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At least 667 records · Page 37Linked to original sources

USGS2020

Multiple mechanisms determine the effect of warming on plant litter decomposition in a dryland

In drylands, where soil fertility is typically low, plant litter decomposition provides particularly critical carbon and nitrogen inputs into soil. Although climate change is projected to increase the already large global extent of drylands, it is unknown how warmer temperatures will affect core ecosystem processes, such as plant litter decomposition, in these systems. To address this key unknown, we conducted a litterbag study in a long-term dryland warming experiment in southeastern Utah, USA. Unexpectedly, we did not find an overall effect of warming on leaf litter mass loss over time. Instead, our results indicated both positive and negative effects of warming on mass loss which offset one another. In particular, our findings suggested that a warming-induced degradation of biological soil crusts (soil surface community of mosses, lichens, and/or cyanobacteria that live in drylands worldwide) increased soil-litter mixing, thereby accelerating decomposition. Results also suggested that warming-induced decreases in litter moisture slowed decomposition. In addition to assessing mass loss, we found that warming lowered the carbon-to-nitrogen ratio of the decomposing litter. These results showed that warming did not alter the total litter mass-loss rates in this ecosystem, but that decomposition patterns were affected through more nuanced changes to both the biological and physical environment of dryland soils.

Utah↗

USGS1983

Precipitation-runoff modeling system; user's manual

The concepts, structure, theoretical development, and data requirements of the precipitation-runoff modeling system (PRMS) are described. The precipitation-runoff modeling system is a modular-design, deterministic, distributed-parameter modeling system developed to evaluate the impacts of various combinations of precipitation, climate, and land use on streamflow, sediment yields, and general basin hydrology. Basin response to normal and extreme rainfall and snowmelt can be simulated to evaluate changes in water balance relationships, flow regimes, flood peaks and volumes, soil-water relationships, sediment yields, and groundwater recharge. Parameter-optimization and sensitivity analysis capabilites are provided to fit selected model parameters and evaluate their individual and joint effects on model output. The modular design provides a flexible framework for continued model system enhancement and hydrologic modeling research and development. (Author 's abstract)

Water-Resources Investigations Report↗

USGS2024

The LTAR Grazing Land Common Experiment at the Jornada Experimental Range: Old genetics, new precision technologies, and adaptive value chains

Rangelands and the supply chains connected to them are central to the agrifood systems of the Southwestern United States. Local ranchers are simultaneously arid lands managers, herd managers, and marketing managers. To stay in business, they must constantly adapt to unpredictable forage resources and markets while conserving soils and vegetation resources for the long term. As climate warming and drying exacerbate the complexity and difficulty of day-to-day production, producers and policy-makers are seeking alternatives to “business as usual”. To meet this need, the LTAR-Jornada team has developed a package of strategies to help producers adapt to the local and inter-regional challenges. The package includes heritage cattle, precision ranching systems, and adaptive value chains. Five ranches across the Southwest have adopted different combinations of the strategies and are partnering to measure their benefits and drawbacks in real-world conditions. Opportunities for controlled experimentation differ among the ranches, so we use LTAR’s indicator system to assess and compare results. Even as we invest in co-producing knowledge about these three strategies, we recognize that progressive aridification and urbanization of Southwestern rangelands create challenges for which a single “silver bullet” agricultural innovation is unlikely to provide durable solutions. We are learning from our customers and stakeholders about ways to adjust the development of new options.

New Mexico↗

USGS2013

Deep subsurface drip irrigation using coal-bed sodic water: part II. geochemistry

Waters with low salinity and high sodium adsorption ratios (SARs) present a challenge to irrigation because they degrade soil structure and infiltration capacity. In the Powder River Basin of Wyoming, such low salinity (electrical conductivity, EC 2.1 mS cm -1 ) and high-SAR (54) waters are co-produced with coal-bed methane and some are used for subsurface drip irrigation(SDI). The SDI system studied mixes sulfuric acid with irrigation water and applies water year-round via drip tubing buried 92 cm deep. After six years of irrigation, SAR values between 0 and 30 cm depth (0.5-1.2) are only slightly increased over non-irrigated soils (0.1-0.5). Only 8-15% of added Na has accumulated above the drip tubing. Sodicity has increased in soil surrounding the drip tubing, and geochemical simulations show that two pathways can generate sodic conditions. In soil between 45-cm depth and the drip tubing, Na from the irrigation water accumulates as evapotranspiration concentrates solutes. SAR values >12, measured by 1:1 water-soil extracts, are caused by concentration of solutes by factors up to 13. Low-EC (<0.7 mS cm -1 ) is caused by rain and snowmelt flushing the soil and displacing ions in soil solution. Soil below the drip tubing experiences lower solute concentration factors (1-1.65) due to excess irrigation water and also contains relatively abundant native gypsum (2.4 ± 1.7 wt.%). Geochemical simulations show gypsum dissolution decreases soil-water SAR to <7 and increases the EC to around 4.1 mS cm-1, thus limiting negative impacts from sodicity. With sustained irrigation, however, downward flow of excess irrigation water depletes gypsum, increasing soil-water SAR to >14 and decreasing EC in soil water to 3.2 mS cm-1. Increased sodicity in the subsurface, rather than the surface, indicates that deep SDI can be a viable means of irrigating with sodic waters.

Wyoming↗

USGS1935

Geology and ground-water resources of the island of Oahu, Hawaii

Oahu, one of the islands of the Hawaiian group, lies in the Mid-Pacific 2,100 miles southwest of San Francisco. The principal city is Honolulu. The Koolau Range makes up the eastern part of the island, and the Waianae Range the western part. Both are extinct basaltic volcanoes deeply dissected by erosion. The Koolau Volcano was the later to become extinct. The Waianae Range is made up of three groups of lavas erupted in Tertiary and possibly in early Pleistocene time. The exposed part of the older lava is nearly 2,000 feet thick and consists largely of thin-bedded pahoehoe. It is separated in most places from the middle lavas by an angular unconformity and talus breccia and in a few places by an erosional unconformity. The middle basalts are about 2,000 feet thick and closely resemble the lower ones except that they contain more aa. The upper lavas reach a thickness of about 2,300 feet and are mostly massive aa flows. The last eruptions produced large cinder cones and some nephelite basalts. The Waianae Volcano, like other Hawaiian volcanoes, produced only small amounts of ash, and the lavas were largely extruded from fissures a few feet wide, now occupied by dikes. The center of activity was near Kolekole Pass, at the head of Lualualei Valley. The Koolau Volcano is made up of two groups of lavas extruded in Tertiary and early Pleistocene (?) time. The older group, the Kailua volcanic series, is greatly altered by hydrothermal action and was extruded from fissures near Lanikai. The flows of the younger group, the Koolau volcanic series, were extruded from fissures about a mile south of the Kailua rift and have an exposed thickness of about 3,000 feet. The Koolau Volcano produced even less ash than the Waianae Volcano, and its flows are thin-bedded pahoehoe and aa. The eruptive center of the Koolau Volcano lies between Kaneohe and Waimanalo. Great amounts of both the Waianae and Koolau Ranges were removed by fluvial and marine erosion during the Pleistocene. The master streams are characterized by deep amphitheater-headed valleys. After this erosion cycle the island was submerged more than 1,200 feet, and these great valleys were drowned and alluviated. Besides this submergence, several strand lines, preserved up to 100 feet above present sea level occur, which may be due to world-wide changes in sea level in response to the withdrawal and restoration of water concurrent with the advances and recessions of the polar ice caps and to accompanying changes in the ocean floor. During this time of shifting ocean levels spasmodic eruptions occurred on the southeast end of the Koolau Range, producing numerous lava flows and tuff cones, most of which are nephelite basalt. The last of these eruptions occurred in Recent time. A description of the climate, rates of run-off, and results of experiments to determine evaporation and transpiration in the areas of high rainfall are given. It was found that the consumptive use decreases materially and becomes a very small percentage of the rainfall in the areas of high precipitation. The lava rocks of the island are very permeable and, because of a rainfall reaching a maximum of 300 inches a year, carry large amounts of ground water, confined and unconfined, basal and perched. The basal ground water floats on salt water because of its lower specific gravity. Consequently for each foot the water table stands above sea level, salt water lies about 42 feet below sea level, in accordance with the sea along the coast as basal ground water. In most places the lava rocks along the shore are overlain by an impermeable or nearly impermeable caprock consisting of submerged lateritic soils and marine noncalcareous sediments. These deposits retard the escape of basal ground water into the sea and give rise to artesian water, but unlike most other artesian systems, this one has no lower restraining formation. The artesian water is the principal source of domestic, municipal, and irrigation supplies. The average annual quantity pumped for the period 1928 to 1933 amounted to about 105,000,000,000 gallons, nearly 90 percent of which came from Koolau hasalt and the remainder from Waianae basalt. There are ten artesian areas in the Koolau Range and two in the Waianae Range. Hydraulic gradients in these basins were found to range from 1.2 to 3 feet to the mile. Because of these extremely flat gradients and the high permeability of the aquifers it is possible to reverse the hydraulic gradients by draft and make the water flow from one artesian area to another. The artesian water levels fluctuate in response to seasonal variations in draft and recharge and in a lesser way to tidal, barometric, and seismic pressures. The water, as shown by chemical analysis, is of excellent quality except where it is contaminated with sea water. Methods have been devised for freshening wells that have gone salty, for detecting leaks, for sealing leaky and defective wells, and for recharging the artesian basins. Owing to the danger of the wells becoming brackish with increased draft, it is believed that further large developments will be more successful if shafts are sunk to sea level in the basalt as far inland as practicable, and tunnels are driven from the bottom of the shafts near the top of the saturated zone. Favorable places for such development exist in Honolulu. In addition to the basal water in the volcanic rocks, water is found in the recent gravel, beach, and dune deposits, and the emerged reef limestone. This water has been recovered by wells and tunnels, and there are favorable localities for developing additional water of this type. The island contains two types of basal springs—those like the Pearl Harbor Springs, which issue from basalt and are supplied by overflow and leakage from the artesian basin, and those which issue from the coastal-plain sediments and are mainly return irrigation water. The total quantity of basal ground water issuing as springs is estimated to be 100,000,000 gallons a day. Ground water occurs at high levels, confined by dikes and perched on tuff, alluvium, and soil beds. These structures give rise to innumerable high-level springs. In the Koolau Range 60 tunnels yield about 33,000,000 gallons daily, of which about 95 percent is obtained from tunnels penetrating the dike complex of the Koolau volcanic series, about 2 percent from tunnels entering post-Koolau ash or tuff deposits, and the remainder from tunnels whose geologic relations are not certainly known. The average daily yield of the tunnels that recover dike water is 2,330 gallons a foot, but the average daily yield of the tunnels in post-Koolau tuff is 450 gallons a foot, and that of the tunnels in alluvium or soil is only 23 gallons a foot. Owing largely to the much lower rainfall on the Waianac Range, its 35 tunnels (not including two new tunnels under construction) yield only about 2,400,000 gallons daily, about 94 percent of which is believed to be obtained from dike systems. The average daily yield of the tunnels in this range that are supplied by dike systems is 581 gallons a foot, as compared to 5 gallons a foot from tunnels in ash or tuff. An extensive tunnel system is proposed to develop a large supply of high-level water for Honolulu from the dike complex of the Koolau series, and high-level water can be recovered by tunnels at many other places. The average daily discharge of all high-level springs in the Koolau Range is about 58,000,000 gallons, of which about 94 percent comes from the Koolau dike complex and about 6 percent from post-Koolau volcanic rocks. The average daily discharge of all high-level springs in the Waianae Range is about 500,000 gallons of which about 81 percent issues from the dike complex.

Hawaii↗

USGS1990

Vapor-phase interactions and diffusion of organic solvents in the unsaturated zone

This article presents an analysis of the interactions and static movement of 37 organic solvents as vapors through the unsaturated soil zone. The physicochemical interactions of the organic vapors with unsaturated soil materials were emphasized with focus on diffusive, and adsorptive interactions. Fick's Law and porous media diffusion coefficients for most of the solvent vapors were either compiled or estimated; coefficients were not available for some of the fluorinated solvents. The adsorption of some of the solvent vapors by silica was concluded to be due to hydrogen bond formation with surface silanol groups. Heats of adsorption data for different adsorbents were also compiled. There were very few data on the adsorption of these solvent vapors by soils, but it appears that the magnitude of adsorption of nonpolar solvents is reduced as the relative humidity of the vapor-solid system is increased. Consequently, the interaction of the vapors may then separated into two processes; (1) gas-water partitioning described by Henry's Law constants, and (2) solid-water adsorption coefficients which may be estimated from liquid-solid partition coefficients (Kd values). ?? 1990 Springer-Verlag New York Inc.

Environmental Geology and Water Sciences↗

USGS2016

Evaluating land cover influences on model uncertainties—A case study of cropland carbon dynamics in the Mid-Continent Intensive Campaign region

Quantifying spatial and temporal patterns of carbon sources and sinks and their uncertainties across agriculture-dominated areas remains challenging for understanding regional carbon cycles. Characteristics of local land cover inputs could impact the regional carbon estimates but the effect has not been fully evaluated in the past. Within the North American Carbon Program Mid-Continent Intensive (MCI) Campaign, three models were developed to estimate carbon fluxes on croplands: an inventory-based model, the Environmental Policy Integrated Climate (EPIC) model, and the General Ensemble biogeochemical Modeling System (GEMS) model. They all provided estimates of three major carbon fluxes on cropland: net primary production (NPP), net ecosystem production (NEP), and soil organic carbon (SOC) change. Using data mining and spatial statistics, we studied the spatial distribution of the carbon fluxes uncertainties and the relationships between the uncertainties and the land cover characteristics. Results indicated that uncertainties for all three carbon fluxes were not randomly distributed, but instead formed multiple clusters within the MCI region. We investigated the impacts of three land cover characteristics on the fluxes uncertainties: cropland percentage, cropland richness and cropland diversity. The results indicated that cropland percentage significantly influenced the uncertainties of NPP and NEP, but not on the uncertainties of SOC change. Greater uncertainties of NPP and NEP were found in counties with small cropland percentage than the counties with large cropland percentage. Cropland species richness and diversity also showed negative correlations with the model uncertainties. Our study demonstrated that the land cover characteristics contributed to the uncertainties of regional carbon fluxes estimates. The approaches we used in this study can be applied to other ecosystem models to identify the areas with high uncertainties and where models can be improved to reduce overall uncertainties for regional carbon flux estimates.

Mid-Continent Intensive Campaign region↗

USGS2021

Evaluating management options to reduce Lake Erie algal blooms using an ensemble of watershed models

Reducing harmful algal blooms in Lake Erie, situated between the United States and Canada, requires implementing best management practices to decrease nutrient loading from upstream sources. Bi-national water quality targets have been set for total and dissolved phosphorus loads, with the ultimate goal of reaching these targets in 9-out-of-10 years. Row crop agriculture dominates the land use in the Western Lake Erie Basin thus requiring efforts to mitigate nutrient loads from agricultural systems. To determine the types and extent of agricultural management practices needed to reach the water quality goals, we used five independently developed Soil and Water Assessment Tool models to evaluate the effects of 18 management scenarios over a 10-year period on nutrient export. Guidance from a stakeholder group was provided throughout the project, and resulted in improved data, development of realistic scenarios, and expanded outreach. Subsurface placement of phosphorus fertilizers, cover crops, riparian buffers, and wetlands were among the most effective management options. But, only in one realistic scenario did a majority (3/5) of the models predict that the total phosphorus loading target would be met in 9-out-of-10 years. Further, the dissolved phosphorus loading target was predicted to meet the 9-out-of-10-year goal by only one model and only in three scenarios. In all scenarios evaluated, the 9-out-of-10-year goal was not met based on the average of model predictions. Ensemble modeling revealed general agreement about the effects of several practices although some scenarios resulted in a wide range of uncertainty. Overall, our results demonstrate that there are multiple pathways to approach the established water quality goals, but greater adoption rates of practices than those tested here will likely be needed to attain the management targets.

Michigan↗

USGS2010

Modeling methods

Simulation models are widely used in all types of hydrologic studies, and many of these models can be used to estimate recharge. Models can provide important insight into the functioning of hydrologic systems by identifying factors that influence recharge. The predictive capability of models can be used to evaluate how changes in climate, water use, land use, and other factors may affect recharge rates. Most hydrological simulation models, including watershed models and groundwater-flow models, are based on some form of water-budget equation, so the material in this chapter is closely linked to that in Chapter 2. Empirical models that are not based on a water-budget equation have also been used for estimating recharge; these models generally take the form of simple estimation equations that define annual recharge as a function of precipitation and possibly other climatic data or watershed characteristics. Model complexity varies greatly. Some models are simple accounting models; others attempt to accurately represent the physics of water movement through each compartment of the hydrologic system. Some models provide estimates of recharge explicitly; for example, a model based on the Richards equation can simulate water movement from the soil surface through the unsaturated zone to the water table. Recharge estimates can be obtained indirectly from other models. For example, recharge is a parameter in groundwater-flow models that solve for hydraulic head (i.e. groundwater level). Recharge estimates can be obtained through a model calibration process in which recharge and other model parameter values are adjusted so that simulated water levels agree with measured water levels. The simulation that provides the closest agreement is called the best fit, and the recharge value used in that simulation is the model-generated estimate of recharge.

Book chapter↗

USGS2024

Towards entity-aware conditional variational inference for heterogeneous time-series prediction: An application to hydrology

Many environmental systems (e.g., hydrology basins) can be modeled as entity whose response (e.g., streamflow) depends on drivers (e.g., weather) conditioned on their characteristics (e.g., soil properties). We introduce Entity-aware Conditional Variational Inference (EA-CVI), a novel probabilistic inverse modeling approach, to deduce entity characteristics from observed driver-response data. EA-CVI infers probabilistic latent representations that can accurately predict response for diverse entities, particularly in out-of-sample few-shot settings. EA-CVI's latent embeddings encapsulate diverse entity characteristics within compact, low-dimensional representations. EA-CVI proficiently identifies dominant modes of variation in responses and offers the opportunity to infer a physical interpretation of the underlying attributes that shape these responses. EA-CVI can also generate new data samples by sampling from the learned distribution, making it useful in zero-shot scenarios. EA-CVI addresses the need for uncertainty estimation, particularly during extreme events, rendering it essential for data-driven decision-making in real-world applications. Extensive evaluations on a renowned hydrology benchmark dataset, CAMELS-GB, validate EA-CVI's abilities.

Conference Paper↗

USGS2010

Public review draft: A method for assessing carbon stocks, carbon sequestration, and greenhouse-gas fluxes in ecosystems of the United States under present conditions and future scenarios

The Energy Independence and Security Act of 2007 (EISA), Section 712, authorizes the U.S. Department of the Interior to develop a methodology and conduct an assessment of the Nation's ecosystems focusing on carbon stocks, carbon sequestration, and emissions of three greenhouse gases (GHGs): carbon dioxide, methane, and nitrous oxide. The major requirements include (1) an assessment of all ecosystems (terrestrial systems, such as forests, croplands, wetlands, shrub and grasslands; and aquatic ecosystems, such as rivers, lakes, and estuaries), (2) an estimation of annual potential capacities of ecosystems to increase carbon sequestration and reduce net GHG emissions in the context of mitigation strategies (including management and restoration activities), and (3) an evaluation of the effects of controlling processes, such as climate change, land use and land cover, and wildlfires. The purpose of this draft methodology for public review is to propose a technical plan to conduct the assessment. Within the methodology, the concepts of ecosystems, carbon pools, and GHG fluxes used for the assessment follow conventional definitions in use by major national and international assessment or inventory efforts. In order to estimate current ecosystem carbon stocks and GHG fluxes and to understand the potential capacity and effects of mitigation strategies, the method will use two time periods for the assessment: 2001 through 2010, which establishes a current ecosystem GHG baseline and will be used to validate the models; and 2011 through 2050, which will be used to assess future potential conditions based on a set of projected scenarios. The scenario framework is constructed using storylines of the Intergovernmental Panel on Climate Change (IPCC) Special Report Emission Scenarios (SRES), along with initial reference land-use and land-cover (LULC) and land-management scenarios. An additional three LULC and land-management mitigation scenarios will be constructed for each storyline to enhance carbon sequestration and reduce GHG fluxes in ecosystems. Input from regional experts and stakeholders will be solicited to construct realistic and meaningful scenarios. The methods for mapping the current LULC and ecosystem disturbances will require the extensive use of both remote-sensing data and in-situ (for example, forest inventory data) to capture and characterize landscape-change events. For future potential LULC and ecosystem disturbances, key drivers such as socioeconomic, policy, and climate assumptions will be used in addition to biophysical data. The product of these analyses will be a series of maps for each future year for each scenario. These annual maps will form the basis for estimating carbon storage and GHG emissions. For terrestrial ecosystems, carbon storage, carbon-sequestration capacities, and GHG emissions under the current and projected future conditions will be assessed using the LULC and ecosystem-disturbance estimates in map format with a spatially explicit biogeochemical ensemble modeling system that incorporates properties of management activities (such as tillage or harvesting) and properties of individual ecosystems (such as elevation, vegetation characteristics, and soil attributes). For aquatic ecosystems, carbon burial in sediments and GHG fluxes are functions of the current and projected future stream flow and sediment transports, and therefore will be assessed using empirical modeling methods. Validation and uncertainty analysis methods described in the methodology will follow established guidelines to assess the quality of the assessment results. The U.S. Environmental Protection Agency's Level II ecoregions map (which delineates 24 ecoregions for the Nation) will be the practical instrument for developing and delivering assessment results. Consequently, the ecoregion will be the reporting unit of the assessment because the mitigation scenarios, assessment results, validation, and uncertainty analysis will be

Open-File Report↗

USGS1987

Hydrogeology of the Salamanca area, Cattaraugus County, New York

The hydrogeology of a 132-sq mi area centered at Salamanca, NY, is summarized in five maps at 1:24,000 scale. The maps show locations of wells and test holes, surficial geology and geologic sections, water-table surface, soil permeability, and land use. The valley-fill aquifer in the Salamanca area serves approximately 7,000 people through two major distribution systems with an average daily pumpage of 1.2 million gal/day. The aquifer, composed of outwash sand and gravel, averages 60 ft in thickness and overlies as much as 200 ft of lacustrine silt and clay. The aquifer is recharged directly from precipitation and through seepage from streams. Average annual recharge to the aquifer from direct precipitation and infiltration of runoff from adjacent hillsides is estimated to be 13 inches or 0.6 million gal/day/sq mi. The glacial features in the Allegheny valley near Salamanca are associated with Illinoian and Wisconsin glaciations. Illinoian features consist of small, isolated exposures of outwash and till emplaced against the valley walls. Wisconsin features deposited during Altonian and Woodfordian Times of the Wisconsin consist mainly of end moraines and valley-train outwash. (USGS)

New York↗

USGS1995

Simulated response of the High Plains aquifer to ground-water withdrawals in the Upper Republican Natural Resources District, Nebraska

The U.S. Geological Survey, in cooperation with the National Soil Tilth Laboratory of the U.S. Department of Agriculture, Agricultural Research Service, conducted a study as part of the multi- scale, interagency Management Systems Evaluation Area (MSEA) program to evaluate the effects of agricultural management (farming) systems on water quality. Data on surface flow, tileflow, and streamflow in the Walnut Creek watershed just south of Ames, Iowa, were collected during April 1991-September 1993 at five sites with drainage areas ranging from 366 to 5,130 hectares. Precipitation, flow discharge, and concentration, loads, and yields of nitrate as nitrogen, atrazine, and metolachlor were analyzed to relate the transport of agricultural chemicals to major water-flow processes and to examine and transport differences among three subwatersheds. Antecedent conditions and basin-characteristic differences had significant effects on the flow response from the subwatersheds. Monthly streamflow-to- precipitation ratios were greater than 1.0, as a result of snowmelt, and negative when streamflow was lost to the ground-water system in the downstream subwatershed. Dry antecedent conditions resulted in ratios less than 0.3 (July 1992), whereas wet antecedent conditions resulted in ratios from 0.7 to almost 1.0 (July 1993) during months with similar large rainfall amounts. Most of the streamflow from the upland subwatersheds came from tileflow. Surface flow (surface runoff, interflow, and return flow0 was highly variable and intermittent, usually lasting for only a few days after a storm, although it could be the dominant source of flow when stormflow was large. Tileflow was less variable and much more persistent, ceasing only after prolonged dry periods. Large quantities of nitrate as nitrogen were transported in Walnut Creek, with concen- trations often greater than the Maximum Contaminant Level of 10 milligrams per liter established by the U.S. Environmental Protection Agency for finished drinking water. In the upland subwatersheds, ground-water flow from the tiles appears to have been the primary means of transport to the streams. Concentrations in tileflow and streamflow generally were 4 to 16 milligrams per liter, with the lower concen- trations often the result of dilution by surface runoff. Loss ratios, chemical yields expressed as a percentage of average application rates of nitrate as nitrogen for October 1992-September 1993, were about 10 percent for surface flow and more than 100 percent for tileflow from the 366-hectare basin and were more than 200 percent for streamflow from the downstream subwatershed. Concentrations of atrazine and metolachlor in streamflow, typically, were less than the Maximum Contaminant Level of 3.0 micrograms per liter, but were as high as 59 and 80 micrograms per liter, respectively, during stormflow. Concentrations as high as 170 micrograms per liter occurred in tileflow, but these were related to surface flow through surface inlets. The transport of herbicides was extremely variable, with most of the loads occurring during stormflow. Atrazine appeared more susceptable to transport losses to streamflow than did metolachlor. Loss ratios for streamflow from the subwatersheds for April- September periods were 0.3 to 20 percent for atrazine and 0.1 to 2.9 percent for metolachlor. Chemical loss ratios indicated differences in the transport characteristics of the three subwatersheds. The downstream subwatershed, which has steeper terrain, a more-developed natural drainage system, and fewer tiles than the two upland subwatersheds, had the largest loss rates for all three chemicals--206 percent for nitrate as nitrogen (October 1992-September 1993) and 20 percent for atrazine and 2.9 percent for metolachlor (April-September 1993). For May-July 1993, when most of the herbicides were transported, the downstream subwatershed also had the largest cumulative unit discharge and the largest streamflow-to-precipitation ra

Water-Resources Investigations Report↗

USGS1986

Forested wetlands of the Southeast: Review of major characteristics and role in maintaining water quality

Forested wetlands occupying floodplains of major rivers in the Southeast are highly productive and diverse ecological systems. The wetlands are produced and maintained by fluvial processes and unique hydrologic regimes consisting of periodic flooding and subsequent drydown. Fluctuations in soil chemistry and biology resulting from this flooding and drydown provide a broad range of environmental conditions that are important in determining the role of forested wetlands in maintaining and improving water quality. The periodic shift between aerobic and anaerobic conditions in floodplain soils in response to flooding facilitates the assimilation of nutrients and organic matter, hastens the degradation of persistent pesticides, and decreases the bioavailability of heavy metals.

Resource Publication↗

USGS1998

Analysis of the sensitivity of soils to the leaching of agricultural pesticides in Ohio

Pesticides have not been found frequently in the ground waters of Ohio even though large amounts of agricultural pesticides are applied to fields in Ohio every year. State regulators, including representatives from Ohio Environmental Protection Agency and Departments of Agriculture, Health, and Natural Resources, are striving to limit the presence of pesticides in ground water at a minimum. A proposed pesticide management plan for the State aims at protecting Ohio's ground water by assessing pesticide-leaching potential using geographic information system (GIS) technology and invoking a monitoring plan that targets aquifers deemed most likely to be vulnerable to pesticide leaching. The U.S. Geological Survey, in cooperation with Ohio Department of Agriculture, assessed the sensitivity of mapped soil units in Ohio to pesticide leaching. A soils data base (STATSGO) compiled by U.S. Department of Agriculture was used iteratively to estimate soil units as being of high to low sensitivity on the basis of soil permeability, clay content, and organic-matter content. Although this analysis did not target aquifers directly, the results can be used as a first estimate of areas most likely to be subject to pesticide contamination from normal agricultural practices. High-sensitivity soil units were found in lakefront areas and former lakefront beach ridges, buried valleys in several river basins, and parts of central and south- central Ohio. Medium-high-sensitivity soil units were found in other river basins, along Lake Erie in north-central Ohio, and in many of the upland areas of the Muskingum River Basin. Low-sensitivity map units dominated the northwestern quadrant of Ohio.

Water-Resources Investigations Report↗

USGS2003

The history and development of FETAX (ASTM standard guide, E-1439 on conducting the frog embryo teratogenesis Assay-Xenopus)

The energy crisis of the 1970's and 1980's prompted the search for alternative sources of fuel. With development of alternate sources of energy, concerns for biological resources potentially adversely impacted by these alternative technologies also heightened. For example, few biological tests were available at the time to study toxic effects of effluents on surface waters likely to serve as receiving streams for energy-production facilities; hence, we began to use Xenopus laevis embryos as test organisms to examine potential toxic effects associated with these effluents upon entering aquatic systems. As studies focused on potential adverse effects on aquatic systems continued, a test procedure was developed that led to the initial standardization of FETAX. Other .than a limited number of aquatic toxicity tests that used fathead minnows and cold-water fishes such as rainbow trout, X. laevis represented the only other aquatic vertebrate test system readily available to evaluate complex effluents. With numerous laboratories collaborating, the test with X. laevis was refined, improved, and developed as ASTM E-1439, Standard Guide for the Conducting Frog Embryo Teratogenesis Assay-Xenopus (FETAX). Collabrative work in the 1990s yielded procedural enhancements, for example, development of standard test solutions and exposure methods to handle volatile organics and hydrophobic compounds. As part of the ASTM process, a collaborative interlaboratory study was performed to determine the repeatability and reliability of FETAX. Parallel to these efforts, methods were also developed to test sediments and soils, and in situ test methods were developed to address "lab-to-field extrapolation errors" that could influence the method's use in ecological risk assessments. Additionally, a metabolic activation system composed of rat liver microsomes was developed which made FETAX more relevant to mammalian studies.

Conference Paper↗

USGS2008

Linking soil organic matter dynamics and erosion-induced terrestrial carbon sequestration at different landform positions

Recently, the potential for terrestrial carbon (C) sequestration by soil erosion and deposition has received increased interest. Erosion and deposition constitute a sink for atmospheric carbon dioxide relative to a preerosional state or a noneroding scenario, if the posterosion watershed C balance is increased due to (1) partial replacement of eroded C by new photosynthate in the eroded site; and (2) preservation from decomposition of at least some eroded soil organic carbon (SOC) arriving in depositional settings. Little is known, however, about differences in C dynamics at different erosional and depositional landform positions within the same eroding system. We determined the contribution of different landform positions to erosion-induced terrestrial C sequestration by measuring rates of net primary productivity (NPP), replacement of eroded C, and decomposition of organic matter (OM) at four categorically different landform positions within a naturally eroding toposequence in northern California. We found that eroded C is replaced by NPP 15 times over in the summit of the site studied and 5 times over in the slope. Profile-averaged, long-term rate constant for SOM decomposition was 2 to 14 times slower in the depositional settings compared with that in eroding slopes. As a result, the inventory of C in the depositional settings was 2 to 3 times larger than that of the eroding positions. Owing to both C replacement at eroding sites and reduced rates of OM decomposition in depositional sites, soil erosion constitutes a C sink from the atmosphere at our study site.

California↗

USGS2016

Experimental studies and model analysis of noble gas fractionation in porous media

The noble gases, which are chemically inert under normal terrestrial conditions but vary systematically across a wide range of atomic mass and diffusivity, offer a multicomponent approach to investigating gas dynamics in unsaturated soil horizons, including transfer of gas between saturated zones, unsaturated zones, and the atmosphere. To evaluate the degree to which fractionation of noble gases in the presence of an advective–diffusive flux agrees with existing theory, a simple laboratory sand column experiment was conducted. Pure CO2 was injected at the base of the column, providing a series of constant CO2 fluxes through the column. At five fixed sampling depths within the system, samples were collected for CO2 and noble gas analyses, and ambient pressures were measured. Both the advection–diffusion and dusty gas models were used to simulate the behavior of CO2 and noble gases under the experimental conditions, and the simulations were compared with the measured depth-dependent concentration profiles of the gases. Given the relatively high permeability of the sand column (5 ´ 10−11 m2), Knudsen diffusion terms were small, and both the dusty gas model and the advection–diffusion model accurately predicted the concentration profiles of the CO2 and atmospheric noble gases across a range of CO2 flux from ?700 to 10,000 g m−2 d−1. The agreement between predicted and measured gas concentrations demonstrated that, when applied to natural systems, the multi-component capability provided by the noble gases can be exploited to constrain component and total gas fluxes of non-conserved (CO2) and conserved (noble gas) species or attributes of the soil column relevant to gas transport, such as porosity, tortuosity, and gas saturation.

Vadose Zone Journal↗