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Over, under, and through: Hydrologic connectivity and the future of coastal landscape salinization

Seawater intrusion (SWI) affects coastal landscapes worldwide. Here we describe the hydrologic pathways through which SWI occurs - over land via storm surge or tidal flooding, under land via groundwater transport, and through watersheds via natural and artificial surface water channels—and how human modifications to those pathways alter patterns of SWI. We present an approach to advance understanding of spatiotemporal patterns of salinization that integrates these hydrologic pathways, their interactions, and how humans modify them. We use examples across the East Coast of the United States that exemplify mechanisms of salinization that have been reported around the planet to illustrate how hydrologic connectivity and human modifications alter patterns of SWI. Finally, we suggest a path for advancing SWI science that includes (a) deploying standardized and well-distributed sensor networks at local to global scales that intentionally track SWI fronts, (b) employing remote sensing and geospatial imaging techniques targeted at integrating above and belowground patterns of SWI, and (c) continuing to develop data analysis and model-data fusion techniques to measure the extent, understand the effects, and predict the future of coastal salinization.

Water Resources Research↗

Flood-plain delineation for Cub Run basin, Fairfax County, Virginia

Flood-plain delineation for Cub Run basin water-surface profiles of the 25-, 50-, and 100-year recurrence interval discharges have been computed for all streams and reaches of channels in Fairfax County, Virginia having a drainage area greater than 1 square mile except for Dogue Creek, Little Hunting Creek, and that part of the Cameron Run above Lake Barcroft. Maps having a 2-foot contour interval and a horizontal scale of 1 inch equals 100 feet have been used for base on which flood boundaries were delineated for 25-, 50-, and 100-year floods to be expected in each basin under ultimate development conditions. This report is one of a series and presents a discussion of techniques employed in computing discharges and profiles as well as the flood profiles and maps on which flood boundaries have been delineated for the Cub Run basin in Fairfax County.

Virginia↗

Water-quality, streamflow, and meteorological data for the Tualatin River Basin, Oregon, 1991-93

Surface-water-quality data, ground-water-quality data, streamflow data, field measurements, aquatic-biology data, meteorological data, and quality-assurance data were collected in the Tualatin River Basin from 1991 to 1993 by the U.S. Geological Survey (USGS) and the Unified Sewerage Agency of Washington County, Oregon (USA). The data from that study, which are part of this report, are presented in American Standard Code for Information Interchange (ASCII) format in subject-specific data files on a Compact Disk-Read Only Memory (CD-ROM). The text of this report describes the objectives of the study, the location of sampling sites, sample-collection and processing techniques, equipment used, laboratory analytical methods, and quality-assurance procedures. The data files on CD-ROM contain the analytical results of water samples collected in the Tualatin River Basin, streamflow measurements of the main-stem Tualatin River and its major tributaries, flow data from the USA wastewater-treatment plants, flow data from stations that divert water from the main-stem Tualatin River, aquatic-biology data, and meteorological data from the Tualatin Valley Irrigation District (TVID) Agrimet Weather Station located in Verboort, Oregon. Specific information regarding the contents of each data file is given in the text. The data files use a series of letter codes that distinguish each line of data. These codes are defined in data tables accompanying the text. Presenting data on CD-ROM offers several advantages: (1) the data can be accessed easily and manipulated by computers, (2) the data can be distributed readily over computer networks, and (3) the data may be more easily transported and stored than a large printed report. These data have been used by the USGS to (1) identify the sources, transport, and fate of nutrients in the Tualatin River Basin, (2) quantify relations among nutrient loads, algal growth, low dissolved-oxygen concentrations, and high pH, and (3) develop and calibrate a water- quality model that allows managers to test options for alleviating water-quality problems.

Oregon↗

Arsenic speciation and reactivity in poultry litter

Recent U.S. government action to lower the maximum concentration levels (MCL) of total arsenic (As) (10 ppb) in drinking water has raised serious concerns about the agricultural use of As-containing biosolids such as poultry litter (PL). In this study, solid-state chemical speciation, desorbability, and total levels of As in PL and long-term amended soils were investigated using novel synchrotron-based probing techniques (microfocused (μ) synchrotron X-ray fluorescence (SXRF) and μ-X-ray absorption near-edge structure (XANES) spectroscopies) coupled with chemical digestion and batch experiments. The total As levels in the PL were as high as ≈50 mg kg - 1 , and As(II/III and V) was always concentrated in abundant needle-shaped microscopic particles (≈20 μm × 850 μm) associated with Ca, Cu, and Fe and to a lesser extent with S, Cl, and Zn. Post-edge XANES features of litter particles are dissimilar to those of the organo-As(V) compound in poultry feed (i.e., roxarsone), suggesting possible degradation/transformation of roxarsone in the litter and/or in poultry digestive tracts. The extent of As desorption from the litter increased with increasing time and pH from 4.5 to 7, but at most 15% of the total As was released after 5 d at pH 7, indicating the presence of insoluble phases and/or strongly retained soluble compounds. No significant As accumulation (<15 mg kg - 1 ) was found in long-term PL-amended agricultural surface soils. This suggests that As in the PL may have undergone surface and subsurface transport processes. Our research results raise concerns about long-term PL amendment effects on As contamination in surrounding soil−water environments.

Environmental Science & Technology↗

Shuttle Radar Topography Mission (SRTM)

Under an agreement with the National Aeronautics and Space Administration (NASA) and the Department of Defense's National Imagery and Mapping Agency (NIMA), the U.S. Geological Survey (USGS) is now distributing elevation data from the Shuttle Radar Topography Mission (SRTM). The SRTM is a joint project between NASA and NIMA to map the Earth's land surface in three dimensions at a level of detail unprecedented for such a large area. Flown aboard the NASA Space Shuttle Endeavour February 11-22, 2000, the SRTM successfully collected data over 80 percent of the Earth's land surface, for most of the area between 60? N. and 56? S. latitude. The SRTM hardware included the Spaceborne Imaging Radar-C (SIR-C) and X-band Synthetic Aperture Radar (X-SAR) systems that had flown twice previously on other space shuttle missions. The SRTM data were collected specifically with a technique known as interferometry that allows image data from dual radar antennas to be processed for the extraction of ground heights.

Fact Sheet↗

Field sampling guidelines for developing and verifying satellite remote sensing chlorophyll a concentration and fluorescence models in inland waters

Harmful algal blooms are increasing in frequency in inland waters across the United States, resulting in a need to monitor phytoplankton bloom events to track ecosystem health and productivity. Remote sensing of chlorophyll a values offers a cost-effective and powerful method for early detection and characterization of bloom events and serves as an overall indicator of water quality and trophic state, with regular, repeated sampling of landscape-wide, high spatial resolution measurements. Field measurements are necessary for developing and verifying chlorophyll a retrieval models. For model verification, chlorophyll a concentration or fluorescence and light attenuation measurements are needed; for model development, turbidity and colored dissolved organic matter concentration measurements are additionally needed; and for model development and verification, radiometric measurements, taxonomic identification of phytoplankton, inherent optical properties, and cyanotoxin concentration are further measurements that can provide context. This report outlines detailed methods and priority considerations for collecting high-quality field data in inland waters (defined as rivers, lakes, reservoirs, estuaries, streams, and wetlands). The described methods include best practices for collecting and preparing discretely collected water samples and for calibration, maintenance, and quality assurance and quality control of field sensors. Whereas the priorities will vary between applications, some general guidelines are to collect field samples (1) as close in time to a satellite overpass as possible, (2) from representative areas of the waterbody to capture the range of spatial variability, and (3) near the surface to match remote sensing reflectance data.

Techniques and Methods↗

Temporal and abiotic fluctuations may be preventing successful rehabilitation of soil-stabilizing biocrust communities

Land degradation is a persistent ecological problem in many arid and semi-arid systems globally (drylands hereafter). Most instances of dryland degradation include some form of soil disturbance and/or soil erosion, which can hinder vegetation establishment and reduce ecosystem productivity. To combat soil erosion, researchers have identified a need for rehabilitation of biological soil crusts (biocrusts), a globally-relevant community of organisms aggregating the soil surface and building soil fertility. The impact of plant and biocrust cover was tested on soil erosion potential in the piñon-juniper woodlands of Bandelier National Monument, NM. Biocrusts were found to be similarly influential to vascular plants in reducing erosion, largely acting by promoting surface roughness. The potential to rehabilitate biocrusts within the Monument was also tested. In a full factorial design, plots were inoculated on eroding soils before the summer monsoon with greenhouse-cultured biocrusts, and administered the erosion intervention treatments of overland water flow barriers (flashing), slash placement, and seeding of vascular plants. Although significant and dynamic changes to soil stability, penetration resistance, and extractable soil nutrients were observed through time, no strong effects with the addition of inoculum, seeding, or erosion intervention treatments were seen. These results suggest possible ways forward to successfully rehabilitate biocrust, including varying the timing of biocrust application, amending inoculum application with different types of soil stabilization techniques, and adding nutrients to soils. The insights gleaned from the lack of response brings us closer to developing effective techniques to arrest soil loss in these important social-ecological dryland systems.

Ecological Applications↗

Synthesis of soil-hydraulic properties and infiltration timescales in wildfire-affected soils

We collected soil-hydraulic property data from the literature for wildfire-affected soils, ash, and unburned soils. These data were used to calculate metrics and timescales of hydrologic response related to infiltration and surface runoff generation. Sorptivity ( S ) and wetting front potential (Ψ f ) were significantly different (lower) in burned soils compared with unburned soils, whereas field-saturated hydraulic conductivity ( K fs ) was not significantly different. The magnitude and duration of the influence of capillarity during infiltration was greatly reduced in burned soils, causing faster ponding times in response to rainfall. Ash had large values of S and K fs but moderate values of Ψ f , compared with unburned and burned soils, indicating ash has long ponding times in response to rainfall. The ratio of S 2 /K fs was nearly constant (~100 mm) for unburned soils but more variable in burned soils, suggesting that unburned soils have a balance between gravity and capillarity contributions to infiltration that may depend on soil organic matter, whereas in burned soils the gravity contribution to infiltration is greater. Changes in S and K fs in burned soils act synergistically to reduce infiltration and accelerate and amplify surface runoff generation. Synthesis of these findings identifies three key areas for future research. First, short timescales of capillary influences on infiltration indicate the need for better measurements of infiltration at times less than 1 min to accurately characterize S in burned soils. Second, using parameter values, such as Ψ f , from unburned areas could produce substantial errors in hydrologic modeling when used without adjustment for wildfire effects, causing parameter compensation and resulting underestimation of K fs . Third, more thorough measurement campaigns that capture soil-structural changes, organic matter impacts, quantitative water repellency trends, and soil-water content along with soil-hydraulic properties could drive the development of better techniques for numerically simulating infiltration in burned areas.

Hydrological Processes↗

Shuttle Radar Topography Mission (SRTM)

Under an agreement with the National Aeronautics and Space Administration (NASA) and the Department of Defense's National Geospatial-Intelligence Agency (NGA), the U.S. Geological Survey (USGS) is distributing elevation data from the Shuttle Radar Topography Mission (SRTM). The SRTM is a joint project of NASA and NGA to map the Earth's land surface in three dimensions at an unprecedented level of detail. As part of space shuttle Endeavour's flight during February 11-22, 2000, the SRTM successfully collected data over 80 percent of the Earth's land surface for most of the area between latitudes 60 degrees north and 56 degrees south. The SRTM hardware included the Spaceborne Imaging Radar-C (SIR-C) and X-band Synthetic Aperture Radar (X-SAR) systems that had flown twice previously on other space shuttle missions. The SRTM data were collected with a technique known as interferometry that allows image data from dual radar antennas to be processed for the extraction of ground heights.

Fact Sheet↗

Spatially explicit rangeland erosion monitoring using high-resolution digital aerial imagery

Nearly all of the ecosystem services supported by rangelands, including production of livestock forage, carbon sequestration, and provisioning of clean water, are negatively impacted by soil erosion. Accordingly, monitoring the severity, spatial extent, and rate of soil erosion is essential for long-term sustainable management. Traditional field-based methods of monitoring erosion (sediment traps, erosion pins, and bridges) can be labor intensive and therefore are generally limited in spatial intensity and/or extent. There is a growing effort to monitor natural resources at broad scales, which is driving the need for new soil erosion monitoring tools. One remote-sensing technique that can be used to monitor soil movement is a time series of digital elevation models (DEMs) created using aerial photogrammetry methods. By geographically coregistering the DEMs and subtracting one surface from the other, an estimate of soil elevation change can be created. Such analysis enables spatially explicit quantification and visualization of net soil movement including erosion, deposition, and redistribution. We constructed DEMs (12-cm ground sampling distance) on the basis of aerial photography immediately before and 1 year after a vegetation removal treatment on a 31-ha Pi&ntilde;on-Juniper woodland in southeastern Utah to evaluate the use of aerial photography in detecting soil surface change. On average, we were able to detect surface elevation change of &plusmn; 8&minus;9cm and greater, which was sufficient for the large amount of soil movement exhibited on the study area. Detecting more subtle soil erosion could be achieved using the same technique with higher-resolution imagery from lower-flying aircraft such as unmanned aerial vehicles. DEM differencing and process-focused field methods provided complementary information and a more complete assessment of soil loss and movement than any single technique alone. Photogrammetric DEM differencing could be used as a technique to quantitatively monitor surface change over time relative to management activities.

Utah↗

Hydrologic modeling to examine the influence of the forestry reclamation approach and climate change on mineland hydrology

Forests in the Appalachian region of the U.S. are threatened by a variety of short- and long-term pressures, including climate change, invasive species, and resource extraction. Surface mining for coal is one of the most important drivers of land-use change in the region, reducing native forest cover, causing forest fragmentation, eliminating intact soil, and affecting water resources. The Forestry Reclamation Approach (FRA) has been demonstrated as a successful best practice for restoring forests on mine-impacted landscapes, but little information exists on how the practice will affect hydrologic processes. A study was initiated to examine soil-water movement, as in-situ saturated hydraulic conductivity (K sat ), combined with soil porosity to quantify the potential influence on streamflow of reclaimed mines relative to an unmined, forested control site in eastern Kentucky. We compared different reclamation techniques and time since reclamation to determine the extent to which hydrologic function can be restored. We also simulated evapotranspiration at the watershed scale as a function of reclamation technique for both historical and projected (2050) climate. Results indicate that conventional grassland reclamation critically changes how soil water transitions to streamflow, primarily due to K sat variability that exceeds that measured for intact and FRA soils. Sites reclaimed using FRA exhibited a soil-water environment that was more similar to the unmined control. However, all reclaimed mine soils were thinner, retained and stored less soil water, and thus could provide less plant-available water during the growing season. The plant-available water stored in reclaimed landscapes may not be sufficient to support forest health and this is exacerbated by projected climate conditions. However, soil development under a combination of FRA techniques has the potential to mitigate this limitation.

Kentucky↗

Trends in Surface-Water Quality at Selected Ambient-Monitoring Network Stations in Kentucky, 1979-2004

Increasingly complex water-management decisions require water-quality monitoring programs that provide data for multiple purposes, including trend analyses, to detect improvement or deterioration in water quality with time. Understanding surface-water-quality trends assists resource managers in identifying emerging water-quality concerns, planning remediation efforts, and evaluating the effectiveness of the remediation. This report presents the results of a study conducted by the U.S. Geological Survey, in cooperation with the Kentucky Energy and Environment Cabinet-Kentucky Division of Water, to analyze and summarize long-term water-quality trends of selected properties and water-quality constituents in selected streams in Kentucky's ambient stream water-quality monitoring network. Trends in surface-water quality for 15 properties and water-quality constituents were analyzed at 37 stations with drainage basins ranging in size from 62 to 6,431 square miles. Analyses of selected physical properties (temperature, specific conductance, pH, dissolved oxygen, hardness, and suspended solids), for major ions (chloride and sulfate), for selected metals (iron and manganese), for nutrients (total phosphorus, total nitrogen, total Kjeldahl nitrogen, nitrite plus nitrate), and for fecal coliform were compiled from the Commonwealth's ambient water-quality monitoring network. Trend analyses were completed using the S-Plus statistical software program S-Estimate Trend (S-ESTREND), which detects trends in water-quality data. The trend-detection techniques supplied by this software include the Seasonal Kendall nonparametric methods for use with uncensored data or data censored with only one reporting limit and the Tobit-regression parametric method for use with data censored with multiple reporting limits. One of these tests was selected for each property and water-quality constituent and applied to all station records so that results of the trend procedure could be compared among stations. Flow-adjustment procedures were used with these techniques at all stations to remove the effects of streamflow on water-quality variability. Flow adjustments were used for all constituents, except temperature. A decreasing trend indicates a decrease in concentration of a particular constituent; whereas, an increasing trend indicates an increase in concentration and potential degradation in water quality. Trend results varied statewide by station and by physical property and water-quality constituent. The results for all stations and all physical properties and water-quality constituents examined had at least one statistically significant (p-value <0.05) increasing or decreasing trend during the specified period of record. Water temperature and concentrations of dissolved oxygen had no significant decreasing trends at any station. Water temperature had one significant increasing trend at the South Fork Cumberland River near Blue Heron station. Specific conductance and concentrations of hardness had one significant decreasing trend at the South Fork Cumberland River near Blue Heron station. pH also had a significant decreasing trend at the Mud River near Gus station. Concentrations of total suspended solids had 1 increasing trend at the Kentucky River at High Bridge station and 10 decreasing trends with 5 of those stations located in the Cumberland River Basin. Major ions analyzed for trends included chloride and sulfate. Concentrations of chloride at the 37 stations had increasing trends at 15 stations, decreasing trends at 3 stations, and no significant trend in concentration over time at 19 stations. Most of the increasing trends in concentrations of chloride are located in the northern part of Kentucky, possibly indicating an increase in the use of road salts for road deicing and (or) the result of resource extraction (oil, gas, and coal). Increasing trends of sulfate concentrations were detected at seven stations, all located in the Appalachian

Scientific Investigations Report↗

Statistical modeling of agricultural chemical occurrence in midwestern rivers

Agricultural chemicals in surface water may constitute a human health risk or have adverse effects on aquatic life. Recent research on unregulated rivers in the midwestern USA documents that elevated concentrations of herbicides occur for 1-4 months following application in late spring and early summer. In contrast, nitrate concentrations in unregulated rivers are elevated during fall, winter, and spring months. Natural and anthropogenic variables of fiver drainage basins, such as soil permeability, amount of agricultural chemicals applied, or percentage of land planted in corn, affect agricultural chemical concentration and mass transport in rivers. Presented is an analysis of selected data on agricultural chemicals collected for three regional studies conducted by the US Geological Survey. Statistical techniques such as multiple linear and logistic regression were used to identify natural and anthropogenic variables of drainage basins that have strong relations to agricultural chemical concentrations and mass transport measured in rivers. A geographic information system (GIS) was used to manage and analyze spatial data. Statistical models were developed that estimated the concentration, annual transport, and annual mean concentration of selected agricultural chemicals in midwestern rivers. Multiple linear regression models were not very successful (R2 from 0.162 to 0.517) in explaining the variance in observed agricultural chemical concentrations during post-planting runoff. Logistic regression models were somewhat more successful, correctly matching the observed concentration category in 61-80% of observations. Linear and multiple linear regression models were moderately successful (R2 from 0.522 to 0.995) in explaining the variance in observed annual transport and annual mean concentration of agricultural chemicals. Explanatory variables that were commonly significant in the regression models include estimates of agricultural chemical use, crop acreage, soil characteristics, and basin topography.

Journal of Hydrology↗

Effect of backwatering a streamgage weir on the passage performance of adult American Shad (Alosa sapidissima)

Streamgage designs often include a full-width artificial hydraulic control (e.g., concrete weir) to aid in the computation of streamflow. While important to water resource managers, these weirs also tend to act as full or partial barriers to fish migration, effectively hindering the health and survival of these populations. In this study, we conducted experiments to quantify the effect of head drop and submergence of a common streamgage weir on the passage performance of an important migratory fish species, the American Shad. Three treatment conditions were selected based on the tailwater surface elevation ( El TW ): unsubmerged ( El TW = 1.05 m; head drop = 0.46 m), equal to the weir crest ( El TW = 1.20 m; head drop = 0.31 m), and submerged ( El TW = 1.36 m; head drop = 0.15 m). Fish movements were recorded via passive integrated transponder telemetry techniques. Results revealed that the backwatered Columbus-type weir was not a complete barrier at any of the three treatments, but passage was shown to be significantly impaired when the weir was unsubmerged. Passage efficiency for the unsubmerged, equal, and submerged treatments was 20.2 ± 6.2, 49.2 ± 7.2, and 64.2 ± 7.4%. Backwatering a weir, rather than removal or other major alterations that would affect weir calibration, may be an acceptable retrofit to increase fish passage.

Journal of Ecohydraulics↗

Hyperspectral narrowband imaging spectroscopy: A new paradigm for Earth observation

This editorial introduces the Special Issue entitled “Hyperspectral Narrowband Imaging Spectroscopy: A New Paradigm for Earth Observation” in the August 2026 issue of Photogrammetric Engineering & Remote Sensing (PE&RS), the flagship journal of the American Society for Photogrammetry and Remote Sensing (ASPRS). This volume represents the fourth dedicated hyperspectral special issue published in PE&RS, following earlier contributions by Thenkabail et al. (2025, 2024a, 2024b), and continues ASPRS’s commitment to advancing cutting‑edge imaging spectroscopy research and its applications across Earth system science. Remote sensing is undergoing one of the most profound transformations in its history. The emergence of hyperspectral narrowband (HNB) imaging spectroscopy data, capable of acquiring hundreds of contiguous, narrow spectral bands, has shifted the discipline from observing Earth in a handful of broad spectral windows to capturing continuous spectral signatures of the Planet. This transition marks a decisive break from the multispectral paradigm that has dominated satellite remote sensing for nearly five decades, driven by the advent of new orbital imaging spectrometers such as EnMAP, PRISMA, and NASA’s EMIT, and by the forthcoming Surface Biology and Geology (SBG) mission ((Pires Silva et al., 2026; Bourriz et al., 2025; Thenkabail et al., 2025; Chabrillat et al., 2024; Aneece et al., 2024; Dave et al., 2024; Thenkabail et al., 2024a; Thenkabail et al., 2024b; Thenkabail, 2024a; Thenkabail, 2024b; Thompson et al., 2022; Kokaly et al., 2022; Aneece & Thenkabail, 2022; Cawse Nicholson et al., 2021; Guanter et al., 2021; Vangi et al., 2021; Thenkabail et al., 2021). These missions (e.g., Table 1) deliver unprecedented spectral fidelity, improved signal to noise ratios, and global coverage capabilities, enabling a new era of quantitative, spectroscopy based Earth observation. Where multispectral broadbands (MBBs) provide only a few discrete measurements along the electromagnetic spectrum, HNB systems deliver rich, diagnostic information that enables scientists to characterize Earth’s surface with unprecedented biochemical, biophysical, and structural detail (Figure 1a, 1b). The implications for environmental monitoring, agriculture, water resources, and mineral exploration are profound. Several overarching themes emerge: • Spectral fidelity matters. The ability to preserve subtle absorption features is essential for mineral mapping, vegetation trait retrieval, and biochemical modeling. • AI and deep learning are indispensable. From destriping to classification, modern analytics must be scalable, label‑efficient, and capable of exploiting the full spectral–spatial richness of HNB data. • Physics‑based and data‑driven approaches must converge. Radiative transfer models such as PROSAIL, enhanced with localized soil parameterizations, remain foundational for biophysical retrievals and model‑based inference. • Dimensionality reduction and feature extraction are critical. Techniques such as L1‑ISOMAP demonstrate that intelligent manifold learning can unlock the structure of fused, high‑dimensional datasets. • Next‑generation architectures must be interactive and multimodal. ICTNet exemplifies the future of hyperspectral classification: hybrid, synergistic, and capable of modeling both local textures and global spectral dependencies.

Photogrammetric Engineering and Remote Sensing (PE↗

A national water-use information program

The U.S. Geological Survey has compiled estimates of water use every five years since 1950. These estimates have been derived from many sources, and have a wide range of accuracy. Therefore, they fall short of providing a national data base that is both current and reliable. In 1977, the Congress of the United States recognized the need for uniform information on water use and directed the U.S. Geological Survey to establish a National Water-Use Information Program to complement the Survey's data on the availability and quality of the Nation's water resources. The National Water-Use Information Program was designed as a cooperative program between the States and the Federal Government. The goals of the program are: to collect and compile water-use data; to develop and refine computerized water-use data systems at both the State and national levels; to devise new methods and techniques to improve the collection and analysis of water-use information; and to disseminate this information to those involved in establishing water-resources policy and to those managing the resources. The program that started in 1978 in 20 States now includes participation by 47 States. Water-Use information is being compiled for 12 categories of use. Each State will have a automated data system that contains site-specific information about the water use in each category. The National Water-Use Data System will contain information for the 12 categories of use summarized by counties and river basins within each State. The national system will aid in defining how much fresh and saline surface water and ground water is withdrawn and for what purpose, how much water is consumed during use, and how much water is returned to a water body (stream, lake, or aquifer) after use.

Open-File Report↗

Bacterial and enchytraeid abundance accelerate soil carbon turnover along a lowland vegetation gradient in interior Alaska

Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the 13C isotopic composition of SOM and respired CO 2 to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in saturated systems, which has been often ignored.

Soil Biology and Biochemistry↗

Vegetation Response to the 1995 Drawdown of the Navigation Pool at Felsenthal National Wildlife Refuge, Crossett, Arkansas

Felsenthal Navigation Pool (?the pool?) at Felsenthal National Wildlife Refuge near Crossett, Ark., was continuously flooded to a baseline elevation of 19.8 m (65.0 ft) mean sea level (m.s.l.) from late fall 1985, when the final in a series of locks and dams was constructed, until the summer of 1995. Water level within the pool was reduced by 0.3 m (1.0 ft) beginning July 5, 1995, exposing about 1,591 ha (3,931 acres) of sediment; the reduced water level was maintained until October 25 of that year. A total of 15 transects was established along the pool margin before the drawdown, extending perpendicular from the pool edge to 19.5 m (64.0 ft) in elevation. Plant species composition and cover were recorded at six to seven quadrats on each transect; 14 of the transects were also monitored three times during the drawdown and in June 1996. Soil near five of the original transects was disturbed two weeks into the drawdown by scraping the soil surface with a bulldozer. Soil cores were collected to characterize soil organic matter, texture class, carbon and nitrogen content, and plant nutrient concentrations; soil samples were also collected to identify species present in the seed bank prior to and during the drawdown. Plant species, several of which were high quality food sources for waterfowl, colonized the drawdown zone within four weeks. Vegetation response, measured by species richness, total cover, and cover of Cyperus species, was often greater at low compared to high elevations in the drawdown zone; this effect was probably intensified by low rainfall during the summer of 1995. Vegetation response on the disturbed transects was reduced compared to that on the undisturbed transects. This effect was attributed to two factors: (1) removal of the existing seed bank by the disturbance technique applied and (2) reduced incorporation of seeds recruited during the drawdown because of unusually low summer rainfall. Seed bank studies demonstrated that several species persisted despite nearly 10 years of continual flooding, and that seed bank species richness increased during the drawdown. Analyses indicated that predominantly clay soils containing relatively low organic matter were present along the pool margin. Levels of the plant nutrients measured were consistent with normal values reported for soils. Although conclusions from this study are limited by its one-year time frame, it is unlikely that permanent change to plant community function in the drawdown zone resulted from the lowered water levels during the summer of 1995. While species composition in the summer following the drawdown differed from that prior to the drawdown, the plant community remained dominated by annual floating-leaved or submersed species. It is probable that any future decrease in summer water levels in the pool will result in increased growth of desirable waterfowl food plants, such as Cyperus erythrorhizos (red-root flat sedge) and Leptochloa fascicularis var. fascicularis (bearded sprangletop), in the drawdown zone.

Open-File Report↗