Sidescan-sonar mapping of benthic trawl marks on the shelf and slope off Eureka, California
A. M. Friedlander, G.W. Boehlert, M.E. Field, J.E. Mason, J.V. Gardner, P. Dartnell
1999, Fishery Bulletin (97) 786-801
The abundance and orientation of trawl marks was quantified over an extensive portion (>2700 km2) of the Eureka, California, outer shelf and slope, an important commercial bottom trawling ground for such high-value species as rockfish, sole, and sablefish. Fishing logbook data indicate that the entire reporting area was trawled about...
Etologia aplicada al manejo de especies amenazadas: el caso del turon de patas negras (Mustela nigripes)
Astrid Vargas, D. Biggins, B. Miller
1999, Etologia 33-39
Los turones de patas negras (Mustela nigripes) son considerados como uno de los mamíferos más amenazados del mundo. La última población silvestre fue descubierta en 1981 en Meeteetse, Wyoming, y en 1985 se extinguió debido a una epidemia de moquillo canino en combinacion con una epidemia de peste bubónica. Antes de...
Observations of turbulence in a partially stratified estuary
M.T. Stagey, Stephen G. Monismith, J.R. Burau
1999, Journal of Physical Oceanography (29) 1950-1970
The authors present a field study of estuarine turbulence in which profiles of Reynolds stresses were directly measured using an ADCP throughout a 25-h tidal day. The dataset that is discussed quantifies turbulent mixing for a water column in northern San Francisco Bay that experiences a sequence of states that...
Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995
P. J. Squillace, M.J. Moran, W.W. Lapham, C. V. Price, R.M. Clawges, J.S. Zogorski
1999, Environmental Science & Technology (33) 4176-4187
As part of the National Water-Quality Assessment Program of the U.S. Geological Survey, an assessment of 60 volatile organic compounds (VOCs) in untreated, ambient groundwater of the conterminous United States was conducted based on samples collected from 2948 wells between 1985 and 1995. The samples represent urban and rural areas...
Large-magnitude, late Holocene earthquakes on the Genoa fault, West-Central Nevada and Eastern California
A. R. Ramelli, J. W. Bell, C.M. DePolo, J. C. Yount
1999, Bulletin of the Seismological Society of America (89) 1458-1472
The Genoa fault, a principal normal fault of the transition zone between the Basin and Range Province and the northern Sierra Nevada, displays a large and conspicuous prehistoric scarp. Three trenches excavated across this scarp exposed two large-displacement, late Holocene events. Two of the trenches contained multiple layers of stratified...
The Puelche volcanic field: Extensive Pleistocene rhyolite lava flows in the Andes of central Chile
Wes Hildreth, J. Fierstein, E. Godoy, Robert E. Drake, B. Singer
1999, Revista Geologica de Chile (26) 275-309
A remote volcanic field in the rugged headwaters of the Río Puelche and Río Invernada (35.8°S) constitutes the largest cluster of Quaternary rhyolite lava flows yet identified in the Andean Southern Volcanic Zone. The Puelche Volcanic Field belongs to an intra-arc belt of silicic magmatic centers that extends, at least,...
Late Quaternary loess in northeastern Colorado: Part II - Pb isotopic evidence for the variability of loess sources
J. N. Aleinikoff, D.R. Muhs, R.R. Sauer, C.M. Fanning
1999, Geological Society of America Bulletin (111) 1876-1883
Loess in eastern Colorado covers an estimated 14 000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned...
General geology and geomorphology of the Mars Pathfinder landing site
A. W. Ward, Lisa R. Gaddis, Randolph L. Kirk, Laurence A. Soderblom, K. L. Tanaka, M.P. Golombek, T. J. Parker, Ronald Greeley, R.O. Kuzmin
1999, Journal of Geophysical Research E: Planets (104) 8555-8571
The Mars Pathfinder (MPF) spacecraft landed on relatively young (late Hesperian-early Amazonian; 3.1-0.7 Ga) plains in Chryse Planitia near the mouth of Ares Vallis. Images returned from the spacecraft reveal a complex landscape of ridges and troughs, large hills and crater rims, rocks and boulders of various sizes and shapes,...
Tools for groundwater protection planning: An example from McHenry County, Illinois, USA
R. C. Berg, B. Brandon Curry, R. Olshansky
1999, Environmental Management (23) 321-331
This paper presents an approach for producing aquifer sensitivity maps from three-dimensional geologic maps, called stack-unit maps. Stack-unit maps depict the succession of geologic materials to a given depth, and aquifer sensitivity maps interpret the successions according to their ability to transmit potential contaminants. Using McHenry County, Illinois, as a...
The factors controlling species density in herbaceous plant communities: An assessment
J.B. Grace
1999, Perspectives in Plant Ecology, Evolution and Systematics (2) 1-28
This paper evaluates both the ideas and empirical evidence pertaining to the control of species density in herbaceous plant communities. While most theoretical discussions of species density have emphasized the importance of habitat productivity and disturbance regimes, many other factors (e.g. species pools, plant litter accumulation, plant morphology) have been...
Estimating effects of limiting factors with regression quantiles
Brian S. Cade, J. W. Terrell, Richard L. Schroeder
1999, Ecology (80) 311-323
In a recent Concepts paper in Ecology, Thomson et al. emphasized that assumptions of conventional correlation and regression analyses fundamentally conflict with the ecological concept of limiting factors, and they called for new statistical procedures to address this problem. The analytical issue is that unmeasured factors may be the active...
Landscape patterns of CH4 fluxes in an alpine tundra ecosystem
A.E. West, P. D. Brooks, M.C. Fisk, Lesley K. Smith, E.A. Holland, C. H. Jaeger III, S. Babcock, R.S. Lai, S.K. Schmidt
1999, Biogeochemistry (45) 243-264
We measured CH4 fluxes from three major plant communities characteristic of alpine tundra in the Colorado Front Range. Plant communities in this ecosystem are determined by soil moisture regimes induced by winter snowpack distribution. Spatial patterns of CH4 flux during the snow-free season corresponded roughly with these plant communities. In...
Mining geology of the Pond Creek seam, Pikeville Formation, Middle Pennsylvanian, in part of the Eastern Kentucky Coal Field, USA
S.F. Greb, J.T. Popp
1999, International Journal of Coal Geology (41) 25-50
The Pond Creek seam is one of the leading producers of coal in the Eastern Kentucky Coal Field. The geologic factors that affect mining were investigated in several underground mines and categorized in terms of coal thickness, coal quality, and roof control. The limits of mining and thick coal are...
A record of hydrocarbon input to San Francisco Bay as traced by biomarker profiles in surface sediment and sediment cores
F. D. Hostettler, W. E. Pereira, K.A. Kvenvolden, A. VanGeen, S. N. Luoma, C. C. Fuller, R. Anima
1999, Marine Chemistry (64) 115-127
San Francisco Bay is one of the world's largest urbanized estuarine systems. Its water and sediment receive organic input from a wide variety of sources; much of this organic material is anthropogenically derived. To document the spatial and historical record of the organic contaminant input, surficial sediment from 17 sites...
Subsurface gas offshore of northern California and its link to submarine geomorphology
J.W. Yun, D.L. Orange, M.E. Field
1999, Marine Geology (154) 357-368
The northern California continental margin contains evidence of abundant subsurface gas and numerous seafloor features that suggest a causative link between gas expulsion and geomorphology. Analyses of seismic reflection, sidescan sonar, and high-resolution multibeam bathymetric data show that the occurrence of subbottom gas and the migration processes beneath the shelf...
Evidence for recent volcanism on mars from crater counts
W.K. Hartmann, M. Malin, A. McEwen, M. Carr, L. Soderblom, P. Thomas, E. Danielson, P. James, J. Veverka
1999, Nature (397) 586-589
Impact craters help characterize the age of a planetary surface, because they accumulate with time. They also provide useful constraints on the importance of surface erosion, as such processes will preferentially remove the smaller craters. Earlier studies of martian crater populations revealed that erosion and dust deposition are important processes...
Constraints on the sedimentation history of San Francisco Bay from 14C and 10Be
A. VanGeen, N. J. Valette-Silver, S. N. Luoma, C. C. Fuller, M. Baskaran, F. Tera, J. Klein
1999, Marine Chemistry (64) 29-38
Industrialization and urbanization around San Francisco Bay as well as mining and agriculture in the watersheds of the Sacramento and San Joaquin rivers have profoundly modified sedimentation patterns throughout the estuary. We provide some constraints on the onset of these erosional disturbances with 10Be data for three sediment cores: two...
Numerical model of a tracer test on the Santa Clara River, Ventura County, California
Tracy Nishikawa, Katherine S. Paybins, John A. Izbicki, Eric G. Reichard
1999, Journal of the American Water Resources Association (35) 133-142
To better understand the flow processes, solute-transport processes, and ground-water/surface-water interactions on the Santa Clara River in Ventura County, California, a 24-hour fluorescent-dye tracer study was performed under steady-state flow conditions on a 45-km reach of the river. The study reach includes perennial (uppermost and lowermost) subreaches and ephemeral subreaches...
Velocity reversals and sediment sorting in pools and riffles controlled by channel constrictions
D.M. Thompson, E.E. Wohl, R.D. Jarrett
1999, Geomorphology (27) 229-241
Keller [Keller, E.A., 1971. Areal sorting of bed-load material; the hypothesis of velocity reversal. Geological Society of America Bulletin 82, 753-756] hypothesized that at high flow, near-bed velocities in pools exceed velocities in riffles and create pool scour. Pools, however, typically have larger cross-sectional areas of flow at bankfull discharge....
Use of cosmogenic 35S for comparing ages of water from three alpine-subalpine basins in the Colorado Front Range
J.K. Sueker, J.T. Turk, R. L. Michel
1999, Geomorphology (27) 61-74
High-elevation basins in Colorado are a major source of water for the central and western United States; however, acidic deposition may affect the quality of this water. Water that is retained in a basin for a longer period of time may be less impacted by acidic deposition. Sulfur-35 (35S), a...
Paleoclimatic significance of δD and δ13C values in pinon pine needles from packrat middens spanning the last 40,000 years
Elise Pendall, Julio L. Betancourt, Steven W. Leavitt
1999, Palaeogeography, Palaeoclimatology, Palaeoecology (147) 53-72
We compared two approaches to interpreting δD of cellulose nitrate in piñon pine needles (Pinus edulis) preserved in packrat middens from central New Mexico, USA. One approach was based on linear regression between modern δD values and climate parameters, and the other on a deterministic isotope model, modified from Craig...
Temporal and spatial variability of the sediment grain-size distribution on the Eel shelf: The flood layer of 1995
D.E. Drake
1999, Marine Geology (154) 169-182
Sediment grain-size characteristics observed on the Eel shelf have been analyzed using a wet-sieving technique that minimizes breakage of aggregates. At several sites on the 70-m isobath north of the river, where a 1995 flood layer attained a maximum thickness of about 9 cm, replicate box cores were collected on...
The search for a source rock for the giant Tar Sand triangle accumulation, southeastern Utah
J. E. Huntoon, P. L. Hansley, N. D. Naeser
1999, American Association of Petroleum Geologists Bulletin (83) 467-495
A large proportion (about 36%) of the worlds oil resource is contained in accumulations of heavy oil or tar. In these large deposits of degraded oil, the oil in place represents only a fraction of what was present at the time of accumulation. In many of these deposits, the source...
Responses of riparian cottonwoods to alluvial water table declines
M. L. Scott, P.B. Shafroth, G.T. Auble
1999, Environmental Management (23) 347-358
Human demands for surface and shallow alluvial groundwater have contributed to the loss, fragmentation, and simplification of riparian ecosystems. Populus species typically dominate riparian ecosystems throughout arid and semiarid regions of North American and efforts to minimize loss of riparian Populus requires an integrated understanding of the role of surface...
Observations at the Mars Pathfinder site: Do they provide "unequivocal" evidence of catastrophic flooding?
M. G. Chapman, J.S. Kargel
1999, Journal of Geophysical Research E: Planets (104) 8671-8678
After Mars Pathfinder landed at the mouth of Ares Valus, a large channel that drains into the Chryse Planitia basin, the mission reports unanimously supported the interpretation that the lander site is the locus of catastrophic flooding by noting that all aspects of the scene are consistent with this interpretation....
