Crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near Bemidji, Minnesota. The degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body. The concentrations of Fe2+ , Mn2+, and CH4, Eh measurements, and the d13C ratios of the total inorganic C indicate that the plume became more reducing over a 5-a period. However, the size of the contaminant plume remained stable during this time. Field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment. In anaerobic microcosm experiments conducted under field conditions, almost complete degradation (98%) was observed for benzene in 125 d and for toluene in 45 d. Concentrations of aqueous Fe2+ and Mn2+ increased in these experiments, indicating that the primary reactions were hydrocarbon degradation coupled with Fe and Mn reduction. Mass transfer calculations on a 40-m flowpath in the anoxic zone, downgradient from the oil body, indicated that the primary reactions in the anoxic zone are oxidation of organic compounds, precipitation of siderite and a ferroan calcite, dissolution of iron oxide and outgassing of CH4 and CO2. The major difference in the two models presented is the ratio of CO2 and CH4 that outgasses. Both models indicate quantitatively that large amounts of Fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume.
The relative merits of an optimized frontal solver and a variety of iterative solution methods for the solution of the shallow water equations were investigated. Applications to two test problems indicate that some types of problem were favourable to the frontal solver, while others were best approached using an iterative approach.
Field and microcosm observations of methanogenic phenolic compound degradation indicate that Monod kinetics governs the substrate disappearance but overestimates the observed biomass. In this paper we present modeling results from an ongoing multidisciplinary study of methanogenic biodegradation of phenolic compounds in a sand and gravel aquifer contaminated by chemicals and wastes used in wood treatment. Field disappearance rates of four phenols match those determined in batch microcosm studies previously performed by E.M. Godsy and coworkers. The degradation process appears to be at steady-state because even after a sustained influx over several decades, the contaminants still are disappearing in transport downgradient. The existence of a steady-state degradation profile of each substrate together with a low biomass density in the aquifer indicate that the bacteria population is exhibiting no net growth. This may be due to the oligotrophic nature of the biomass population in which utilization and growth are approximately independent of concentration for most of the concentration range. Thus a constant growth rate should exist over much of the contaminated area which may in turn be balanced by an unusually high decay or maintenance rate due to hostile conditions or predation.
The hyporheic zone is now generally understood to be part of the landscape that contains water of both subsurface and stream channel origin. This specific point of view has developed in a succession of studies in which interdisciplinary groups have worked to develop concepts of the hydrologic connections between streams and their catchments: (1) a pipe receiving nutrients (or other solutes) from the catchment: (2) or integral parts of the catchment system focusing on the dynamic, bidirectional nature of connections within the system. The concepts are relevant to studies of biogeochemistry and physical solute transport. At least two time-scales can be identified for storage of stream solutes in subsurface environments. Work on the hydrology of the hyporheic zone has been limited, thus the hydrology lacks a widely recognized or standardized approach for characterization. One approach to characterization is to determine the influence of the zone on nutrient (or other solute) transport at individual sampling locations along the stream; a second approach is to consider the transport of solutes over the catchment-wide downvalley gradient with the hyporheic zone viewed as a continuation of the porous media throughout the subsurface of the catchment. Future research is needed to identify the processes of fluid mechanics that occur at the interface of catchment and stream hydrology. Continued work on hyporheic zone ecology needs to be accompanied by study of the fluid mechanic processes resolved to the fine scale of specific biogeochemical processes.
Changes in the distribution of inorganic solutes in a shallow ground water contaminated by crude oil document a series of geochemical reactions initiated by biodegradation of the oil. Upgradient of an oil body floating on the water table, oxidation of oil to carbonic acid dissolves carbonate minerals in the aquifer matrix. In this oxidized zone pH is depressed similar to 1 pH unit, and the concentrations of Ca, Mg and HCO3- increase to more than twice that of the native ground water. In the anoxic zone beneath the oil body concentrations of dissolved SiO2, Sr, K, Fe and Mn increase significantly. Here, Fe is mobilized by microbial reduction, pH is buffered by the carbonate system, and silicates weather via hydrolysis and organic-acid-enhanced dissolution. Farther down-gradient the ground water is reoxygenated and Fe precipitates from solution, possibly as iron hydroxide or iron carbonates, while SiO2 precipitates as amorphous silica. Other solutes, such as Mg, are transported more conservatively down-gradient where contaminated and native ground waters mix. The observed changes in inorganic aqueous chemistry document changes in water-mineral interactions caused by the presence of an organic contaminant. These organic-initiated interactions are likely present in many contaminated aquifers and may be analogous to interactions occurring in other organic-rich natural waters.
Tracer dilution experiments and associated solute transport simulations provided estimates of discharge and time of travel along several reaches of Saint Kevin Gulch, a stream receiving acidic effluent from mine tailings in Lake County, Colorado. Profiles of time-varying tracer (lithium chloride) concentration were simulated with a transport model depicting advection, dispersion, lateral inflow, and the transient storage of solutes in immobile zones along the stream channel. Simulated profiles were sensitive to variations in the model's transient-storage parameters, including the cross-sectional area of the storage zone and the stream-storage exchange coefficient. Although similar to values calibrated in simulations of tracer profiles in other mountain streams, these transient storage parameters were specific to individual reaches and could not be predicted from linear combinations of simple hydraulic variables. Parameters that were calibrated for the simulation of lithium concentrations could be used without adjustment to simulate measured concentrations of chloride. This result increased confidence in the ability of the model to simulate the nonreactive behavior of any solute. The steady-state profile of lithium concentrations during the plateau stage of the experiment also was simulated successfully. Assumptions underlying tracer-dilution methods are violated in losing reaches of streams. Injection of a second tracer (sodium bromide) and a direct measurement of discharge provided an improved estimate of the flow rate downstream from a losing reach of Saint Kevin Gulch.
Correlation analysis in conjunction with principal-component and multiple-regression analyses were applied to laboratory chemical and petrographic data to assess the usefulness of these techniques in evaluating selected physical and hydraulic properties of carbonate-rock aquifers in central Pennsylvania. Correlation and principal-component analyses were used to establish relations and associations among variables, to determine dimensions of property variation of samples, and to filter the variables containing similar information. Principal-component and correlation analyses showed that porosity is related to other measured variables and that permeability is most related to porosity and grain size. Four principal components were found to be significant in explaining the variance of data. Stepwise multiple-regression analysis was used to see how well the measured variables could predict porosity and/or permeability for this suite of rocks. The variation in permeability and porosity is not totally predicted by the other variables, but the regression is significant at the 5% significance level.
Detectable concentrations of chlorofluorocarbons (CFC's) were observed in groundwater and unsaturated-zone air at the Idaho National Engineering Laboratory (INEL) and vicinity. The recharge ages of waters were determined to be from 4 to > 50 yr on the basis of CFC concentrations and other environmental data; most groundwaters have ages of 14-30 yr. The Big Lost River, Birch Creek, the Little Lost River, and the Mud Lake-Terreton area appear to be major sources of recharge of the Snake River Plain aquifer at INEL. An average recharge temperature of 9.7oC was calculated from dissolved nitrogen and argon concentrations in the groundwater, a temperature that is similar to the mean annual soil temperature of 9oC measured at INEL. Soil-gas concentrations at Test Area North (TAN) are well explained by diffusion theory. The measured difference between apparent ages based on CFC-11 and CFC-12 concentrations is 7.5 yr for the soil atmosphere near the water table at TAN. The results indicate that the groundwater equilibrated near or within the thin soil zone and then moved rapidly through the fractured basalts to the water table without gas-water reequilibration. Groundwaters near the southwest of the Radioactive Waste Management Complex, the Test Reactor Area (TRA), and the Idaho Chemical Processing Plant contain levels of CFC's that are indicative of contamination. The CFC data indicate that a large CFC-12 waste plume may originate in the vicinity of TRA.
Several long sediment cores from the Cheyenne River Embayment of Lake Oahe, a 250-km long Missouri River reservoir in South Dakota, have been analyzed for radionuclides and stable elements. The Cheyenne River basin is a source of easily erodible siltstone and shale and also easily erodible mine tailings that have been released by gold-mining activities in the Black Hills, South Dakota. The combination of fine-scale sampling and rapid sedimentation produces radionuclide distributions that can be used to estimate the detailed chronology of particle transport processes in the Oahe reservoir system. A self-consistent and quantitative treatment of the 137Cs data suggests processes to which characteristic times may be associated. Times that characterize system-wide processes include: (1) an integration time of several years reflecting retention of the sediment-bound tracer in regions within or external to the reservoir; (2) a relaxation time of approximately 15 years reflecting a decreasing rate of sediment accumulation ascribed to shoreline stabilization; (3) a time of a few months characterizing the breadth of riverine signatures in cores due to integration effects in the Cheyenne River system and deltaic deposits; and (4) times of a few years associated with propagation of riverine load signatures along the embayment. The distribution of total sedimentary arsenic confirms the validity of the variable sedimentation model. In 1977, a tailings retention facility was built at the Homestake Mine site, and the unrestricted input of As ceased. As a result of this remedial action, the concentration of sedimentary As decreased dramatically. In the upper section of the core, above the depth represented by the year 1976, the concentration of As decreases tenfold. In this same core the distribution of lithologically discriminating chemical elements, calcium and vanadium, relate to major flow events in the Cheyenne River basin. Stable element signatures, in addition to radiotracers, may be used to reconstruct hydrologic events in drainage basins that contribute sediment to lakes and reservoirs, because there is minimal diagenesis of chemical constituents.
Salinity in the San Francisco Bay Estuary almost always experiences its yearly maximum during late summer, but climate variability produces marked interannual variations. The atmospheric circulation pattern impacts the estuary primarily through variations of runoff from rainfall and snowmelt from the Sierra Nevada and, secondarily, through variations in the near-surface salinity in the coastal ocean. While winter precipitation is the primary influence upon salinity in the estuary, spring climate variations also contribute importantly to salinity fluctuations. Spring atmospheric circulation influences both the magnitude and the timing of freshwater flows, through anomalies of precipitation and temperature. To help discriminate between the effects of these two influences, the record is divided into subsets according to whether spring conditions in the region are cool and wet, warm and wet, cool and dry, or warm and dry. Warm springs promote early snowmelt-driven flows, and cool springs result in delayed flows. In addition to effects of winter and spring climate variability operating on the watershed, there are more subtle effects that are transmitted into the estuary from the coastal ocean. These influences are most pronounced in cool and dry springs with high surface salinity (SS) in the coastal ocean versus cool and wet springs with low SS in the coastal ocean. A transect of SS records at stations from the mouth to the head of the bay suggests that the coastal ocean anomaly signal is attenuated from the mouth to the interior of the estuary. In contrast, a delayed, postsummer signal caused by winter and spring runoff variations from the upstream watershed are most pronounced at the head of the estuary and attenuate toward the mouth.
The majority of the water stored for agricultural, residential, and commercial use in western North America is accumulated from precipitation runoff in high elevation watersheds. The influence of climatic parameters on seasonal streamflow was investigated in watersheds over a range of elevations (less than 1000 m, 1000-2000 m, and greater than 2000 m) in California and Oregon to provide background for anticipating impacts of climate change on surface hydrology by assessing the sensitivity to present-day natural climate variability. Effects of precipitation, temperature, and snow water content (SWC) were diagnosed using linear regression models and categoric composites. Most of the models explained more than 60 to 80% of the seasonal streamflow variability. The models and the composites provide insight into the climatic influences which drive the individual watersheds. Low (warmer) basins have little snow and little memory of prior seasons' climatic variability. High (cooler) basins, with more snow, have longer memories. Precipitation has the greatest influence on streamflow variations in spring. Temperature is important in spring in the middle and high elevations. By late spring, SWC accounts for nearly all of the summer streamflow variation at middle and high elevations, but earlier in the runoff season, precipitation and temperature add variance. The variations in surface climate parameters, including streamflow, are generally controlled by atmospheric circulation anomalies with a spatial scale much larger than those in watersheds. Large scaled averages (over climate divisions or states) of temperature and precipitation perform nearly as well as local measures from individual watersheds in accounting for streamflow variability.
Contrasting approaches to the derivation of the stability limit for the Froude number in laminar sheet flow are considered and a way of correcting the discrepancy between them developed. One approach used the Orr-Sommerfeld equation, while the other used the cross-section averaged equations of continuity and motion. Published values for the approaches differed, suggesting a defect in at least one of them. Analysis showed that the cross-section-averaged equation of motion was dependent on the frame of reference. By formulating a frame-independent equation of motion relative to a co-ordinate system moving with constant velocity, a new expression for the stability limit which yielded consistent results was derived.
The formation of siderite (ferrous carbonate) concretions in a salt-marsh sediment was investigated. Siderite concretions at this site, on the Norfolk coast, resulted from the activity of sulphate-reducing bacteria. Rather than reducing iron(III) indirectly through the production of hydrogen sulphide, as previously thought, some of these bacteria were capable of reducing iron(III) directly to iron(II) through an enzymatic mechanism, resulting in the formation of siderite rather than iron sulphides. The role of sulphate-reducing bacteria in reducing iron(III) in aquatic sediments and groundwater is discussed.
The method developed for determining Scheffe-type confidence intervals for output (or other function parameters) g(beta) is general in that parameter uncertainty can be specified by any statistical distribution having a log probability density function (log pdf) that can be expanded in a Taylor series. However, for this study parameter uncertainty i s specified by a statistical multivariate beta distribution that incorporates hydrogeologic information in the form of the best estimates of parameters and a grouping of random variables representing possible parameter values so that each group is defined by maximum and minimum bounds and an ordering according to increasing value. The new method forms the confidence intervals from maximum and minimum limits of g(beta) on a contour of a linear combination of: (1) the quadratic form for the parameters used by Cooley and Vecchia; and (2) the log pdf for the multivariate beta distribution. By using three example problems it is shown that different weights generally produced similar confidence intervals, whereas the method of Cooley and Vecchia often produced much larger confidence intervals.
Calibration data (observed values corresponding to model- computed values of dependent variables) were incorporated into a general method of computing exact Scheffe-type confidence intervals analogous to the confidence intervals developed previously for a function of parameters derived from a groundwater flow model. Parameter u ncertainty is specified by a distribution of parameters conditioned on the calibration data. This distribution was obtained as a posterior distribution by applying Bayes' theorem to the hydrogeologically derived prior distribution of parameters previously determined and a distribution of differences between the calibration data and corresponding model-computed dependent variables. Tests showed that the new confidence intervals can be much smaller than the previously derived intervals because the prior parameter variance-covariance structure was altered so that combinations of parameters that give poor model fit to the data are unlikely. The previous confidence intervals and the new confidence intervals can be effectively employed in a sequential method of model construction whereby new information is used to reduce confidence interval widths at each stage.
Modifications to the computer code for nonlinear regression solution of steady-state ground-water flow problems in "Regression modeling of ground-water flow" (Techniques of Water Resources Investigations, Book 3, Chapter B4, 1990) improve the performance of the code. The changes 1) allow any model parameters to be transformed to natural logarithms, and 2) improve the procedure for computing the parameter that damps changes in the values of model parameters for each iteration of the solution method. In addition, the user is shown how to read prior information separately from the initial set of parameter values.
Reliable assessment of the hazards or risks arising from groundwater contamination requires the capability to predict the movement and fate of dissolved solutes in groundwater. The modeling of metal transport in groundwater requires adsorption coefficients to describe ion adsorption. Metal-ion sorption in natural systems is usually thought to be controlled by surface reactions with Fe and Al oxyhydroxides and organic coatings on particles. The importance of surface coatings makes it difficult to relate the bulk mineralogical composition of a sample to its adsorptive reactivity. Determining the predominant adsorbing surface in a mineral assemblage can be a useful approach to modeling adsorption with a surface complexation model. One objective of this study was to search for a geochemical 'indicator' of the mineral surface(s) controlling lead (Pb) and zinc (Zn) sorption on the aquifer sand. The spatial variability of parameters used in models for solute transport in groundwater are of significance in the simulations of solute movement. Variability of hydraulic conductivity has been shown to be a key cause of observations of macroscale dispersion in sand and gravel aquifers. Like hydraulic conductivity, adsorption coefficients and other geochemical properties of the porous medium are expected to be spatially variable. In this study, 14 continuous cores of subsurface material were collected from a shallow sand and gravel aquifer where the spatial variability of hydraulic conductivity had been previously studied. Each core was sectioned into subsamples. Measurements were made of: (1) grain size distribution to estimate hydraulic conductivity and (2) lead and zinc adsorption for a constant set of experimental conditions.
Crude oil spilled from a pipeline break in a remote area of north-central Minnesota has contaminated a shallow glacial outwash aquifer. Part of the oil was sprayed over a large area to the west of the pipeline and part of it accumulated in an oil body that floats at the water table to the east of the point of discharge. Total dissolved organic carbon (TDOC) concentrations in shallow groundwater collected in the oil spray area reach 16 mg/l. This is nearly an order of magnitude higher than the TDOC concentrations of native groundwater ( similar to 2-3 mg/l). The additional TDOC derives from the partial degradation of petroleum residues deposited at the land surface and transported to the aquifer by vertical recharge. In the vicinity of the oil body, TDOC concentrations in groundwater are 48 mg/l, 58% of the TDOC being composed of non-volatile organic C. The majority of the volatile DOC (63%) is a mixture of low-molecular-weight saturated, aromatic and alicyclic hydrocarbons derived from the oil. Downgradient from the oil body along the direction of groundwater flow, concentrations of all measured constituents of the TDOC pool decrease. Concentrations begin to decline most rapidly, however, in the zone where dissolved O2 concentrations begin to increase, similar to 50 m downgradient from the leading edge of the oil. Within the anoxic zone near the oil body, removal rates of isomeric monoaromatic hydrocarbons vary widely. This indicates that the removal processes are mediated mainly by microbiological activity. Molecular and spectroscopic characterization of the TDOC and its spatial and temporal variation provide evidence of the importance of biogeochemical processes in attenuating petroleum contaminants in this perturbed subsurface environment.
The C6-C10 aromatic hydrocarbons represent powerful molecular probes of biogeochemical processes affecting the fate of petroleum in aquatic environments. Me thods to detect benzene, alkylbenzenes and other aromatic compounds in water are becoming increasingly important to monitor groundwater pollution from landfill leachates, surface runoff, and leakage from underground storage tanks. A method was developed to determine the C6-C10 aromatic hydrocarbons in water based on purge-and-trap capillary gas chromatography with flame ionization and mass spectrometric detection. Retention time data and 70 eV mass spectra were obtained for benzene and all 35 C7-C10 aromatic hydrocarbons. Routine conditions of analysis were as follows: purge gas, nitrogen; purge flow, 40 ml/min; purge time, 11 min; dry purge time, 4 min; trap temperature (during purge), 22oC; (during desorption), 175oC; desorption time 4 min. Sample components were transferred from the trap to the column using helium carrier gas at a flow-rate of about 1.5 ml/min (linear velocity at 150 C= about 30 cm/sec). The column was maintained at -50 C; it was programmed to 40 C at 50 C/min (5-min hold), then to 150 C at 3 C/min followed by a 25-min isothermal hold. This temperature program was developed after evaluating and optimizing the conditions of separation using complex oil-contaminated groundwater samples. With optimized chromatographic conditions and mass spectrometric detection, benzene and 33 of the 35 alkylbenzenes can be identified and measured in a 45-min run. Use of a flame ionization detector permits the simultaneous determination of benzene and 26 alkylbenzenes with a detection limit of approximately 30 nanograms/L. The precision of the method is generally less than 10%, and recovery of surrogates spiked in contaminated field samples ranges from 85-108%.
The existence of an upper limit to the magnitude of floods in a region is a long-standing and controversial hypothesis in flood hydrology. Regional envelope curves encompassing maximum flood magnitudes stabilize with progressive increases in the areal coverage and period of observation. However, the short lengths of conventional gaging records limit substantial advances in testing whether this stabilization is evidence of an upper limit. In the Colorado River basin there are 32,120 station years of gage data, but the average period at a gaging station is only 20 years, with most stations having less than 70 years of observation. Paleoflood magnitudes derived from sediments of large prehistoric floods from 25 sites on rivers in Arizona and Utah provide additional data to extend the records of the largest floods. The paleoflood data identify the maximum flood discharges that have occurred on individual rivers over the last several hundred to several thousand years. Even with this increase in the observational period, the largest paleoflood discharges do not exceed the upper bound of maximum peak discharges delineated by the envelope curve derived from the available gaged and historical records. This result accords with the hypothesis of an upper physical limit for flood magnitudes and suggests that, for the Colorado River basin, the upper limit can be approximated by existing systematic and historical data for large floods. Similar relationships also hold when paleofloods and gaged records are presented for the subregion of southern Arizona.
Subsurface oil, water and air saturation distributions were determined using 146 samples collected from seven boreholes along a 120 m transect at a crude oil spill site near Bemidj, Minnesota. The field data, collected ten years after the spill, show a clearly defined oil body that has an oil saturation distribution that appears to be influenced by sediment heterogeneities and water table fluctuations. The center of the oil body has depressed the water-saturated zone boundary and the oil appears to have migrated laterally within the capillary fringe. A multiphase cross-sectional flow model was developed and used to simulate the movement of oil and water at the spill site. Comparisons between observed and simulated oil saturation distributions serve as an indicator of the appropriateness of using such models to predict the actual spread of organic immiscible liquids at spill sites. Sediment hydraulic properties used in the model were estimated from particle size data. The general large-scale features of the observed oil body were reproduced only when hysteresis with oil entrapment and representations of observed spatial variability of hydraulic properties were incorporated into the model. The small-scale details of the observed subsurface oil distribution were not reproduced in the simulations. The discrepancy between observed and simulated oil distributions reflects the considerable uncertainty in model parameter estimates and boundary conditions, three-phase capillary pressure saturation-relative permeability functions, representations of spatial variability of hydraulic properties, and hydrodynamics of the groundwater flow system at the study site.
To study the effect of spatial variability of sediment hydraulic properties on multiphase flow, oil infiltration into a hypothetical glacial outwash aquifer, followed by oil extraction, was simulated using a cross-sectional multiphase flow model. The analysis was simplified by neglecting capillary hysteresis. Two hundred days of oil infiltration followed by 200 days of oil extraction were simulated for a number of different cases, and the resulting distributions of oil saturation were compared. The first simulation used a uniform mean permeability and mean retention curve. This was followed by 50 Monte Carlo simulations conducted using 50 spatially variable permeability realizations and corresponding spatially variable retention curves. It was found that, for a correlation structure similar to that of glacial outwash deposits, use of mean hydraulic properties reproduced the ensemble average oil saturation distribution obtained from the Monte Carlo simulations. However, spatial variability caused the oil saturation distribution in an individual oil lens to differ significantly from that of the mean lens. Oil saturations at a given location may be considerably higher than would be predicted using uniform mean properties. During cleanup by oil extraction from a well, considerably more oil may remain behind in the heterogeneous case than in the spatially uniform case. In the more complex three-dimensional systems encountered in the field having hysteresis, fluid entrapment, and water table fluctuations, the heterogeneous lens may differ even more from the mean lens.
The gases dissolved in Lake Nyos, Cameroon, were quantified recently (December 1989 and September 1990) by two independent techniques: in-situ measurements using a newly designed probe and laboratory analyses of samples collected in pre-evacuated stainless steel cylinders. The highest concentrations of CO2 were 0.30 mol/kg, and 1.7 mmol/kg for CH4, measured in cylinders collected 1 m above lake bottom. Probe measurements of in situ gas pressure at three different stations showed that horizontal variations in total dissolved gas were negligible. Total dissolved gas pressure near the lake bottom is 1.06 MPa (10.5 atm), 50% as high as the hydrostatic pressure of 2.1 MPa (21 atm). Comparing the CO2 profile constructed from the 1990 data to one obtained in May 1987 shows that CO2 concentrations have increased at depths below 150 m. Based on these profiles, the average rate of CO2 input to bottom waters was 0.26 Gmol/a. Increased deep water temperatures require an average heat flow of 0.32 MW into the hypolimnion over the same time period. The transport rates of CO2, heat, and major ions into the hypolimnion suggest that a low-temperature reservoir of free CO2 exists a short distance below lake bottom, and that convective cycling of lake water through the sediments is involved in transporting the CO2 into the lake from the underlying diatreme. Increased CH4 concentrations at all depths below the oxycline and a high 14C content (41% modern) in the CH4, 4 m above lake bottom show that much of the CH4 is biologically produced within the lake. The CH4 production rate may vary with time, but if the CO2 recharge rate remains constant, CO2 saturation of the entire hypolimnion below 50 m depth would require about 140 a, given present-day concentrations.
Tracers were injected into South Cascade Glacier to determine the flow condition and geometry of the subglacial water system. Results indicate that two distinct drainage basins on the glacier feed the two main streams flowing from the glacier. In the largest basin, two parallel drainage networks exist, one englacial and the other subglacial. The englacial system is an arboresecent network of conduits, whereas the subglacial system is a distributed flow system. Both systems connect to a single subglacial conduit which appears as a stream at the glacier's terminus. The comparison between the travel time of the tracers and stream discharge indicated that the single conduit was pressurized in Jul and partly filled in Aug and Sep. To estimate the flow geometry (e.g. path length, flow depth and velocity), the advection-diffusion equation was formulated to express the water velocity as a function of water depth. Longitudinal dispersion of the tracer was calculated from the shear in longitudinal water velocity. Results indicate that the flow is very wide compared to its depth and that the path is sinuous. The estimated flow speed in the conduits is an order of magnitude larger than the measured speed through the glacier, indicating that other flow processes, probably englacial, route the water much more slowly. The other, smaller, basin drains the water from the surface to the subglacial distributed flow system. Based on the travel time of the individual concentration peaks, the water could be flowing through a linked-cavity system or interconnected bands of highly permeable debris separated by zones of less permeability.
More accurate alternatives to the widely used harmonic mean interblock transmissivity are proposed for block-centered finite-difference models of groundwater flow in unconfined aquifers and in aquifers having smoothly varying transmissivity. The harmonic mean is the exact interblock transmissivity for steady-state one-dimensional flow with no recharge if the transmissivity is assumed to be spatially uniform over each finite-difference block but it may be inferior to other means if transmissivity varies in a continuous or smooth manner between nodes. Alternative interblock transmissivity functions are analytically derived for the case of steady-state one-dimensional flow with no recharge. The exact interblock transmissivity, the logarithmic mean, for one-dimensional flow has been derived when transmissivity is a linear function of distance in the direction of flow. The logarithmic mean transmissivity is also exact for uniform flow parallel to the direction of changing transmissivity in a two- or three-dimensional model, regardless of grid orientation relative to the flow vector. For the case of horizontal flow in homogeneous unconfined or water table aquifers with a horizontal bottom and areally distributed recharge, the exact interblock transmissivity is the unweighted arithmetic mean of transmissivity at the nodes. For horizontal flow in an unconfined aquifer with no recharge where hydraulic conductivity is a linear function of distance in the direction of flow the exact interblock transmissivity is the product of the arithmetic mean saturated thickness and the logarithmic mean hydraulic conductivity. For several hypothetical two- and three-dimensional cases with smoothly varying transmissivity or hydraulic conductivity, the harmonic mean is shown to yield the least accurate solution to the flow equation of the alternatives considered. Application of the alternative interblock transmissivities to a regional aquifer system model indicates that the changes in computed heads and fluxes are typically small, relative to model calibration error. For this example, the use of alternative interblock transmissivities resulted in an increase in the computational effort of < 3%. Numerical algorithms to compute alternative interblock transmissivity functions in a modular three-dimensional flow model are presented and documented.
Analytical and numerical solutions are employed to examine the concentration history of a dissolved substance in water pumped from a leaky aquifer. Many aquifer systems are characterized by stratificaiton, for example, a sandy layer overlain by a clay layer. To obtain information about separated hyrogeologic units, aquifer pumping tests are often conducted with a well penetrating only one of the layers. When the initial concentration distribution is also stratified (the concentration varies with elevation only), the concentration breakthrough in the pumped well may be interpreted to provide information on aquifer hydraulic and transport properties. To facilitate this interpretation, we present some simple analytical and numerical solutions for limiting cases and illustrate their applicatoin to a fractured bedrock/glacial drift aquifer system where the solute of interest is dissolved radon gas. In addition to qualitative information on water source, this method may yield estimates of effective porosity and saturated thickness (or fracture transport aperture) from a single-hole test. Little information about dispersivity is obtained because the measured concentration is not significantly affected by dispersion in the aquifer.
Excessive rainfall and severe flooding in the upper Mississippi River basin during mid-June through early August 1993 swept abnormally large amounts of agricultural chemicals (herbicides and nitrate) into the Mississippi River, many of its tributaries, and finally into the Gulf of Mexico. Daily loads of herbicides transported in some reaches of the river were as much as 70 percent higher than those measured previously. The loads of nitrate transported into the Gulf of Mexico during July and August 1993 were as much as 5,735 metric tons per day. The transport of above normal loads of nitrate and large amounts of freshwater into the Gulf of Mexico during midsummer could increase phytoplankton biomass and affect the Gulf ecosystem along the Louisiana coast.
Solute transport concepts in soil are based on speculation that solutes are distributed nonuniformly within large and small pores. Solute concentrations have not previously been measured across a range of pore sizes and examined in relation to hydrological properties. Modified pressure cells were used to measure variation in concentration of a solute tracer across a range of pore sizes. Intact cores were removed from the site of a field tracer experiment, and soil water was eluted from ten or more discrete classes of pore size. Simultaneous changes in water content and unsaturated hydraulic conductivity were determined on cores using standard pressure cell techniques. Bromide tracer concentration varied by as much as 100% across the range of pore sizes samples. Immediately following application of the bromide tracer on field plots, bromide was more concentrated in the largest pores; concentrations were lower in pores of progressively smaller sizes. After 27 days, bromide was most dilute in the largest pores and concentrations were higher in the smaller pores. A sharp, threefold decrease in specific water capacity during elution indicated separation of two major pore size classes at a pressure of 47 cm water and a corresponding effective pore diameter of 70 microm. Variation in tracer concentration, on the other hand, was spread across the entire range of pore sizes investigated. A two-porosity characterization of the transport domain, based on water retention criteria, only broadly characterized the pattern of variation in tracer concentration across pore size classes during transport through a macroporous soil.
A new mass-conservative method for solution of the one-dimensional advection-dispersion equation (ADE) has been derived. The ADE describes the movement of miscible fluids and is used to describe the transport of solutes in groundwater and surface water. Test results demonstrate that the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) outperforms standard finite-difference methods, in terms of accuracy and efficiency, for solute transport problems that are dominated by advection. For dispersion-dominated problems, the performance of the method is similar to that of standard methods. Like previous ELLAM formulation, FVELLAM systematically conserves mass globally with all types of boundary conditions. FVELLAM differs from other ELLAM approaches in that integrated finite differences, instead of finite elements, are used to approximate the governing equation. The mass storage integral is numerically evaluated at the current time level, and quadrature points are then tracked forward in time to the next level. Forward tracking permits a straightforward treatment of inflow boundaries, thus avoiding the inherent problem in backtracking, as used by most characteristic methods, of characteristic lines intersecting inflow boundaries. FVELLAM extends previous ELLAM results by obtaining mass conservation locally on Lagrangian space-time elements. Details of the integration, tracking, and boundary algorithms are presented. Test results are given for problems in Cartesian and radial coordinates.
The Panola Mountain Research Watershed (PMRW), located in the Panola Mountain State Conservation Park near Stockbridge, Georgia has been selected as a core research watershed under the Water, Energy and Biogeochemical Budgets (WEBB) research initiative of the U.S. Geological Survey (USGS) Global Climate Change Program. This research plan describes ongoing and planned research activities at PMRW from 1984 to 1994. Since 1984, PMRW has been studied as a geochemical process research site under the U.S. Acid Precipitation Thrust Program. Research conducted under this Thrust Program focused on the estimation of dry atmospheric deposition, short-term temporal variability of streamwater chemistry, sulfate adsorption characteristics of the soils, groundwater chemistry, throughfall chemistry, and streamwater quality. The Acid Precipitation Thrust Program continues (1993) to support data collection and a water-quality laboratory. Proposed research to be supported by the WEBB program is organized in 3 interrelated categories: streamflow generation and water-quality evolution, weathering and geochemical evolution, and regulation of soil-water chemistry. Proposed research on streamflow generation and water-quality evolution will focus on subsurface water movement, its influence in streamflow generation, and the associated chemical changes of the water that take place along its flowpath. Proposed research on weathering and geochemical evolution will identify the sources of cations observed in the streamwater at Panola Mountain and quantify the changes in cation source during storms. Proposed research on regulation of soil-water chemistry will focus on the poorly understood processes that regulate soil-water and groundwater chemistry.
The hydrogeology of Kilauea volcano and adjacent areas has been studied since the turn of this century. However, most studies to date have focused on the relatively shallow, low-salinity parts of the groundwater system, and the deeper hydrothermal system remains poorly understood. The rift zones of adjacent Mauna Loa volcano bound the regional ground-water flow system that includes Kilauea, and the area bounded by the rift zones of Kilauea and the ocean may comprise a partly isolated subsystem. Rates of groundwater recharge vary greatly over the area, and discharge is difficult to measure, because streams are ephemeral and most groundwater discharges diffusely at or below sea level. Hydrothermal systems exist at depth in Kilauea's east and southwest rift zone, as evidenced by thermal springs at the coast and wells in the lower east-rift zone. Available data suggest that dike-impounded, heated groundwater occurs at relatively high elevations in the upper east- and southwest-rift zones of Kilauea, and that permeability at depth in the rift zones (probably less than or equal to 10-15m2) is much lower than that of unaltered basalt flows closer to the surface ( greater than or equal to 10-10 m2). Substantial variations in permeability and the presence of magmatic heat sources influence the structure of the fresh water-salt water interface, so the Ghyben-Herzberg model will often fail to predict its position. Numerical modeling studies have considered only subsets of the hydrothermal system, because no existing computer code solves the coupled fluid-flow, heat- and solute-transport problem over the temperature and salinity range encountered at Kilauea.
Organic carbon fluxes in San Francisco Bay (California) were estimated. Sources for the southern reach were dominated by phytoplankton and benthic microalgal production. River loading of organic matter was an additional important factor in the northern reach. Tidal marsh export and point sources played a secondary role. Autochthonous production in San Francisco Bay appears to be less than the mean for temperate-zone estuaries, primarily because turbidity limits microalgal production and the development of sea-grass beds. Exchange between the Bay and the Pacific Ocean plays an unknown but potentially important role in the organic carbon balance. Interannual variability in the organic carbon supply was assessed for Suisun Bay, a northern reach subembayment that provides habitat for important fish species (delta smelt, Hypomesus transpacificus, and larval striped bass, Morone saxatilus). The total supply fluctuated by an order of magnitude; depending on the year, either autochthonous sources (phytoplankton production) or allochthonous sources (riverine loading) could be dominant. The primary cause of the year-to-year change was variability of freshwater inflows from the Sacramento and San Joaquin rivers, and its magnitude was much larger than long-term changes arising from marsh destruction and point-source decreases. Although interannual variability of the total organic carbon supply could not be assessed for the southern reach, year-to-year changes in phytoplankton production were much smaller than in Suisun Bay, reflecting a relative lack of river influence.
About 50 days after the Exxon Valdez oil spill, the US Geological Survey began a series of investigations to determine the geologic and geochemical fate of the spilled oil. Aliphatic and aromatic hydrocarbons were measured on oil residues from beaches on six islands in Prince William Sound, Alaska. In addition to altered products from the Exxon Valdez oil spill of 1989, residues were also found, at two widely separated locations, that are similar to each other but chemically distinct from the spilled oil. Terpanes, steranes, monoaromatic steranes, and carbon isotopic compositions of total extracts were most useful in correlating the altered products of the spilled oil. These same parameters revealed that the two non-Valdez samples are likely residues of oil originally produced in California. The results indicate that oil residues currently on the beaches of this estuary have at least two quite different origins (Alaska and California), and that non-Exxon Valdez residues may be more common on the shores of Prince William Sound than was previously realized.
The origin, distribution, and interactions of low-molecular-weight organic acid anions have become an intensively studied field in geochemistry since their widespread occurrence in formation waters of sedimentary basins was first documented by Carothers and Kharaka (1978). High concentrations (up to 10,000 mg/l) of monocarboxylic (mainly acetate, propionate, and butyrate) and dicarboxylic (mainly oxalate, malonate, and succinate) acid anions have been reported from many sedimentary basins, with the highest values present in relatively young (Cenozoic age) petroleum reservoir rocks at subsurface temperatures of 80-120oC. Geochemical interest in these organic anions stems mainly from their important role in mineral diagenesis in sedimentary basins. In particular, these species act as sources or sinks of protons, as a source of CO2 and as pH and Eh buffering agents. They also form complexes with cations and metals such as Ca, Al, Fe, Pb, and Zn. Because of the wide range in the reported concentrations and because dicarboxylic acid anions generally form stronger complexes with Al, Fe, and other cations than do monocarboxylic acid anions, we resampled four oil wells in the San Joaquin basin, California, in order to better assess the role of these acid anions in water-rock interactions in sedimentary basins.
A numerical model that simulates groundwater flow and solute transport for cases in which fluid properties are variable was applied in one dimension (vertical) to the shallow, low-permeability, clayey, confining layer in Donana National Park in southwestern Spain. The salinity in the 80-m-thick confining layer decreases from a brine near the land surface to fresh water near its base. Results of model simulations indicated that the system could be in, or close to, a steady-state condition. The model calibration was very sensitive to small variations in individual model parameters and was non-unique in the sense that equally good calibrations could be achieved by compensatory joint perturbations in the permeability, diffusion coefficient, and overall governing hydraulic gradient. At present, there is probably an upward flow of the order of 1 mm/yr to 1 cm/yr and a balance in the solute flux between upward advection and downward diffusion. The time scale of calculated responses to changes in boundary conditions in this low-permeability system ranges from thousands to hundreds of thousands of years when considering extremes within the range of uncertainty of values of the evaluated parameters.
Ammonium bound to silicate and sulfate minerals has recently been located at several major hydrothermal systems in the western U.S. utilizing newly-discovered near-infrared spectral properties. Knowledge of the origin and mineralogic relations of ammonium minerals at known hydrothermal systems is critical for the proper interpretation of remote sensing data and for testing of possible links to mineralization. Submicroscopic analysis of ammonium minerals from two mercury- and gold-bearing hot-springs deposits at Ivanhoe, Nevada and McLaughlin, California shows that the ammonium feldspar, buddingtonite, occurs as fine-grained euhedral crystals coating larger sulfide and quartz crystals. Ammonium feldspar seems to precipitate relatively late in the crystallization sequence and shows evidence for replacement of NH4+ by K+ or other monovalent cations. Some buddingtonite is observed in close association with mercury, but not with gold. Ammonioalunite is found in a variety of isolated crystal forms at both deposits. Nitrogen isotopic values for ammonium-bearing minerals show a 14 per mil range in composition, precluding assignment of a specific provenance to the nitrogen. The correlations of nitrogen isotopic values with depth and ammonium content suggest some loss of nitrogen in the oxidizing supergene environment, possibly as a metastable mineral. The high ammonium content in these hydrothermal systems, the close association to mercury, and the small crystal size of the ammonium-bearing minerals all suggest that ammonium may be transported in a late-stage vapor phase or as an organic volatile. Such a process could lead to the formation of a non-carbonaceous organic aureole above a buried geothermal source. The discovery of a 10-km outcrop of ammonium minerals confirms that significant substitution of ammonium in minerals is possible over an extensive area and that remote sensing is a feasible means to detect such aureoles.
Trace contaminants enter major estuaries such as San Francisco Bay from a variety of point and nonpoint sources and may then be repartitioned between solid and aqueous phases or altered in chemical speciation. Chemical speciation affects the bioavailability of metals as well as organic ligands to planktonic and benthic organisms, and the partitioning of these solutes between phases. Our previous work in south San Francisco Bay indicated that sulfide complexation with metals may be of particular importance because of the thermodynamic stability of these complexes. Although the water column of the bay is consistently well-oxygenated and typically unstratified with respect to dissolved oxygen, the kinetics of sulfide oxidation could exert at least transient controls on metal speciation. Our initial data on dissolved sulfides in the main channel of both the northern and southern components of the bay consistently indicate submicromolar concentrations (from <1 nM to 162 nM), as one would expect in an oxidizing environment. However, chemical speciation calculations over the range of observed sulfide concentrations indicate that these trace concentrations in the bay water column can markedly affect chemical speciation of ecologically significant trace metals such as cadmium, copper, and zinc.
A semi-analytical model is developed to determine transmissivity and storativity from the interpretation of transient flow in an observation well due to pumping in a source well where the two wells are connected by a single fracture. Flow rate can be determined using a heat-pulse flowmeter located above the intersection of the fracture in the observation well. The results of a field experiment were interpreted using the new model and compared with drawdown data from the same test. Good agreement between the transmissivity estimates was observed whereas estimates of storativity were found to be better determined from the analysis of flow rate.
The modular hydrologic modeling system (MHMS) is an integrated system of computer software that has been developed to provide the research and operational framework needed to support the development, testing, and evaluation of hydrologic-process algorithms and to facilitate the integration of user-selected sets of algorithms into an operational hydrologic model. MHMS uses a master library that contains compatible modules for simulating water, energy, and biogeochemical processes. Modules in the library have been derived from the U.S. Geological Survey's Precipitation Runoff Modeling System, the National Weather Service's River Forecast System, the Streamflow Synthesis and Reservoir Regulation model, and TOPMODEL. A geographic information system interface is being designed to provide tools for the analysis and manipulation of spatial data.
The potential for sulfate-reducing bacteria (SRB) to enzymatically reduce Fe(III) and U(VI) was investigated. Five species of Desulfovibrio as well as Desulfobacterium autotrophicum and Desulfobulbus propionicus reduced Fe(III) chelated with nitrilotriacetic acid as well as insoluble Fe(III) oxide. Fe(III) oxide reduction resulted in the accumulation of magnetite and siderite. Desulfobacter postgatei reduced the chelated Fe(III) but not Fe(III) oxide. Desulfobacter curvatus, Desulfomonile tiedjei, and Desulfotomaculum acetoxidans did not reduce Fe(III). Only Desulfovibrio species reduced U(VI). U(VI) reduction resulted in the precipitation of uraninite. None of the SRB that reduced Fe(III) or U(VI) appeared to conserve enough energy to support growth from this reaction. However, Desulfovibrio desulfuricans metabolized H2 down to lower concentrations with Fe(III) or U(VI) as the electron acceptor than with sulfate, suggesting that these metals may be preferred electron acceptors at the low H2 concentrations present in most marine sediments. Molybdate did not inhibit Fe(III) reduction by D. desulfuricans. This indicates that the inability of molybdate to inhibit Fe(III) reduction in marine sediments does not rule out the possibility that SRB are important catalysts for Fe(III) reduction. The results demonstrate that although SRB were previously considered to reduce Fe(III) and U(VI) indirectly through the production of sulfide, they may also directly reduce Fe(III) and U(VI) through enzymatic mechanisms. These findings, as well as our recent discovery that the S degrees -reducing microorganism Desulfuromonas acetoxidans can reduce Fe(III), demonstrate that there are close links between the microbial sulfur, iron, and uranium cycles in anaerobic marine sediments.
Equations for estimating the 7-day 2-year and 7-day 10-year low flow at sites on ungaged streams are presented. Regression analysis was used to develop equations relating basin characteristics and low-flow characteristics at 58 continuous record gaging stations and 151 partial record sites. Significant basin characteristics in the equations are drainage area and percentage of drainage basin underlain by permeable bedrock units. The study area, which encompasses the western two-thirds of the State, is divided into three regions on the basis of similarities of basin characteristics within each regions. The analysis includes records for only those stations that are not highly regulated and have drainage areas < 1,000 sq mi. A two-step method is used to estimate low-flow characteristics at ungaged sites. The first step involves the use of a logistic regression to determine the probability that the 7-day annual minimum flow is zero at the site of interest. The second step uses this estimated probability of 7-day annual zero flow to determine if the estimated value of the 7-day 2-year or 7-day 10-year low flow is zero or needs to be estimated from one of the regional equations, which are based on a generalized-least-squares model for sites with non-zero flow. Computer software has been written to facilitate the computation of low-flow characteristics at sites of interest, the software is provided in written form and on a disk.
Areas of uncertainty involved in using bioassays to assess the toxicity of contaminants in sediments are discussed. Failure to consider the effect of all the factors that could operate in nature can result in either over-estimation or underestimation of sediment toxicity, while the simplified conditions used in bioassays could not be directly extrapolated to ecosystems. Some guidelines that could result in greater confidence in management decisions for managing contaminants in natural systems are outlined.
Three polar desert lakes (Lake Fryxell, Lake Hoare and Lake Vanda) were investigated to determine relations between source and composition of dissolved organic matter in lakes with different physical, chemical, and biological characteristics. The lakes were sampled during December 1987 at sites located among the deepest areas of the lakes. Profiles of dissolved organic matter in the water column, calculations of streamflow contribution of dissolved organic matter over the age of the lakes, inorganic profiles, and dissolved organic matter fractionation tests were conducted to determine autochthonous versus allochthonous sources. Chemical characteristics of the major dissolved organic carbon fractions (fulvic and hydrophilic acids) are very similar among lakes and may reflect the overwhelming influence of precursor compounds on the chemistry of microbially derived hydrophilic and fulvic acids. Two patterns for dissolved organic carbon concentrations were apparent: in lacustrine environments where the water column is highly stabilized by steep vertical density gradients, the DOC concentrations increase with increasing depth to higher values in the range of 25-30 mg C/L; in lacustrine environments where dissolved salts are more dilute and there is greater potential for actual advective transport, DOC concentrations are low (1-4 mg C/L). A good comprehension of the relationships between the sources and the chemical characteristics of dissolved organic matter may potentially lead to a better understanding of the entire carbon cycle in temperate lakes.
Stream habitat is characterized in the U.S. Geological Survey's National Water-Quality Assessment Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. The goal of stream habitat characterization is to relate habitat to other physical, chemical, and biological factors to describe water-quality conditions. To accomplish this goal, environmental settings are described at sites selected for water-quality assessment. In addition, spatial and temporal patterns in habitat are examined at local, regional, and national levels. Although habitat characterization is an important component of a number of Federal, State, and local water-quality assessment programs, no current set of habitat evaluation procedures meets the objectives of the habitat assessment component of the National Water-Quality Assessment Program. Evaluation of stream habitat is based on a spatially hierarchical framework that incorporates habitat data at basin, segment, reach, and microhabitat scales. This framework provides a basis for national consistency in collection techniques while allowing flexibility in habitat assessment within individual study units. Procedures are described for collecting habitat data at basin and stream segment scales that include use of geographic information system data bases, maps, and aerial photographs. Data collected at the stream reach scale include more than 34 riparian and instream habitat characteristics evaluated during one-time site visits, and surveys of the channel and riparian area during repeated sampling.
Changes in adenylate energy charge (ECA) and in total adenine nucleotides (AT) and DNA content (both normalized to the abundance of free-living, groundwater bacteria) in response to carbon loading were determined for a laboratory-grown culture and for a contaminated aquifer. The latter study involved a 3-km-long transect through a contaminant plume resulting from continued on-land discharge of secondary sewage to a shallow, sandy aquifer on Cape Cod, Mass. With the exception of the most contaminated groundwater immediately downgradient from the contaminant source, DNA and adenylate levels correlated strongly with bacterial abundance and decreased exponentially with increasing distance downgradient. ECAs (0.52 to 0.60) and the ratios of ATP to DNA (0.001 to 0.003) were consistently low, suggesting that the unattached bacteria in this groundwater study are metabolically stressed, despite any eutrophication that might have occurred. Elevated ECAs (up to 0.74) were observed in glucose-amended groundwater, confirming that the metabolic state of this microbial community could be altered. In general, per bacterium DNA and ATP contents were approximately twofold higher in the plume than in surrounding groundwater, although ECA and per bacterium levels of AT differed little in the plume and the surrounding uncontaminated groundwater. However, per bacterium levels of DNA and AT varied six- and threefold, respectively, during a 6-hr period of decreasing growth rate for an unidentified pseudomonad isolated from contaminated groundwater and grown in batch culture. These data suggest that the DNA content of groundwater bacteria may be more sensitive than their AT to the degree of carbon loading, which may have significant ramifications in the use of nucleic acids and adenine nucleotides for estimating the metabolic status of bacteria communities within more highly contaminated aquifers.
The movement of water and tritium through the unsaturated zone was studied at a low level radioactive waste disposal site near Sheffield, Bureau County, IL, from 1981 to 1985. Water and tritium movement occurred in an annual, seasonally timed cycle; recharge to the saturated zone generally occurred in the spring and early summer. Mean annual precipitation (1982-85) was 871 mm; mean annual recharge to the disposal trenches (July 1982 through June 1984) was estimated to be 107 mm. Average annual tritium flux below the study trenches was estimated to be 3.4 mCi/yr. Site geology, climate, and waste disposal practices influenced the spatial and temporal variability of water and tritium movement. Of the components of the water budget, evapotranspiration contributed most to the temporal variability of water and tritium movement. Disposal trenches were constructed in complexly layered glacial and postglacial deposits that average 17 m in thickness and overlie a thick sequence of Pennsylvanian shale. The horizontal saturated hydraulic conductivity of the clayey-silt to sand-sized glacial and postglacial deposits ranges from 0.048 to 0.00034 mm/d. Vertical water movement directly above the trenches was impeded by a zone of compaction within the clayey-silt trench covers. Time-of-travel of water moving from the trench covers to below the trenches was estimated to be as rapid as 41 days (assuming individual water molecules move this distance in one recharge cycle). Tritium concentrations in water from the unsaturated zone ranged from 200 (background) to 10 million pCi/L. Tritium concentrations generally were higher below trench bases (averaging 91,000 pCi/L) than below inter-trench sediments (averaging 3,300 pCi/L), and in the sub-trench Toulon Member of the Glasford Formation (sand) (averaging 110,000 pCi/L) than in the Hulick Till Member of the Glasford Formation (clayey silt) (averaging 59,000 pCi/L). Average sub-trench tritium concentration increased from 38,000 to 100,000 pCi/L during the study period. Within the trench covers, there was a strong seasonal trend in tritium concentrations; the highest concentrations occurred in late summer when soil moisture contents were at a minimum.
A numerical experiment using an atmospheric general circulation model was employed to estimate the sensitivity of the global water cycle to the water-holding capacity of soils. An increase of the globally constant capacity from 4 cm to 60 cm yielded an increase (24 cm) of evaporation from land, a decrease (-11 cm) of runoff, and an increase (13 cm) of precipitation onto land. Decreased runoff was balanced by decreased water-vapor flux convergence over the continents. In the tropics, the induced weakening of the monsoonal circulations was the major factor in this net export of water vapor to the oceans; in the middle latitudes, moistening of continental air masses, with resultant reduction in onshore vapor transport by transient eddies, was the dominant mechanism.
The accumulation of soil water during rainfall events and the subsequent depletion of soil water by evaporation between storms can be described, to first order, by simple accounting models. When the alternating supplies (precipitation) and demands (potential evaporation) are viewed as random variables, it follows that soil-water storage, evaporation, and runoff are also random variables. If the forcing (supply and demand) processes are stationary for a sufficiently long period of time, an asymptotic regime should eventually be reached where the probability distribution functions of storage, evaporation, and runoff are stationary and uniquely determined by the distribution functions of the forcing. Under the assumptions that the potential evaporation rate is constant, storm arrivals are Poisson-distributed, rainfall is instantaneous, and storm depth follows an exponential distribution, it is possible to derive the asymptotic distributions of storage, evaporation, and runoff analytically for a simple balance model. A particular result is that the fraction of rainfall converted to runoff is given by (1-1/R)/, in which R is the ratio of mean potential evaporation to mean rainfall and alpha is the ratio of soil water- holding capacity to mean storm depth. The problem considered here is analogous to the well-known problem of storage in a reservoir behind a dam, for which the present work offers a new solution for reservoirs of finite capacity. A simple application of the results of this analysis suggests that random, intraseasonal fluctuations of precipitation cannot by themselves explain the observed dependence of the annual water balance on annual totals of precipitation and potential evaporation.
A method involving numerical inversion of the Laplace transform solution was developed for the evaluation of Neuman's analytical solution for flow to a well in a homogeneous anisotropic water table aquifer. The proposed solution in Laplace space was simpler in form than the real-time solution since the integrand of the semi-infinite integral did not involve an infinite series or the need to evaluate the roots of equations. Rapid evaluation of the integrand allowed the use of advanced methods of numerical integration to improve accuracy, with lower overall computation time. The time required for the computation of type curves was lower by factors of 2 to 20 than that required for the closed-form real-time solution.
During May 15-17, 1990, an intense rainstorm moved across Iowa, Illinois, Indiana, and Ohio where triazine herbicides are heavily used for growing agricultural crops. Following the storm, the peak concentrations of triazine herbicides in some secondary tributaries to the Upper Mississippi and Ohio Rivers were as high as 36 mg/L. This runoffwater was funneled into the Lower Mississippi River at the Upper Mississippi-Ohio River confluence at Cairo, IL. The spatial variability of this runoff event was measured by collecting midchannel water samples for triazine herbicide analysis from 1 to 2 m below the surface of the Mississippi River every similar to 16 km from Baton Rouge, LA, upriver to the Mississippi-Ohio River confluence during May 26-29, 1990. All samples were analyzed for triazine herbicides by using an enzyme-linked immunosorbant assay. The results showed a background level of similar to 2.7 mg/L, an upriver gradient of 0.2 mg/L per 100 km, and longitudinal spatial variability that is hypothesized to be the result of cross-channel gradients and "slugs" of water from various upriver tributaries length scales of 100-150 km and amplitudes of similar to 1 mg/L.
Bed sediment, water, and suspended sediment samples were collected from 33 sites on the Mississippi River and some of its tributaries. Four cruises were made at high water during a 16-month period from March 9, 1989, to June 27, 1990. The maximum measured water discharge was about 34,100 m3/sec on March 10, 1990, in the Mississippi River at Vicksburg, MS, and the maximum measured suspended sediment discharge was 1,330,000 metric tons/d in the Mississippi River at Thebes, IL, on June 13, 1990. Depth-integration and pumping methods were used at equally spaced locations across the river to collect two composite samples of river water containing suspended sediment. The depth-integrated composite samples were approximately 100 L and the pumped composite samples were approximately 500 L. Both sampling methods used Teflon or Teflon-coated parts to prevent chemical contamination. This report contains the following data associated with the samples: cross-sectional area of the river, water depths, depth-averaged velocities, water discharge, surface temperature and specific conductance, concentrations of the suspended sand and silt/clay and colloid fractions, and particle sizes of bed material and suspended sediment. These data provide the framework for interpreting subsequent chemical analyses of the water and suspended sediment samples collected during the four cruises and for calculating bed load transport in the Mississippi River and some of its tributaries.
A geophysical logging program was undertaken to vertically profile changes in the hydrology and hydrochemistry of the Snake River Plain aquifer that underlies the Idaho National Engineering Laboratory. Field investigations were concentrated within an area west of the Idaho Chemical Processing Plant (ICPP) in three wells that penetrated the upper 190 ft of the aquifer. The logs obtained in these wells consisted of temperature, caliper, nuclear (neutron porosity and gamma-gamma density), natural gamma, borehole televiewer, gamma spectral, and thermal flowmeter (with and without pumping). The nuclear, caliper, and televiewer logs were used to delineate individual basalt flows or flow units and to recognize breaks between flows or flow units at interflow contact zones and sedimentary interbeds. The temperature logs and flowmeter measurements obtained under ambient hydraulic head conditions identified upward fluid-circulation patterns in the three wells. Reversal of in-hole fluid-flow direction indicated hydraulic communication between well 46 and the supply well CPP2 at the ICPP. The vertical distributions of hydraulic conductivity in wells 44 and 45 were determined by measuring fluid flow in the wells concurrently with pumping. The large variations in the vertical distributions and magnitudes of hydraulic conductivity determined from these field tests testify to the complex, heterogeneous nature of the geohydrologic system at the ICPP. Gamma-spectral analyses performed at several depths in each well showed that the predominant source of gamma radiation in the formation at this site originates mainly from potassium (40-K). However, the anthropogenic, gamma-emitting isotope 137Cs was detected at 32 ft below land surface in well 45. Results from an empirical investigation of the effect of source-receiver spacing on the response of the neutron-porosity logging tool indicated that large spacings of >4 ft are required to effectively use the conventional porosity calibration approach for this purpose.
The Long Valley Exploratory Well is being drilled in the Long Valley caldera in east-central California to investigate active magmatic intrusion processes. In an effort to obtain hydrologic information concerning deep hydrothermal circulation beneath the caldera floor, a flowmeter-injection test was performed in the well. The test was designed to determine the vertical distribution of hydraulic conductivity in the lowermost section of the borehole left uncased after completion of Phase-II drilling. Total depth of the well in May 1992 was 2,313 meters, with the lower 215 meters being open hole. A total of approximately 30,000 liters of water was injected into the well over 22 hours while water levels in the inner Ocean Drilling Program drill pipe and the outer-casing annulus were independently monitored and measurements of vertical fluid flow were recorded as a function of depth. Flowmeter measurements obtained in the open hole indicate no detectable fluid movement, and volumetric calculations indicate that all of the water introduced into the well can be accounted for by the attendant increases in water levels. Temperature logs obtained immediately before and after injection support the hypothesis that injected fluid simply shunted the open hole directly below the Ocean Drilling Program drill pipe and subsequently filled the outer-casing annulus above. The low hydraulic conductivity of the open hole is also manifested in the chemical analysis of fluid samples that show no evidence of formation fluids in the well. The hydraulic conductivity of the lowermost section of the Long Valley Exploratory Well after Phase-II drilling proved to be too low to quantify accurately by means of the flowmeter-injection field technique. Hydraulic communication between fluid within the inner Ocean Drilling Program drill pipe and fluid filling the outer-casing annulus further complicated the situation and introduced additional uncertainties. Nevertheless, the field data and a record of falling water levels for 6 months enable the permeability of the open hole to be constrained. An upper bound on the permeability of the formation between 2,098 and 2,313 meters is estimated to be in the microdarcy range.
An instrument combining sedimentation field-flow fractionation and inductively-coupled plasma mass spectrometry was developed to produce element-based size distributions of colloidal samples. Using suitable tracer elements it was possible to identify size distributions of specific components in complex mixtures. this method was used to analyse some clay minerals and suspended colloids from the Darling river in Australia. Ion response and element molar ratio distributions were plotted to reflect changes in mineralogy across the particle size distribution of a sample. Both major and minor elements could be detected.
The proceedings of the Lowland Streams Restoration Workshop, Lund, Sweden, August 1991, are reported. Approximately 50 papers and posters were presented. Attenders participated in one of several working groups to discuss the state of knowledge of stream restoration and to identify critical areas of information measurements. Most restoration efforts were emission-orientated. Successful stream restoration required a multidisciplinary approach. Post-project evaluation was required. It was recommended that systems in pristine conditions serve as a point of reference and not for a goal for most restoration projects. The restoration goals had to be very carefully defined. Participants agreed that preserving the terrestrial-aquatic interface by setting aside land corridors was critical in catchment development. Research needs were identified. The papers presented at the workshop addressed the relationship between fluvial processes and biotic structure; biogeochemical aspects of stream restoration; specific approaches to stream restoration and evaluation procedures; and the economics of stream management.
A study of the Mississippi River and its tributaries during July-August 1991, October-November 1991, and April-May 1992 showed that the entire navigable reach of the river is contaminated with a complex mixture of agrochemicals and their transformation products derived from nonpoint sources. Twenty-three compounds were identified, including triazine, chloroacetanilide, thiocarbamate, phenylurea, pyridazine, and organophosphorus pesticides. The upper and middle Mississippi River Basin farm lands are major sources of herbicides applied to corn, soybeans and sorghum. Farm lands in the lower Mississippi River Basin are a major source of rice and cotton herbicides. Inputs of the five major herbicides atrazine, cyanazine, metolachlor, and simazine to the Mississippi River are mainly from the Minnesota, Des Moines, Missouri and Ohio Rivers. Ratios of desethylatrazine/atrazine potentially are useful indicators of groundwater and surface water interactions in the Mississippi River. These ratios suggested that during baseflow conditions, groundwater significantly contributes to the river. The Mississippi River thus serves as a drainage channel for pesticide-contaminated surface and groundwater from the midwestern United States. Conservative estimates of annual mass transport indicated that about 160 tons of atrazine, 71 tons of cyanazine, 56 tons of metolachlor, and 18 tons of alachlor were discharged into the Gulf of Mexico in 1991.
Nearly a decade of intensive geophysical logging at fractured rock hydrology research sites indicates that geophysical logs can be used to identify and characterize fractures intersecting boreholes. However, borehole-to-borehole flow tests indicate that only a few of the apparently open fractures found to intersect boreholes conduct flow under test conditions. This paper presents a systematic approach to fracture characterization designed to define the distribution of fractures along boreholes, relate the measured fracture distribution to structure and lithology of the rock mass, and define the nature of fracture flow paths across borehole arrays. Conventional electrical resistivity, gamma, and caliper logs are used to define lithology and large-scale structure. Borehole wall image logs obtained with the borehole televiewer are used to give the depth, orientation, and relative size of fractures in situ. High-resolution flowmeter measurements are used to identify fractures conducting flow in the rock mass adjacent to the boreholes. Changes in the flow field over time are used to characterize the hydraulic properties of fracture intersections between boreholes. Application of this approach to an array of 13 boreholes at the Mirror Lake, New Hampshire site demonstrates that the transient flow analysis can be used to distinguish between fractures communicating with each other between observation boreholes, and those that are hydraulically isolated from each other in the surrounding rock mass. The Mirror Lake results also demonstrate that the method is sensitive to the effects of boreholes on the hydraulic properties of the fractured-rock aquifer. Experiments conducted before and after the drilling of additional boreholes in the array and before and after installation of packers in existing boreholes demonstrate that the presence of new boreholes or the inflation of packers in existing boreholes has a large effect on the measured hydraulic properties of the rock mass surrounding the borehole array.
The extent of iron(III) reduction in freshwater sediments of the Potomac river had previously been shown to be limited by the fact that most of the iron(III), though extractable with oxalate, was not available for microbial reduction. The possibility that the oxalate-extractable iron(III) unavailable for microbial reduction was in the form of crystalline iron(III) oxides, rather than that of mixed iron(III) and iron(II) forms as previously suggested was studied. Evidence for this was provided by experiments in which the production of small quantities of iron(II) during the initial stages of iron(III) reduction allowed oxalate to extract an iron(III) phase which was not microbially reducible from the sediment.
Paleowaters from the Floridan aquifer system in the southeastern Atlantic coastal plain have higher D/H and 18O/16O ratios than local Holocene ground water. Maximum d18O enrichments in ground water having adjusted radiocarbon ages of 20,000 to 26,000 years are 0.7 to 2.3 per mil. The trend in isotopic enrichment in paleowaters is the reverse of that normally observed in continental glacial age ground water. Dissolved nitrogen and argon concentrations indicate, however, that the average recharge temperature was 5.3 degree C cooler than that today. The data indicate cool conditions in the southeast Atlantic coastal plain during the last glacial maximum, with recharge limited primarily to late summer tropical cyclones and hurricanes.
Surface waters draining three different volcanoes in Costa Rica, ranging from dormant to moderately active to explosive, have a wide range of solute compositions that partly reflects the contribution of different types of solute-rich, geothermal waters. Three major physical transport vectors affect flows of geothermally derived solutes: thermally driven convection of volcanic gases and geothermal fluids; lateral and gravity-driven downward transport of geothermal fluids; and wind dispersion of ash, gases, and acid rain. Specific vector combinations interact to determine landscape patterns in solute chemistry and biota: indicator taxa of algae and bacteria reflect factors such as high temperature, wind-driven or hydrologically transported acidity, high concentrations of various solutes, and chemical precipitation reactions. Many steams receiving geothermally derived solutes have high levels of soluble reactive phosphorus (SRP) (up to 400 mg/L), a nutrient that is typically not measured in geochemical studies of geothermal waters. Regional differences in levels of SRP and other solutes among volcanoes were typically not significant due to high local variation in solute levels among geothermally modified streams and between geothermally modified and unmodified streams on each volcano. Geothermal activity along the volcanic spine of Costa Rica provides a natural source of phosphorus, silica, and other solutes and plays an important role in determining emergent landscape patterns in the solute chemistry of surface waters and aquatic biota.
Diurnal variations of the acetone concentration in an outdoor model stream were measured with and without a nitrate supplement to determine if the nitrate supplement would stimulate bacterial degradation of the acetone. Acetone loss coefficients were computed from the diurnal data using a fitting procedure based on a Lagrangian particle model. The coefficients indicated that bacterial degradation of the acetone was occurring in the downstream part of the stream during the nitrate addition. However, the acetone concentrations stabilized at values considerably above the limit of detection for acetone determination, in contrast to laboratory respirometer studies where the acetone concentration decreased rapidly to less than the detection limit, once bacterial acclimation to the acetone had occurred. One possible explanation for the difference in behavior was the limited 6-hr residence time of the acetone in the model stream.
This report presents data on the quantity and chemical quality of precipitation collected by the U.S. Geological Survey (USGS) from the USGS precipitation-collection station at Catoctin Mountain, in Cunningham Falls State Park, near Thurmont, Maryland, from January 1982 through December 1991. Data on the quantity of precipitation are presented as daily, monthly, and annual totals of precipitation, in inches. Data on the chemical quality of precipitation are presented in tables as concentrations, in microequivalents/L. Data on the quantity and chemical quality of precipitation and statistical information about the data are summarized in tables. Data for annual precipitation-weighted mean concentrations of constituents in precipitation are summarized in tables. Annual precipitation-weighted mean concentrations of selected constituents are illustrated in graphs.
The ability of Desulfuromonas acetoxidans to reduce iron(III) in anoxic conditions was tested, since a closely-related freshwater bacterium, Geobacter metallireducens performed such a reduction. In cell suspension experiments, D. acetoxidans grown in acetate-malate medium reduced soluble iron(III), and iron(III) complexed with nitriloacetic acid. Results of cytochrome oxidation studies indicated that iron(III) and manganese(IV) could serve as terminal acceptors for electron transport. D. acetoxidans grew in the presence of acetate as sole electron donor, and either iron(III) or manganese(IV) as electron acceptor. Ethanol, propanol and pyruvate also served as electron donors. End products of iron(III) reduction were mainly magnetite and siderite; manganese(IV) was reduced by rhodochrosite. Biogeochemical significance of these reductions is discussed.
Best estimates of evaporation at Williams Lake, north central Minnesota, were determined by the energy budget method using optimum sensors and optimum placement of sensors. These best estimates were compared with estimates derived from using substitute data to determine the effect of using less accurate sensors, simpler methods, or remotely measured data. Calculations were made for approximately biweekly periods during five open water seasons. For most of the data substitutions that affected the Bowen ratio, new values of evaporation differed little from best estimates. Recalculations based on these data substitution methods showed that the three methods that caused the largest deviations from the best evaporation estimates were (1) using changes in the daily average surface water temperature as an indicator of the lake heat storage term (as much as 89% difference from the best estimates), (2) using shortwave radiation, air temperature, and atmospheric vapor-pressure data from a site 110 km away (21% difference), and (3) using an analog surface-water temperature probe (10% difference). The data substitution method that provided evaporation values that most closely matched the best estimates was measurement of the lake heat-storage term at one location in the lake, rather than at 16 locations. Evaporation values resulting from this substitution method usually were within 2% of the best estimates.
The distribution and transport of selected hydrophobic halogenated organic compounds on suspended sediment from the lower Mississippi River were determined using discharge-weighted sampling with concurrent discharge measurements. Trends in compound concentration from upstream to downstream and the effects of selected tributaries were determined. The compounds identified on the suspended sediment include pentachlorobenzene, hexachlorobenzene, pentachloroanisole, dacthal, chlordane (trans-), nonachlor (trans-), chlorthalonil, and penta-, hexa-, hepta- and octachlorobiphenyls. Loads of most of the compounds increased from upstream to downstream on the main stem of the Mississippi River. Of the tributaries studied, the Ohio River had the most significant effect on the loads.
Abstract Nitrogen in downward-infiltrating wastewater discharged from seepage pits (dry wells) at residences in the upper Mojave River Basin, California represents a significant potential source of nitrate contamination to the underlying ground water. However, increases in nitrate concentration in the ground water have not yet been observed. The low nitrate concentration in the ground water may be the result of lateral dispersion in the unsaturated zone, dilution below the water table, or denitrification of wastewater nitrate in the unsaturated zone. Measured vertical rates indicate that some wastewater has reached the water table beneath communities that are older than 5 to 10 years. As wastewater percolates from seepage pits into the unsaturated zone, reduced nitrogen is converted rapidly to nitrate at shallow depths and the nitrate concentrations commonly decrease with depth. The largest nitrate decreases seem to coincide with increased content of fine-grained sediments or with proximity to the water table. Between lysimeters at 160 and 199 feet at one residence, the decrease in nitrate concentration coincided with a large increase in sulfate, decrease in alkalinity, and increase in 815N in nitrate. Those data are consistent with denitrification by oxidation of iron sulfide to produce ferric oxides; but if such a reaction occurs, it must be in domains that are small in comparison with the sampled volumes because the waters also contain substantial quantities of dissolved oxygen. The predominantly low nitrate concentrations in the area's ground water are consistent with the operation of a nitrogen-removal mechanism, possibly denitrification; however, the reducing capacity of the sediments to maintain denitrification is not known.
This study is part of a long-term research program designed to identify and quantify acid rain damage to carbonate stone. Acidic deposition accelerates the dissolution of carbonate-stone monuments and building materials. Sequential sampling of runoff from carbonate-stone (marble) and glass (reference) microcatchments in the Adirondack Mountains in New York State provided a detailed record of the episodic fluctuations in rain rate and runoff chemistry during individual summer storms. Rain rate and chemical concentrations from carbonate-stone and glass runoff fluctuated three to tenfold during storms. Net calcium-ion concentrations from the carbonatestone runoff, a measure of stone dissolution, typically fluctuated twofold during these storms. High net sulfate and net calcium concentrations in the first effective runoff at the start of a storm indicated that atmospheric pollutants deposited on the stone surface during dry periods formed calcium sulfate minerals, an important process in carbonate stone dissolution. Dissolution of the carbonate stone generally increased up to twofold during coincident episodes of low rain rate (less than 5 millimeters per hour) and decreased rainfall (glass runoff) pH (less than 4.0); episodes of high rain rate (cloudbursts) were coincident with a rapid increase in rainfall pH and also a rapid decrease in the dissolution of carbonate-stone. During a storm, it seems the most important factors causing increased dissolution of carbonate stone are coincident periods of low rain rate and decreased rainfall pH. Dissolution of the carbonate stone decreased slightly as the rain rate exceeded about 5 millimeters per hour, probably in response to rapidly increasing rainfall pH during episodes of high rain rate and shorter contact time between the runoff and the stone surface. High runoff rates resulting from cloudbursts remove calcium sulfate minerals formed during dry periods prior to storms and also remove dissolution products formed in large measure by chemical weathering as a result of episodes of low rain rate and decreased rainfall pH during a storm.
This study is part of a long-term research program designed to identify and quantify acid rain damage to carbonate stone. Acidic deposition accelerates the dissolution of carbonate-stone monuments and building materials. Sequential sampling of runoff from carbonate-stone (marble) and glass (reference) microcatchments in the Adirondack Mountains in New York State provided a detailed record of the episodic fluctuations in rain rate and runoff chemistry during individual summer storms. Rain rate and chemical concentrations from carbonate-stone and glass runoff fluctuated three to tenfold during storms. Net calcium-ion concentrations from the carbonatestone runoff, a measure of stone dissolution, typically fluctuated twofold during these storms. High net sulfate and net calcium concentrations in the first effective runoff at the start of a storm indicated that atmospheric pollutants deposited on the stone surface during dry periods formed calcium sulfate minerals, an important process in carbonate stone dissolution. Dissolution of the carbonate stone generally increased up to twofold during coincident episodes of low rain rate (less than 5 millimeters per hour) and decreased rainfall (glass runoff) pH (less than 4.0); episodes of high rain rate (cloudbursts) were coincident with a rapid increase in rainfall pH and also a rapid decrease in the dissolution of carbonate-stone. During a storm, it seems the most important factors causing increased dissolution of carbonate stone are coincident periods of low rain rate and decreased rainfall pH. Dissolution of the carbonate stone decreased slightly as the rain rate exceeded about 5 millimeters per hour, probably in response to rapidly increasing rainfall pH during episodes of high rain rate and shorter contact time between the runoff and the stone surface. High runoff rates resulting from cloudbursts remove calcium sulfate minerals formed during dry periods prior to storms and also remove dissolution products formed in large measure by chemical weathering as a result of episodes of low rain rate and decreased rainfall pH during a storm.
The changes in soil properties induced by the construction of a simulated waste burial trench were measured at a radioactive waste disposal site in the semi-arid southeast region of Idaho. Samples of an aridisol soil were collected, using a hydraulically-driven sampler to minimize sample disruption, from both a simulated waste trench and an undisturbed area nearby. Results show an undisturbed profile with distinct horizons, whereas in the waste trench these layers are absent. Porosity was increased in the disturbed cores, and, correspondingly, saturated hydraulic conductivities were higher. Unsaturated hydraulic conductivities for the undisturbed cores were typically greater than the disturbed cores at higher water contents (greater than 0.32). At lower water contents a majority of the disturbed cores have greater hydraulic conductivities. In general the vertical movement of water is retarded in a layered medium, suggesting that the construction of the landfill has destroyed impediments to downward flow.
Accurate application of evapotranspiration models to wild vegetation, especially in arid and semiarid climates, is a difficult task. The relative merits of the Penman-Monteith, Shuttleworth-Wallace, and modified Priestley-Taylor models, as used to model wild-land evapotranspiration, were investigated. Eddy correlation measurements of sensible and latent heat flux were used with measurements of net radiation, soil heat flux, and other micrometeorological variables to test the accuracy of the three models. The site used for field measurements was the San Luis Valley in Colorado. The Penman-Monteith model, a one-component model designed for use with dense crops, was not sufficiently accurate at the study site (coefficient of determination = 0.56 for hourly data and 0.60 for daily data). The Shuttleworth-Wallace model, a two-component logical extension of the Penman-Monteith model for use with sparse crops, performed significantly better (coefficient of determination = 0.78 for hourly data and 0.85 for daily data). The modified Priestely-Taylor model, a one-component simplified form of the Penman potential evapotranspiration model, surprisingly performed as well as the Shuttleworth-Wallace model. The rigorous Shuttleworth-Wallace model predicted that about one quarter of the vapor flux to the atmosphere is from bare-soil evaporation. Further, during daylight hours, small leaves are sinks for sensible heat produced at the hot soil surface.
Radium isotope activities (226Ra, 228Ra, and 224Ra), chemical compositions, and sulfur isotope ratios in sulfate were determined for water samples from thermal areas in Yellowstone National Park, Wyoming. Activities of 226-Ra in these waters range from < 0.2 to 37.9 dpm/kg. Activity ratios of 228Ra/226Ra range from 0.26 to 14.2, and those of 224Ra/228Ra range from 0.73 to 3.1. Radium concentrations are inversely correlated with aquifer equilibration temperatures while Ra/Ba (aq) and 228Ra /226Ra activity ratios depend on U/Ba and Th/U ratios in aquifer rocks. Major controls on Ra concentration in Yellowstone thermal water are inferred to be barite saturation (at Norris Geyser Basin, Mammoth Hot Springs, and other northern areas) and zeolite-water ion exchange (at Upper Geyser Basin). The data are consistent with a model in which radium and barium are supplied to water by bulk dissolution of aquifer rock and chemical equilibration of water with rock is rapid relative to the 1602 yr half-life of 226Ra. The 228Ra /226Ra activity ratios of the waters may in some cases reflect surface enrichments of 232Th and/or may indicate that alpha-recoil input of 228Ra is rapid relative to water-rock chemical equilibration. Activity ratios of 224Ra/228Ra indicate a nearly ubiquitous 224Ra excess that generally increases with decreasing pH.
Linear alkylbenzene sulfonate (LAS), the active component in most detergents, is one of the most common synthetic organic chemicals to be found in natural water and sediment. A detailed sampling program was undertaken to examine a 2900 kilometer (km) section of the Mississippi River from Minneapolis, MN to New Orleans, LA to determine the occurrence and fate of LAS and to evaluate its use as a molecular indicator of sewage contamination in the river. Surface grab water samples were collected in mid-channel at 32 km intervals, with 3-point cross section samples collected every 160 km and below significant tributaries and municipalities. Depth-integrated water samples were collected at selected sites, along with composite bed sediment samples. Sampling was conducted in the summer and fall of 1991 and in the spring of 1992. LAS and its biodegradation intermediate sulfophenyl carboxcylic acid (SPC) were identified and quantified using a solid phase extraction /derivatization/gas chromatography/mass spectrometry procedure with a LAS detection limit of 0.05 micrograms/liter (mg/L). LAS was found on all bed sediments with concentrations ranging from 0.01-0.6 milligrams/kilogram (mg/kg), and dissolved LAS was identified in 26% of the water samples with concentrations ranging from <0.05-12 mg/L. Sorbed SPC was found on all bed sediments at concentrations of 0.03-7.8 mg/kg, while dissolved SPC was found rarely and occurred at values less than 0.5 mg/L. The results indicate that LAS and SPC are ubiquitous contaminants in Mississippi River bottom sediments and that dissolved LAS and SPC are found mainly below the sewage outfalls of cities. The important processes controlling LAS fate in the riverine system are dilution, sorption, and biodegradation. Dilution factors for sewage effluent discharged into the river ranged from 50-1500 for large cities and were much higher for smaller cities and towns along the river. LAS homolog and isomer distributions indicate that sorption and biodegradation are processes which affect dissolved LAS within its first 8 hours residence time in the river, before dilution is complete. A simple sorption model predicted that 2-30% of dissolved LAS would sorb to suspended sediments, dependent upon suspended sediment concentration. Primary biodegradation removes an estimated 50-96% of dissolved LAS and appears to be the most important process affecting the ultimate fate of LAS in the river.
The terrestrial-aquatic interface beneath Little Lost Man creek, Calif., U.S.A., was investigated as a region of hydrological and biological control of nutrient flux. The subsurface pathways of water and associated solutes between the channel and hyporheic zone were investigated using tracer studies. Subsurface flow beneath the riparian zone approximated a straight path entering at meanders but could also cross beneath the stream, possibly using relic channels. Dissolved oxygen concentration in the hyporheic zone was regulated by the balance between the biotic demand and physical transport from the channel. The magnitude and timing of lateral water exchange is discussed with reference to previously published studies of nitrification and denitrification. Nitrification potential and channel exchange decreased with distance from the channel and were absent at sites lacking effective exchange, due to low dissolved oxygen. Field amendments of acetylene and nitrate to a flow path with low dissolved oxygen and minimal channel exchange indicated denitrification of amended nitrate. The implications of the results for stream restoration are discussed.
The Salto river received groundwater inputs of geothermally-based soluble reactive phosphorus (SRP). Channel water ranged between 50 and 200 mg phosphorus per litre depending on storm runoff dilution. Pantano creek, an unimpacted tributary, had SRP concentrations less than 10 mg per litre. Nitrogen:phosphorus ratios varied widely in the Salto river. Dissolved inorganic nitrogen (DIN) was a result of mineralization. DIN composition reflected local redox conditions. Ammonium concentration was higher than nitrate concentration in the groundwaters but lower in the channel water suggesting nitrification during subsurface and channel transport. Sediments indicated nitrification potential. Ammonium and nitrate amendments did not affect SRP concentration in either stream. Abiotic factors regulated SRP concentration. Biotic and abiotic mechanisms regulated DIN concentration and composition.
Samples collected in December 1990 and July 1991 show that dissolved Cd, Cu, Ni, and Zn distributions in the Gulf of the Farallones are dominated by mixing of two end-members: metal-enriched San Francisco Bay water and offshore California Current water. The range of dissolved metal concentrations observed is 0.2-0.9 nmol/kg for Cd, 1-20 nmol kg-1 for Cu, 4-16 nmol/kg for Ni, and 0.2-20 nmol/kg for Zn. Effective concentrations in fresh water discharged into San Francisco Bay during 1990-1991 (estimated by extrapolation to zero salinity) are 740-860 mmol/kg for silicate, 21-44 mmol/kg for phosphate, 10-15 nmol/kg for Cd, 210-450 nmol/kg for Cu, 210-270 nmol/kg for Ni, and 190-390 nmol/kg for Zn. Comparison with effective trace metal and nutrient concentrations for freshwater discharge reported by Flegal et al. (1991) shows that input of these constituents to the northern reaches of San Francisco Bay accounts for only a fraction of the input to Gulf of the Farallones from the estuary system as a whole. The nutrient and trace metal composition of shelf water outside a 30-km radius from the mouth of the estuary closely resembles that of California Current water further offshore. In contrast to coastal waters elsewhere, there is little evidence of Cd, Cu, Ni, and Zn input by sediment diagenesis in continental shelf waters of California.
A stream made acidic by strip mining was sampled at 4 locations before it entered the ground, at a point in a cave and where it emerged as a spring. The rate of dissolution of calcium carbonate was measured in the surface water by suspending Iceland spar crystals in nylon mesh bags in the stream for 61 or 139 d. Rapid chemical changes occurred as the low pH water dissolved calcium carbonate in the catchment and uncontaminated waters entered; the solubility of trace metals fell, some precipitating as oxyhydroxides. The dissolution experiments yielded rates of 0.026-0.079 nmol per cm2.second over the pH range of 3.6-7.7. These were several orders of magnitude slower than those predicted by the laboratory studies of Plummer. The reduction was caused by dissolved iron and possibly other solutes.
The detailed and well-dated 500,000-yr record of oxygen-18 variations found in vein calcite core DH-11 taken from Devils Hole in Nevada provides several challenges to the Milankovitch theory for the occurrence of Quaternary glaciations. A recent discussion paper (Imbrie and others, 1993) has dismissed the relevance of this well-dated core for determining the timing of global climatic fluctuations and, moreover, asserts that the Devils Hole record provides support for the Milankovitch theory. Upon analysis of the arguments found in this discussion, the authors found nothing to dissuade them from the original conclusion that the Devils Hole chronology does present a serious challenge to the Milankovitch theory.
The effects of potential climate change on water resources in the Delaware River basin were determined. The study focused on two important water-resource components in the basin: storage in the reservoirs that supply New York City, and the position of the salt front in the Delaware River estuary. Current reservoir operating procedures provide for releases from the New York City reservoirs to maintain the position of the salt front in the estuary downstream from freshwater intakes and ground-water recharge zones in the Philadelphia metropolitan area. A hydrologic model of the basin was developed to simulate changes in New York City reservoir storage and the position of the salt front in the Delaware River estuary given changes in temperature and precipitation. Results of simulations indicated that storage depletion in the New York City reservoirs is a more likely effect of changes in temperature and precipitation than is the upstream movement of the salt front in the Delaware River estuary. In contrast, the results indicated that a rise in sea level would have a greater effect on movement of the salt front than on storage in the New York City reservoirs. The model simulations also projected that, by decreasing current mandated reservoir releases, a balance can be reached wherein the negative effects of climate change on storage in the New York City reservoirs and the position of the salt front in the Delaware River estuary are minimized. Finally, the results indicated that natural variability in climate is of such magnitude that its effects on water resources could overwhelm the effects of long-term trends in precipitation and temperature.
Woo, M-K., and Winter, T. C., 1993, The role of permafrost and seasonal frost in the hydrology of northern wetlands in North America: Journal of Hydrology, v. 141, p. 5-31.
The effect of frozen ground on wetland hydrology in the Arctic, Subarctic and northern Temperate zones of North America was assessed, with specific attention to surface runoff, evapotranspiration and interaction with subsurface water. Similar early-spring surface-water processes were produced in all 3 zones by the melting of seasonal snow and ice, but evapotranspiration and groundwater movement differed among the 3 zones because of the differing effects of permafrost. The principal characteristics of evapotranspiration in wetlands and interactions between wetlands and groundwater flow systems in each of the zones were examined.
Multielement analysis was performed on individual annual rings of trees growing at and near an abandoned wood-preserving plant site in Jackson, Tennessee, that operated from the early 1930's until 1981. Numerous organic compounds associated with the wood-preserving process have been detected in soils, ground water, and surface water within much of the site. Tree-ring investigations were conducted prior to investigations of ground water downgradient from the site to determine if trees preserved an areal and temporal record of contaminant movement into offsite areas.
Increment cores were collected from trees on the abandoned plant site, in downgradient areas west and south of the site, and at two locations presumably unaffected by contamination from the site. Multielement analysis by proton-induced X-ray emission was performed on 5 to 15 individual growth rings from each of 34 trees that ranged in age from about 5 to 50 years. Concentrations of 16 elements were evaluated by analyzing average concentrations within the 1987, 1989, and 1990 rings of all trees; analyzing element-concentration trends along entire core radii; and analyzing element correlations between and among trees.
Concentrations of some nutrients and trace metals were elevated in the outermost sapwood rings of some trees that grow south and southwest of the most contaminated part of the site; small trees on the main part of the site and larger trees to the west generally contained fewer rings with elevated concentrations, particularly of trace metals. Concentrations of several elements elevated in tree rings also were elevated in water samples collected from the reach of a stream that flows near the southwestern part of the site.
Multielement analysis of each ring of a willow growing along the southern boundary of the site detected extremely large concentrations of chromium, nickel, and iron in rings that formed in 1986 and thereafter. Relative increases in the concentrations of these elements also were detected in a silver maple growing next to the willow, but not in another silver maple growing 150 meters farther to the west. An oak growing in the southwestern part of the study area contained large concentrations of calcium and several trace elements, and some trees south of the abandoned site contained large concentrations of phosphorus or potassium.
Concentrations of trace metals and nutrients in some trees may be related to wood-preserving activities at the site and possibly to remedial efforts conducted during the early to mid 1980's.However, the possibility cannot be discounted that large concentrations of some elements are from sources other than the wood-preserving facility, or in part from flooding of the South Fork Forked Deer River.
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