Scientific Investigations Report 2008–5026
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5026
YSI model 600XLM, 6920, or 6600 continuous multiparameter water quality monitors (sondes) were placed at 13 sites in Upper Klamath Lake and 2 sites in Agency Lake (fig. 2; table 1). At all these locations, sondes were placed vertically at a fixed depth of 1 m from the lake bottom. If the depth at a site was less than 2 m, the sonde was placed horizontally at the midpoint of the water column. A typical sonde mooring is shown in figure 3. The placement depth of 1 m from the bottom was chosen to provide data relevant to the endangered suckers of Upper Klamath Lake, which are bottom feeding fish. To observe water quality conditions near the water surface and provide comparisons to conditions near the lake bottom, a second sonde was placed on the same mooring at a fixed depth 1 m from the surface at three of the deepest locations, MDT, EPT, and MDN (fig. 2). All sondes recorded dissolved oxygen concentration, pH, specific conductance, and temperature at the beginning of every hour.
Sondes were cleaned and field measurements of site depth were made during weekly site visits to ensure proper placement of the instrument in the water column. Separate field measurements of dissolved oxygen concentration, pH, specific conductance, and temperature at the depth of each sonde were made as an additional check of sonde performance. During cleanings, measurements were made to compensate for the effect of biological fouling. Deployments generally lasted 3 weeks; at the end of this time the sonde at the site was replaced with a freshly calibrated instrument. Calibration of the sonde was checked for each parameter in the laboratory after retrieval to account for the effect of calibration drift. Data internally logged during deployment in the field were downloaded from retrieved sondes in the laboratory. These raw data were then loaded into the USGS Automated Data Processing System (ADAPS). Quality of the data was assured by the field information collected at weekly site visits and by processing the time series according to the procedures in Wagner and others (2000). Data corrections resulting from biological fouling and calibration drift were entered into ADAPS, which calculated the corrected values.
Of the 15 continuous water quality monitoring sites, 6 sites, MDN, WMR, EPT, MDT, HDB, and MDL (fig. 2), were selected for nutrient and chlorophyll a analyses. Water samples were collected on a weekly basis according to established protocols (U.S. Geological Survey, variously dated). Samples were analyzed for chlorophyll a, total phosphorus, total ammonia (ammonia plus ammonium), orthophosphate, and nitrite-plus-nitrate concentrations. To protect samples from contamination during the collection process, quality control protocols were followed as described in the National Field Manual for the Collection of Water-Quality Data (U.S. Geological Survey, variously dated). Two sampling methods were used relative to the type of constituent measured. Water samples analyzed for dissolved nutrients, including total ammonia, orthophosphate and nitrite-plus-nitrate, were collected from either one or two points in the water column, depending on the depth at the site. At the deep sites MDT and EPT, dissolved nutrient samples were collected from two points in the water column—one-quarter and three-quarters of the total water column depth—to investigate the difference between the upper and lower sections of the water column. At the shallow sites MDN, WMR, HDB, and MDL, dissolved nutrient samples were collected from middepth of the water column. Dissolved nutrient samples were collected by pumping through a hose (lowered to the appropriate depth in the water column) connected to a 0.45-µm capsule filter. Whole (unfiltered) water samples analyzed for total phosphorus and chlorophyll a constituted an equal integration over the depth of the water column. To collect depth-integrated samples, a weighted cage holding two 1-L bottles was lowered at a constant rate into the water to 0.5 m from the bottom at sites less than 10.5 m depth and to 10 m from the surface at sites greater than 10.5 m depth. Each bottle had two small ports, one for water to flow in and one for the escape of displaced air. The contents of the bottles from multiple collections of the cage sampler were combined in a churn splitter from which samples were collected for determination of total phosphorus and chlorophyll a concentration. Samples to be analyzed for total phosphorus were preserved with 1 mL of 4.5N (4.5 normal) H2S04, and chlorophyll a samples were fixed with MgCO3. Samples to be analyzed for dissolved nutrients and total phosphorus were chilled onsite and sent to the National Water Quality Laboratory (NWQL) in Denver, Colorado, for analysis. Finalized data were stored in the USGS National Water Information Systems (NWIS) database. Samples to be analyzed for chlorophyll a concentration were chilled onsite and sent to Aquatic Analysts in White Salmon, Washington. Results of the 2005 quality assurance program are discussed in the appendix.
Experiments were conducted to provide measurements of dissolved oxygen production and consumption rates in Upper Klamath Lake (fig. 4). Biological oxygen demand (BOD) bottles, with a volume of 300 mL and made of type 1 borosilicate glass, were filled with lake water integrated over the entire water column. BOD bottles were filled from the churn splitter with the same collection of lake water as chlorophyll a samples. This procedure allowed the chlorophyll a data to be used in the analysis of data from the dissolved oxygen production and consumption experiments. After filling, initial dissolved oxygen concentration and temperature were measured in the bottles with a YSI model 52 dissolved oxygen meter. Three bottles were attached to rest horizontally on racks at each of two depths. One bottle out of each group of three was dark (made so by wrapping it and its stopper with black electrical tape). Once attached to the incubator rack, the bottles were lowered into the water.
The experiment apparatus was moored at the site for at least 1 hour and typically retrieved before 3 hours. Dissolved oxygen concentration and temperature were again measured in each bottle, and incubation time was noted. The change in dissolved oxygen concentration was calculated in each bottle, and the incubation time was used to express the rate of dissolved oxygen change in milligrams of oxygen per liter per hour. Most experiments were conducted between the hours of 10:00 a.m. and 3:00 p.m. Logistical constraints did not allow for this experiment to be done at every water sample collection site during every week of sampling, but an attempt was made to collect the dissolved oxygen rate data at each of the six sites throughout the season, if not on a weekly basis (table 2). The upper rack generally was positioned 0.5 m below the water surface. Early in the season experimentation was done with the position of the lower rack before settling on 2 m depth to give sufficient contrast with the upper rack. As the season progressed, the lower rack was raised to 1.5 m, and toward the end of the season the lower rack was raised to 1 m at the shallow sites. Some sites became too shallow toward the end of the field season to incorporate the lower rack into the experiment.
Light intensity was measured in a vertical profile from the water surface to a depth of 2.5 m (or the lake bottom) in 0.5-m increments by using a LiCor LI-193SB underwater spherical quantum sensor. These measurements were used to estimate the depth of the photic zone, defined here as the point at which 99 percent of incident light is absorbed (or, 1 percent of incident light is transmitted), by using Beer’s law, which describes the penetration of solar radiation through the water column as an exponential relation (Welch, 1992):
(1)
α was estimated for each set of measurements by fitting equation (1) to the vertical profile of the light meter readings. The depth of the photic zone zp was then calculated as:
(2)
Measurements were made at each site on each date at the beginning of the incubation period (“early” measurements) and immediately after the incubation period (“late” measurements). The early and late measurements were then combined to provide the average depth of photic zone throughout the duration of each experiment at each site.
The location of meteorological measurement sites in the Upper Klamath Lake basin is shown in figure 2 and listed in table 3. Floating meteorological sites have been part of the Upper Klamath Lake monitoring program in previous years. Land-based meteorological sites were a new addition to the monitoring effort in 2005.
A schematic diagram of the typical land-based meteorological site is shown in figure 5. Wind speed and direction data were collected by an RM Young model 05103 wind monitor. Air temperature and relative humidity data were collected by a Campbell Scientific CS500 or HMP35C relative humidity and air temperature sensor. Additionally, solar radiation data were collected only at the WMR MET station by using a Li-Cor LI200SZ pyranometer. Floating sites were configured similarly to the land-based sites, although the mast attached to the buoy provided a height, measured from the surface of the water, of 2 m for wind monitors and 1.5 m for relative humidity and temperature sensors. Relative humidity and temperature data were not collected at the MDN MET, BLB MET, or SSHR MET sites during the 2005 field season. Data collected from all sensors at a site were stored every 15 minutes by a Campbell Scientific CR510, CR10, or CR10X datalogger located at the station. Power was provided by a 12-volt battery at the station charged by a solar power array. Data were collected during site visits, about every 2 weeks during the field season. During these visits, sensors were checked for proper function by comparison with hand-held instruments and were cleaned and maintained if necessary. Information necessary to correct data that may have been corrupted by fouling or drifts from proper calibration was collected as needed. Raw meteorological data were loaded into ADAPS and processed in the same manner as the water quality data.
Before calculating any statistics, data recorded by continuous water quality monitors were screened using temporal and, when appropriate for the statistic, spatial criteria. In this report, daily statistics are used for continuous water quality monitoring data. For a day’s worth of data to be acceptable for computing daily statistics, at least 80 percent of the day’s possible measurements were necessary, constituting a “qualifying day” of data. A spatial criterion was applied when data over the entire lake were compiled to compute a statistic, such as lakewide daily median dissolved oxygen concentration. This criterion specified that at least 7 percent of the lake’s water quality monitoring sites had to have qualifying daily data to in order to compute the lakewide statistic for a particular day.
For statistics at individual meteorological sites, the temporal criterion ensured that at least 80 percent of the day’s possible measurements were available to constitute a qualifying day of data. To compute lakewide meteorological statistics, the SSHR MET site was not included in calculations because this site was not established until August 18, 2005. Different levels of spatial acceptability were applied depending on the parameter because not all parameters were collected at all sites, and there were relatively few meteorological sites around the Upper Klamath Lake basin. Statistics of solar radiation were computed only with data collected during daylight hours. Solar radiation data were collected at only one site, so no spatial criterion was applied to these data. Air temperature and relative humidity data were collected at three sites, so the spatial criterion for these parameters ensured that two of the three sites (67 percent) had daily qualifying data to compute a lakewide daily statistic. Wind speed data were collected at all meteorological sites, so the spatial criterion for wind speed ensured that four of the five sites (80 percent) had daily qualifying data to compute a lakewide daily statistic. Lakewide statistics were not computed for wind direction. Statistics of direction can be potentially misleading or uninformative. For example, a mean wind direction may indicate a direction that was not an actual wind direction during the time the statistic was computed, and because wind direction is a value between 0 and 359, daily minimum and maximum values of direction tend to be 0 and 359, respectively.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2008/5026
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