National Research Program

Partial List of Abstracts, 1995

Aiken, G. and Cotsaris, E., 1995, Soil and Hydrology: Their effect on natural organic matter: Journal of the American Water Works Association, Vol. 87, pp. 36-45.

The importance of source materials, soil chemistry and hydrology on the amount and composition of DOC in aquatic systems is discussed, showing how each factor influences the amount and reactivity of the organic material. Sources of DOC in aquatic ecosystems can be categorized as allochthonous and autochthonous. Organic matter derived from different source materials has distinctive chemical characteristics. As yet, the relative contributions of allochthonous and autochthonous sources to different water bodies cannot be characterized based on the chemical characterization of DOC. Much of the DOC in surface waters is allochthonous material originating in soils. Geochemical interactions between organic matter and inorganic constituents influence the amount of DOC and result in chemical fractionation of the organic matter, which alter the composition and reactivity of the DOC. Transport of allochthonous organic carbon into surface waters depends on hydrologic conditions within the watershed. The flow path of water depends on the soil's physical properties.

Aiken, G.R., McKnight, D.M., Harnish, R.A., and Wershaw, R.L., 1995, Geochemistry of aquatic humic substances in the Lake Fryxell Basin: Antarctica: Biogeochemistry.

Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modern 14C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water, 3) The addition of recent organic matter to the bottom waters of the lake from the moat.

Back, William, 1995, Water Management by Early People in the Yucatan, Mexico: Environmental Geology, v. 25.

The Yucatan Peninsula is a coastal plain underlain by permeable limestone and receives abundant rainfall. Such hydrogeologic conditions should provide major supplies of water; however, factors of climate and hydrogeology have combined to form a hydrologic system with chemical boundaries that limits the amount of fresh water available. Management of water resources has long had a major influence on the cultural and economic development of the Yucatan. The Mayan culture of the northern Yucatan developed on extensive use of groundwater. The religion was water oriented and the Mayan priests prayed to Chac, the water god, for assistance in water management, primarily to decrease the severity of droughts. The Spaniards arrived in 1517 and augmented the supply by digging wells, which remained the common practice for more than 300 years. Many wells now have been abandoned because of serious problems of pollution. A historical perspective of a paper such as this provides insight into the attitudes concerning water of early people and perhaps provides insight into current attitudes concerning water. Hydrogeologists possess the expertise to generate relevant information required by water managers to arrive at management programs to achieve sustainable development.

Back, William, Landa, E.R., and Meeks, L.M., 1995, Bottled water, spas and early years of water chemistry: Ground Water, v. 33, no. 4, pp. 605-614

Although hot springs have been used and enjoyed for thousands of years, it was not until the late 1700s that they changed the course of world civilization by being the motivation for development of the science of chemistry. The pioneers of chemistry such as Priestley, Cavendish, Lavoisier, and Henry were working to identify and generate gases, in part, to determine their role in carbonated beverages. In the 18th century, spas in America were developed to follow the traditional activities of popular European spas. However, they were to become a dominant political and economic force in American history on three major points: (1) By far the most important was to provide a place for the leaders of individual colonies to meet and discuss the need for separation from England and the necessity for the Revolutionary War; (2) the westward expansion of the United States was facilitated by the presence of hot springs in many locations that provided the economic justification for railroads and settlement; and (3) the desire for the preservation of hot springs led to the establishment of the National Park Service. Although mineral springs have maintained their therapeutic credibility in many parts of the world, they have not done so in the United States. We suggest that the American decline was prompted by: (1) the establishment of The Johns Hopkins School of Medicine in 1893; (2) enactment of the Pure Food and Drug Act of 1907; and (3) the remarkable achievement of providing safe water supplies for American cities by the end of the 1920s. The current expanding market for bottled water is based in part on bottled water being an alternative beverage to alcohol and sweetened drinks and the inconsistent palatability and perceived health hazards of some tap waters.

Bales, R.C., Li, S., Maguire, K.M., Yahya, M.T., Gerba, C.P., and Harvey, R.W., 1995, Virus and bacteria transport in a sandy aquifer, Cape Cod, MA: Ground Water, v. 33, p. 653-661.

Transport of the bacteriophage PRD-1, bacteria, and latex microspheres was studied in a sandy aquifer under natural-gradient conditions. The field injection was carried out at the U.S. Geological Survey's Toxic Substances Hydrology research site on Cape Cod. The three colloids and a salt tracer (Br-) moved along the same path. There was significant attenuation of the phage, with PRD-1 peak concentrations less than 0.001 percent of Br- peaks 6 m from the source; but the low detection limit (one per ml) enabled tracking movement of the PRD-1 plume for 12 m downgradient over the 25-day experiment. Attenuation of phage was apparently due to retention on soil particles (adsorption). Attenuation of bacteria and microspheres was less, with peak concentrations 6 m from the source on the order of 10 and 0.4 percent of Br-, respectively. Injection of a high-pH pulse of water 20 days into the experiment resulted in significant remobilization of retained phage, demonstrating that attached phage remained viable, and that PRD-1 attachment to and detachment from the sandy soil particles was highly pH dependent. Phage behavior in this experiment, i.e. attenuation at pH 5.7 and rapid resuspension at pH 6-8, was consistent with that observed previously in laboratory column studies. Results illustrate that biocolloids travel in a fairly narrow plume in sandy (relatively homogeneous) media, with virus concentrations dropping below detection limit several meters away from the source; bacteria concentrations above detection limits can persist over longer distances.

Bennett, J.P., 1995, Algorithm for resistance to flow and transport in sand-bed channel: Journal of Hydraulic Engineering, v. 121, no. 8. p. 578-590

An algorithm is developed that relates depth to discharge and determines bed- and suspended-load transport for the entire range of bed forms found in sand-bed channels; equilibrium-state geometry of lower flow regime bedforms is also predicted. Grain shear stress and form resistance are differentiated using a drag coefficient closure and a two-segment logarithmic velocity profile. A Meyer-Peter-type formulation is used to compute sand transport in the bed-load layer and for computing suspended sand transport, McLean's procedure of 1991 and 1992 is adopted. A bed-form classification scheme is developed that uses a particle size parameter and the transport strength to predict bed-form type; it correctly identifies 73% of the 1,192 mostly flume-scale calibration data sets. For 194 sets of dune-transition bed-form calibration data, a modified version of van Rijn's 1984 bed-form geometry predictor yields a geometric average predicted to observed height ratio of 1.00. After calibration, the algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1.00. For a verification data set of 855 observations, mostly from rivers and canals, the overall geometric averages of predicted to observed depth and transport are 0.87 and 1.14.

Benson, L.V., Kashgarian, M. and Rubin M., 1995, Carbonate deposition, Pyramid Lake subbasin, Nevada: 2. Lake levels and polar jet stream positions reconstructed from radiocarbon and elevations of carbonate deposits (tufas): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 117, p. 1-30.

Most of the tufas in the Pyramid Lake subbasin were deposited within the last 35,000 yr, including most of the mound tufas that border the existing lake. Many of the older tufas (>21,000 yr B.P.) contained in the mounds were formed in association with ground-water discharge. The radiocarbon (14C) ages of the older tufas represent maximum estimates of the time of their formation. Lake Lahontan experienced large and abrupt rises in level at ~22,000, 15,000, and 11,000 yr B.P. and three abrupt recessions in level at ~16,000, 13,600, and 10,000 yr B.P. The lake-level rises that were initiated at ~23,500 and 15,500 yr B.P. are believed to indicate the passage of the polar jet stream over the Lahontan basin. During expansion of the Laurentide Ice Sheet, the jet stream moved south across the basin, and during the contraction of the Ice Sheet, the jet stream moved north across the basin.

The bulk of the carbonate contained in the mound tufas was deposited during the last major lake cycle (~23,500-12,000 yr B.P.), indicating that ground- and surface-water discharges increased at ~23,500 and decreased at ~12,000 yr B.P. A lake-level oscillation that occurred between 11,000 and 10,000 yr B.P. is represented by a 2-cm thick layer of dense laminated tufa that occurs at and below 1180 m in the low-elevation tufa mounds and at 1205 m in the Winnemucca Lake subbasin.

Boyer, E.W., Hornberger, G.M., Bencala, K.E., McKnight, D.M., 1995, Overview of a simple model describing variation of dissolved organic carbon in anupland catchment: Ecological Modelling.

Hydrological mechanisms controlling the variation of dissolved organic carbon (DOC) were investigated in the Deer Creek catchment located near Montezuma, CO. Patterns of DOC in streamflow suggested that increased flows through the upper soil horizon during snowmelt are responsible for flushing this DOC-enriched interstitial water to the streams. We examined possible hydrological mechanisms to explain the observed variability of DOC in Deer Creek by first simulating the hydrological response of the catchment using TOPMODEL and then routing the predicted flows through a simple model that accounted for temporal changes in DOC. Conceptually the DOC model can be taken to represent a terrestrial (soil) reservoir in which DOC builds up during low flow periods and is flushed out when infiltrating meltwaters cause the water table to rise into this "reservoir". Concentrations of DOC measured in the upper soil and in streamflow were compared to model simulations. The simulated DOC response provides a reasonable reproduction of the observed dynamics of DOC in the stream at Deer Creek.

Caffrey, J.M. 1995, Spatial and seasonal patterns in sediment nitrogen remineralization and ammonium concentrations in San Francisco Bay, California: Estuaries, v. 18, p. 219-233.

Nitrogen remineralization and extractable ammonium concentrations were measured in sediments from several locations in North and South San Francisco bays. In South Bay, remineralization rates decreased with depth in sediment and were highest in the spring following the seasonal phytoplankton bloom. At the channel stations, peak remineralization lagged peak water-column phytoplankton biomass (as measured by chlorophyll a) by a month. Remineralization rates were generally higher in South Bay than North Bay. The lower remineralization rates in North Bay may be a result of anomalously low phytoplankton production and thus reduced deposition to the sediments, as well as low riverine organic inputs to the upper estuary in recent years. Remineralization rates were positively correlated to carbon and nitrogen content of the sediments. In general, ammonium profiles in South Bay sediments showed no increase in deeper (4-8 cm) sediments. In North Bay, ammonium concentrations were greatest at stations with highest remineralization rates, and, in contrast to South Bay, extractable ammonium increased in deeper sediment. Differences in ammonium pools between North Bay and South Bay may be a result of increased irrigation by deep-dwelling macrofauna, which are more abundant in South Bay.

Cain, D.J., Luoma, S.N., and Axtmann, E.V., 1995, Influence of gut content in immature aquatic insects on assessments of environmental contamination: Canadian Journal of Fisheries and Aquatic Sciences, v. 52, no. 12, p. 2736-2745.

We evaluated the effect of metal associated with the gut content in immature aquatic insects (larvae and nymphs) on spatial and interspecific comparisons of whole-body metal concentrations. Four species, common to cobble-bottom rivers and streams, were collected along an established contamination gradient in the Clark Fork River, and from tributaries of the Clark Fork. Metal concentrations were determined in the gut and its content and in the insect body. Whole-body metal concentrations were higher and more variable as a result of gut content. The positive bias produced by the gut content did not alter interpretations of site contamination in most cases. Interspecific comparisons of metal bioaccumulation also were not greatly affected by the presence of gut content. The influence of gut content was specific for metal, species, and site. Feeding habit, gut size, and metal bioaccumulation in the body affected the relative contribution of the gut and its content to metal concentrations in the whole insect.

Calvo, J.P., Jones, B.F., Bustillo, M., Fort, R., Alonzo Zarza, A.M., and Kendall, C., 1995, Sedimentology and geochemistry of carbonates from lacustrine sequences in the Madrid Basin, central Spain: Chemical Geology, v. 123, p. 173-191.

Lacustrine and alluvial carbonate facies have been investigated in middle Miocene successions of the western side of the Madrid Basin in order to evaluate paleoenvironments in which carbonates formed. Carbonate facies are varied and include: (1) calcrete and dolocrete; (2) pond deposits; (3) lake margin dolostone; (4) mudflat carbonate; and (5) open-lake carbonate facies. The dominant mineralogy of these is dolomite and/or low-Mg calcite. No high-Mg calcite or aragonite have been detected in any sample. d18O- and d13C-values range from -8.20 to -1.80 per mil PDB and -10.25 to -0.70 per mil PBD, respectively. More negative d18O- and d13C-values correspond to predominantly calcite calcretes and to carbonate deposited in ponds at the foot of arkosic alluvium. Higher delta d18O-values are from both lacustrine carbonate and dolocrete. This latter lithofacies has strong geochemical similarities to dolostones deposited in a lake margin environment. Mudflat carbonate, deposited on shallow platforms subject to lake water oscillation, shows great heterogeneity in both stable isotope value and trace-element content. The mineralogy of these carbonates is dominated by calcite and the limestones contain molds of gypsum. Occurrence of calcitized dolomite textures in these facies suggests the influence of fresher water during expanding lacustrine cycles or further interaction with less saline groundwater. Trace-element contents are considered to be potential indicators of the different carbonate facies types, thus aiding the paleoenvironmental interpretation. However, discrimination among carbonate facies on the basis of trace-element contents appears to be dependent on the statistical method utilized for treatment of data. More information is needed to ascertain their use as paleoenvironmental indicators.

Cozzarelli, IM; Herman, JS; Baedecker, MJ, 1995, Fate of microbial metabolites of hydrocarbons in a coastal plain aquifer: The role of electron acceptors: Environmental Science and Technology, v. 29, no. 2, p. 458-469.

A combined field and laboratory study was undertaken to understand the distribution and geochemical conditions that influence the prevalence of low molecular weight organic acids in groundwater of a shallow aquifer contaminated with gasoline. Aromatic hydrocarbons from gasoline were degraded by microbially mediated oxidation-reduction reactions, including reduction of nitrate, sulfate, and Fe(III). The biogeochemical reactions changed over time in response to changes in the hydrogeochemical conditions in the aquifer. Aliphatic and aromatic organic acids were associated with hydrocarbon degradation in anoxic zones of the aquifer. Laboratory microcosms demonstrated that the biogeochemical fate of specific organic acids observed in groundwater varied with the structure of the acid and the availability of electron acceptors. Benzoic and phenylacetic acid were degraded by indigenous aquifer microorganisms when nitrate was supplied as an electron acceptor. Aromatic acids with two or more methyl substituents on the benzene ring persisted under nitrate-reducing conditions. Although iron reduction and sulfate reduction were important processes in situ and occurred in the microcosms, these reactions were not coupled to the biological oxidation of aromatic organic acids that were added to the microcosms as electron donors

Day-Lewis, F. D., Person, M. A., and Konikow, L. F., 1995, A computer program (MACPUMP) for interactive aquifer-test analysis: U.S. Geological Survey Water-Resources Investigations Report 95-4012, 32 p.

This report introduces MACPUMP (Version 1.0), an aquifer-test-analysis package for use with Macintosh4 computers. The report outlines the input- data format, describes the solutions encoded in the program, explains the menu-items, and offers a tutorial illustrating the use of the program. The package reads list-directed aquifer-test data from a file, plots the data to the screen, generates and plots type curves for several different test conditions, and allows mouse-controlled curve matching. MACPUMP features pull-down menus, a simple text viewer for displaying data-files, and optional on-line help windows. This version includes the analytical solutions for nonleaky and leaky confined aquifers, using both type curves and straight-line methods, and for the analysis of single-well slug tests using type curves. An executable version of the code and sample input data sets are included on an accompanying floppy disk.

Dettinger, M.D. and Cayan,D.R. 1995, Large-scale atmospheric forcing of recent trends toward early snowmelt runoff in California: J. of Climate, v. 8, p. 606-623.

Since the late 1940s, snowmelt and runoff have come increasingly early in the water year in many basins in northern and central California. This subtle trend is most pronounced in moderate-altitude basins, which are sensitive to changes in mean winter temperatures. Such basins have broad areas in which winter temperatures are near enough to freezing that small increases result initially in the formation of less snow and eventually in early snowmelt. In moderate-altitude basins of California, a declining fraction of the annual runoff has come in April-June. This decline has been compensated by increased fractions of runoff at other, mostly earlier, times in the water year. Weather stations in central California, including the central Sierra Nevada, have shown trends toward warmer winters since the 1940s. A series of regression analyses indicate that runoff timing responds equally to the observed decadal-scale trends in winter temperature and interannual temperature variations of the same magnitude, suggesting that the temperature trend is sufficient to explain the runoff-timing trends. The immediate cause of the trend toward warmer winters in California is a concurrent, long-term fluctuation in winter atmospheric circulations over the North Pacific Ocean and North America that is not immediately distinguishable from natural atmospheric variability. The fluctuation began to affect California in the 1940s, when the region of strongest low-frequency variation of winter circulations shifted to a part of the central North Pacific Ocean that is teleconnected to California temperatures. Since the late 1940s, winter wind fields have been displaced progressively southward over the central North Pacific and northward over the west coast of North America. These shifts in atmospheric circulations are associated with concurrent shifts in both West Coast air temperatures and North Pacific sea surface temperatures.

Edmond, J.M., Palmer, M.R., Measures, C.I.; Grant, B., and Stallard, R.F., 1995, The fluvial geochemistry and denudation rate of the Guayana Shield in Venezuela, Colombia, and Brazil: Geochimica et Cosmochimica Acta, v. 59, no. 16, p. 3301-3325.

The Guayana Shield is composed of Early to Mid-Precambrian igneous and metamorphic basement rocks with a quartzitic platform cover. The complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment. Total erosion rates are extremely slow, approcimately 10 m/m.y., with equal contributions from the dissolved and suspended loads. However, the former is largely silica with ratios of Si to total cation equivalents [Si:TZ +] ranging to in excess of three. Weathering is "complete" to kaolinite and gibbsite, i.e., the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate. In basins of relatively homogeneous lithology, Rb/Sr isochrons constructed from the river data agree with the whole-rock ages from the drainages; thus, all the common, refractory, Rb-containing minerals (K-feldspar, mica) are completely dissolved. The thick, lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other Southern Hemisphere Shields. In the absence of active tectonics or greatly accelerated mechanical erosion, the weathering rates of these basement rocks must be quite insensitive to environmental change.

Edmunds, J.L., Cole, B.E.., Cloern, J.E., Caffrey, J.M., and Jassby, A.D., 1995, Studies of the San Francisco Bay, CA, estuarine ecosystem. Pilot Regional Monitoring Program Results, 1994: USGS Open File Report 95-378, 436 p.

As part of a pilot regional monitoring program, water samples were collected in the San Francisco Bay estuary during 22 cruises from January through November 1994. Conductivity, temperature, light attenuation, turbidity, oxygen, and in-vivo chlorophyll fluorescence were measured longitudinally and vertically in the main channel of the estuary from south of the Dumbarton Bridge in the southern part of the bay to Rio Vista on the Sacramento River. Discrete water samples were analyzed for chlorophyll a, phaeopigments, suspended particulate matter, and dissolved oxygen. Water density was calculated from salinity. temperature, and pressure (depth), and is included in the data summaries. Phytoplankton species abundance and cell volume were determined at selected stations every other month.

Ellis, G.S., Huckins, J.N., Rostad, C.E., Schmitt, C.J., Petty, J.D., and MacCarthy, P., 1995, Evaluation of lipid-containing semipermeable membrane devices for monitoring organochlorine contaminants in the upper Mississippi River: Environmental Toxicology and Chemistry, v. 14, no. 11, p. 1875-1884.

Organochlorine contaminants sequestered in lipid-containing semipermeable membrane devices (SPMDs) were compared to those found in tangential-flow ultrafilter permeates as part of a pilot study at 10 sites in the Upper Mississippi River system. Caged and feral fish from three primary sites were also analyzed for comparison. Concentrated organochlorine (OC) compounds were readily extracted from the SPMDs by dialysis into hexane, and samples were analyzed by gas chromatography-negative chemical ionization-mass spectrometry. Fish and water samples were processed by conventional methods. Reasonable agreement was found between analyte SPMD-derived water concentrations and measured values of ultrafilter permeates; however, concentrations of the same analytes in caged fish did not appear to be proportional to water concentrations derived from SPMDs and ultrafilter permeates. The greatest number of OC compounds was detected in SPMDs; fewer were detected in caged fish and feral fish.

Greene, E.A., and Rahn, P.H., 1995, Localized anisotropic transmissivity in a karst aquifer: Ground Water, v. 33, no. 5, p. 806-816.

Maps of cave passageways in the outcrop area of the uplifted Madison Limestone in the Black Hills, South Dakota, show that principal cavern development is oriented in the major direction of ground-water flow, roughly radial to the Black Hills. Fracture-trace analysis and measurement of joints in the Wind Cave area show that these orientation coincide with cave passageways. Aquifer testing at Rapid City indicates that a local principal transmissivity tensor is oriented in the direction of cave development and along the strikes of bedding-plane fractures. This indicates that much of the permeability of the Madison aquifer is modern karst (post-Laramide-Orogeny). From the above, we conclude that a localized anisotropic permeability (principal direction of transmissivity) is developed by ground water flowing through fractures, dissolving the rock, and producing dissolution-enhanced conduits along the direction of ground-water flow. This localized principal direction of transmissivity can be deduced from analysis of the potentiometric surface, stream-aquifer hydrographs, mapped cave passageways, aquifer tests, fracture traces, and measurements of joints in the field.

Grimm, M.M., Wohl, E.E., and Jarrett, R.D., 1995, Coarse-sediment distribution as evidence of an elevation limit for flash flooding, Bear Creek, Colorado: Geomorphology, v. 14, no. 12, p. 199-210.

Bear Creek is a tributary of the South Platte River in central Colorado. The stream flows east from an elevation of 4348 m at the Continental Divide to the mountain front at 1670 m. It thus encompasses the 2300 m elevation limit for substantial rainfall flooding in the Colorado Front Range proposed by Jarrett. Maximum paleoflood discharges estimated from flood deposits at four sites along Bear Creek demonstrate a consistent decrease in unit discharge with increasing elevation and support the hypothesis of an upper elevation limit for rainfall floods. The unit discharge values were used to explain coarse-sediment distribution along Bear Creek. Measurements of coarse-grained channel sediment at 19 sites along the creek indicate a decrease in particle size in flood deposits with increasing elevation, as well as a decrease in the size of clasts introduced to the main channel along tributaries. These changes in grain size are hypothesized to reflect changes in the competence of channel transport as a result of snowmelt-dominated versus rainfall-dominated discharge regimes above and below 2100 m elevation. Calculations of flow competence versus entrainment thresholds for the deposits may support this interpretation. One of the geomorphic implications of the elevation limit on flash flooding is a reversal of the usual downstream-fining trend in coarse channel sediments.

Harvey, J.W., Chambers, R.M. and Hoelscher, J.R., 1995, Preferential flow and segregation of porewater solutes in wetland sediment: Estuaries, v. 18, no.4, p. 568-578.

Sediment macropores (with effective diameters larger than 100 mm) comprise 11% of the bulk sediment volume in a tidal freshwater wetland vegetated with Peltandra virginica. In order to determine effects of macroporous sediment structure on solute transport, we conducted a solute tracer experiment in the sediment. The effective transport volume (qeff), the volume of sediment through which solute was transported normalized to sediment bulk volume, was 0.15 cm3/cm3, which is considerably smaller than the total pore space that is potentially available for transport (porosity of sediment is 0.63 cm3/cm3). A mean transport time of 13 d was required to flush preferential flow paths in Peltandra hummocks; hydrologic turnover of the volumetrically dominant matrix pores (0.53 cm3/cm3) was apparently much slower. Based on porewater sampler design and hydrological principles, we suggest that N2-purged tension solution samplers and diffusion equilibrators preferentially sample porewater from macropore and matrix domains, respectively. Dissolved ammonium and orthophosphate concentrations were three-fold higher in matrix pores compared to macropores, which is consistent with our finding that more rapid hydrological flushing occurred in macropores compared to matrix pores. Further evaluation of porewater sampler designs in macroporous sediment is needed to improve studies of hydrologic transport and biogeochemical cycling in wetlands.

Harvey, R.W., Kinner, N.E., Bunn, A., McDonald, D., and Metge, D., 1995, Transport behavior of groundwater protozoa and protozoan-sized microspheres in sandy aquifer sediments: Applied and Environmental Microbiology, v. 61, p. 209-217.

Transport behaviors of unidentified flagellated protozoa (flagellates) and flagellate-sized carboxylated microspheres in sandy, organically contaminated aquifer sediments were investigated in a small-scale (1 to 4-m travel distance) natural-gradient tracer test on Cape Cod and in flow-through columns packed with sieved (0.5- to 1.0-mm grain size) aquifer sediments. The minute (average in situ cell size, 2 to 3 mm) flagellates, which are relatively abundant in the Cape Cod aquifer, were isolated from core samples, grown in a grass extract medium, labeled with hydroethidine (a vital eukaryotic stain), and coinjected into aquifer sediments along with bromide, a conservative tracer. The 2-mm flagellates appeared to be near the optimal size for transport, judging from flowthrough column experiments involving a polydispersed (0.7 to 6.2 mm in diameter) suspension of carboxylated microspheres. However, immobilization within the aquifer sediments accounted for a log unit reduction over the first meter of travel compared with a log unit reduction over the first 10 m of travel for indigenous, free-living groundwater bacteria in earlier tests. High rates of flagellate immobilization in the presence of aquifer sediments also was observed in the laboratory. However, immobilization rates for the laboratory-grown flagellates (initially 4 to 5 mm) injected into the aquifer were not constant and decreased noticeably with increasing time and distance of travel. The decrease in propensity for grain surfaces was accompanied by a decrease in cell size, as the flagellates presumably readapted to aquifer conditions. Retardation and apparent dispersion were generally at least twofold greater than those observed earlier for indigenous groundwater bacteria but were much closer to those observed for highly surface active carboxylated latex microspheres. Field and laboratory results suggest that 2-mm carboxylated microspheres may be useful as analogs in investigating several abiotic aspects of flagellate transport behavior in groundwater.

Harvey, J.W. and Nuttle, W.K.,1995, Fluxes of water and solute in a coastal wetland sediment 2: Effect of macropores on solute exchange with surface water: Journal of Hydrology, v. 164, p.109-125.

We investigated interactions between sediment physical structure and solute transport in an intertidal coastal wetland. Two distinct pore-size classes in the sediment were identified. Macropores had effective diameters greater than 100 mm and a normalized volume of 5%; matrix pores had effective diameters smaller than 100 mm and were the volumetrically dominant pore-size class (95%). We found that infiltration and evaporation-driven water fluxes were segregated between macropores and matrix pores, respectively, which had the effect of enhancing diffusive effluxes of chloride from the sediment to surface water. Chloride was highly concentrated relative to seawater in matrix porewater but was comparatively dilute in macropores. Concentration differences in pore-size classes declined with depth until indistinguishable below 10 cm. The segregated chloride distribution can be explained if recharge to the sediment occurred by downward infiltration in macropores and discharge occurred by an upward flux in matrix pores to satisfy evapotranspiration. Without disturbance by the downward infiltration flux in macropores, upward advection of chloride in matrix pores and evapoconcentration increased chloride concentrations in matrix pores to a level well above the concentration in seawater. The resulting high concentrations of chloride in matrix pores induced a large diffusive efflux of chloride into surface water that was sufficient to balance new input of chloride by infiltration of seawater in macropores (0.085 mmol Cl cm-2 day -1). Transport models that were constrained by water balance measurements at the field site explained both the exponential form of the vertical distribution of chloride in matrix pores and the rate of change in storage of chloride in sediment porewater over a 1 month period. We conclude that segregation of water and solute fluxes in two pore-size classes strongly influences sediment salinity of coastal wetlands, which has direct bearing on primary productivity of dominant vegetation and on exchange of dissolved nutrients and contaminants between intertidal wetlands and open water.

Hodge, S.A. and Tasker, G.D., 1995, Magnitude and Frequency of Floods in Arkansas: U.S. Geological Survey Water-Resources Investigations Report 95-4224, 275 p.

Methods are presented for estimating the magnitude and frequency of peak discharges of streams in Arkansas. Regression analyses were developed in which a stream's physical and flood characteristics were related. Four sets of regional regression equations were derived to predict peak discharges with selected recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years on streams draining less than 7,770 square kilometers. The regression analyses indicate that size of drainage area, main channel slope, mean basin elevation, and the basin shape factor were the most significant basin characteristics that affect magnitude and frequency of floods. The region of influence method is included in this report. This method is still being improved and is to be considered only as a second alternative to the standard method of producing regional regression equations. This method estimates unique regression equations for each recurrence interval for each ungaged site. The regression analyses indicate that size of drainage area, main channel slope, mean annual precipitation, mean basin elevation, and the basin shape factor were the most significant basin and climatic characteristics that affect magnitude and frequency of floods for this method. Certain recommendations on the use of this method are provided. A method is described for estimating the magnitude and frequency of peak discharges of streams for urban areas in Arkansas. The method is from a nationwide U.S. Geeological Survey flood frequency report which uses urban basin characteristics combined with rural discharges to estimate urban discharges. Annual peak discharges from 204 gaging stations, with drainage areas less than 7,770 square kilometers and at least 10 years of unregulated record, were used in the analysis. These data provide the basis for this analysis and are published in the Appendix of this report as supplemental data. Large rivers such as the Red, Arkansas, White, Black, St. Francis, Mississippi, and Ouachita Rivers have floodflow characteristics that differ from those of smaller tributary streams and were treated individually. Regional regression equations are not applicable to these large rivers. The magnitude and frequency of floods along these rivers are based on specific station data. This section is provided in the Appendix and has not been updated since the last Arkansas flood frequency report (1987b), but is included at the request of the cooperator.

Jassby, A.D., Kimmerer, W.J., Monismith, S., Armor, C., Cloern, J.E., Powell, T.M., Schubel, J.R., and Vendlinski, T. 1995, Isohaline position as a habitat indicator for estuarine resources: San Francisco Bay-Delta, California, U.S.A.: Ecological Applications, v. 5, p. 272-289.

Populations of native and introduced aquatic organisms in the San Francisco Bay/Sacramento-San Joaquin Delta Estuary ("Bay/Delta") have undergone significant declines over the past two decades. Decreased river inflow due to drought and increased freshwater diversion have contributed to the decline of at least some populations. Effective management of the estuary's biological resources requires a sensitive indicator of the response to freshwater inflow that has ecological significance, can be measured accurately and easily, and could be used as a "policy" variable to set standards for managing freshwater inflow. Positioning of the 2ppt (grams of salt per kilogram of seawater) bottom salinity value along the axis of the estuary was examined for this purpose. The 2ppt bottom salinity position (denoted by X2) has simple and significant statistical relationships with annual measures of many estuarine resources, including the supply of phytoplankton and phytoplankton-derived detritus from local production and river loading; benthic macroinvertebrates (molluscs); mysids and shrimp; larval fish survival; and the abundance of planktivorous, piscivorous, and bottom-foraging fish. The actual mechanisms are understood for only a few of these populations. X2 also satisfies other recognized requirements for a habitat indicator and probably can be measured with greater accuracy and precision than alternative habitat indicators such as net freshwater inflow into the estuary. The 2ppt value may not have special ecological significance for other estuaries (in the Bay/Delta, it marks the locations of an estuarine turbidity maximum and peaks in the abundance of several estuarine organisms), but the concept of using near-bottom isohaline position as a habitat indicator should be widely applicable. Although X2 is a sensitive index of the estuarine community's response to net freshwater inflow, other hydraulic features of the estuary also determine population abundances and resource levels. In particular, diversion of water for export from or consumption within the estuary can have a direct effect on population abundance independent of its effect on X2. The need to consider diversion, in addition to X2, for managing certain estuarine resources is illustrated using striped bass survival as an example. The striped bass survival data were also used to illustrate a related important point: incorporating additional explanatory variables may decrease the prediction error for a population or process, but it can increase the uncertainty in parameter estimates and management strategies based on these estimates. Even in cases where the uncertainty is currently too large to guide management decisions, an uncertainty analysis can identify the most practical direction for future data acquisition.

Kile, D.E., Chiou, C.T., Zhou, H., Li, H., and Xu, O., 1995, Partition of nonpolar organic pollutants from water to soil and sediment organic matters: Environmental Science and Technology, v. 29, p. 1401-1406.

The partition coefficients (Koc) of carbon tetrachloride and 1,2-dichlorobenzene between normal soil/sediment organic matter and water have been determined for a large set of soils, bed sediments, and suspended solids from the United States and the People's Republic of China. The Koc values for both solutes are quite invariant either for the soils or for the bed sediments; the values on bed sediments are about twice those on soils. The similarity of Koc values between normal soils and between normal bed sediments suggests that natural organic matters in soils (or sediments) of different geographic origins exhibit comparable polarities and possibly comparable compositions. The results also suggest that the process that converts eroded soils into bed sediments brings about a change in the organic matter property. The difference between soil and sediment Koc values provides a basis for identifying the source of suspended solids in river waters. The very high Koc values observed for some special soils and sediments are diagnostic of severe anthropogenic contamination.

Kimball, B.A., Callender, E., and Axtmann, E.V., 1995, Effects of colloids on metal transport in a river receiving acid mine drainage, Upper Arkansas River, Colorado, U.S.A.: Appl. Geochem., v. 10, p. 285-306.

Inflows of metal-rich, acidic water that drain from mine dumps and tailings piles in the Leadville, Colorado, area enter the non-acidic water in the upper Arkansas River. Hydrous iron oxides precipitate as colloids and move downstream in suspension, particularly downstream from California Gulch, which has been the major source of metal loads. The colloids influence the concentrations of metals dissolved in the water and the concentrations in bed sediments. To determine the role of colloids, samples of water, colloids, and fine-grained bed sediment were obtained at stream-gaging sites on the upper Arkansas River and at the mouths of major tributaries over a 250-km reach. Dissolved and colloidal metal concentrations in the water column were operationally defined using tangential-flow filtration through 0.001-mm membranes to separate the water and the colloids. Surface-extractable and total bed sediment metal concentrations were obtained on the <60-mm fraction of the bed sediment. The highest concentrations of metals in water, colloids, and bed sediments occurred just downstream from California Gulch. Iron dominated the colloid composition, but substantial concentrations of As, Cd, Cu, Mn, Pb, and Zn also occurred in the colloidal solids. The colloidal load decreased by one half in the first 50 km downstream from the mining inflows due to sedimentation of aggregated colloids to the streambed. Nevertheless, a substantial load of colloids was transported through the entire study reach to Pueblo Reservoir. Dissolved metals were dominated by Mn and Zn, and their concentrations remained relatively high throughout the 250-km reach. The composition of extractable and total metals in bed sediment for several kilometers downstream from California Gulch is similar to the composition of the colloids that settle to the bed. Substantial concentrations of Mn and Zn were extractable, which is consistent with sediment-water chemical reaction. Concentrations of Cd, Pb, and Zn in bed sediment clearly result from the influence of mining near Leadville. Concentrations of Fe and Cu in bed sediments are nearly equal to concentrations in colloids for about 10 km downstream from California Gulch. Farther downstream, concentrations of Fe and Cu in tributary sediments mask the signal of mining inflows. These results indicate that colloids indeed influence the occurrence and transport of metals in rivers affected by mining.

Kvenvoiden, K.A., Hostettler, F.D., Carlson, P.R., Rapp, J.B., Thredkeld, C.N., and Warden, A., 1995, Ubiquitous tar balls with a California-source signature on the shorelines of Prince William Sound, Alaska: Environmental Science and Technology, v. 29, p. 2684-2694.

Although the shorelines of Prince William Sound still bear traces of the 1989 Exxon Valdez oil spill, most of the flattened tar balls that can be found today on these shorelines are not residues of Exxon Valdez oil. Instead, the carbon-isotopic and hydrocarbon-biomarker signatures of 61 tar ball samples, collected from shorelines throughout the northern and western parts of the Sound, are all remarkably similar and have characteristics consistent with those of oil products that originated from the Monterey Formation source rocks of California. The carbon-isotopic compositions of the tar balls are all closely grouped ( d13CPDB = -23.7 ± 0.2ppt), within the range found in crude oils from those rocks, but are distinct from isotopic compositions of 28 samples of residues from the Exxon Valdez oil spill (d13CPDB = -29.4 ± 0.1ppt). Likewise, values for selected biomarker ratios in the tar balls are all similar but distinct from values of residues from the 1989 oil spill. Carbon-isotopic and biomarker signatures generally relate the tar balls to oil products used in Alaska before similar to 1970 for construction and pavements. How these tar balls with such similar geochemical characteristics became so widely dispersed throughout the northern and western parts of the Sound is not known with certainty, but the great 1964 Alaska earthquake was undoubtedly an important trigger, causing spills from ruptured storage facilities of California-sourced asphalt and fuel oil into Prince William Sound.

LaBaugh, J.W., 1995, Relation of algal biovolume to chlorophyll a in selected lakes and wetlands in the north-central United States: Canadian Journal of Fisheries and Aquatic Sciences, volume 52, p. 416-424.

Algal chlorophyll a is commonly used as a surrogate for algal biomass. Data from three lakes in western Nebraska, five wetlands in north-central North Dakota, and two lakes in north-central Minnesota represented a range in algal biovolume of over four orders of magnitude and a range in chlorophyll a from less than 1 to 380 mg/m3. Analysis of these data revealed that there was a linear relation, log10 algal biovolume = 5.99 + 0.09 chlorophyll a (r2 = 0.72), for cases in which median values of chlorophyll a for open-water periods were less than 20 mg/m3. There was no linear relation in cases in which median chlorophyll a concentrations were larger than 20 mg/m3 for open-water periods, an occurrence found only in shallow prairies lakes and wetlands for years in which light penetration was the least.

LaBaugh, J.W., Rosenberry, D.O., and Winter, T.C., 1995, Groundwater contribution to the water and chemical budgets of Williams Lake, Minnesota, 1980-1991: Canadian Journal of Fisheries and Aquatic Sciences, v. 52, p. 754-767.

Groundwater seepage was the largest annual flux of water into (58-76%) and out of (73-83%) Williams Lake during a 12-year study, during which the entire volume of the lake was replaced four times. The only other water fluxes to and from the lake, which has no surface-water inlet or outlet, were atmospheric precipitation and evaporation. Nearly all of the annual input of calcium, magnesium, sodium, potassium, chloride, sulfate, and silica was provided by groundwater. Although much of the calcium and most of the silica input was retained in the lake, this retention did not result in increased chemical mass in the lake water mass because biologically mediated removal of calcium and silica to the sediments equaled or exceeded loss by lake seepage to groundwater. Groundwater represented as much as one-half the annual hydrological input of phosphorus and nitrogen; the remainder was supplied by atmospheric precipitation. From about 70 to 90% of the annual input of phosphorus and nitrogen was retained in the lake. Although water and chemical fluxes varied from year to year, interaction of the lake with groundwater determined the hydrological and chemical characteristics of Williams Lake.

Lambing, J. H., Hornberger, M. I., Axtmann, E. V., and others, 1995, Water-quality, bed-sediment, and biological data (October 1993 through September 1994) and statistical summaries of data for streams in the Upper Clark Fork Basin, Montana, U. S. Geological Survey, Open-File report 95-429, 104 pages.

Water, bed sediment, and biota were sampled in streams from Butte to below Missoula as part of a program to characterize aquatic resources in the upper Clark Fork basin of western Montana. Water- quality data were obtained periodically at 16 stations during October 1993 through September 1994 (water year 1994); daily suspended-sediment data were obtained at six of these stations. Bed-sediment and biological data were obtained at 11 stations in August 1994. Sampling stations were located on the Clark Fork and major tributaries. The primary constituents analyzed were trace elements associated with mine tailings from historical mining and smelting activities. Water-quality data include concentrations of major ions, trace elements, and suspended sediment in samples collected periodically during water year 1994. Daily values of streamflow, suspended-sediment concentration, and suspended- sediment discharge are given for six stations. Bed- sediment data include trace-element concentrations in the fine and bulk fractions. Biological data include trace-element concentrations in whole-body tissue of aquatic benthic insects. Quality-assurance data are reported for analytical results of water, bed sediment, and biota. Statistical summaries of bed sediment, and biological data are provided for the period of record at each station since 1985.

Leavesley, G. H., 1995, Modeling the effects of climate change on water resources - A review: Climatic Change v. 28, n. 2, p. 159-177.

Hydrologic models provide a framework in which to conceptualize and investigate the relationships between climate and water resources. A review of current studies that assess the impacts of climate change using hydrologic models indicates a number of problem areas common to the variety of models applied. These problem areas include parameter estimation, scale, model validation, climate scenario generation, and data. Research needs to address these problems include development of (1) a more physically based understanding of hydrologic processes and their interactions; (2) parameter measurement and estimation techniques for application over a range of spatial and temporal scales; (3) quantitative measures of uncertainty in model parameters and model results; (4) improved methodologies of climate scenario generation; (5) detailed data sets in a variety of climatic and physiologic regions; and (6) modular modeling tools to provide a framework to facilitate interdisciplinary research. Solutions to these problems would significantly improve the capability of models to assess the effects of climate change.

Leenheer, J. A., Wershaw, R. L., and Reddy, M. M., 1995, Strong-acid, carboxyl-group structures in fulvic acid from the Suwannee River, Georgia. 1. Minor structures: Environmental Science and Technology, v. 29, p. 393-398.

An investigation of the strong-acid characteristics (pKa 3.0 or less) of fulvic acid from the Suwannee River, Georgia, was conducted. Quantitative determinations were made for amino acid and sulfur-containing acid structures, oxalate half-ester structures, malonic acid structures, keto acid structures, and aromatic carboxyl-group structures. These determinations were made by using a variety of spectrometric (13C-nuclear magnetic resonance, infrared, and ultraviolet spectrometry) and titrimetric characterizations on fulvic acid or fulvic acid samples that were chemically derivatized to indicate certain functional groups. Only keto acid and aromatic carboxyl-group structures contributed significantly to the strong-acid characteristics of the fulvic acid; these structures accounted for 43% of the strong-acid acidity. The remaining 57% of the strong acids are aliphatic carboxyl groups in unusual and/or complex configurations for which limited model compound data are available.

Leenheer, J. A., Wershaw, R. L., and Reddy, M. M., 1995, Strong-acid, carboxyl-group structures in fulvic acid from the Suwannee River, Georgia. 2. Major structures: Environmental Science and Technology, v. 29, 399-405.

Polycarboxylic acid structures that account for the strong-acid characteristics (pKa near 2.0) were examined for fulvic acid from the Suwannee River. Studies of model compounds demonstrated that pKa values near 2.0 occur only if the alpha-ether or alpha-ester groups were in cyclic structures with two to three additional electronegative functional groups (carboxyl, ester, ketone, aromatic groups) at adjacent positions on the ring. Ester linkage removal by alkaline hydrolysis and destruction of ether linkages through cleavage and reduction with hydriodic acid confirmed that the strong carboxyl acidity in fulvic acid was associated with polycarboxylic alpha-ether and alpha-ester structures. Studies of hypothetical structural models of fulvic acid indicated possible relation of these polycarboxylic structures with the amphiphilic and metal-binding properties of fulvic acid.

Leland, H.V., 1995, Distribution of phytobenthos in the Yakima River Basin, Washington, in relation to geology, land use, and other environmental factors: Canadian Journal of Fisheries and Aquatic Sciences, v. 52, p. 1108-1129.

Benthic-algal distributions in the Yakima River, Washington, basin were examined in relation to geology, land use, water chemistry, and stream habitat using indicator-species classification (TWINSPAN) and canonical correspondence analysis (CCA). Algal assemblages identified by TWINSPAN were each associated with a narrow range of water-quality conditions. In the Cascade geologic province, where timber harvest and grazing are the dominant land uses, differences in community structure (CCA site scores) and concentrations of major ions (Ca and Mg) and nutrients (solute P, SiO2, and inorganic N) varied with dominant rock type of the basin. In agricultural areas of the Columbia Plateau province, differences in phytobenthos structure were based primarily on the degree of enrichment of dissolved solids, inorganic N, and solute P from irrigation-return flows and subsurface drainage. Habitat characteristics strongly correlated with community structure included reach altitude, turbidity, substratum embeddedness (Columbia Plateau), large woody-debris density (Cascade Range) and composition and density of the riparian vegetation. Algal biomass (AFDM) correlated with composition and density of the riparian vegetation but not with measured chemical-constituent concentrations. Nitrogen limitation in streams of the Cascade Range favored nitrogen-fixing blue-green algae and diatoms with endosymbiotic blue-greens, whereas nitrogen heterotrophs abundant in agricultural areas of the Columbia Plateau.

Leenheer, J.A., Noyes, T.I., and Brown, P.A., 1995, Data on naturalorganic substances in dissolved, colloidal, suspended-silt and clay, and bed-sediment phases in the Mississippi River and some of its tributaries, 1987-1990: U.S. Geological Survey Water-Resources Investigations Report 93-4204, 71 p.

The Mississippi River and some of its tributaries were sampled for natural organic substances dissolved in water and in suspended and bed sediments during seven sampling cruises from 1987-90. The sampling cruises were made during different seasons, in the free-flowing reaches of the river from St. Louis, Missouri, to New Orleans, Louisiana. The first three cruises were made during low-water conditions, and the last four cruises during high-water conditions. The purpose for sampling and characterizing natural organic substances in the various phases in the river was to provide an understanding of how these substances facilitate contaminant transport and transformations in the Mississippi River.

Significant conclusions of this study were: (1) Natural organic substances appear to stabilize certain colloids against aggregation; therefore, these colloids remain in suspension and can act as transport agents that are not affected by sedimentation. Bacteria were found to be a significant fraction of organic colloids. (2) A new class of organic contaminants (polyethylene glycols) derived from nonionic surfactant residues was discovered dissolved with natural organic substances in water. These polyethylene glycols have the potential to affect both organic and inorganic contaminant transport in water. (3) The entire dissolved organic-matter component under varying hydrologic and seasonal conditions was characterized. (4) A method was developed to characterize organic matter in sediment by solid-state, 13C-nuclear magnetic resonance spectrometry. (5) The organic matter in suspended sediments was characterized by a variety of spectral and nonspectral methods. The protein component (significant in trace-metal binding) and lipid component (significant in organic-contaminant binding) were found to be major constituents in natural organic matter in suspended sediment. (6) Pools are reservoirs acting as traps of sedimentary organic matter of allochthonous origin and export material of autochthonous nitrogen. (7) A major portion of the mass of organic colloids in transport consisted of bacterial cells.

Ling, C. H., 1995, Criteria for incipient motion of spherical sediment particles: Journal of Hydraulic Engineering, American Society of Civil Engineers, v. 121, no. 6, p. 472-478.

Initiation of bed-load transport of uniform spherical sediment particles on a horizontal bed in an open-channel flow is studied. On the basis of micromechanical and fluid dynamical considerations, two separate criteria for the initiation of motion are derived: one for rolling and one for lifting. Fluid forces such as drag, shear lift, Magnus lift, and lift due to centrifugal force are included in the derivation. The formulation of the lift force is theoretical. No empirical coefficient is used other than the drag coefficient Cd, which is well established in the literature. In the low particle Reynolds number regime, the dimensionless stress required to initiate lifting is found to be much higher than that of rolling, the former substantially above the Shields' curve while the latter is substantially below it. The theory is compared with Vanoni's 1964 data, with meaningful results. For higher particle Reynolds number, the dimensionless stress needed to initiate lifting is closer to that of rolling. The Shields' curve for the most part lies between the two theoretical thresholds.

Luoma, S.N., Bryan, G.W. and Ho, Y.B., 1995, Fate, bioavailability and toxicity of silver in estuarine environments: Marine Pollution Bulletin, v. 31, p. 44-54.

The chemistry and bioavailability of Ag contribute to its high toxicity in marine and estuarine waters. Silver is unusual, in that both the dominant speciation reaction in seawater and the processes important in sorbing Ag in sediments favour enhanced bioavailability. Formation of a stable chloro complex favours dispersal of dissolved Ag, and the abundant chloro complex is available to biota. Sequestration by sediments also occurs, but with relatively slow kinetics. Amorphous aggregated coatings enhance Ag accumulation in sediments, as well as Ag uptake from sediments by deposit feeders. In estuaries, the bioaccumulation of Ag increases 56-fold with each unit of increased Ag concentration in sediments. Toxicity for sensitive marine species occurs at absolute concentrations as low as those observed for any non-alkylated metal, partly because bioaccumulation increases so steeply with contamination. The environmental window of tolerance to Ag in estuaries could be narrower than for many elements.

McCabe, G.J., and Dettinger, M.D., 1995. Relations Between Winter Precipitation and Atmospheric Circulation Simulated by the Geophysical Fluid Dynamics Laboratory General Circulation Model: International Journal of Climatology, v. 15., p. 625-638.

General circulation model (GCM) simulations of atmospheric circulation are more reliable than GCM simulations of temperature and precipitation. Thus, some researchers are developing empirical relations between observed atmospheric circulation and observed temperature and precipitation to translate GCM estimates of future atmospheric circulation into estimates of future regional temperature and precipitation. Developing climate-change scenarios in this manner assumes, at least, that relationships between atmospheric circulation and surface climate variables, such as temperature and precipitation, are properly simulated by GCMs. In this study, temporal correlations between 700 hPa height anomalies (700 hPa anomalies) over North America simulated by the Geophysical Fluid Dynamics Laboratory (GFDL) GCM and GFDL-GCM-simulated (GFDL-simulated) winter precipitation at eight locations in the conterminous United States are compared with corresponding correlations in observations. The objectives are to (i) characterize the relations between atmospheric circulation and winter precipitation simulated by the GFDL GCM for selected locations in the conterminous USA, (ii) determine whether these relations are similar to those found in observations of the actual climate system, and (iii) determine if GFDL-simulated precipitation is forced by the same circulation patterns as in the real atmosphere. Results indicate that the GFDL GCM simulates relations between 700 hPa anomalies and local winter precipitation that are similar to relations found in observed data for most of the locations analysed in this study. Results also indicate that at regional scales GFDL GCM simulations of the relations between 700 hPa anomalies and winter precipitation are most similar to observed relations for locations near oceanic sources of atmospheric moisture. These results suggest that the GFDL GCM may not adequately simulate variations in advection of atmospheric moisture into the interior parts of the USA and/or that this moisture is not adequately converted into precipitation in the interior parts of the country. This problem may be due, in part, to (i) the inadequate representation of topography in the GFDL GCM, (ii) stronger-than-observed mean winter zonal winds simulated by the GFDL GCM and the consequent more west-to-east paths of air flow and storm systems across North America, (iii) the relative weakness of important synoptic patterns in GFDL simulations, such as the Pacific North American circulation pattern, and (iv) the occurrence of 'spectral rain'. In addition, for some locations, the GFDL-simulated relationships between precipitation and 700 hPa anomalies can be quite different from observed relations. The differing relationships suggest that GFDL-simulated changes in regional precipitation in response to changes in atmospheric circulation could differ from changes that would occur in the actual climate system.

McCabe, G.J., and Fountain, A.G., 1995. Relations Between Atmospheric Circulation and the Mass Balance of South Cascade Glacier, Washington: Arctic and Alpine Research, v. 27, no. 3, p. 226-233.

The yearly net mass balance of South Cascade Glacier, Washington, has decreased since the mid-1970s. Results show that the decrease is primarily caused by a significant decrease in the winter mass balance. The decrease in winter mass balance is caused, in part, by changes in winter mean atmospheric circulation that began during the mid-1970s. Approximately 60% of the variability in winter mass balance can be explained by variations in winter mean 700-mb heights over western Canada. Since the mid-1970s, there has been an increase in winter mean 700-mb heights over western Canada and the northern western contiguous United States and a decrease in winter mean 700-mb heights in the eastern North Pacific Ocean centered near the Aleutian Islands. These changes in atmospheric circulation indicate a decrease in the movement of storms and moisture from the Pacific Ocean into the western contiguous United States. In addition, the increase in winter mean 700-mb heights over western Canada and the northern western contiguous United States indicates an increase in subsidence, which results in a warming and drying of the air that further reduces precipitation and also increases the ratio of rain to snow during the cold season. These factors contribute to below-average winter mass balances.

McKnight, D.M., Smith, R.L., Bradbury, J.P., Baron, J.J., and Spaulding, S., 1990, Phytoplankton dynamics in Three Rocky Mountain lakes, Colorado, U.S.A.: Arctic and Alpine Research, v. 22, no. 3, p. 264-274.

In 1984 and 1985 seasonal changes in phytoplankton were studied in a system of three lakes in Loch Vale, Rocky Mountain National Park, Colorado, to determine the effects of urban atmospheric deposition. Three periods were evident: (1) A spring bloom, during snowmelt, of the planktonic diatom Asterionella formosa, (2) a midsummer period of minimal algal abundance, and (3) a fall bloom of the blue-green alga Oscillatoria limnetica. Seasonal phytoplankton dynamics in these lakes are controlled partially by the rapid flushing rate during snowmelt and the transport of phytoplankton from the highest lakes to the lower lakes by the stream, Icy Brook. During snowmelt, the A. formosa population in the most downstream lake has a net rate of increase of 0.34/d, which is calculated from the flushing rate and from the A. formosa abundance in the inflow from the upstream lake and in the downstream lake. Measurement of photosynthetic rates at different depths during the three periods confirmed the rapid growth of A. formosa during the spring. The decline in A. formosa after snowmelt may be related to grazing by developing zooplankton populations. The possible importance of seasonal variations in nitrate concentrations were evaluated in in situ enrichment experiments. For A. formosa and O. limnetica populations, growth stimulation resulted from 8 or 16 micromolar amendments of calcium nitrate and sulfuric acid, but the reason for this stimulation could not be determined from these experiments.

Meade, R.H., ed., 1995, Contaminants in the Mississippi River, 1987-92: U.S. Geological Survey Circular 1133, 140p.

This volume contains a selection of some of the more interesting results of a 5-year study conducted by the U.S. Geological Survey of contaminants in the Mississippi River and some of its major tributaries. During the first 3 years of the study, 1987-90, the rivers were sampled on seven different occasions between St. Louis, Missouri, and New Orleans, Louisiana. During the last 2 years of the study, 1991-92, the scope of the program was increased to include three further samplings of the full length of the river between Minneapolis-St. Paul, Minnesota, and New Orleans. The sampling and analytical efforts were focused on three phases of contaminants in the rivers: (1) contaminants transported in the dissolved phase, (2) contaminants transported in the adsorbed phase-that is, in association with the suspended silts and colloids-and (3) contaminants stored in the bottom sediments in the navigation pools of the Upper Mississippi River. Contaminants were assessed for the period of sampling, 1987-92. Given that samples were collected no more frequently than twice a year, the 5-year period was not sufficiently long to establish any time trends-whether, that is, the contaminant levels were increasing or decreasing. Included in the analysis were only a few data that had been collected before our study. Yet to be assessed are the subsequent effects on river quality of the great flood of 1993. Contaminants are assessed mostly in a spatial rather than a temporal context. This report, in other words, is a snapshot rather than a chronicle.

Michel, R.L., and Kraemer, T.F., 1995, Use of isotopic data to estimate residence times of the Finger Lakes, New York, Journal of Hydrology, v. 164, p. 1-18.

A relatively inexpensive method for the estimation of water residence times for groups of lakes where climatic and tritium deposition factors were similar was developed for application to the Finger lakes, a group of 11 lakes in central New York state. A tritium-balance model was used to estimate residence times. With 2 exceptions (Seneca lake and Skaneateles lake), results obtained from model simulations were in agreement with earlier estimates based on runoff and chloride balances. Possible reasons for the exceptions related to the sensitivity of the model to parameter changes were investigated. The discrepancy in the case of Seneca lake is explained in terms of groundwater input to the lake.

Moench, A.F., 1995, Combining the Neuman and Boulton models for flow to a well in an unconfined aquifer: Ground Water, v. 33, no. 3, p. 378-384.

A Laplace transform solution is presented for flow to a well in a homogeneous, water-table aquifer with noninstantaneous drainage of water from the zone above the water table. The Boulton convolution integral is combined with Darcy's law and used as an upper boundary condition to replace the condition used by Neuman. Boulton's integral derives from the assumption that water drained from the unsaturated zone is released gradually in a manner that varies exponentially with time in response to a unit decline in hydraulic head, whereas the condition used by Newman assumes that the water is released instantaneously. The result is a solution that reduces to the solution obtained by Neuman as the rate of release of water from the zone above the water table increases. A dimensionless fitting parameter, gamma , is introduced that incorporates vertical hydraulic conductivity, saturated thickness, specific yield, and an empirical constant alpha sub(1), similar to Boulton's alpha . Results show that theoretical drawdown in water-table piezometers is amplified by noninstantaneous drainage from the unsaturated zone to a greater extent than drawdown in piezometers located at depth in the saturated zone. This difference provides a basis for evaluating gamma by type-curve matching in addition to the other dimensionless parameters. Analysis of drawdown in selected piezometers from the published results of two aquifer tests conducted in relatively homogeneous glacial outwash deposits but with significantly different hydraulic conductivities reveals improved comparison between the theoretical type curves and the hydraulic head measured in water-table piezometers.

Moody, J.A., 1995, Propagation and composition of the flood wave on the Upper Mississippi River, 1993: U.S. Geological Survey Circular 1120-F, 22 p.

The flood wave on the upper Mississippi River started downstream near St. Paul, Minnesota, in June 1993. The maximum discharge propagated downstream at about 50 kilometers per day and was 5 to 7 times the mean daily discharge at streamgaging sites on the river. The propagation speed of the flood wave was influenced more by hydrologic factors such as tributary inflow and flood-plain storage than by hydraulic factors. The maximum discharge at St. Louis, Missouri (29,700 m3/s) occurred on August 1, 1993; but because of flood-plain storage resulting from levee failures and seepage through and under levees downstream, the maximum discharge at Thebes, Illinois, (27,700 m3/s) did not occur until August 7 which was about 4 days later than normal.

Neuzil, C.E., 1995, Abnormal pressures as hydrodynamic phenomena: American Journal of Science, v. 295, no. 6, p. 745-789.

So-called abnormal pressures, subsurface fluid pressures significantly higher or lower than hydrostatic, have excited speculation about their origin since subsurface exploration first encountered them. Two distinct conceptual models for abnormal pressures have gained currency among earth scientists. The static model sees abnormal pressures generally as relict features preserved by a virtual absence of fluid flow over geologic time. The hydrodynamic model instead envisions abnormal pressures as phenomena in which flow usually plays an important role. In this paper I develop the theoretical framework for abnormal pressures as hydrodynamic phenomena, show that it explains the manifold occurrences of abnormal pressures, and examine the implications of this approach. Abnormal pressures can be explained as occurring in flow regimes that are both equilibrated and disequilibrated hydrodynamically. The former are "adjusted" to their geologic and hydrologic surroundings while the latter are not. Equilibrium-type abnormal pressures generally result from topographically-driven flow (as in artesian basins) but may also occur as a result of osmosis or fluid density contrasts. The more common and varied disequilibrium-type abnormal pressures are caused by natural geologic processes such as compaction, diagenesis, and deformation. These processes have the effect of distributed fluid sources or sinks and are manifested either as actual fluid sources/sinks or as virtual ones involving changing porosity and/or temperature. Disequilibrium-type abnormal pressures can be characterized in terms of three quantities: the size and permeability of their domains and the vigor of the "geologic forcing" or magnitude of the source/sink term. Published estimates reveal a surprising number of distinct geologic processes that can generate forcing sufficient to maintain abnormal pressures in dynamic systems. This observation is crucial to understanding why abnormal pressures need not indicate regimes that have been static over geologic time. Low-permeability regions play key roles in both equilibrium- and disequilibrium-type abnormal pressures. Extensive low-permeability strata are generally required to generate abnormal pressures in topographically-driven flow regimes, while osmotically-driven flow and hydrodynamic disequilibrium occur only within regions composed of or encompassed by low-permeability media. Analyzing abnormal pressures as hydrodynamic phenomena often allows these low permeabilities to be estimated, something that is otherwise difficult to do. In some instances hydrodynamic analyses also shed light on rates of geologic processes and a region's geologic history.

Nuttle, W.K. and Harvey, J.W., 1995, Fluxes of water and solute in a coastal wetland sediment 1: The contribution of regional groundwater discharge: Journal of Hydrology, v. 164, p. 89-107.

Upward discharge of fresh groundwater into a mid-Atlantic intertidal wetland contributed 62% of the water needed to replace evapotranspiration losses from the sediment during an 11 day period in September. Infiltration during flooding by tides provided most of the balance; thus there was a net advection of salt into the sediment. The amount of groundwater discharge was estimated from changes in water storage in the sediment, as inferred from measurements of hydraulic head made every 10 min. We argue that this approach is inherently more accurate than calculating the flux as the product of hydraulic conductivity and head gradient. Evapotranspiration was estimated from direct measurements of net radiation. On an annual time-scale, our results suggest that groundwater discharge at this site may exceed the evapotranspiration flux during months of reduced evapotranspiration. Should this occur, groundwater-driven advection would supplement diffusion, during flooding, in removing salt from the sediment.

Oremland, R.S., Miller, L.G., Dowdle, P., Connell, T., and Barkay, T., 1995, Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the Carson River, Nevada: Appl. Environ. Microbiol., v. 61, p. 2745-2753.

Sediments from mercury-contaminated and uncontaminated reaches of the Carson River, Nevada, were assayed for sulfate reduction, methanogenesis, denitrification, and monomethylmercury (MeHg) degradation. Demethylation of [14C]MeHg was detected at all sites as indicated by the formation of 14CO2 and 14CH4. Oxidative demethylation was indicated by the formation of 14CO2 and was present at significant levels in all samples. Oxidized/reduced demethylation product ratios (i.e., 14CO2/ 14CH4 ratios) generally ranged from 4.0 in surface layers to as low as 0.5 at depth. Production of 14CO2 was most pronounced at sediment surfaces which were zones of active denitrification and sulfate reduction but was also significant within zones of methanogenesis. In a core taken from an uncontaminated site having a high proportion of oxidized, coarse-grain sediments, sulfate reduction and methanogenic activity levels were very low and 14CO2 accounted for 98% of the product formed from [14C]MeHg. There was no apparent relationship between the degree of mercury contamination of the sediments and the occurrence of oxidative demethylation. However, sediments from Fort Churchill, the most contaminated site, were most active in terms of demethylation potentials. Inhibition of sulfate reduction with molybdate resulted in significantly depressed oxidized/reduced demethylation product ratios, but overall demethylation rates of inhibited and uninhibited samples were comparable. Addition of sulfate to sediment slurries stimulated production of 14CO2 from [14C]MeHg, while 2-bromoethanesulfonic acid blocked production of 14CH4. These results reveal the importance of sulfate-reducing and methanogenic bacteria in oxidative demethylation of MeHg in anoxic environments.

Osterkamp, W.R.,ed., 1995, Effects of scale on interpretation and management of sediment and water quality: International Association of Hydrological Sciences Publication No. 226, IAHS Press, Wallingford, Oxfordshire, UK, 301 p.

The proceedings of an international symposium held in Boulder, Colo., U.S.A., in July 1995 are presented. The symposium was focused on evaluating spatial and temporal scale effects on hydrologic processes.

Osterkamp, W.R., Hupp, C.R., and Schening, M.R., 1995, Little River revisited -- thirty five years after Hack and Goodlett: Geomorphology, v. 13, p. 1-20.

In possibly the first detailed study to relate geomorphology, vegetation, and hydrology at a watershed scale, Hack and Goodlett (1960) documented variation in the eastern forest with topographic positions of cove, side slope, and nose. Runoff identified as convergent, parallel, or divergent, supported forest types, respectively, of northern hardwood, oak, and yellow pine. The study, conducted in the Little River Basin of northwestern Virginia, also described effects on landforms and vegetation of a catastrophic flood that occurred in June, 1949. Field investigations, conducted nearly 4 decades later, review selected parts of the study by Hack and Goodlett (1960). Replicate data provide a basis to evaluate interpretations of Hack and Goodlett, to document geomorphic change within the Little River Basin since the 1949 flood, and to identify vegetation change in uplands and bottomlands. Results suggest that change to hillslope landforms has been minor since 1949, but that changes have occurred to the Little River and its tributaries, seemingly during flow events of 1952, 1955, and 1985. Change in areal extent of forest types was not detected. Change in the relative abundances of dominant species may have resulted from 20th-century fire suppression.

Paillet, F.L., and Hess, A.E., 1995, Geophysical log data from basalt aqufiers near Waipahu on the island of Oahu and Pahoa on the island of Hawaii, Hawaii: U.S. Geological Survey Open-File Report 95-383, p. 62.

Two relatively new geophysical logging techniques, the digitally enhanced borehole acoustic televiewer and the heat-pulse flowmeter, were tested from 1987 to 1991 at two sites in Hawaii: Waipahu on the island of Oahu, and Pahoa on the island of Hawaii. Although these data were obtained in an effort to test and improve these two logging techniques, the measurements are of interest to hydrologists studying the aquifers in Hawaii. This report presents a review of the measurements conducted during this effort and summarizes the data obtained in a form designed to make that data available to hydrologists studying the movement of ground water in Hawaiian aquifers. Caliper logs obtained at the Waipahu site indicate the distribution of openings in interbed clinker zones between relatively dense and impermeable basalt flows.The flowmeter data indicate the pattern of flow induced along seven observation boreholes that provide conduits between interbed zones in the vicinity of the Mahoe Pumping Station at the Waipahu site. The televiewer image logs obtained in some of the Waipahu Mahoe boreholes do not show any significant vertical or steeply dipping fractures that might allow communication across the dense interior of basalt flows. Acoustic televiewer logs obtained at the Pahoa site show that a number of steeply dipping fractures and dikes Cut across basalt flows. Although flow under ambient hydraulic-head conditions in the Waipahu Mahoe Observation boreholes is attributed to hydraulic gradients associated with pumping from a nearby pumping station, flow in the Waipio Deep Observation borehole on Oahu and flow in the Scientific Observation borehole on Hawaii are attributed to the effects of natural recharge and downward decreasing hydraulic heads associated with that recharge.

Parkhurst, D.L.., 1995, User's guide to PHREEQC--A computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations, Water-Resources Ivestigations Report 95-4227, 143 p.

PHREEQC is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations; (2) batch-reaction and one-dimensional (1D) transport calculations involving reversible reactions, which include aqueous, mineral, gas, solid-solution, surface-complexation, and ion-exchange equilibria, and irreversible reactions, which include specified mole transfers of reactants, kinetically controlled reactions, mixing of solutions, and temperature changes; and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits.

Parkhurst, R.S., Sturrock, A.M., Rosenberry, D.O., and Winter, T.C., 1995, Climatic and lake temperature data for wetland P1, Cottonwood Lake area, Stutsman County, North Dakota, 1982- 87: U.S. Geological Survey Open-File Report 94-546, 40 p.

Research on the hydrology of Wetland P1 and the Cottonwood Lake Area includes the study of evaporation. Presented here in a graphical format are those data collected during the open-water seasons of 1982-87 that were needed for energy- budget and mass-transfer evaporation studies. The data include air temperatures, water surface and lake-bottom temperatures, windspeed, radiation, humidity, and precipitation. Data were collected at a raft station and two land stations.

Revesz, K., Coplen, T.B., Baedecker, M.J., Glynn, P.D., and Hult, M., 1995, Methane production and consumption monitored by stable H and C isotope ratios at a crude oil spill site, Bemidji, Minnesota: Applied Geochemistry, v.10, p. 505-516.

Stable isotopic ratios of C and H in dissolved CH4 and C in dissolved inorganic C in the ground water of a crude-oil spill near Bemidji, Minnesota, support the concept of CH4 production by acetate fermentation with a contemporaneous increase in HCO3- concentration. Methane concentrations in the saturated zone decrease from 20.6 mg L-1 to less than 0.001 mg L-1 along the investigated flow path. Dissolved N2 and Ar concentrations in the ground water below the oil plume are 25 times lower than background; this suggests that gas exsolution is removing dissolved CH4 (along with other dissolved gases) from the ground water. Oxidation of dissolved CH4 along the flow path seems to be minimal because no measurable change in isotopic composition of CH4 occurs with distance from the oil body. However, CH4 is partly oxidized to CO2 as it diffuses upward from the ground water through a 5- to 7-m thick unsaturated zone; the d13C of the remaining CH4 increases, the d13C of theCO2 decreases, and the partial pressure of CO2 increases. Calculations of C fluxes in the saturated and unsaturated zones originating from the degradation of the oil plume lead to a minimum estimated life expectancy of 110 years. This is a minimum estimate because the degradation of the oil body should slow down with time as its more volatile and reactive components are leached out and preferentially oxidized. The calculated life expectancy is an order of magnitude estimate because of the uncertainty in the average linear ground-water velocities and because of the factor of 2 uncertainty in the calculation of the effective CO2 diffusion coefficient.

Rice, K.C. and Bricker, O.P., 1995, Seasonal cycles of dissolved constituents in streamwater in two forested catchments in the mid-Atlantic region of the Eastern U.S.: Journal of Hydrology, v. 170, p. 137-158.

Streamwater discharge and chemistry of two small catchments on Catoctin Mountain in north-central Maryland have been monitored since 1982. Repetitive seasonal cycles in streamwater chemistry have been observed each year, along with seasonal cycles in the volume of stream discharge and in groundwater levels. The hypothesis that the observed streamwater chemical cycles are related to seasonal changes in the hydrological flow paths that contribute to streamflow is examined using a combination of data on groundwater levels, shallow and deep groundwater chemistry, streamwater discharge, streamwater chemistry, soil-water chemistry, and estimates of water residence times. The concentrations of constituents derived from rock weathering, particularly bicarbonate and silica, increase in streamwater during the summer when the water table is below the regolith-bedrock interface and stream discharge consists primarily of deep groundwater from the fractured-bedrock aquifer. Conversely, the concentrations in streamwater of atmospherically derived components, particularly sulfate, increase in winter when the water table is above the regolith-bedrock interface and stream discharge consists primarily of shallow groundwater from the regolith. Tritium and chlorofluorocarbon (CFC) measurements suggest that the groundwater in these systems is young, with a residence time of less than several years. The results of this study have implications for the design of large-scale water-quality monitoring programs.

Sanford, W.E., Konikow, L.F., Rowe, G.L., and Brantley, S.L., 1995, Ground- water transport of crater-lake brine at Poas Volcano, Costa Rica: Journal of Volcanology and Geothermal Research, v. 64, no. 3-4, p. 269-293.

Poe1s Volcano is an active stratovolcano in Costa Rica that has a lake in its active crater. The crater lake has high temperatures (50-90oC), high acidity (pH ~ 0.0), and a high dissolved-solids content (100 g/kg). The volcano has numerous freshwater springs on its flanks, but a few on the northwestern flank are highly acidic (pH =1.6-2.5) and have high dissolved-solids concentrations (2-22 g/kg). This study analyzes the regional groundwater system at Poe1s and demonstrates the likelihood that the water discharging from the acidic springs in the Rio Agrio watershed originates at the acidic crater lake. Both heat and solute transport are analyzed on a regional scale through numerical simulations using the HST3D finite-difference model, which solves the coupled equations for fluid flow, heat transport, and solute transport. The code allows fluid viscosity and density to be functions of both temperature and solute concentration. The simulations use estimates for recharge to the mountain and a range of values and various distributions of permeability and porosity. Several sensitivity analyses are performed to test how the uncertainty in many of the model parameters affects the simulation results. These uncertainties yield an estimated range of travel times from the crater lake to the Rio Agrio springs of 1-30 years, which is in close agreement with the results of tritium analyses of the springs. Calculated groundwater fluxes into and out of the crater lake are both about several hundred kg/s. These fluxes must be accounted for in water budgets of the crater lake.

Sanford, W. E. and Wood, W. W., 1995, A paleohydrologic record from lake brine on the Southern High Plains: Geology, v. 23, p. 229-232.

estimated using dissolved-chloride profiles across an underlying shale layer. Lake conditions over the past 30 to 50 ka can be inferred from the chloride profiles by using the advective velocity of the pore water through the shale and an appropriate coefficient of molecular diffusion. The profiles suggest that net-evaporative conditions existed over the southern High Plains for the past 50 ka, with a period of increasing salinity in the lake beginning at ~ 20 ka and reaching current levels at ~ 5 ka. In addition, deflationary conditions were present for at least 4 ka, and likely began or were accelerated during the most recent altithermal period at ~ 5 ka. This type of lake-brine record may also exist in many other saline lake environments present throughout the Great Plains of North America.

Schemel, L.E., 1995, Benthic macrofauna data for San Francisco Bay, California, September, 1986: U.S. Geological Survey Open File Report 95-291.

Benthic macrofauna were collected during September 1986 to evaluate locations for long-term monitoring stations as part of the U.S. Geological Survey Regional Effects Monitoring Program in San Francisco Bay, California. Three to ten replicate samples were collected with a modified Van Veen sampler (0.05 m2 area) at ten locations. One box core sample (0.06 m2 area) was collected at seven to the ten locations. Six of the box core samples were split into an upper 10 cm sample and a deeper sample before analysis. Macrofauna specimens were identified to the lowest possible taxon, usually genus and species, then counted. An average of 88 percent of the benthic macrofauna specimens were identified to the species level. The fraction identified varied among stations from 54 to 98 percent. Nematodes and oligochaetes accounted for most of the unidentified specimens. Relative to the total number of species identified in five replicates at each location, an average of 90 percent of the species were collected with three replicates. In general, species with high to moderate abundances were present in all replicates, and species collected only after three or more replicates averaged less than one specimen per replicate. Results from the box cores showed that the dominant species were most abundant in the upper 10 cm, the depth of sediment that can be adequately sampled with a modified Van Veen sampler. On the basis of the number of species and their abundances at each location, seven of the ten locations were selected for sampling in the regular program, which began in March 1987.

Schemel, L.E., 1995, Supporting data for hdrologic studies in San Francisco Bay, California: Meteorological measurements at the Port of Redwood City during 1992-94: U.S. Geolgical Survey Open-File Report 95-327

Meteorological data were collected during 1992-94 at the Port of Redwood City, California, to support hydrologic studies in southern San Francisco Bay. The meteorological variables that were measured were air temperature, atmospheric pressure, quantum flux (insolation), and four parameters of wind speed and direction: scalar mean horizontal wind speed, (vector) resultant horizontal wind speed, resultant wind direction, and standard deviation of the wind direction. Hourly mean values based on measurements at five-minute intervals were logged at the site, then transferred to a portable computer monthly. Daily mean values were computed for temperature, insolation, pressure, and scalar wind speed. Hourly- mean and daily-mean values are presented in time- series plots and daily variability and seasonal and annual cycles are described. All data are provided in ASCII files on an IBM-formatted disk. Observations of temperature and wind speed at the Port of Redwood City were compared with measurements made at the San Francisco International Airport. Most daily mean values for temperature agreed within one- to two-tenths of a degree Celsius between the two locations. Daily mean wind speeds at the Port of Redwood City were typically half the values at the San Francisco International Airport. During summers, the differences resulted from stronger wind speeds at the San Francisco International Airport occurring over longer periods of each day. A comparison of hourly wind speeds at the Palo Alto Municipal Airport with those at the Port of Redwood City showed that values were similar in magnitude.

Schemel, L.E., 1995, Measurements of salinity, temperature, and tides in South San Francisco Bay, California, at Dumbarton Bridge: 1990-93 water years: U.S. Geological Survey Open File Report 95-326.

The U.S. Geological Survey measures salinity, temperature, and water levels (tides) in southern San Francisco Bay at Dumbarton Bridge as part of a cooperative program with the California State Department of Water Resources. During water years 1990-93, measurements were made at 15-minute intervals with electonic sensors located approximately one meter above the substrate in approximately six meters of water (at mean water level). During March and April of 1991 and 1992, salinity and temperature also were measured with a self-contained system floating one meter below the surface of the water. Sections of the data set were selected to illustrate influences of tidal currents, weather events, and seasonal and interannual variations in climate on salinity, temperature, and water levels at this location. The edited data are provided on high-density disks in comma-delimited, ASCII text files.

Schmidt, JC; Grams, PE; Webb, R.H., 1995, Comparison of the magnitude of erosion along two large regulated rivers: Water Resources Bulletin, v. 31, no. 4, p. 617-632.

Historical inventories of sand bar number and area are sufficient to detect large-scale differences in geomorphic adjustment among regulated rivers that flow through canyons with abundant debris fans. In these canyons, bedrock and large boulders create constrictions and expansions, and alluvial bars occur in associated eddies at predictable sites. Although these bars may fluctuate considerably in size, the locations of these bars rarely change, and their characteristics can be compared through time and among rivers. The area of sand bars exposed at low discharge in Hells Canyon has decreased 50 percent since dam closure, and most of the erosion occurred in the first nine years after dam closure. The number and size of sand bars in Grand Canyon downstream from Glen Canyon Dam have decreased much less; the number of sand bars decreased by 40 percent in some 8.3-km reaches, but by less than 20 percent elsewhere. These differences are in part related to the fact that flood regulation is much greater in Grand Canyon than in Hells Canyon, and that downstream tributaries resupply sediment to Grand Canyon but not to most of Hells Canyon.

Shanley, J.B., Sundquist, E.T., and C. Kendall, 1995, Water, energy, and biogeochemical budget research at Sleepers River Research Watershed, Vermont: U.S. Geological Survey Open-File Report 94-475, 22 p.

The U.S. Geological Survey has selected the Sleepers River Research Watershed (Sleepers River) near Danville, Vt., as one of five sites for the investigation of Water, Energy, and Biogeochemical Budgets (WEBB). Sleepers River was chosen because it is a well-designed outdoor laboratory with a long history of hydrologic data collection and research, and also because it provides an ideal opportunity for collaboration among the U.S. Geological Survey, other Federal agencies, and universities at the site. The multiple subwatersheds at Sleepers River present a unique opportunity to investigate hydrologic, energy, and biogeochemical processes over a variety of spatial scales. This WEBB study builds on fundamental research on process mechanisms and rates at the plot scale (in this case, a hillslope). Results then are scaled up to interpret the hydrochemical response of first- and higher- order basins. Five research elements make up the Sleepers River WEBB project. Individually, each of the five elements is designed to investigate specific WEBB processes (such as CO2 efflux through a snowpack), address specific WEBB issues (such as scaling and flowpaths), or apply specific WEBB approaches (such as integrated chemical and physical study of a hillslope). The research elements overlap so that many of the processes investigated will be assessed in more than one way, thus allowing independent verification of research results. For example, flowpath information will be derived separately by use of isotopic tracers, conservative chemical solutes, and soil-moisture fluxes. Collectively, the five elements constitute an integrated approach to a comprehensive understanding of WEBB processes needed for the prediction of the effects of global change.

Shapiro, A.M., and Greene, E.A., 1995, Interpretation of prematurely terminated air-pressurized slug tests: Ground Water, v. 33, no. 4, p. 539-546.

Air-pressurized slug tests offer a means of estimating formation transmissivity and storativity without extensive downhole equipment and in situations where contact with formation fluids may pose a health concern. An air-pressurized slug test, as discussed in this paper, consists of applying a constant pressure to the column of air in a well, monitoring the declining water level, and then releasing the air pressure and monitoring the recovering water level. If the maximum declining (or new equilibrium) water level is achieved for a constant applied air pressure, the slug-test solution of Cooper et al. (1967) can be used to interpret the water-level recovery data and estimate the formation properties. In low-permeability terranes, the time required to achieve the equilibrium water level during the pressurized part of the test may be too long for practical purposes, and it may be necessary to terminate the applied air pressure prior to establishing a new equilibrium. To analyze data from such tests, a solution to the boundary-value problem for the declining and recovering water level during an air-pressurized slug test is developed for an arbitrary time-dependent air pressure applied to the well. For the special case of applying a constant air pressure and then reducing it instantaneously to atmospheric pressure at a prescribed time, the general solution reduces to the superposition of the solution of Cooper et al. (1967) at two displaced times. Type curves are generated to estimate formation transmissivity and storativity from the recovering water level associated with prematurely terminated air-pressurized slug tests. The application of the type curves is illustrated in tests conducted in wells completed in the Minnelusa and Madison aquifers near Rapid City and Spearfish, South Dakota.

Taylor, H.E., and Shiller, A.M., 1995, Mississippi River methods comparison study: implications for water quality monitoring of dissolved trace elements: Environmental Science and Technology, v. 29, no 5, p. 1313- 1317.

Recent reports have questioned the validity of dissolved trace elements concentrations reported by the U.S. Geological Survey's National Stream Quality Accounting Network (NASQAN) as well as by other water-quality monitoring programs. To address these concentrations and to evaluate the NASQAN protocols, the U.S. Geological Survey undertook the Mississippi River Methods Comparison Study. We report here the major results and implications of this study. In particular, we confirm the possible inaccuracy of previous NASQAN dissolved trace element data. The results suggest that all steps of the NASQAN protocol (sampling, processing, and analysis) require revision, though the sample filtration step appears to be of particular concern.

Tindall, J.A., Petrusak, R.L., and McMahon, P.B., 1995, Nitrate transport and transformation processes in unsaturated porous media: Journal of Hydrology, v. 169, p. 51-94.

A series of experiments was conducted on two contrasting agricultural soils to observe the influence of soil texture, preferential flow, and plants on nitrate transport and denitrification under unsaturated conditions. Calcium nitrate fertilizer was applied to the surface of four large undisturbed soil cores (30 cm diameter by 40 cm height). Two of the cores were a structured clay obtained from central Missouri and two were an unstructured fine sand obtained from central Florida. The cores were irrigated daily and maintained at a matric potential of -20 kPa, representative of soil tension in the rooting zone of irrigated agricultural fields. Volumetric water content (q), concentration of nitrate-N in the soil solution, and nitrous oxide flux at the surface, 10, 20, and 30 cm were monitored daily. Leaching loss of surface-applied NO3--N was significant in both the sand and the clay. In unplanted sand cores, almost all of the applied nitrate was leached below 30 cm within 10 days. Gaseous N loss owing to denitrification was no greater than 2% of the nitrate-N applied to the unplanted sand cores and, in general, was less than 1%. Although leaching was somewhat retarded in the clay cores, about 60% of the applied nitrate-N was leached from the unplanted clay soil in 5-6 weeks. Under unsaturated conditions, the clay had little to no tendency to denitrify despite the greater moisture content of the clay and retarded leaching of nitrate in the clay. The planted sand cores had surprisingly large gaseous N loss owing to denitrification, as much as 17% of the nitrate-N. Results from both the clay and sand experiments show that the dynamics of nitrate transport and transformation in unsaturated soils are affected by small, localized variations in the soil moisture content profile, the gaseous diffusion coefficient of the soil, the rate at which the nitrate pulse passes through the soil, the solubility of N2O and N2 and the diffusion of the gasses through the soil solution, and development of a water content profile in the soil. Limited denitrification in the clay soil was due to a limited volume of soil available for infiltration after internal catchment and the development of denitrifying conditions resulting from the presence of an extensive macropore system.

Toy, T. J., and Osterkamp, W. R., 1995, The applicability of RUSLE to geomorphic studies: Journal of Soil and Water Conservation, v. 50 no. 5, p. 498-503.

The Universal Soil Loss Equation (USLE) has been the best, most convenient technology for estimating soil loss in a wide variety of investigations. Recent revisions to USLE incorporated new knowledge and improved the versatility of the revised USLE (RUSLE). Following a brief description of the evolution and utilization of USLE, this presentation addresses the applicability of RUSLE in geomorphic research. In general, consideration of both temporal and spatial scales is essential for the appropriate application of RUSLE in geomorphic research. Soil-loss estimates may be extended into the past only so long as the environmental conditions remain virtually the same as those used in the computations. Soil-loss estimates are likely to be of satisfactory accuracy at spatial scales ranging from landscape profiles (hillslopes) up to small drainage basins in which there is minimal sediment storage.

Walter, D.A., Rea, B.A., Stollenwerk, K.G., and Savoie, J., 1995, Geochemical and hydrologic controls on phosphorus transport in a sewage-contaminated sand and gravel aquifer near Ashumet Pond, Cape Cod, Massachusetts: U.S. Geological Survey Open-File Report 95-381, 89 p.

The disposal of secondarily treated sewage onto rapid infiltration sand beds at the Massachusetts Military Reservation, Cape Cod, Massachusetts, has created a sewage plume in the underlying sand and gravel aquifer; the part of the\x11sewage plume that contains dissolved phosphorus extends about 2,500 feet downgradient of the sewage-disposal beds. A part of the plume that contains nearly 2 milligrams per liter of phosphorus currently (1993) discharges into Ashumet Pond along about 700 feet of shoreline. The sewage plume discharges from about 59 to about 76 kilograms of phosphorus per year into the pond. Hydraulic-head measurements indicate that the north end of Ashumet Pond is a ground-water sink and an increased component of ground-water discharge and phosphorus flux into the pond occurs at higher water levels. Phosphorus was mobile in ground water in two distinct geochemical environments-an anoxic zone that contains no dissolved oxygen and as much as 25 milligrams per liter of dissolved iron, and a more areally extensive suboxic zone that contains little or no iron, low but detectable dissolved oxygen, and as much as 12 milligrams per liter of dissolved manganese. Dissolved phosphorus is mobile in the suboxic geochemical environment because continued phosphorus loading has filled available sorption sites in the aquifer. Continued disposal of sewage since 1936 has created a large reservoir of sorbed phosphorus that is much greater than the mass of dissolved phosphorus in the ground water; the average ratio of sorbed to dissolved phosphorus in the anoxic and suboxic parts of the sewage plume were 31:1 and 155:1, respectively. Column experiments indicate that phosphorus in the anoxic core of the plume containing dissolved iron may be immobilized within 17 years by sorption and coprecipitation with new iron oxyhydroxides following the cessation of sewage disposal and the introduction of uncontaminated oxygenated ground water into the aquifer in December 1995. Residual oxygen demand associated with sorbed organic compounds and ammonia could retard the movement of oxygenated water into the aquifer. Sorbed phosphorus in the suboxic zone of the aquifer will continue to desorb into the ground water and will remain mobile in the ground water for perhaps hundreds of years. Also, the introduction of uncontaminated water into the aquifer may cause dissolved-phosphorus concentrations in the suboxic zone of the aquifer to increase sharply and remain higher than precessation levels for many years due to the desorption of loosely bound phosphorus. Data from three sampling sites, located along the eastern and western boundaries of the sewage plume and downgradient of abandoned sewage-disposal beds, indicate that ground-water mixing and phosphorus desorption may already be occurring in the aquifer in response to the introduction of uncontaminated recharge water into previously contaminated parts of the aquifer.

Welch, A.H., Szabo, Zoltan, Parkhurst, D.L., Van Metre, P.C., and Mullin, A.H., 1995, Gross-beta activity in ground water: natural sources and artifacts of sampling and laboratory analysis: Applied Geochemistry, v. 10, p. 491-503.

Gross-beta activity has been used as an indicator of beta-emitting isotopes in water since at least the early 1950s. Originally designed for detection of radioactive releases from nuclear facilities and weapons tests, analysis of gross-beta activity is widely used in studies of naturally occurring radioactivity in ground water. Analyses of about 800 samples from 5 ground-water regions of the United States provide a basis for evaluating the utility of this measurement. The data suggest that measured gross-beta activities are due to (1) long-lived radionuclides in ground water, and (2) ingrowth of beta-emitting radionuclides during holding times between collection of samples and laboratory measurements.

Although 40K and 228Ra appear to be the primary sources of beta activity in ground water, the sum of 40K plus 228Ra appears to be less than the measured gross-beta activity in most ground-water samples. The difference between the contribution from these radionuclides and gross-beta activity is most pronounced in ground water with gross-beta activities > 10 pCi/L, where these 2 radionuclides account for less than one-half the measured gross-beta activity. One exception is ground water from the Coastal Plain of New Jersey, where 40K plus 228Ra generally contribute most of the gross-beta activity. In contrast, 40K and 228Ra generally contribute most of beta activity in ground water with gross-beta activities < 1 pCi/L.

The gross-beta technique does not measure all beta activity in ground water. Although 3H contributes beta activity to some ground water, it is driven from the sample before counting and therefore is not detected by gross-beta measurements. Beta-emitting radionuclides with half-lives shorter than a few days can decay to low values between sampling and counting. Although little is known about concentrations of most short-lived beta-emitting radionuclides in environmental ground water (water unaffected by direct releases from nuclear facilities and weapons tests), their activities are expected to be low.

Ingrowth of beta-emitting radionuclides during sample holding times can contribute to gross-beta activity, particularly in ground water with gross-beta activities > 10 pCi/L. Ingrowth of beta-emitting progeny of 238U, specifically 234Pa and 234Th, contributes much of the measured gross-beta activity in ground water from 4 of the 5 areas studied. Consequently, gross-beta activity measurements commonly overestimate the abundance of beta-emitting radionuclides actually present in ground water. Differing sample holding times before analysis lead to differing amounts of ingrowth of the two progeny. Therefore, holding times can affect observed gross-beta measurements, particularly in ground water with 238U activities that are moderate to high compared with the activity of 40K plus 228Ra. Uncertainties associated with counting efficiencies for beta particles with different energies further complicate the interpretation of gross-beta measurements.

Wood, T.M., Baptista, A.M., Kuwabara, J.S. and Flegal, A.R., 1995, Diagnostic modeling of trace metal partitioning in South San Francisco Bay: Limnology and Oceanography, v. 40, no. 2, p. 345-358.

The two-dimensional numerical model ELAmet was used to investigate the effect of adsorption kinetics on the apparent distribution coefficients of Cu, Cd, and Zn in south San Francisco Bay, California. The numerical experiments were designed to determine whether adsorption kinetics can control the basin-scale variability of the observed partitioning and to define the conditions under which adsorption kinetics could account for strong interannual variability in partitioning. The numerical results indicate that aqueous speciation will control basin-scale spatial variations in the apparent distribution coefficient, Kad, if the system is close to equilibrium. However, basin-scale spatial variations in Kad are determined by the location of the sources of metal and the suspended solids concentration of the receiving water if the system is far from equilibrium. The overall spatial variability in Kad also increases as the system moves away from equilibrium.

Wood, W.W. and Imes. J.L., 1995, How wet is wet? Precipitation constraints on late Quaternary climate in the southern Arabian Peninsula: Journal of Hydrology, v. 164, p. 263-268.

It is generally recognized that the southern Arabian Peninsula has had two wet periods in the late Quaternary. To quantify "wet" a 28,000 year old capillary surface associated with a paleowater-table was mapped and used as a surrogate for the water table in a ground-water model. Analysis of this model suggests 1.4 mm/yr. of recharge is necessary to support the water table at the mapped elevations during the wet period. Climatic relations between rainfall and recharge in arid areas infer that annual rainfall during this wet period was approximately 200 plus or minus 50 mm/yr. or approximately 5 times the present rate.

Wood, W.W. and Sanford, W.E., 1995, Chemical and isotopic methods for quantifying ground-water recharge in a regional, semiarid environment: Ground Water, v. 33, no. 3, p. 458-468.

The High Plains aquifer underlying the semi-arid Southern High Plains of Texas and New Mexico, USA was used to illustrate solute and isotopic methods for evaluating recharge fluxes, runoff, and spatial and temporal distribution of recharge. The chloride mass-balance method can provide, under certain conditions, a time-integrated technique for evaluation of recharge flux to regional aquifers that is independent of physical parameters. Applying this method to the High Plains aquifer of the Southern High Plains suggests that recharge flux is approximately 2 percent of precipitation, or approximately 11 +/- 2 mm/y, consistent with previous estimates based on a variety of physically based measurements. The method is useful because long term average precipitation and chloride concentrations in rain and ground water have less uncertainty and are generally less expensive to acquire than physically based parameters commonly used in analyzing recharge. Spatial and temporal distribution of recharge was evaluated by use of d 2H, d 18O and tritium concentrations in both ground water and the unsaturated zone. Analyses suggests that nearly half of the recharge to the Southern High Plains occurs as piston flow through playa basin floors that occupy approximately 6 percent of the area and that macropore recharge may be important in the remaining recharge. Tritium and chloride concentrations in the unsaturated zone were used in a new equation developed to quantify runoff. Using this equation and data from a representative basin, runoff was found to be 24 +/- 3 mm/y, that is in close agreement with values obtained from water-balance measurements on experimental watersheds in the area. Such geochemical estimates are possible because tritium is used to calculate a recharge flux that is independent of precipitation and runoff, whereas recharge flux based on chloride concentration in the unsaturated zone is dependent upon the amount of runoff. The difference between these two estimates yields the amount of runoff to the basin.

Wood, W. W. and Sanford, W. E., 1995, Eolian transport, saline lake basins, and groundwater solutes: Water Resources Research, v. 31 p. 3121-3129.

Eolian processes associated with saline lakes are shown to be important in determining solute concentration in ground water in arid and semi-arid areas. Steady-state mass-balance analyses of chloride in the ground water at Double Lakes, a saline lake basin in the Southern High Plains of Texas, USA, suggest that approximately 4.5 x 105 kg of chloride are removed from the relatively small (4.76 km2) basin floor each year by deflation. This mass enters the ground water down the wind gradient from the lake degrading the water quality. The estimates of mass transport were independently determined by evaluation of solutes in the unsaturated zone and by solute mass balance calculations of ground water flux. Transport of salts from the lake was confirmed over a short term (2 years) by strategically placed dust collectors. Results consistent with those at Double Lake were obtained from dune surfaces collected up and downwind from a sabkha near the city of Abu Dhabi in the United Arab Emirates. The eolian transport process provides an explanation of the degraded ground-water quality associated with the 30 to 40 saline-lake basins on the southern half of the Southern High Plains of Texas and New Mexico and in many other arid and semi-arid areas.

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