the Pontchartrain Basin
Coast 2050 is a multi-disciplinary initiative to develop and implement a strategic plan for the protection and restoration our states valuable coastal resources. This initiative is a partnership involving various federal and state agencies (the Louisiana Wetland Conservation and Restoration Authority; the Coastal Wetland Planning, Protection, and Restoration Act (Breaux Act) Task Force; The Office of the Governor; and the Department of Natural Resources (DNR) Coastal Zone Management (CZM) Authority), parish and local governments, business and industry, scientists, landowners, environmental groups, and concerned citizens. Coast 2050 has, as its mission, to "develop, by December 22, 1998, in partnership with the public, a technically sound strategic plan to sustain coastal resources and provide an integrated multiple use approach to ecosystem management."
The initiative provides the opportunity for the public and all levels of government to adopt a common plan for future coastal restoration and protection projects. This plan takes into account major coastal uses and resources that are vital to our future. Such things as flood protection, transportation, oil and gas production, navigation, fish and wildlife production, fresh water supply, and community stability among others are being considered.
Through the Coast 2050 initiative, we are:
The Pontchartrain Basin is one of four major regions identified in the Coast 2050 initiative for the purpose of large-scale coastal planning. The region has been further divided into 21 mapping units for the development of smaller-scale coastal plans. Both large and small-scale strategies will be evaluated in terms of defined habitat (fresh marsh, intermediate marsh , brackish marsh, forested wetlands, etc.) and resource (saltwater finfish, oil and gas, navigation, flood water retention) objectives solicited from the public. These strategies and the objectives they are designed to meet will be incorporated in this plan which is expected to form the basis for an amended Breaux Act Restoration Plan, the Louisiana Strategic Plan, and become part of Louisianas Coastal Zone Management Program in the Pontchartrain Basin.
Alex McCorquodale, Katy Haralampides, University of New Orleans, New Orleans LA:
Framework for an Ecosystem Response Model
A model is being developed to assess the environmental exposure and impacts of contaminants on the Lake Pontchartrain ecosystem. The impact on the Lake water quality and biota of an influx of agriculturally-based contaminants, pollutants entering the system during freshwater diversions for wetland restoration and flood control, sediment-bound compounds, and contaminants entering through the Pearl River can be investigated.
For a model to simulate realistic conditions in the Lake, all of the processes governing the dynamics of the system must be incorporated. Physical influences such as wind, runoff, tides, and storm surges which govern the lake hydrodynamics and sediment dynamics are included. A water quality model which quantifies the nutrient levels, pH, and salinity in the water, as well as the toxics abundance in the Lake is needed as input into the model. Conventional loadings as well as heavy metals and toxic organics in the system need to be quantified. The surface chemistry of the contaminant of interest, including its partitioning and adsorption/desorption characteristics, is required in order to predict the amount that will be present in a dissolved state or that will be associated with fine particulate. The biology of the ecosystem must also be established, including the primary producers, the presence of specific species in the system [and the predator-prey interactions between them], and the physiology of the biota [including metabolism, growth, depuration, consumption, and respiration rates].
Phase 1 of the model development is a one-cell concept which includes a water budget and sediment dynamics [resuspension/deposition] components based on the principle of conservation of mass in the Lake. Five trophic levels were identified for the Lake Pontchartrain ecosystem, including benthic coupling to the contaminated bed.
Table 1 shows a generic predator-prey matrix that is being adapted to the fish diet data set [Darnell, 1961 and UNO 1997-98 fish survey data].
McCorquodale, Alex, Katy Haralampides and Alim Hannoura University of New Orleans, New Orleans, LA:
Lake Pontchartrain Monitoring for 1997 Spillway Opening Event
On 17 March 1997, the US Corps of Engineers, in response to a flood danger at New Orleans, commenced the opening of the Bonnet Carré Spillway. The spillway remained open for approximately one month discharging Mississippi River water into Lake Pontchartrain with a maximum discharge of approximately 240 000 cfs, and an average discharge of 154 000 cfs. The Mississippi River water has distinctively different characteristics than the ambient Lake Pontchartrain water. For example, Lake Pontchartrain has salinities of the order 4 ppt, while the Mississippi River is essentially zero; there is a significant temperature difference in the spring, with the river water being approximately 5 to 10 ° C colder than the lake. Shortly after the opening of the spillway, the UNO Civil Engineering Department undertook a monitoring program to track the water temperature, salinity, and conductivity throughout the lake; these samples were taken for subsequent analysis by the Biology Department. At the same time, complimentary studies were conducted by the LADEQ, the LADNR, the USACE, and the USGS. A cooperative agreement was established amongst these groups for exchange of information. Five transacts were established by UNO from Pass Manchac to Lake Borgne, with a total of twenty-three stations. Samples were taken 1 m below the water surface.
The initial plume of Mississippi River water remained near the south shore of the lake for approximately ten days, until southeasterly winds resulted in a northward expansion of the plume. After about three weeks, the spillway plume occupied 80-90% of the lake area. Approximately one month after opening, the plume occupied the entire lake and a significant portion of Lake Borgne had reduced salinities. The USACE completed the closing of the spillway on April 17, 1997. Monitoring has continued since that date to assess the lake recovery rate to more normal salinity levels. The recovery process is much slower than the flushing phase because the return of salt water is governed by the limited tidal exchange, exchange due to storm surges, and some flows through the Gulf Outlet. Also, the recovery was further retarded because of leakage through the spillway, and freshwater runoff due to heavy rains on the Lake Basin. The salinities along the Causeway on June 13 were in the range of 10 to 20% of the values before the spillway was opened. Algal blooms were observed in the lake on June 10, 1997 and were monitored during the summer of 1997. Surveys of the entire lake have continued monthly, with samples from the causeway taken biweekly. Salinities had reached normal levels on the south part of the Lake by 29 August 1997, however low salinities persisted along the north shore until early October 1997. Full-lake monitoring on 22 October 1997 indicated that most parts of Lake Pontchartrain had recovered to pre-spillway-opening salinity values.
Due to the record amount of rainfall that occurred in early 1998, the lake salinity again decreased significantly. A full-lake survey carried out on 8 February 1998 indicated that salinity values had dropped by approximately 40% - 50% from the recovered state. This is an important observation because it illustrates the impact that natural occurrences such as high rainfall can have on the lake system.
The data collected from the monitoring program can be used to calculate flushing times for Lake Pontchartrain. The South Point [Southern Railway] was selected as an outflow control section. This analysis provides an estimate of the amount of time that it takes for a chemical to pass through the Lake if it enters with the Mississippi River diversion water during a spillway opening event; preliminary results indicate a mean residence time of 12 days for the 1997 spillway opening.
The analysis also shows that the shortest travel time is 6 days; the hydraulic detention time for the Lake with the March - April 1997 average freshwater inflow of 167 000 cfs is 13.0 days. The short circuiting between the spillway and the eastern narrows of the lake is indicated by the ratio of the first arrival time to the detention time which is 0.45 which is similar to a rectangular settling tank. For no short circuiting, this ratio would be 1.O. The saline recovery is a completely different process which takes up to 6 months to re-establish the pre-opening concentrations. Similar although less dramatic flushing and recovery processes will accompany large rainfall events.
A lake system hydrodynamic/mass transport model is being calibrated with the available Lake data. This model will be used to investigate the effects of wind, storm surges and rainfall events on the Lake Pontchartrain response characteristics.
Hartzog, Larry, U.S. Army Corps of Engineers, New Orleans District, LA; Mississippi Department of Marine Resources, MS; Gulf Coast Research Laboratory, MS; Gulf Engineers and Consultants Inc., LA; and Steimle and Associates, Inc., LA:
Monitoring the Impacts of the 1997 Flood Opening of the Bonnet Carré Spillway in Louisiana and Mississippi
The U.S. Army Corps of Engineers (Corps) opened the Bonnet Carré Spillway (Corps) on March 17, 1997, for only the seventh time since 1937. The BCS is part of a comprehensive plan for flood control in the Lower Mississippi Valley, protecting New Orleans and associated communities from Mississippi River floodwater. The BCS was opened due to heavy rainfall in the Ohio Valley that entered the river system. When the BCS is opened, floodwater from the Mississippi River is diverted through Lake Pontchartrain, the Rigolets, Mississippi Sound, and eventually into the Gulf of Mexico.
The purpose of this 9-month study was to gather biological, recreational, and hydrological data on the effects of the 1997 BCS opening in Lake Pontchartrain area, the Bonnet Carré Spillway, and the western Mississippi Sound. The study was conducted in two major research efforts, one concentrating on the BCS and Lake Pontchartrain, and the other concentrating on Western Mississippi Sound. GEC, Inc., located in Baton Rouge, LA, and Steimle and Associates Inc., located in Metairie, LA, conducted the Lake Pontchartrain and BCS portion of the study. The Western Mississippi Sound portion of the study was conducted by the Mississippi Department of Natural Resources, located in Biloxi, MS., and the Gulf Coast Research Laboratory, located in Ocean Springs, MS, with coordination and oversight by Dames and Moore, Inc, located in Bethesda, MD.
A variety of parameters were measured in this study, beginning the day of the BCS opening, and continuing for 9 months into November 1997. In the LA portion of the study, oyster effects were measured in Lake Borgne, and trawl samples for shrimp and finfish, blue crabs, and water quality parameters were measured in Lake Pontchartrain. Recreational activity was measured both in the BCS and Lake Pontchartrain. In the Western Mississippi Sound portion of the study, oysters, finfish and invertebrate trawl samples, and water quality parameters were measured.
In the Lake Pontchartrain portion of the study, several conclusions may be reached after reviewing the data. The opening of the BCS had no adverse impact on the oyster populations sampled. Trawl sampling showed species shifts and movement, particularly brown shrimp, in response to Mississippi River water influences. Blue crabs showed no adverse impact. Measured water quality effects included reduced salinity and Secchi visibility. Lake recreation experienced a short-term reduction in quality and quantity of fishing and other recreation activities in parts of the study area. BCS recreation returned to normal once access was reestablished.
In the Western Mississippi Sound portion of the study area, conclusions similar to the Lake Pontchartrain area were reached after reviewing the data. No significant oyster mortality was noted for those populations sampled. Trawl sampling indicated short-term impacts in terms of species shifts and movement for both finfish and invertebrates. Water quality data showed a temporary reduction of salinity. It is important to note that the Western Mississippi Sound may have been influenced by increased flow from the Pearl River.
Overall, impacts from the opening of the BCS appeared to be temporary for those parameters measured in this study. This study also has revealed several aspects that could improve the quality of future investigations. A similar intensive investigation also should be performed during a non-BCS opening year, particularly when the previous year did not have an opening. A study should be for an entire year, with sampling in all measured parameters for that year. Trawl sampling intensity could be more targeted. The trawl sampling appears to be useful in evaluating historic population patterns. Given that anomalous events usually occur during a BCS opening or can occur at any time, future studies should have the capacity for contingency investigations.
Kindinger, Jack L., U.S. Geological Survey, St. Petersburg, FL, S. Jeffress Williams, U.S. Geological Survey, Reston, VA, Shea Penland, University of New Orleans, New Orleans, LA, James G. Flocks, U.S. Geological Survey, St. Petersburg, FL, and Paul Connor, University of New Orleans, New Orleans, LA.:
Holocene Geologic Framework of Lake Pontchartrain Basin, Southeastern Louisiana
The Pontchartrain Basin is the largest marginal deltaic basin in North America measuring about 75 by 200 km, with the modern lakes (Lakes Maurepas, Pontchartrain, and Borgne) covering the southern portion of the basin. The basin is bounded by incised Pleistocene terraces to north, the Mississippi River delta plain to the south/southwest and the Chandeleur Islands to the south/southeast. In 1994, the USGS began a study of the geology, geomorphology, coastal processes, and environmental quality of the Pontchartrain Basin for use by Federal, state and local officials in coastal management and restoration planning. Existing geological information has been integrated with high-resolution seismic profiles (>700 line km), 76 vibracores , and more than 1000 geochemical samples to develop a geologic history of the basin.
Pontchartrain Basins complex depositional history dominated by relative sea-level change. During the late Wisconsin lowstand, the region was entrenched by rivers. Beneath the southern margin of Lake Pontchartrain is the buried incised channel of the Mississippi River. The basin subaerial exposed surface was truncated during the late Wisconsinan aerial exposure, and subsequent sea-level transgression. The Pleistocene unit is a stiff olive-gray clay to light grayish-yellow, borrowed with oxidized organic (wood, peat, etc.) burrows filled with sand and silt, and sharp unit contact with siderite nodules. This surface identified from vibracores as the Pleistocene/Holocene contact. The Pleistocene/Holocene contact crops out along the northeastern shore and dips toward the southwest portion of the lake.
Rising sea level flooded the "Pontchartrain Embayment" and depositing transgressive nearshore or estuarine sediments across the area. Slower sea-level rise at ~4,000 BP initiated formation of a barrier shoreline. Sediments eroding from Pleistocene terraces and Pearl River delta shores to the east of present day Lake Pontchartrain merged with sandy material moving westward along shore built the large recurved spit and barrier (Pine Island barrier trend) that bounds the southeast portion of the basin. The basin remained open to the south, and back barrier deposits partially filled the open estuary. Drainage of the Pleistocene terrace to the north produced small deltas that prograded across the northernmost portion of the basin, adding to the Holocene sequence. The next depositional event (at ~3,000 BP) was the eastward progradation of the St. Bernard delta complex from the Mississippi River valley. Deltaic sediments enclosed the Pontchartrain Basin to the south and eventually included the Pine Island barrier. The physical processes associated with the restricted flow into and out of the basin as a result of the enclosure define the depositional patterns seen in the basin today. Due in part to the structure of the Pleistocene surface and in part to the delta sediments from the Mississippi River, Holocene sediments have been differentially deposited in Lake Pontchartrain to the north (~0.3 m) compared to the south (~5.0 m). Cypress swamps and wetlands formed in the upper basin and intermediate to saline marshes formed in the lower Basin. From the late Holocene to the present, active growth faults have also influenced basin geometry and geomorphology, particularly along the north shore. In most recent time, anthopogenic influence has controlled sedimentation (deposition and erosion) in the basin, particularly along the southern and western shores of Lake Pontchartrain. Urbanization affects the quality of the sediments being deposited in the basin.
List, J. H., and Signell, R. P., U.S. Geological Survey, Woods Hole, MA:
Modeling and Measurements of Waves, Circulation, and Suspended Sediment in Lake Pontchartrain
As a component of the U.S. Geological Surveys Lake Pontchartrain Project, we are studying the physical processes affecting the resuspension and transport of sediments in Lake Pontchartrain. Two critical processes related to sediment transport in the lake are (1) the resuspension of sediments due to wind-generated storm waves and (2) the movement of resuspended material by lake currents during storm-wind events. These processes are being studied by modeling and measuring wind-induced waves and their associated bottom currents, by modeling and measuring tide and wind-induced circulation, and by analyzing data on the basins suspended sediment concentrations under a variety of conditions.
Wind-generated waves and their associated currents are likely to be the primary cause of both sediment resuspension in Lake Pontchartrain and shoreline erosion around the basin. We modeled waves in Lake Pontchartrain with HISWA (Hindcasting Shallow-Water Waves), and verified the results using three months of field measurements. Using HISWA predictions, we also found a strong correlation between modeled bottom currents and suspended sediment concentrations as measured by beam attenuation data. HISWA simulations, using a wide range of wind speeds and directions, were weighted by long-term wind statistics to give the spatial and temporal variability of wave-induced currents at the bottom. This "regional wave climatology" seems to show a correlation with both the historic distribution of submerged aquatic vegetation and the rates of shoreline change around the basin.
Circulation within the basin has been studied by means of a 3D model which includes a free surface, nonlinear advective terms, coupled density and velocity fields, river runoff, tides, and heating and cooling of the sea surface. Model predictions have led to a better understanding of the roles of remote and local wind-forcing in flushing suspended sediments from the basin. Efficient eastward movement of material along the north or south shore of the lake occurs when westerly winds are present due to the local wind response. Efficient export of lake water to Mississippi Sound, however, occurs when water levels in Mississippi Sound (and hence Lake Pontchartrain) drop, a situation that often occurs when westerly winds are increasing or easterly winds are decreasing. However, verification of the circulation-model results awaits field measurements of basin currents. The USGS is presently collecting time series of currents, as well as beam attenuation (for suspended sediment concentrations), waves, salinity, and temperature, at two sites in the Lake. One site is about two miles east of the center of the causeway, and the other is a few miles west of the southern end of the causeway. These measurements will be used to verify the numerical model of storm-driven circulation in the lake and to further study sediment resuspension and transport. The University of New Orleans will continue making measurements at our southern site when the USGS instruments are removed; if successful the result will be the first year-long time series observations of currents and water properties in the lake.
Suspended sediment distributions within the basin are being studied by comparing model results and in-situ measurements of beam attenuation, as well as other short- and long-term sources of suspended-sediment data. This work is expected to lead to a conceptual and/or quantitative model of the distribution and transport of suspended sediment within the basin.
Manheim, F.T., and McIntire, A.G., USGS, Woods Hole, MA.:
Sediment Quality Database Development and Geochemical Assessment of Sediments from Lake Pontchartrain and Surrounding Waterways
With contributions from George C. Flowers, Charles W. Holmes, Marcy E. Marot, James G. Flocks, S. Jeffress Williams, and Scott E. Noakes.
A cooperative database effort has retrieved all available (pre-1996) chemical and other sediment data on bottom sediments from Lakes Pontchartrain, Maurepas, and Borgne. They have been evaluated for quality and comparability, and placed in an accessible database as a resource for regional scientific and environmental assessment. This work is designed to help address concern about impacts on the lake from contaminants from New Orleans, the Mississippi River (through Bonnet Carré Spillway), and other sources.
The preliminary data release on an Internet web site (http://coast-enviro.er.usgs.gov/pontgeochem/) reflects an increase in available electronic data from less than 100 samples at the beginning of the work to nearly 1000 samples currently. Extensive data are available from Lake Pontchartrain and certain peripheral waterways, fewer for Lake Maurepas, and still fewer for Lake Borgne. [2008 Update: The data was published in 2002 and can be found at https://pubs.usgs.gov/prof/p1634j/.]
Most samples from Lakes Pontchartrain and Maurepas that meet preliminary quality tests do not exceed the lowest concentration levels for bulk sediment toxicity criteria utilized in the recent EPA National Sediment Inventory. In more centrally located parts of the Lakes metals like zinc, copper, lead, silver, and mercury approach ranges for pristine sediments. Data for organic toxic components are fewer, but likewise show concentration ranges well below lowest bulk sediment toxicity ranges. Metal and organic contaminants show no significant enrichment in the vicinity of the Bonnet Carré Spillway. However, water samples taken concurrently with a detailed bottom sediment sampling traverse adjacent to the Spillway during an opening in 1994 (USGS-Water Resources Division; USEPA) showed high nutrient concentrations. Such nutrient loadings have been suggested to contribute to the massive plankton blooms recorded after the 1997 Spillway opening.
Increases in contaminant concentrations occur in samples near New Orleans canals discharging to Lake Pontchartrain. Contamination ranging from moderate to severe can be documented in certain peripheral canals and waterways, especially Bayou Trepagnier. Additional data on areas close to the urban centers and other peripheral waterways are desirable and are being recovered. The data will be integrated into a GIS and will be included in a CD-ROM incorporating the sediment database.
Preliminary comparisons have been made between the quality-controlled conventional sample data and underway fine-fraction sediment sampling surveys conducted by University of Georgia researchers in cooperation with USGS in 1996. The results show substantial agreement, given allowance for the different sample fractions and other operational differences.
In summary, the database and its visual expressions show that compilation of heterogeneous historical data from diverse sources can contribute usefully to chemical characterization of sediments from estuaries and waterways that have been impacted by urban areas and industrial operations.
Polloni, C.F., Manheim, F.T., McIntire, A.G., USGS, Woods Hole, MA., and McFaul, E.J., USGS, Reston, VA.:
Interactive Electronic Publication of Chemical-environmental data from Lake Pontchartrain Basin: Exploration of Applications with Landview III, the New Interagency Database/map Query System
A software database and map illustration tool, Landview III, has been developed jointly by the U.S. Environmental Protection Agency (EPA), the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Census Bureau (Census), with inputs from other federal agencies. It has been combined experimentally with a chemical and environmental database for sediments (see Manheim and McIntire, this Symposium), web-site and other information to provide users with an extensive resource for spatial analysis of the Lake Pontchartrain Basin.
The Landview III package consists of ten regional CD-ROMs and a national index CD-ROM that display in maps and tables EPA databases on regulatory site locations, Census TIGER/line map data, demographic and economic data, USGS topographic and water data, and other information. The database package is combined with a mapping application, (MARPLOT) that allows users to select, display and manipulate information, and print maps and reports. The State of Louisiana has participated in the development of the latest release, and contributed a variety of special maps and geographic data to the Louisiana Landview III CD-ROM.
Landview III is designed to work with supplementary databases, allowing them to be fully integrated with the databases in the above mentioned CD-ROM by query systems that resemble a simple GIS, but do not require extensive operator skills. The experimental incorporation of Landview III with local databases and other data into a new CD-ROM was designed to build maps and graphic displays for the Lake Pontchartrain Basin region. The CD-ROM has been produced in accordance with the ISO-9660 CD-ROM standard, and is therefore capable of being read on any computing platform that has appropriate CD-ROM driver software installed.
While the new software system offers powerful new options for integrating a variety of data, it is not designed to have the capabilities of desktop GIS systems like ArcviewTM or MapInfoTM. However it is useful for aggregating and evaluating data and making preliminary assessments of spatial integrity and data quality. Data are easily added to the database system for local query to the mapping component. When data are selected, the mapping tool allows for setting scale ranges and other variables for controlled display at various map scales. Extensive national data sets integrated with Landview III provide for responsive generation of visual products for a variety of informational needs. The display of the chemical and sediment data sets with other environmental data is useful to determine possible sources of various data anomalies and their proximity to population centers.
Mathies, Linda and Nord, Beth U.S. Army Corps of Engineers, New Orleans, LA 70116; Penland, Shea, UNO; Westphal, Karen and Zganjar, Cris , Center for Coastal Energy and Environmental Resources, LSU:
The Creation of New Habitats through the Beneficial Use of Dredge Material in the Pontchartrain Basin
The U.S. Army Corps of Engineers New Orleans District (USACE-NOD) operates and maintains three major navigation channels in Louisiana that require maintenance dredging. Sediment is dredged annually and the USACE-NOD coordinates with state and federal natural resource agencies to determine the most appropriate methods for the disposal of dredged material and where possible, to beneficially use this material to create or enhance wetlands and other coastal habitats. The USACE-NOD have developed long-term disposal plans incorporating beneficial use for each of these navigation channels. Scientists from the UNO and LSU monitoring team assisted the USACE-NOD with the implementation of a large-scale monitoring program to quantify the amount of new habitat created and to improve placement techniques to maximize acres of wetland habitat created through the beneficial use of dredged material.
The beneficial use of dredged material is a very effective and cost-efficient tool to create, restore, and preserve valuable wetlands and other coastal habitats in Louisiana. Since 1985, the has created 1668.1 acres of new habitat within the study areas at the following navigation channels: Mississippi River - Gulf Outlet and Baptiste Collette Bayou. The location of the fourteen navigation channels in the Pontchartrain Basin where coastal erosion and wetland loss has created vast expenses of shallow open water provides almost unlimited opportunity for the beneficial use of dredged material for wetland restoration. The maintenance of these navigation channels offers the Coastal Wetland Planning, Protection, and Restoration Act (CWPPRA) the opportunity to partner with the USACS-NOD to increase the beneficial use of dredged material to sustain and create wetlands and other important habitats.
TABLE 1: Coastal habitats created by the beneficial use of dredged material.
1Land created between 1985-1996 measured in acres.
Noakes, Scott E., Dvoracek, Douglas K., and Noakes, John E., Center for Applied Isotope Studies, University of Georgia, Athens, GA:
Rapid Lakebed Metals Assessment of Lake Pontchartrain, Louisiana
In September 1996, the Center for Applied Isotope Studies at the University of Georgia (CAIS) worked in conjunction with the U.S. Geological Survey (USGS) to conduct a regional bottom sediment survey of Lake Pontchartrain (CAIS, 1997). Using a CAIS- developed rapid survey system for in situ collection of data and samples, more than 750 surficial sediment samples were collected over the entire lake region. The samples were analyzed for elemental content using non-destructive energy-dispersive x-ray fluorescence spectroscopy (XRF). The results provided a baseline of elemental distribution values for the lakebed sediments that will aid in the decision making for ecosystems management and environmental restoration issues for the Pontchartrain Basin.
In March 1997, the Bonnet Carré Spillway connecting the Mississippi River and Lake Pontchartrain was opened by the U.S. Army Corps of Engineers in a controversial move to reduce the risk of flooding in the New Orleans area during heavy spring rains. During the ten weeks that the spillway was open, an estimated 25% of the water and suspended sediment from the Mississippi River flowed into Lake Pontchartrain, reaching a maximum velocity of 240,000 cfs. Approximately 1.5 kg/m2 of sediment (equal to average yearly inputs to Gulf of Mexico estuaries) was deposited as bottom sediment in the lake during the spillway opening.
In an effort to determine the changes in the surficial sediment chemistry that occurred as a result of the temporary opening of the Bonnet Carré Spillway, the CAIS conducted a second sediment mapping survey in August 1997. For purposes of comparison, the 1997 samples were collected at the 1996 sample stations and analyses were completed using the same methods applied previously. Results of the 1997 survey demonstrated that the changes in the surficial sediment chemistry from the input of Mississippi River waters were significant, and that these changes occurred across the entire lake region.
Examples of the changes occurring in Lake Pontchartrain are presented in Figures 1a,b and 2a,b. Figures 1a and 1b compare the 1996 and 1997 survey results for elemental aluminum concentrations in surficial sediments. In September 1996, the aluminum concentrations were found to vary more or less randomly across the lake region. In August 1997, the concentrations are noted to be more uniformly distributed, with the lowest concentrations found along the shoreline and the highest concentrations located in the center of the lake. Similar results were indicated by surficial concentrations of the sand-associated elements silicon and titanium (not shown), which were highest along the western and northern shorelines of the lake.
Another prominent finding of the September 1996 survey was the delineation of high lead concentrations along the southern shoreline of Lake Pontchartrain between the causeway and Lakefront Airport (Figure 2a). This is a region that has been subjected to high density urbanization and industrial outflows for many years. After the opening of the Bonnet Carré Spillway, the redistribution of the lead concentrations of surficial sediments in this area changed dramatically (Figure 2b). In addition, locally higher levels of surficial lead concentrations were found to be present in the central part of the lake region. Similar alterations in surficial sediment concentrations were typical for several other elements examined as well (e.g. tin and chromium), where former areas of high elemental concentration now exhibited low to moderate concentrations, and marked differences were seen in the concentrations found on the periphery of the lake versus the central part of the lake.
Pedalino, F.C., M.A. Poirrier. Department of Biological Sciences, University of New Orleans, Lakefront, New Orleans, Louisiana, 70148:
Effects of Salinity Stratification and Algal Blooms on Benthic Invertebrate Populations in Southern Lake Pontchartrain
A non-mixing, bottom layer of more saline water occurs in southern Lake Pontchartrain due to saltwater intrusion through the Inner Harbor Navigation Canal. Organic material from urban runoff and algal growth accumulates in this bottom layer and reduces dissolved oxygen concentrations which causes stress on benthic organisms. Areas of the bottom that lack large invertebrates have been termed "Dead Zones." Conditions in Lake Pontchartrain during the summer of 1995 were favorable for the expansion of the dead zones. Heavy rainfall in April and early May of 1995 introduced plant nutrients and organic material. After this rainfall and associated flooding, a period of more than twenty days without rain occurred which allowed the movement of saline bottom water into the Lake. Nutrient rich Mississippi River water entered Lake Pontchartrain through the Bonnet Carré Spillway during June and July of 1995 and intense blooms of the blue-green algae and associated fish kills occurred during that summer.
Sites in southern Lake Pontchartrain were sampled on November 19, 1995 to determine the status of benthic invertebrate populations after summer blue-green algal blooms. They were re-sampled on July 31 and August 1, 1996 to determine if recovery from any adverse effects of the bloom had occurred. Salinity and dissolved oxygen measurements were made and benthic invertebrates were sampled at nine stations in 1995 and eleven stations in 1996. Stations were located along two transects that ran from the mouth of the Inner Harbor Navigation Canal west to the Lake Pontchartrain Causeway at 2.5 and 5.0 miles from the shore. During November of 1995, strong north winds that sometimes mix south shore waters occurred before sampling, however salinity stratification and low bottom dissolved oxygen concentrations were still present. Offshore from the Inner Harbor Navigation Canal during July and August of 1996 salinity stratification and low bottom dissolved oxygen concentrations were present, as generally occurs in late summer.
Past studies of benthic invertebrate populations in the same study area found communities dominated by annelids, indicative of stressful conditions, near the Inner Harbor Navigation Canal and a transition to communities dominated by mollusks, indicative of normal conditions, occurring with distance from the Canal. In contrast, November 1995 samples indicated stressful conditions at all sites on the two transects. The benthic invertebrate community was dominated by oligochaetes and polychaetes known to tolerate stress, while mollusks, including the clam, Rangia cuneata and the snails, Texadina sphinctsoma and Probythinella protera were rare at all sites. The presence of few mollusks and many annelids at all sites indicated that the dead zone expanded after the 1995 algal bloom. In 1996, recovery to normal communities dominated by mollusks occurred at the transect sites farthest away from the Inner Harbor Navigation Canal. The expansion of the dead zone in 1995 after the algal bloom and recovery in 1996 when no bloom occurred demonstrates the adverse effects of algal blooms on benthic invertebrates in areas of Lake Pontchartrain where salinity stratification occurs.
Penland, Shea, Department of Geology and Geophysics, University of New Orleans, New Orleans, LA 70118; Wayne, Lynda, Center for Coastal, Energy and Environmental Resources, Louisiana State University, Baton Rouge, LA 70803 and Britsch, Louis D., U.S. Army Corps of Engineer, New Orleans, LA 70116:
GIS Analysis of Natural and Human Causes of Coastal Land Loss in the Pontchartrain Basin
The dramatic loss of the Pontchartrain Basins coastal wetlands and barrier shorelines is well recognized by government agencies, industry, universities, and the public. Between 1930 and 1990 Pontchartrain Basin lost over 188,000 acres of land due to a complex suite of causes. Controversy and debate continues as to the causes of coastal loss in Louisiana. Estimates of the contribution of man to the land loss problem ranges between 10 percent and 90 percent. In many cases the role of natural processes and the multiple causality of the coastal land loss problem are overlooked. The GIS analysis sought to classify and quantify the forms and processes of coastal land loss using new digital data. This analysis captures the local types and causes of coastal land loss interwoven with regional land loss controls like subsidence and flood control.
The geomorphic classification captures information about the physical form of land loss areas. Development of the geomorphologic classification scheme was based upon two fundamental observations: 1) areas of land loss are, by definition, water, and 2) morphology cannot imply action or process. The first class, shoreline, applies to loss areas that occur relative to existing waterbodies. The second class, interior, applies to loss areas that occur independent of existing waterbodies. The geomorphic class can be further subdivided into different shoreline and interior types.
Land loss is typically the result of complex interactions among natural and human activities upon the landscape. Therefore, it is difficult to isolate an activity as the singular cause of a specific area of land loss. However, general assumptions can be made for most areas regarding the primary process that removed or submerged the land, as well as the actions and catalysts that initiated the process. By employing a hierarchical classification scheme which grades from general land loss processes to specific cultural and natural landscape activities, each loss area was classified as specifically as possible based on available information and scientific consensus.
The first level of the classification hierarchy addresses the basic processes of land loss. For purposes of this classification scheme, the term land is defined as all subaerial materials including surface vegetation, sediments, and organic soils. Three primary land loss process classes were identified:
1) erosion - mechanical removal and transport of land by water action,
2) submergence - increase of water level relative to ground surface elevation, and
3) direct removal - physical removal of land by actions other than water.
The primary land loss classes can be further subdivided into more detail process types.
The results of the geomorphic classification analysis indicated 49% of the coastal land loss in the Pontchartrain Basin is classed as interior and 51% is classed as shoreline. Interior ponding (73%) and gulf shoreline (23%) were the major geomorphic loss classes.
The results of the process classification indicated erosion (52.7%) was the most important primary process class followed by submergence (34.2%) and direct removal (13.1%). To interpret the process results and determine the major causes of coastal land loss requires ranking the individual classes and in some cases classes must be grouped to obtain a true ranking. An example of class grouping would the combination of direct oil/gas canal impacts with the indirect impacts of altered hydrology-oil/gas. Natural wave erosion is responsible for 47.5% of the coastal land loss in the Pontchartrain Basin followed by the direct and indirect effects of oil and gas activities which is responsible for 15.6% of the loss. The remaining 14 process classes are responsible for 36.9% of the coastal land loss. The importance of this study is the quantification of the form and processes of coastal land loss and the recognition of the multiple causes of coastal land loss within the Pontchartrain Basin.
MISSISSIPPI RIVER DELTA PLAIN COASTAL LAND LOSS - GEOMORPHOLOGY
MISSISSIPPI RIVER DELTA PLAIN COASTAL LAND LOSS - PROCESS
RANKING OF COASTAL LAND LOSS PROCESSES IN THE MISSISSIPPI RIVER DELTA PLAIN
Penland, Shea, Department of Geology and Geophysics, University of New Orleans, LA
Poirrier, M.A., C.D. Franze and S.M. Arthur. Department of Biological Sciences University of New Orleans, Lakefront, New Orleans, LA 70148:
The Occurrence of the Wood-boring Isopod, sphaeroma terebrans, in Littoral Cypress of Lake Pontchartrain and Lake MaurepasSphaeroma terebrans Bate 1866 is a wood-boring isopod that causes extensive damage to wooden structures in tropical and subtropical estuarine environments throughout the world. Wood-boring isopods are commonly known as gribbles. Sphaeroma terebrans has been reported from the Atlantic and Gulf of Mexico estuaries. It is known to burrow into mangroves and wooden boats, piers, pilings, and bridges. It has been studied in Florida where it might damage the tips of prop roots of red mangroves. Some workers have claimed that it caused significant damage and contributed to mangrove decline while others have suggested that it might benefit mangroves by inducing root spreading. Wounded mangrove tissue is known to initiate S. terebrans boring activity.
Much of our knowledge of S. terebrans comes from studies conducted in India. It was found that they do not use wood as a source of food, but burrow in wood for shelter. The same study suggested that they may be filter-feeders or consume algae and diatoms from the surface of their burrows. In India, it has been reported that salinities below 0.5ppt and above 50ppt were lethal. Rainfall and evaporation during a low tide when burrows are exposed to the air might explain this wide salinity tolerance. The optimum salinity range for growth and reproduction was between 4 ppt and 28 ppt. It was found that S. terebrans could withstand sudden changes of salinity, but when changing from a lower to a higher salinity the boring activity decreased. In the Cochin region of India, reproduction of S. terebrans occurred throughout the year. However, the water temperature variation in this region is very small (27.9 oC to 31.8 oC) and this pattern may not be seen elsewhere.
The distribution of S. terebrans in Lake Pontchartrain and Lake Maurepas was studied during the spring and summer of 1996. It was abundant in littoral cypress trees and other wooden structures in low salinity waters (0.5 to 5 ppt) of Lake Pontchartrain and Lake Maurepas. It did not occur in western Lake Maurepas where its distribution may be limited by fresh water. Many dead specimens were found in late winter 1996 indicating that in Louisiana they may be killed by cold temperatures. It was found to actively burrow in cypress and was most abundant in dead wood, but it also occurred in the prop roots of live trees. Damage is most common in the intertidal zone. In Louisiana, S. terebrans is an active filter feeder and, unlike high salinity gribbles, does not eat wood. Based on the presence of young in burrows, it breeds during late spring, summer and fall in Lake Pontchartrain. During the fall of 1997, measurements of its density in cypress wood were conducted near Fontainebleau State Park. More than 500 individuals per cubic decimeter were found. Although S. terebrans does not eat wood, it does produce extensive damage to wooden structures in Lakes Pontchartrain and Maurepas. It may contribute to shoreline erosion by weakening the prop roots of live trees causing them to fall, and through the destruction of the roots and stumps of dead trees that help stabilize eroding shorelines. Studies are in progress to determine if it borrows in areas of live cypress where bark has been removed. Although it cannot tolerate the low salinities of western Lake Maurepas, its distribution and abundance in Lake Pontchartrain does not appear to have been affected by the March 1997 Bonnet Carré Spillway opening.
Poirrier, M.A., B. Maglic, J. C. Francis, C. D. Franze, H.J. Cho. Department of Biological Sciences, UNO, Lakefront, New Orleans, LA. :
Effects of the 1997 Bonnet Carré Spillway Opening on Grassbeds in Lake Pontchartrain
Grassbeds, also known as submersed aquatic vegetation or SAV, provide valuable habitat for estuarine organisms. Lake Pontchartrain grassbeds have been in a state of gradual decline since first studied in 1953. An ongoing study of environmental factors which effect the distribution and abundance of Lake Pontchartrain grassbeds provided baseline information to determine possible effects of the March 1997 Bonnet Carré Spillway opening. Vallisneria americana and Ruppia maritima abundance were measured using the line-intercept method at Pointe aux Herbes, Lacombe, Goose Point and Fontainebleau State Park during late summer and fall of 1996 and 1997. A Myriophyllum spicatum bed at the mouth of Bayou St. John was also monitored from January through June of 1997. Temperature, salinity, dissolved oxygen, pH, alkalinity, Secchi disk transparency, turbidity and PAR (photosynthetically active radiation) were measured monthly at most of these sites before Spillway opening. Supplemental weekly measurements were made during and immediately after the Spillway opening and once every two weeks during summer algal blooms. Phytoplankton and macroalgal abundance were also monitored.
The introduction of Mississippi River water through the Spillway had immediate short-term effects on SAV. Salinity was reduced from low salinity brackish water to fresh water and water clarity was reduced. Plant nutrients were also introduced with River water. These nutrients adversely affected SAV by promoting rapid growth of phytoplankton and epiphytic algae which reduced available light. A significant decrease in PAR occurred at a depth of 1 m from April 3 through July 10, 1997. Values averaged 6.3 % of surface irradiance during this period compared to an average of 24% at other times. Values below 6.3 % are known to limit the growth of Ruppia but not Vallisneria. There was no statistically significant change in the abundance of Vallisneria, but a 65% decrease in Ruppia occurred between the surveys. Shading from phytoplankton adversely affected Ruppia in deep water, but overgrowth by Cladophora occurred in shallow water. Abundant growth of the filamentous green alga Cladophora occurred on Ruppia and Myriophyllum, but not Vallisneria. Cladophora growth on Ruppia made it more susceptible to shading from phytoplankton and uprooting by wave energy. This resulted in Ruppia being selectively lost from grassbeds. Large surface mats of Cladophora and increased turbidity from blue-green algal blooms eliminated the Myriophyllum bed in Bayou St. John.
Poirrier, Michael A. and J.M. King. Department of Biological Sciences, University of New Orleans, Lake Front, New Orleans, Louisiana, 70148:
Observations on Lake Pontchartrain Blue-green Algal Blooms and Fish Kills
Blue-green algal blooms occurred in Lake Pontchartrain during the summers of 1994,1995 and 1997, and a few local fish kills were documented during the 1995 and 1997 blooms. The causes and environmental effects of these blooms are controversial because they might show adverse effects of the Bonnet Carré Freshwater Diversion Project. Abundant surface growth of the blue-green alga Anabaena was reported in Lake Pontchartrain in the early 1950's, and small surface accumulations have occurred during most summers.
Although increased phytoplankton growth has been noted after spillway openings, there is no documentation of major surface blooms of blue-green algae after the 1973, 1975, 1979, and 1983 Spillway openings. Also no major blue-green algal blooms were noted in years between and after these openings. Proponents of the diversion project point to increased plant nutrient levels from development within the basin, particularly on the north shore, and unusual weather as the cause of the blooms, while opponents point to Bonnet Carré Spillway discharges. The blue-green algal blooms and associated events are indicative of high levels of plant nutrients.
A small surface accumulation of the blue-green alga, Anabaena circinalis was observed near Mandeville in June 1993, and large surface accumulations of A.circinalis occurred in late June 1994. A major bloom of A.circinalis occurred from late June through mid July 1995 and surface accumulations were present over most of the Lake during the peak of the bloom. Local fish kills occurred on the south shore during the 1995 bloom. No blue-green algal blooms occurred in 1996. An experimental opening of the Bonnet Carré Spillway was authorized in 1994, and an unauthorized opening occurred during 1995.
An extensive and persistent blue-green algal bloom occurred during the summer of 1997, after the March opening of the Spillway. Accumulations of A. circinalis and Anabaena spiroides first occurred near Mandeville on May 25, 1997. This bloom was disrupted by a cold front on May 31, 1997. Blooms of A. circinalis and Microcystis aeruginosa occurred in early June and continued through July. Algal cell counts as high as 1010 cells/L were found near Mandeville. Fish kills occurred at the mouth of Bayou St. John on June 15, near the mouth of Bayou Lacombe on June 22, and from Goose Point eastward on July 29.
Algal distribution and density were difficult to quantify during blooms because algae accumulated at the surface and moved with wind. At times algae were present throughout the estuary, and at other times they were concentrated near shore depending upon wind direction. During the summer when southerly winds prevailed, surface accumulations were more abundant on the north shore. Thick accumulations of algae near the shore and in embayments resembled concentrated pea soup. Duckweeds were often present with the blooms suggesting that movement of floating algae from wetlands may have contributed to the surface blooms. Floating algae were also probably lost from the Lake surface when high water and wind moved them over wetlands and natural shorelines.
Algal blooms may be more common in Lake Pontchartrain than they were in the past. Increased concentrations of nutrients in River water may explain why blooms have occurred after recent River discharges, but did not occur after past discharges. Increased nutrient loading from development in the basin, increased water clarity due to the cessation of shell dredging, and the retention time for nutrients and freshwater are also contributing factors to these blooms. Whatever the sources of blooms, the solution to controlling them is reducing nutrient loading. The value of any project that adds nutrients to the system should be questioned.
Pope, D.E. , Louisiana Geological Survey, Baton Rouge, LA.:
Geologic Framework of the Lake Pontchartrain Area
Opening of the Gulf: Although Lake Pontchartrain has existed for only about 5000 yearsor lessthe geological history of the underlying area can be broadly traced back some 200 to 250 millions of years. It was during the Triassic (earliest) period of the Mesozoic era of geologic time that the super continent Pangea began to split, or rift, into the continents that we now know. Pilger (1981) wrote that as a result of the rifting of Pangea, the Gulf of Mexico (GOM) opened about 180 to 130 million years before present. Other authors are generally in agreement with this timing. These years cover the upper half of the Jurassic (middle) period of the Mesozoic and extend upward into the Cretaceous (latest) period of the Mesozoic. The developing GOM was near the center of the rifting that is believed to have produced results that have affected the course of geological history of the study area through ensuing time.
Significant Geological Features (subsurface): Present in or near the study area, north to south, are: 1) the Mississippi salt-dome basin, 2) the Wiggins Uplift with its southwesterly trending branch, the Hancock County (Mississippi) ridge, 3) the Lower Cretaceous shelf edge/barrier reef trend, 4) the Tepetate-Baton Rouge-Lake Pontchartrain fault system, 5) the many en echelon faults plus Tertiary reefs and unconformities in the lake, and 6) the south Louisiana salt-dome basin, to the south, with its numerous large growth faults.
The Mississippi salt-dome basin trends NW-SE through the southern part of that state, extending into central Louisiana on the west, and into southern Alabama on the east. The Wiggins uplift is considered to have been caused by a horst (raised) block of the early basement rocks. It extends from southern Alabama, through southern Mississippi, and into Louisianas Florida parishes (those north of Lake Pontchartrain and east of the Mississippi River), well north of the lake. A branch of the Wiggins Uplift trends southwestward through Hancock County, plunging under the sediments of St. Bernard Parish. This positive salient is believed to be the cause of the strike of the older beds in the eastern area of Lake Pontchartrain to bow to the south. The Lower Cretaceous (LK) shelf edge is also known as the barrier reef trend, which is composed of various LK calcareous facies. It extends across the Florida parishes from northwestern West Feliciana Parish, southeastward to southeastern St. Tammany, crossing that parish just north of Lake Pontchartrain. This is also the approximate northern trace of the deep lowermost UK Lower Tuscaloosa (WNW-ESE) trend, with the southern trace including the northern half of the lake. Depths to the top of the Lower Tuscaloosa in the lake range (N-S) from about 15,000' to 21,000'. Major Lower Tuscaloosa production is found in a 10 -15 mile wide belt about 70 miles long, from southern Ayovelles to eastern Livingston Parish. There is then an interruption of about 80 miles to the southeast, where lesser production is found at Ft. Pike Field in St. Tammany and Orleans parishes, on the north shore of Lake Pontchartrain, and Rigolets Field in St. Bernard Parish. The Tuscaloosa is predominately sand and shale. The upper part of the UK is composed of the Austin-Navarro chalk. These two have a combined average thickness in the lake area of about 1250'. There has been production from the Austin as far east as central Livingston Parish. The UK Chalk trend overlaps that of the Tuscaloosa and extends southward in a belt to cover virtually all of Lake Pontchartrain. Depths to the Austin-Navarro in the lake range (N-S) from about 13,000' to 19,000'. The Tepetate-Baton Rouge fault was first recognized decades ago in the subsurface as a part of a system of normal, down-to-coast, more or less continuous, partly en echelon faults spanning the state at several latitudes in south Louisiana. Tepetate, is an oil field in NW Acadia Parish, while Baton Rouge here refers to the oil field, about five miles SE of the city. In more recent years, evidence of active surface, and subsurface, faulting has been recorded in the city of Baton Rouge, and extending eastward through northern Lake Pontchartrain. Several workers have documented this in B.R., while Lopez (1991) has called attention to bridge offsets in Lake Pontchartrain, and other related features. These faults in Lake Pontchartrain are almost certainly a part of the same fault system found in Baton Rouge. A distinct gulfward steepening in regional dip of subsurface beds at the latitude of Baton Rouge has been recognized for many years. The Tepetate-Baton Rouge-Lake Pontchartrain fault system helps explain this regional hinge line. Subsurface studies in Lake Pontchartrain have revealed a number of roughly east-west trending faults with structural contour closure on the downthrown (south) side. This is in keeping with the several ( mostly Miocene) oil fields found in the southern part of the lake, and to the east and especially to the west. The LaPlace-Bonnet Carré fields on the southwestern shore of the lake are fault-closure fields, aligned E-W with fields in the lake. The same is true of the Unknown Pass-Lake St. Catherine fields to the east of the lake. To the south of Lake Pontchartrain lies the south Louisiana salt-dome and growth-faulted basin.
Stratigraphy: The oldest possible sediments of the general area are probably the Triassic terrestrial red beds of the Eagle Mills Formation. The Jurassic of this area is best known for the Louann Salt that forms the salt domes of the salt basins to the north and south, but salt domes are absent in the immediate area of Lake Pontchartrain. The Cretaceous formations have been discussed above. The Tertiary formations become more and more calcareous moving from west to east in this area, especially the normally sandy facies of the (Paleocene-Eocene) Wilcox, the upper Frio (Oligocene), and much of the Miocene. A clue to this is offered by Forman and Schlanger (1957), who discussed a strong calcareous environment encroaching from the east, with a thick tongue of limestone developed in Lake Pontchartrain during Oligocene Anahuacian Heterostegina time, and just before and after. This is usually called the Het reef, although most of the approximately 1000 feet of limestone is very dense (cryptocrystalline), as compared to the porous, vuggy reefs found on the top of some salt domes on trend to the west. This "Florida-type" environmental influence from the east is the apparent cause of the increasing calcareous environment seen when moving eastward in the Lake Pontchartrain area. It is quite possible that the dense Het lime may have zones or pockets of patch reefs or sandy facies that would permit porosity locally. Virtually all formations in the lake area exhibit a general WNW-ESE strike, while thickening to the south, with the older beds thinning to the east, this latter being due the effect of the Hancock County high.
Formation of Lake Pontchartrain: Most authors (e.g., Saucier, 1963; Otvos, 1978; Tornqvist et al., 1996) generally agree on the following sequence of events, although the timing varies. Some 5000 to 6000 years ago the present lake vicinity was a marshy or swampy area. Later, barrier sand ridges began to form, with those to the south causing an embayment. To the north, the Pleistocene Prairie Terrace served as the containment. Then, the St. Bernard delta, the third of five major deltas forming the present now-buried deltaic complex, completed the formation of the Lake Pontchartrain-Lake Borgne area, essentially as we know it today. Proposed closure dates range from 4000 to 1550 years B.P. Lopez (1991) offers a different scenario for the formation of Lake Pontchartrain. He suggests a dynamic approach, with active faulting being the controlling factor. It should be noted that Lake Pontchartrain would today be much closer to the Gulf, southerly, except for the vast quantities of sediments that the Mississippi Rivers various deltas have deposited to the south of the lake, as the river has changed its course repeatedly over the past several thousand years.
Ramsey, Karen E. and Penland, Shea, Department of Geology and Geophysics, University of New Orleans, New Orleans, LA 70148, Kindinger, Jack U.S. Geological Survey, St. Peterburg, FL 33701, and Williams, S. Jeffress, U.S. Geological Survey, Reston, VA 22092:
Relative Sea Level Rise in the Pontchartrain Basin
The Pontchartrain Basin is defined as the area east of the Mississippi River through South Pass, south of the Pleistocene Terraces in the Florida Parishes, and west of the Chandeleur Islands. The basin is comprised of three distinct geomorphic regions, consisting of a marginal deltaic basin containing Lakes Maurepas, Pontchartrain, and Borgne, the St. Bernard delta, and the Balize delta. Relative sea level rise and subsidence is viewed as an important process driving coastal habitat change and land loss. Data from the U.S. Army Corps of Engineers-New Orleans District gage networks in Louisiana were analyzed to determine local and regional trends in relative sea level rise. Eustatic correction factors were applied to the rates of relative sea level rise to determine rates of subsidence.
Lakes Maurepas, Pontchartrain, and Borgne lie in a marginal deltaic basin located between the Pleistocene terraces in the Florida Parishes and the St. Bernard delta complex. The progradation of the St. Bernard delta complex 3,000 yr. ago along the eastern side of the Mississippi River delta plain enclosed the Pontchartrain Basin, which consists of Lake Maurepas connected to Lake Pontchartrain by Pass Manchac, Lake Pontchartrain connected to Lake Borgne by the Rigolets, and Lake Borgne connected to the Gulf of Mexico by Mississippi Sound. The Holocene section of the basin pinches out against the Pleistocene terraces to the north and thickens to 10-15 m toward the south adjacent to the St. Bernard delta. The USACE maintains 11 tide gage stations in this marginal deltaic basin. Of these only three have records suitable for analysis: the West End, Frenier, and Mandeville tide gage stations.
The West End tide gage station lies at the western end of Lake Pontchartrain. Its records date back to 1931 and continue to 1983. The analysis of the West End water-level history revealed a relative sea level rise rate of 0.43 cm/yr. The rate increased from 0.00 cm/yr for the first epoch to 0.15 cm/yr for the second.
The Mandeville tide gage station, located on the north shore of Lake Pontchartrain has a period of record from 1931 to 1983. The analysis of its water-level history indicates a relative sea level rise rate of 0.48 cm/yr for the entire record. The rate increased from 0.22 cm/yr for the first epoch to 0.75 cm/yr during the second.
The St. Bernard delta represents the depositional surface of the abandoned St. Bernard delta complex, which is more than 3,000 yr old. The transgressive submergence of this delta complex over the last 2,000 yr has generated the Chandeleur barrier island arc, which is separated from the mainland by Chandeleur Sound. Numerous large passes and tidal inlets connect the St. Bernard wetlands and Chandeleur Sound with the Gulf of Mexico. The Holocene section in this area increases in thickness from 15-20 m near Little Woods to over 100 m near Breton Island.
The USACE maintains 10 tide gage stations in the St. Bernard delta plain. Only two of these stations had records suitable for analysis. These stations are South Shore and Little Woods, located on the Bayou Sauvage delta of the St. Bernard delta complex, which separates Lake Pontchartrain and Lake Borgne.
The South Shore tide gage station lies immediately west of Point aux Herbes. Its period of records is 1949-1983. The analysis of the entire water-level history yielded a relative sea level rise rate of 1.00 cm/yr. The rate increased from 0.01 cm/yr for the 1942-1962 lunar epoch to 1.41 cm/yr for the 1962-1983 lunar epoch.
The Little Woods tide gage station is 10 km southwest of the South Shore station. It has records dating from 1931 to 1977. A relative sea level rise rate of 1.09 cm/yr was calculated for the entire period of record. The rate of relative sea level rise rose from 0.77 cm/yr for the first epoch to 2.15 cm/yr for the second. The average relative sea level rise rate for the St. Bernard delta is 1.02 cm/yr.
The Balize delta plain is a smaller, active deep-water delta of the larger Modern delta complex. This delta lies south of Venice and consists of seven major distributaries. The delta has been building toward the edge of the continental shelf for approximately 400 yr. Termed the "birdfoot," the Balize delta consists of a sequence of subdeltas that have overlapped to form the depositional surface. The thickness of the Holocene section exceeds 100 m. The main distributaries of the Balize delta are Southwest Pass, South Pass, Southeast Pass, Northeast Pass, North pass, Pass a Loutre, and Main Pass. The tidal regime in this coastal region is heavily influenced by the stages of the Mississippi River.
The USACE maintains 10 tide gage stations in the Balize delta plain and adjacent Mississippi River. A review of these stations indicated that only one station has records of sufficient quality and duration for analysis. The Port Eads tide gage station is located at South Pass about 4-5 km north of the Gulf of Mexico. The erratic character of the records reflects repeated flooding. The period of record is 1944-1983. The analysis indicated a relative sea level rise rate of 1.28 cm/yr. The rate increased from 0.61 cm/yr for the 1942-1962 epoch to 0.84 cm/yr for the 1962-1983 epoch.
Rohli, R.V., Kent State University, Kent OH 44242:
Thermal and Energy Budget Estimates over Lake Pontchartrain, Louisiana
In order to attain a full understanding of the physical, chemical, and biological processes of a lake, an understanding of the atmospheric properties and surface energy balance is important. Unfortunately, despite the ecological, economic, and recreational significance of Lake Pontchartrain, relatively little is known about its atmospheric and energy balance properties. Although it is most desirable to take field-based measurements of the energy balance components for the lake, such measurements do not exist because they require that expensive radiometers be mounted over an area that is logistically difficult to place equipment.
One goal of this research is to use a newly-available hourly data set collected by automated NWS platforms and archived by the Southern Regional Climate Center to describe the air and water temperature (Tair and Tsea, respectively) climatology of Lake Pontchartrain. Tair data are used for three sites: at the north shore near the Causeway Bridge ("Northshore"), adjacent to the bridge nine miles from the south shore ("Midlake"), and approximately two miles inland from the south shore at New Orleans International Airport ("Moisant"). Tsea observations are collected at the former two sites. This allows for the identification of local-scale temperature features such as an urban heat island, land/sea breeze thermal modification, and "continentality" effects produced by the "inland" site.
This study then applies the Tair and Tsea values, along with observed dew point temperature (Td) and wind data, to a derived equation that approximates the energy balance during times in which the atmospheric static stability is near-neutral or unstable. The equation gives a physically-based estimate of the Bowen Ratio (b) (the ratio of the turbulent flux densities of sensible heating (Qh) to latent heating (Qe)) over the Lake without requiring field-based measurement.
Midlake is used to represent Lake Pontchartrain in the energy balance analysis. Since Td is unavailable at Midlake, the Northshore value is substituted. However, to ensure that Td is representative of the atmosphere over the lake, only the hours during which the wind direction at Midlake is between 140° and 230° are used in the energy balance analysis.
Results suggest that January/February minimum Tair averages 9-11°C, while afternoon highs range from 14°-16°C. Lake Pontchartrain appears to moderate winter temperatures, as Midlake has the smallest daily Tair range. Furthermore, the "inland" Moisant site warms far more than the other sites in the afternoon. Apparently, the relatively common winter northerly winds collect sufficient moisture to prevent minimum temperatures at Moisant from falling as low as those at Northshore, despite its "inland" site.
In July/August, minimum Tair averages 25-28°C, and mean afternoon highs are 30-32°C. As in winter, the summer diurnal temperature regime at Moisant shows some features of "continentality" compared to the other sites. Midlake demonstrates spurious values in summer mid-afternoon hours, possibly resulting from instrument exposure problems due to the proximity of the concrete bridge. Thus, caution should be exercised in interpreting results and in future applications of Tair data at Midlake.
The flatness of the summer afternoon temperature curve at Northshore suggests that a sea breeze may be advecting enough moist air onshore to suppress maximum Tair. Such a pattern is not found at Moisant, either because the site is too far inland to be affected by such a local-scale circulation or because the relatively common summertime synoptic-scale southerly winds do not advect lake moisture over Moisant. This phenomenon should be investigated further in future research.
Average diurnal Tsea values for January/February and July/August suggest that, as expected, a short time lag exists between Tair and Tsea curves, with Tair showing much greater extremes. Not surprisingly, Midlake shows a much smaller diurnal Tsea range than Northshore, and is cooler than Northshore in summer. More surprising, however, is the tendency for Midlake to be cooler than Northshore in winter. Furthermore, the results suggest that Tsea at Northshore averages near 32°C in summer, a value that seems far too high, especially considering that the July-August Tair at Covington (11 miles north of Northshore) over the same period averages only 33°C. One possible explanation for this questionable Tsea value is that the sensor may be extending above the water level during "low tide" periods at the shore. Another possibility is that the Northshore sensor is sufficiently near the substrate in very shallow water to be influenced by radiation incident on the substrate rather than "true" Tsea. Again, caution should be exercised in future uses of the NWS automated Tsea data from the Northshore site.
Mean b during times when wind direction at Midlake was 140°-230° and neutral or unstable atmospheric conditions prevailed was 0.10, with a standard deviation of 0.09. These values correspond well with those calculated for similar water bodies. Presumably, the relatively high standard deviation results from differences in dew point, which affects Qe. Results of seasonal analyses suggest that b remains remarkably consistent in the seasonal cycle with slightly greater values in winter, when evaporation values are lowest. In the diurnal cycle, b is again consistently near 0.10, with similar standard deviations as before. Results show that during midday hours, it is relatively unusual that Tair < Tsea (unstable or near-neutral conditions), but when it is, sensible heating takes on a slightly greater role than during other times.
Although some sensor exposure problems exist, the data are generally useful for environmental assessments of the Lake. Lake Pontchartrain demonstrates many of the same local- to meso-scale atmospheric features that exist in other similar environments, such as the land/sea breeze phenomenon and the thermal modification of a large water body. Values of b are estimated at 0.10 - 0.14, and are remarkably consistent in the diurnal and seasonal cycles. Such information is useful to those requiring more detailed estimates of the energy balance because Qh or Qe can be calculated using field methods, while the other turbulent flux can be derived based on the known flux and estimated b.
Stafford, Tom, Louisiana Department of Environmental Quality :
Louisiana Department of Environmental Quality's (LDEQ): Decision Document for Bayou Trepagnier (the Bayou)
The Decision Document 1) Provides brief information about the location and history of the site since the beginning of petroleum refining at Norco; 2) Summarizes data from the LDEQ-Water Pollution Control Division's (LDEQ-WPCD) Impact Assessment that indicated that there were elevated concentrations of metals and significant concentrations of Polycylclic Aromatic Hydrocarbons present in the Bayou; 3) Summarizes the Remedial Investigation conducted by Shell Oil Co. that confirmed the findings of the LDEQ-WPCD; 4) summarizes the (Draft) Feasibility Study of Remedial Alternatives for Bayou Trepagnier, by Shell Oil Co. This document reported the results of additional sampling data from biota, sediment, and spoil banks. Characterized the risks presented by the site as minimal. Evaluated various remedial methods that could be performed on the site. Selected the remedy that was proposed by Shell Oil Co.; 5) Summarizes supplemental data gathered by Tulane and Xavier Universities that adds validity to the work performed by LDEQ and Shell Oil Co.; 6) Summarizes the comments LDEQ received on the Draft Decision Document for Bayou Trepagnier, (DDD); 7) Describes how the remedy is protective of human health and the environment; 8) Summarizes the changes will be made in the DFS for the (Final) Feasibility Study Report; 8) describes the environmental project that Shell Oil has agreed to perform at the request of the LDEQ; and 9) describes the events that may trigger a change in the remedial strategy.
Attachments to this document include: 1) Louisiana Department of Environmental Quality's Responses to Public Comment Concerning the Draft Decision Document for Bayou Trepagnier, in which the LDEQ presents its responses to comments concerning LDEQ's Draft Decision Document for Bayou Trepagnier received from various individuals and groups; 2) Copies of comment letters received from various groups and individuals; and 3) LDEQ's Draft Decision Document for Bayou Trepagnier.
Turner, R. E., Louisiana State University, Baton Rouge, LA., and Q. Dortch and N. N. Rabalais, LUMCON, Chauvin, LA 70344:
Control of Algal Populations in Lake Pontchartrain
Short-term and long-term changes in estuarine turbidity influence phytoplankton production, pelagic food chain dynamics, and benthic community development. Two common management issues related to estuarine light conditions are eutrophication and dredging. The former may reduce light penetration through increased phytoplankton species shifts and accumulation; the latter may have the same effect through re-suspension of bottom sediments. Either dredging or eutrophication may result in the decline of benthic macrophytes, for example, by reducing light penetration. Light conditions in shallow estuaries are also influenced by seasonal and annual variations in local wind speed that drive water currents that re-suspend inorganic and organic matter.
Shell dredging from Lake Pontchartrain apparently caused more turbid conditions than would be experienced without dredging (dredging stopped in the spring, 1990). Although the annual variations in wind and salinity are confounding factors in any analysis of long-term trends in light levels, light conditions have clearly improved with the cessation of dredging.
The experience of the 1997 opening demonstrates that turbidity in the Lake will increase under the proposed new Bonnet Carré Spillway (NGDM). Turbid conditions will increase immediately after the diversion opens and continue in the central and western portion of the lake for up to two months after the diversion stops. Because the NGDM diversion starts in the spring, turbid conditions will last well into the summer, if not the end of the summer (August).
The changes from the diversion will reverse the recent gains in water clarity achieved from the cessation of shell dredging in the Lake. These reversals will likely affect (negatively) the remaining grassbeds found on the north shore and prohibit re-establishment of grassbed once present in the 1950s. The light decline is that the Secchi disk depth will decrease from the present level of around 1 m, to about 60 cm.
Experimental and field observations have demonstrated that the introduction of Mississippi River water into Lake Pontchartrain stimulated phytoplankton growth, probably because the receiving water appears to mostly nitrogen limited which the river has in relatively high concentration. This eutrophication will cause the accumulation of phytoplankton in the lake and receiving coastal waters to be many times higher than before or after the diversion. The amounts will increase from somewhere around the 5-15 u g/l Ch1 a without the diversion to around 65 u g/l Ch1 a (or higher) with the NGDM. The 1997 bloom will be discussed in general terms, but in greater detail in another paper (Dortch et al.). A general relationship between nitrogen loading to the lake and potential (peak) bloom conditions will be demonstrated.
The diversion of riverwater under the NGDM will introduce different quantities and quality of riverwater into Lake Pontchartrain than that from any other diversion. The amounts of nitrogen will be of historically high amounts, and remain in the Lake for longer periods than anything previously described for this system. In effect, the lake will have a continuous exposure of high nutrient water all year and the likely result is that phytoplankton blooms be established. The additional nitrogen loading will be equal to four times the amount of nitrate entering from local river sources. The nitrogen load is not likely to be absorbed within the lake, but will move into Mississippi Sound and Lake Borgne, with additional water quality impacts therein.
Turner, R. E., Louisiana State University, Baton Rouge, LA.:
Bonnet Carré Diversions: Will Significant Nutrient Removal Occur in Wetlands?
There are limits to the transformation and storage rates for nutrients in water flowing through wetlands. This paper examines the empirical evidence for these limits as they apply to proposed diversions of Mississippi River water into Lake Pontchartrain. A comparison was made of nutrient concentrations entering and leaving the Atchafalaya River basin, a relatively natural and large (4,662 km2) alluvial swamp in south Louisiana (USA) with well-defined input and outlet channels that are monitored monthly for water quality. Total suspended solids, carbon, nitrogen and phosphorus are removed (51, 10, 6 and 28%, respectively) from the Atchafalaya River during the transit downstream through the swamp basin. Dissolved nitrate concentration, a major constituent of concern, remains essentially unchanged (+4%) from upstream to downstream monitoring stations. Alluvial swamp forests retain a much smaller amount of these elements flooding them than do wetland wastewater over- or below ground flow systems. These analyses document how: 1) diverting main stem Mississippi River water through a flood control spillway (part of a proposed wetland restoration project) will remove an insignificant amount of nutrients, and, 2) the reduction of overbank flooding from flood protection levees did not significantly diminish nutrient loading to the continental shelf. These results imply that nitrogen and phosphorus concentrations for large rivers in pre-industrial times did not decline significantly during overbank flooding.
Waters, J. P. , Lake Pontchartrain Basin Foundation, Metairie, LA; Guest, B., Vaughan, C., and Yamazaki, G., Department of Geology and Geophysics, University of New Orleans, New Orleans, LA:
Shoreline Change in the Upper Pontchartrain Basin
The Upper Pontchartrain Basin encompasses the wetlands bounded by the Pleistocene Terrace to the north, the settlements along the Mississippi River to the west, the Bonnet Carré Spillway to the south and the open waters of Lake Pontchartrain to the east. The basin includes the following Management Units as outlined in the 2050 initiative: Amite/Blind Rivers, Lake Maurepas, Tickfaw River Mouth, Manchac Land Bridge (East and West), Tangipahoa River Mouth, and Tchefuncte River Mouth. There is much speculation concerning the nature and extent of problems confronting the Upper Pontchartrain Basin. The bulk of the existing information is anecdotal with little supporting data. The purpose of this study is to compile existing geologic information in order to better understand controls on subsidence and surface hydrology and to conduct a shoreline change analysis for the Upper Pontchartrain Basin.
As part of the geologic investigation, an evaluation of the western extent of the Milton's Island Trend was undertaken. Saucier (I 963) originally proposed the Milton's Island Trend as a regressive barrier island beach sand which extends from the Mississippi coast in the east to the Upper Pontchartrain Basin in the west and was formed during Holocene sea level rise. The trend has been recognized by the presence of poorly sorted sand units on Milton's Island and in sand units encountered during coring prior to the construction of the Lake Pontchartrain causeway. Within Lake Pontchartrain, the trend is recognized by the presence of a series of low relief shoals that can be distinguished when contouring at one foot intervals on navigation charts (Saucier, 1963). The western extension of the trend in the Upper Pontchartrain Basin is recognized as a series of linear patches of fresh marsh immediately south of Pontchatoula which are apparent on aerial photos and landsat images.
As part of this study, a single vibracore was collected in the fresh marsh approximately IO km. south of Pontchatoula. The core location is on floating marsh less than I km. south of the Baton Rouge Fault. The 5.0 meter core TD'd in Pleistocene clay which is immediately overlain by dark gray lacustrine clay of Holocene age. The lacustrine clay is overlain by a thin, black, organic-rich horizon which is heavily rooted and appears to be a soil horizon. A total of 2.9 meters of sediment was recovered from the core barrel and the floating marsh was approximately 0.5 meters thick. Therefore, approximately 1.5 meters of water separates the base of the floating marsh and the top of the submerged soil horizon. The presence of the submerged soil horizon suggests that the floating marsh may have formed due to detachment of the fresh marsh vegetation during subsidence on the downthrown block of the Baton Rouge Fault rather than the capture of an existing lake by floatant vegetation. In any event, the core is devoid of Holocene sand, and the floating marsh in the Upper Pontchartrain Basin is not the western extension of the Milton's Island Trend.
The shoreline change analysis utilizes 1899 topographic sheets (T-sheets) and 1995 aerial photos. The 1899 shoreline data are taken directly from the mylar based T-sheets. The high water shoreline was measured using standard field surveying techniques. Although much care was taken in performing these measurements, the data are neither continuous nor synoptic. The 1995 aerial photos were transferred to USGS 7.5' quadrangle maps using a Bausch and Lomb zoom transfer scope. The high water shoreline was traced onto transparent acetate sheets. Aerial data are continuous and synoptic.
The 1899 and 1995 acetate sheets were scanned at 150 dpi in Adobe Photoshop and digitized using Microstation MGE software and Workstation. The resultant images were georeferenced using a minimum of four known latitude/longitude coordinates. Shoreline data for each year was converted to a common projection (Polyconic), coordinate system (latitude-longitude), datum (NAD 27), and ellipsoid (Clarke, 1866) using Intergraph World Mapping Software (WMS).
Willard, Debra A., and Waibel, Neil, U.S. Geological Survey, Reston, VA:
Palynomorph Assemblages from Lake Pontchartrain: Proxy Records of vegetation and Eutrophication
Palynomorphs preserved in shallow cores (< l meter) from southeastern Lake Pontchartrain provide a history of regional vegetational changes as well as the occurrence of algal blooms and changes in sedimentation rate. Two cores have been analyzed to date: core 9 (300 6' 38" N, 900 6' 18" W) was collected at a water depth of 16 feet and is 59 cm long, and core 7 (300 4' 39" N, 900 2' 11 " W) was collected at a water depth of 16.5 feet close to shore and is 62 cm long (Figure 1). Both cores were sampled at 2 cm increments, and pollen assemblages and the colonial green alga Pediastrum were quantified.
All pollen assemblages are dominated by Pinus (pine) pollen, with members of the Chenopodiaceae/Amaranthaceae (pigweed/saltwort families) the typical subdominant. Other common taxa include Quercus (oak), Taxodium (cypress), Poaceae (grass family), Cyperaceae (sedge family), and Asteraceae (daisy family). In core 9, from the more central location in the lake, pollen assemblages change little throughout the core, but peaks in pollen concentration at 4-8 cm and 32-36 cm may represent periods of more rapid sedimentation. These peaks correspond with peak abundances of Pediastrum, a colonial green alga commonly associated with eutrophication. Pollen assemblages from core 7 show a change in pollen composition and concentration at 38 cm depth. Below 38 cm, pollen of the pigweed/saltwort families are at their highest abundance, pollen concentration is low, and Pediastrum is absent. Above 38 cm, there is a fivefold increase in pollen and Pediastrum concentration, and pollen of the pigweed/saltwort families gradually decrease in abundance. Determination of an age model for this core should allow correlation of this event with known environmental changes.
In samples from both cores, well-preserved, reworked Cretaceous pollen is common. The Cretaceous was a time of well-documented floral provinciality, and the distribution of pollen assemblages characteristic of the provinces has been established in detail. The Cretaceous grains preserved in these cores represent the Aquilapollenites province, a boreal province extending approximately from the Rocky Mountains (1200 W longitude) westward across Eurasia to the Ural Mountains (1200 E longitude). The southernmost Cretaceous sites containing the palynomorphs preserved in these cores are in Wyoming and Montana, and the palynomorphs probably were transported to Lake Pontchartrain via the Mississippi River and its tributaries.
Planned analyses of vibracores (3-4 meters in length) from the central and northern parts of the lake will allow documentation of the temporal distribution of the reworked grains. If there are periodic pulses of high concentrations of the grains throughout the core, they probably represent flood events and could be used to help establish the periodicity of flooding throughout part of the Holocene. If the reworked grains are present in constant amounts throughout the core, however, it would seem more likely that they have been consolidated in Pleistocene deposits upstream from the lake from which they now are being eroded along with Pleistocene palynomorphs that probably cannot be distinguished reliably from Holocene taxa. Concurrent analyses of pollen and algal assemblages from the vibracores will clarify the natural patterns of palynomorph deposition, the history of eutrophication in the lake, and help determine whether recent changes are within the bounds of natural variation or represent a greater and more rapid response to anthropogenic activities in the region.