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At least 1,279 records · Page 71Linked to original sources
USGS2025

Ice thickness regulates heat flux in permanently ice-covered lakes

The permanently ice-covered lakes of Taylor Valley, Antarctica, are rare ecosystems where permanent ice cover and year-round vertically stable water columns provide critical redox zones for cold-adapted microorganisms. Using 30 yr of limnological data from the McMurdo Dry Valleys Long-Term Ecological Research program, we assessed the water column heat flux of four permanently ice-covered lakes in the context of global lake ice decline and lake warming. Our study reveals that heat flux in Taylor Valley lakes is driven by ice cover dynamics, both annual changes in ice thickness as well as overall ice thickness. During periods of ice thinning, like those observed from 2020 to 2023, the lakes accumulate heat. Lake Fryxell, Lake Hoare, and West Lake Bonney have repeatedly cooled and warmed over our record, with only East Lake Bonney cooling due to lake level rise. Ice thickness is largely synchronous among the four lakes, with periods of asynchronicity likely caused by lake-specific changes in surface albedo driven by changes in optical properties of the ice covers and in-ice sediment dynamics.

Limnology and Oceanography↗
USGS1997

U.S. Geological Survey studies of water co-produced with oil and gas: Implications for future petroleum resource development

The U.S. Geological Survey is conducting research on the impacts of produced waters on petroleum resource development and the environment. Ongoing multidisciplinary investigations are focused on the 1) quantity and quality of current water production, 2) geologic and geochemical parameters that influence the viability of injection wells, and 3) processes that affect the dispersion of inorganic and organic constituents of produced water that are released into the surface and near-surface environment.

Conference Paper↗
USGS2011

Microbial ecology of deep-water mid-Atlantic canyons

The research described in this fact sheet will be conducted from 2012 to 2014 as part of the U.S. Geological Survey's DISCOVRE (DIversity, Systematics, and COnnectivity of Vulnerable Reef Ecosystems) Program. This integrated, multidisciplinary effort will be investigating a variety of topics related to unique and fragile deep-sea ecosystems from the microscopic level to the ecosystem level. One goal is to improve understanding, at the microbiological scale, of the benthic communities (including corals) that reside in and around mid-Atlantic canyon habitats and their associated environments. Specific objectives include identifying and characterizing the microbial associates of deep-sea corals, characterizing the microbial biofilms on hard substrates to better determine their role in engineering the ecosystem, and adding a microbial dimension to benthic community structure and function assessments by characterizing micro-eukaryotes, bacteria, and archaea in deep-sea sediments.

Fact Sheet↗
USGS2003

Occurrence and temporal variability of methyl tert -butyl ether (MTBE) and other volatile organic compounds in select sources of drinking water : results of the focused survey

The large-scale use of the gasoline oxygenate methyl tert -butyl ether (MTBE), and its high solubility, low soil adsorption, and low biodegradability, has resulted in its detection in ground water and surface water in many places throughout the United States. Studies by numerous researchers, as well as many State and local environmental agencies, have discovered high levels of MTBE in soils and ground water at leaking underground gasoline-storage-tank sites and frequent occurrence of low to intermediate levels of MTBE in reservoirs used for both public water supply and recreational boating. In response to these findings, the American Water Works Association Research Foundation sponsored an investigation of MTBE and other volatile organic compounds (VOCs) in the Nation's sources of drinking water. The goal of the investigation was to provide additional information on the frequency of occurrence, concentration, and temporal variability of MTBE and other VOCs in source water used by community water systems (CWSs). The investigation was completed in two stages: (1) reviews of available literature and (2) the collection of new data. Two surveys were associated with the collection of new data. The first, termed the Random Survey, employed a statistically stratified design for sampling source water from 954 randomly selected CWSs. The second, which is the focus of this report, is termed the Focused Survey, which included samples collected from 134 CWS source waters, including ground water, reservoirs, lakes, rivers, and streams, that were suspected or known to contain MTBE. The general intent of the Focused Survey was to compare results with the Random Survey and provide an improved understanding of the occurrence, concentration, temporal variability, and anthropogenic factors associated with frequently detected VOCs. Each sample collected was analyzed for 66 VOCs, including MTBE and three other ether gasoline oxygenates (hereafter termed gasoline oxygenates). As part of the Focused Survey, 451 source-water samples and 744 field quality-control (QC) samples were collected from 78 ground-water, 39 reservoir and (or) lake, and 17 river and (or) stream source waters at fixed intervals for a period of 1 year. Using a common assessment level of 0.2 μg/L (micrograms per liter) (2.0 μg/L for methyl ethyl ketone), 37 of the 66 VOCs analyzed were detected in both surveys. However, VOCs, especially MTBE and other gasoline oxygenates, were detected more frequently in the Focused Survey than in the Random Survey. MTBE was detected in 55.5 percent of the CWSs sampled in the Focused Survey and in 8.7 percent of those sampled in the Random Survey. Little difference in occurrence, however, was observed for trihalomethanes (THMs), which were detected in 16.4 and 14.8 percent of Focused Survey and Random Survey CWSs, respectively. This may indicate a pervasive occurrence of THMs in several source-water types, regardless of CWS size or geographic location. Using data at or above the method detection limit to assess temporal variability and anthropogenic factors associated with frequent detection of select VOCs, concentrations in the Focused Survey in ground-water, reservoir, and river source waters were typically less than 1 μg/L. Also, at a 95-percent confidence interval, no statistically significant differences were observed in comparing concentrations in the first and second ground-water sample. A weak seasonal pattern was observed in samples collected from reservoirs and lakes where gasoline oxygenates and other gasoline compounds were detected more frequently during spring and summer, presumedly a result of increased use of motorized watercraft during these seasons. In contrast, seasonal patterns were not observed in samples collected from rivers and streams. The lack of seasonal differences in river and stream source waters sampled may indicate a common and continuous source of contamination. The most frequently detected VOC (MTBE) and the two most frequently occurring subgroups of VOCs (gasoline oxygenates and THMs) detected in CWS source waters were further characterized to evaluate some anthropogenic factors that may better explain their frequent occurrence. Gasoline oxygenates were detected in 73.9 percent of all CWSs sampled. The concentration of gasoline oxygenates was slightly correlated with watercraft use on reservoirs inside MTBE high-use areas (r2=0.3783) but not outside of these areas (r2=0.0242). In general, the concentration of gasoline oxygenates increased as watercraft use increased. THMs were detected in 47.8 percent of the CWSs supplied by surface water. The frequent occurrence of THMs in reservoir source waters was determined to be an artifact of disinfection and the recycling of chlorinated water to these reservoirs. All CWSs with frequent occurrence of THMs served by a reservoir indicated that chlorine was added to waters for various reasons and that the chlorinated water was then released back to, or upstream of, the reservoir or lake that was sampled.

Water-Resources Investigations Report↗
USGS1978

Summary appraisals of the Nation's ground-water resources; Alaska

Alaska has enormous surface-water resources, but many of the streams are frozen for most of the year and most contain glacial silt that makes them unacceptable for human use. These factors lend special significance to ground water as a water-supply source, even though perennially frozen ground (permafrost) profoundly modifies ground-water flow systems in much of Alaska north of the maritime southern coast and southeastern panhandle areas. Frozen ground is a virtually impermeable layer that restricts recharge, discharge, and movement of ground water, acts as a confining layer and limits the volume of unconsolidated deposits and bedrock in which water may be stored. Ground water is an untested resource in most of Alaska, but in many areas potential development of ground water far exceeds current use. Alluvium of major river valleys, such as the Yukon, Tanana, Kuskokwim and Susitna Rivers, probably contains the most extensive aquifers in the State. Large amounts of ground water are also stored in glacial outwash aquifers that underlie coastal basins and valleys, such as those at Kenai and Anchorage in the Cook Inlet lowland. Individual wells yielding more than 1,000 gallons per minute have been developed in the Tanana River valley, Cook Inlet lowland, and the coastal valleys at Seward and Juneau. Comparable yields should be possible in other areas that have similar geohydrologic environments. No major aquifers have been identified in glacial and glaciolacustrine deposits of interior valleys or in deltaic deposits. Major bedrock aquifers have been identified only in carbonate rocks of the Brooks Range and on the north side of the Alaska Range. Springs issuing from the carbonate rocks of the Brooks Range have discharges as great as 16,000 gallons per minute. Most ground-water recharge occurs beneath reaches of stream channels that are losing flow to the ground-water system. Most ground-water discharge also takes place along reaches of stream channels. This discharge augments streamflows during summer and maintains low flows during winter when there is no surface-water runoff. On the basis of a streamflow hydrograph separation technique and using the 60 percent flow-duration value as an indicator of ground-water discharge, it is estimated that 25 percent of the total volume of streamflow in Alaska (exclusive of coastal, maritime environments) is contributed by ground-water discharge. The thawing of frozen ground in the permafrost regions of Alaska causes construction and engineering problems. Disturbance of the ground surface disrupts the natural thermal equilibrium and tends to thaw part of the permafrost. Thawing can cause loss of strength, a decrease in volume, and an increase in erosion potential, particularly if the frozen ground is fine grained and poorly drained. Present deficiencies in the ground-water information base are obvious limiting factors to ground-water development in Alaska. There is a need to extend the ground-water data-collection network and to pursue special research into the quantitative aspects of ground-water hydrology in cold regions, particularly the continuous permafrost zone.

Alaska↗
USGS2007

Hydrogeologic Setting and Ground-Water Flow in the Leetown Area, West Virginia

The Leetown Science Center is a research facility operated by the U.S. Geological Survey that occupies approximately 455-acres near Kearneysville, Jefferson County, West Virginia. Aquatic and fish research conducted at the Center requires adequate supplies of high-quality, cold ground water. Three large springs and three production wells currently (in 2006) supply water to the Center. The recent construction of a second research facility (National Center for Cool and Cold Water Aquaculture) operated by the U.S. Department of Agriculture and co-located on Center property has placed additional demands on available water resources in the area. A three-dimensional steady-state finite-difference ground-water flow model was developed to simulate ground-water flow in the Leetown area and was used to assess the availability of ground water to sustain current and anticipated future demands. The model also was developed to test a conceptual model of ground-water flow in the complex karst aquifer system in the Leetown area. Due to the complexity of the karst aquifer system, a multidisciplinary research study was required to define the hydrogeologic setting. Geologic mapping, surface- and borehole-geophysical surveys, stream base-flow surveys, and aquifer tests were conducted to provide the hydrogeologic data necessary to develop and calibrate the model. It would not have been possible to develop a numerical model of the study area without the intensive data collection and methods developments components of the larger, more comprehensive hydrogeologic investigation. Results of geologic mapping and surface-geophysical surveys verified the presence of several prominent thrust faults and identified additional faults and other complex geologic structures (including overturned anticlines and synclines) in the area. These geologic structures are known to control ground-water flow in the region. Results of this study indicate that cross-strike faults and fracture zones are major avenues of ground-water flow. Prior to this investigation, the conceptual model of ground-water flow for the region focused primarily on bedding planes and strike-parallel faults and joints as controls on ground-water flow but did not recognize the importance of cross-strike faults and fracture zones that allow ground water to flow downgradient across or through less permeable geologic formations. Results of the ground-water flow simulation indicate that current operations at the Center do not substantially affect either streamflow (less than a 5-percent reduction in annual streamflow) or ground-water levels in the Leetown area under normal climatic conditions but potentially could have greater effects on streamflow during long-term drought (reduction in streamflow of approximately 14 percent). On the basis of simulation results, ground-water withdrawals based on the anticipated need for an additional 150 to 200 gal/min (gallons per minute) of water at the Center also would not seriously affect streamflow (less than 8 to 9 percent reduction in streamflow) or ground-water levels in the area during normal climatic conditions. During drought conditions, however, the effects of current ground-water withdrawals and anticipated additional withdrawals of 150 to 200 gal/min to augment existing supplies result in moderate to substantial declines in water levels of 0.5-1.2 feet (ft) in the vicinity of the Center's springs and production wells. Streamflow was predicted to be reduced locally by approximately 21 percent. Such withdrawals during a drought or prolonged period of below normal ground-water levels would result in substantial declines in the flow of the Center's springs and likely would not be sustainable for more than a few months. The drought simulated in this model was roughly equivalent to the more than 1-year drought that affected the region from November 1998 through February 2000. The potential reduction in streamflow is a result of capture of ground water tha

Scientific Investigations Report↗
USGS2001

Water-Chemistry and On-Site Sulfur-Speciation Data for Selected Springs in Yellowstone National Park, Wyoming, 1996-1998

Fifty-eight water analyses are reported for samples collected from 19 hot springs and their overflow drainages and one ambient-temperature acid stream in Yellowstone National Park (YNP) during 1996-98. These water samples were collected and analyzed as part of research investigations on microbially mediated sulfur oxidation in stream waters and sulfur redox speciation in hot springs in YNP and chemical changes in overflow drainages that affect major ions, redox species, and trace elements. The research on sulfur redox speciation in hot springs is a collaboration with the State University of New York at Stony Brook, Northern Arizona University, and the U.S. Geological Survey (USGS). One ambient-temperature acidic stream system, Alluvium Creek and its tributaries in Brimstone Basin, was studied in detail. Analyses were performed adjacent to the sampling site, in an on-site mobile laboratory truck, or later in a USGS laboratory, depending on stability and preservability of the constituent. Water temperature, specific conductance, pH, Eh, dissolved oxygen (D.O.), and dissolved H2S were determined on-site at the time of sampling. Alkalinity and F were determined within a few days of sample collection by titration and by ion-selective electrode, respectively. Concentrations of S2O3 and SxO6 were determined as soon as possible (minutes to hours later) by ion chromatography (IC). Concentrations of Cl, SO4, and Br were determined by IC within a few days of sample collection. Concentrations of Fe(II) and Fe(total) were determined by ultraviolet/visible spectrophotometry within a few days of sample collection. Densities were determined later in the USGS laboratory. Concentrations of Li, Na, and K were determined by flame atomic absorption (Li) and emission (Na, K) spectrometry. Concentrations of Al, As(total), B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe(total), Mg, Mn, Ni, Pb, Si, Sr, V, and Zn were determined by inductively-coupled plasma optical emission spectrometry. Trace concentrations of Cd, Se, As(total), Ni, and Pb were determined by Zeeman-corrected graphite-furnace atomic-absorption spectrometry. Trace concentrations of As(total) and As(III) were determined by hydride generation using a flow-injection analysis system.

Open-File Report↗
USGS2024

Streamflow depletion caused by groundwater pumping: Fundamental research priorities for management-relevant science

Reductions in streamflow caused by groundwater pumping, known as “streamflow depletion,” link the hydrologic process of stream-aquifer interactions to human modifications of the water cycle. Isolating the impacts of groundwater pumping on streamflow is challenging because other climate and human activities concurrently impact streamflow, making it difficult to separate individual drivers of hydrologic change. In addition, there can be lags between when pumping occurs and when streamflow is affected. However, accurate quantification of streamflow depletion is critical to integrated groundwater and surface water management decision making. Here, we highlight research priorities to help advance fundamental hydrologic science and better serve the decision-making process. Key priorities include (a) linking streamflow depletion to decision-relevant outcomes such as ecosystem function and water users to align with partner needs; (b) enhancing partner trust and applicability of streamflow depletion methods through benchmarking and coupled model development; and (c) improving links between streamflow depletion quantification and decision-making processes. Catalyzing research efforts around the common goal of enhancing our streamflow depletion decision-support capabilities will require disciplinary advances within the water science community and a commitment to transdisciplinary collaboration with diverse water-connected disciplines, professions, governments, organizations, and communities.

Water Resource Research↗
USGS2017

Landform features and seasonal precipitation predict shallow groundwater influence on temperature in headwater streams

Headwater stream responses to climate change will depend in part on groundwater‐surface water exchanges. We used linear modeling techniques to partition likely effects of shallow groundwater seepage and air temperature on stream temperatures for 79 sites in nine focal watersheds using hourly air and water temperature measurements collected during summer months from 2012 to 2015 in Shenandoah National Park, Virginia, USA. Shallow groundwater effects exhibited more variation within watersheds than between them, indicating the importance of reach‐scale assessments and the limited capacity to extrapolate upstream groundwater influences from downstream measurements. Boosted regression tree (BRT) models revealed intricate interactions among geomorphological landform features (stream slope, elevation, network length, contributing area, and channel confinement) and seasonal precipitation patterns (winter, spring, and summer months) that together were robust predictors of spatial and temporal variation in groundwater influence on stream temperatures. The final BRT model performed well for training data and cross‐validated samples (correlation = 0.984 and 0.760, respectively). Geomorphological and precipitation predictors of groundwater influence varied in their importance between watersheds, suggesting differences in spatial and temporal controls of recharge dynamics and the depth of the groundwater source. We demonstrate an application of the final BRT model to predict groundwater effects from landform and precipitation covariates at 1075 new sites distributed at 100 m increments within focal watersheds. Our study provides a framework to estimate effects of groundwater seepage on stream temperature in unsampled locations. We discuss applications for climate change research to account for groundwater‐surface water interactions when projecting future thermal thresholds for stream biota.

Virginia↗
USGS2007

Denitrification in the shallow ground water of a tile-drained, agricultural watershed

Nonpoint-source pollution of surface water by N is considered a major cause of hypoxia. Because Corn Belt watersheds have been identified as major sources of N in the Mississippi River basin, the fate and transport of N from midwestern agricultural watersheds have received considerable interest. The fate and transport of N in the shallow ground water of these watersheds still needs additional research. Our purpose was to estimate denitrification in the shallow ground water of a tile-drained, Corn Belt watershed with fine-grained soils. Over a 3-yr period, N was monitored in the surface and ground water of an agricultural watershed in central Illinois. A significant amount of N was transported past the tile drains and into shallow ground water. The ground water nitrate was isotopically heavier than tile drain nitrate, which can be explained by denitrification in the subsurface. Denitrifying bacteria were found at depths to 10 m throughout the watershed. Laboratory and push-pull tests showed that a significant fraction of nitrate could be denitrified rapidly. We estimated that the N denitrified in shallow ground water was equivalent to 0.3 to 6.4% of the applied N or 9 to 27% of N exported via surface water. These estimates varied by water year and peaked in a year of normal precipitation after 2 yr of below average precipitation. Three years of monitoring data indicate that shallow ground water in watersheds with fine-grained soils may be a significant N sink compared with N exported via surface water. ?? ASA, CSSA, SSSA.

Journal of Environmental Quality↗
USGS2008

A Study of the Connection Among Basin-Fill Aquifers, Carbonate-Rock Aquifers, and Surface-Water Resources in Southern Snake Valley, Nevada

The Secretary of the Interior through the Southern Nevada Public Lands Management Act approved funding for research to improve understanding of hydrologic systems that sustain numerous water-dependent ecosystems on Federal lands in Snake Valley, Nevada. Some of the streams and spring-discharge areas in and adjacent to Great Basin National Park have been identified as susceptible to ground-water withdrawals (Elliott and others, 2006) and research has shown a high potential for ground-water flow from southern Spring Valley into southern Snake Valley through carbonate rocks that outcrop along a low topographic divide known as the Limestone Hills (Welch and others, 2007). Comprehensive geologic, hydrologic, and chemical information will be collected and analyzed to assess the hydraulic connection between basin-fill aquifers and surface-water resources, water-dependent ecological features, and the regional carbonate-rock aquifer, the known source of many high-discharge springs. Understanding these connections is important because proposed projects to pump and export ground water from Spring and Snake Valleys in Nevada may result in unintended capture of water currently supplying springs, streams, wetlands, limestone caves, and other biologically sensitive areas (fig. 1). The methods that will be used in this study may be transferable to other areas in the Great Basin. The National Park Service, Bureau of Land Management, U.S. Fish and Wildlife Service, and U.S. Forest Service submitted the proposal for funding this research to facilitate science-based land management. Scientists from the U.S. Geological Survey (USGS) Water Resources and Geologic Disciplines, and the University of Nevada, Reno, will accomplish four research elements through comprehensive data collection and analysis that are concentrated in two distinct areas on the eastern and southern flanks of the Snake Range (fig. 2). The projected time line for this research is from July 2008 through September 2011.

Fact Sheet↗
USGS2006

Development of water level regulation strategy for fish and wildlife, upper Mississippi River system

Water level regulation has been proposed as a tool for maintaining or enhancing fish and wildlife resources in navigation pools and associated flood plains of the Upper Mississippi River System. Research related to the development of water level management plans is being conducted under the Long Term Resource Monitoring Program. Research strategies include investigations of cause and effect relationships, spatial and temporal patterns of resource components, and alternative problem solutions. The principal hypothesis being tested states that water level fluctuations resulting from navigation dam operation create less than optimal conditions for the reproduction and growth of target aquatic macrophyte and fish species. Representative navigation pools have been selected to describe hydrologic, engineering, and legal constraints within which fish and wildlife objectives can be established. Spatial analyses are underway to predict the magnitude and location of habitat changes that will result from controlled changes in water elevation.

Mississippi River↗
USGS2000

Finding minimal herbicide concentrations in ground water? Try looking for their degradates

Extensive research has been conducted regarding the occurrence of herbicides in the hydrologic system, their fate, and their effects on human health and the environment. Few studies, however, have considered herbicide transformation products (degradates). In this study of Iowa ground water, herbicide degradates were frequently detected. In fact, herbicide degradates were eight of the 10 most frequently detected compounds. Furthermore, a majority of a herbicide's measured concentration was in the form of its degradates — ranging from 55 to over 99%. The herbicide detection frequencies and concentrations varied significantly among the major aquifer types sampled. These differences, however, were much more pronounced when herbicide degradates were included. Aquifer types presumed to have the most rapid recharge rates (alluvial and bedrock/karst region aquifers) were those most likely to contain detectable concentrations of herbicide compounds. Two indirect estimates of ground-water age (depth of well completion and dissolved-oxygen concentration) were used to separate the sampled wells into general vulnerability classes (low, intermediate, and high). The results show that the herbicide detection frequencies and concentrations varied significantly among the vulnerability classes regardless of whether or not herbicide degradates were considered. Nevertheless, when herbicide degradates were included, the frequency of herbicide compound detection within the highest vulnerability class approached 90%, and the median total herbicide residue concentration increased over an order of magnitude, relative to the parent compounds alone, to 2 μg/l. The results from this study demonstrate that obtaining data on herbicide degradates is critical for understanding the fate of herbicides in the hydrologic system. Furthermore, the prevalence of herbicide degradates documented in this study suggests that to accurately determine the overall effect on human health and the environment of a specific herbicide its degradates should also be considered.

Iowa↗
USGS2024

Knowledge gaps and opportunities in water-quality drivers of aquatic ecosystem health

This report identifies key scientific gaps that limit our ability to predict water quality effects on health of aquatic ecosystems and proposes approaches to address those gaps. Topics considered include (1) coupled nutrient-carbon cycle processes and related ecological-flow-regime drivers of ecosystem health, (2) anthropogenic and geogenic toxin bioexposure, (3) fine sediment drivers of aquatic ecosystem health, and (4) freshwater salinization. Each topic is addressed in terms of scientific gaps, approaches, and timelines to help guide portions of the U.S. Geological Survey Water Mission Area ( https://www.usgs.gov/mission-areas/water-resources ) research portfolio and other national research efforts. The report provides an assessment of several of the major challenges and opportunities concerning water quality impacts on aquatic ecosystem health. It will be important to maintain broad-based expertise and flexibility to address the full range of long-term water quality issues facing the Nation’s water resources.

Open-File Report↗
USGS2003

Methods of analysis by the U.S. Geological Survey Organic Geochemistry Research Group: Determination of acetamide herbicides and their degradation products in water using online solid-phase extraction and liquid chromatography/mass spectrometry

An analytical method for the determination of 6 acetamide herbicides (acetochlor, alachlor, dimethenamid, flufenacet, metolachlor, and propachlor) and 16 of their degradation products in natural water samples using solid-phase extraction and liquid chromatography/mass spectrometry is described in this report. Special consideration was given during the development of the method to prevent the formation of degradation products during the analysis. Filtered water samples were analyzed using octadecylsilane as the solid-phase extraction media on online automated equipment followed by liquid chromatography/mass spectrometry. The method uses only 10 milliliters of sample per injection. Three different water-sample matrices, a reagent-water, a ground-water, and a surface-water sample spiked at 0.10 and 1.0 microgram per liter, were analyzed to determine method performance. Method detection limits ranged from 0.004 to 0.051 microgram per liter for the parent acetamide herbicides and their degradation products. Mean recoveries for the acetamide compounds in the ground- and surface-water samples ranged from 62.3 to 117.4 percent. The secondary amide of acetochlor/metolachlor ethanesulfonic acid (ESA) was recovered at an average rate of 43.5 percent. The mean recoveries for propachlor and propachlor oxanilic acid (OXA) were next lowest, ranging from 62.3 to 95.5 percent. Mean recoveries from reagent-water samples ranged from 90.3 to 118.3 percent for all compounds. Overall the mean of the mean recoveries of all compounds in the three matrices spiked at 0.10 and 1.0 microgram per liter ranged from 89.9 to 100.7 percent, including the secondary amide of acetochlor/metolachlor ESA and the propachlor compounds. The acetamide herbicides and their degradation products are reported in concentrations ranging from 0.05 to 2.0 micrograms per liter. The upper concentration limit is 2.0 micrograms per liter for all compounds without dilution. With the exception of the secondary amide of acetochlor/metolachlor ESA, good precision and accuracy for the chloroacetanalide herbicides and their degradation compounds were demonstrated for the method in buffered reagent water, ground water, and surface water. The extraction method as used did not optimize the recovery of the secondary amide of acetochlor/metolachlor ESA.

Open-File Report↗
USGS2014

Hyporheic flow and transport processes: mechanisms, models, and biogeochemical implications

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed."

Reviews of Geophysics↗