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At least 1,369 records · Page 76Linked to original sources
USGS2014

Long-term trends in alkalinity in large rivers of the conterminous US in relation to acidification, agriculture, and hydrologic modification

Alkalinity increases in large rivers of the conterminous US are well known, but less is understood about the processes leading to these trends as compared with headwater systems more intensively examined in conjunction with acid deposition studies. Nevertheless, large rivers are important conduits of inorganic carbon and other solutes to coastal areas and may have substantial influence on coastal calcium carbonate saturation dynamics. We examined long-term (mid-20th to early 21st century) trends in alkalinity and other weathering products in 23 rivers of the conterminous US. We used a rigorous flow-weighting technique which allowed greater focus on solute trends occurring independently of changes in flow. Increasing alkalinity concentrations and yield were widespread, occurring at 14 and 13 stations, respectively. Analysis of trends in other weathering products suggested that the causes of alkalinity trends were diverse, but at many stations alkalinity increases coincided with decreasing nitrate + sulfate and decreasing cation:alkalinity ratios, which is consistent with recovery from acidification. A positive correlation between the Sen–Thiel slopes of alkalinity increases and agricultural lime usage indicated that agricultural lime contributed to increasing solute concentration in some areas. However, several stations including the Altamaha, Upper Mississippi, and San Joaquin Rivers exhibited solute trends, such as increasing cation:alkalinity ratios and increasing nitrate + sulfate, more consistent with increasing acidity, emphasizing that multiple processes affect alkalinity trends in large rivers. This study was unique in its examination of alkalinity trends in large rivers covering a wide range of climate and land use types, but more detailed analyses will help to better elucidate temporal changes to river solutes and especially the effects they may have on coastal calcium carbonate saturation state.

Science of the Total Environment↗
USGS2010

The chemistry of iron, aluminum, and dissolved organic material in three acidic, metal-enriched, mountain streams, as controlled by watershed and in-stream processes

Several studies were conducted in three acidic, metal-enriched, mountain streams, and the results are discussed together in this paper to provide a synthesis of watershed and in-stream processes controlling Fe, Al, and DOC (dissolved organic carbon) concentrations. One of the streams, the Snake River, is naturally acidic; the other two, Peru Creek and St. Kevin Gulch, receive acid mine drainage. Analysis of stream water chemistry data for the acidic headwaters of the Snake River shows that some trace metal solutes (Al, Mn, Zn) are correlated with major ions, indicating that watershed processes control their concentrations. Once in the stream, biogeochemical processes can control transport if they occur over time scales comparable to those for hydrologic transport. Examples of the following in-stream reactions are presented: (1) photoreduction and dissolution of hydrous iron oxides in response to an experimental decrease in stream p H, (2) precipitation of Al at three stream confluences, and (3) sorption of dissolved organic material by hydrous iron and aluminum oxides in a stream confluence. The extent of these reactions is evaluated using conservative tracers and a transport model that includes storage in the substream zone.

Water Resources Research↗
USGS2021

Pervasive changes in stream intermittency across the United States

Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the three intermittency signatures, and changes in no-flow duration were most pervasive (41% of gages). Changes in intermittency were substantial for many streams, and 7% of gages exhibited changes in annual no-flow duration exceeding 100 days during the study period. Distinct regional patterns of change were evident, with widespread drying in southern CONUS and wetting in northern CONUS. These patterns are correlated with changes in aridity, though drivers of spatiotemporal variability were diverse across the three intermittency signatures. While the no-flow timing and duration were strongly related to climate, dry-down period was most strongly related to watershed land use and physiography. Our results indicate that non-perennial conditions are increasing in prevalence over much of CONUS and binary classifications of 'perennial' and 'non-perennial' are not an accurate reflection of this change. Water management and policy should reflect the changing nature and diverse drivers of changing intermittency both today and in the future.

Environmental Research Letters↗
USGS1984

State hydrologic unit maps

A set of maps depicting approved boundaries of, and numerical codes for, river-basin units of the United States has been developed by the U.S. Geological Survey. These ' State Hydrologic Unit Maps ' are four-color maps that present information on drainage, culture, hydrography, and hydrologic boundaries and codes: (1) the 21 major water-resources regions and the 222 subregions designated by the U.S. Water Resources Council; (2) the 352 accounting units of the U.S. Geological Survey 's National Water Data Network; and (3) the 2,149 cataloging units of the U.S. Geological Survey 's Catalog of Information on Water Data. The maps are plotted on the Geological Survey State base-map series at a scale of 1:500,000 and, except for Alaska, depict hydrologic unit boundaries for all drainage basins greater than 700 mi squared (1,813 km squared). A complete list of all the hydrologic units, along with their drainage areas, their names, and the names of the States or outlying areas in which they reside, is contained in the report. These maps and associated codes provide a standardized base for use by water-resources organizations in locating, storing, retrieving, and exchanging hydrologic data. The Hydrologic Unit Codes shown on the maps have been approved as a Federal Information Processing Standard for use by the Federal establishment. (USGS)

Open-File Report↗
USGS1990

Water Resources Research Grant Program project descriptions, fiscal year 1989

Information on the 36 new projects funded by the US Geological Survey 's (USGS) Water Resources Research Grant Program in fiscal year 1989 and on 27 projects completed during the year, is presented. For the new projects, the report gives the grant number, project title, performing organization, principal investigator(s), project duration, and a project description that includes: (1) identification of water-related problems and problem-solution approach; (2) contribution to problem solution; (3) objectives; and (4) approach. The 36 projects include 6 in groundwater transport and flow, 4 in the water quality treatment processes, 5 in water quality processes, 5 in biology, 9 in economics and management, and 7 in climate and hydrology. For the 27 completed projects, the report gives the grant number, project title, performing organization, principal investigator(s), starting date, date of receipt of final report, and an abstract of the final report. Each project description provides the information needed to obtain a copy of the final report. The report also contains tables showing: (1) proposals received according to area of research interest; (2) grant awards and funding according to area of research interest; (3) proposals received according to type of submitting organization; and (4) awards and funding according to type of organization. (Lantz-PTT)

Open-File Report↗
USGS2005

Base flow in the Great Lakes Basin

Hydrograph separations were performed using the PART, HYSEP 1, 2, and 3, BFLOW and UKIH methods on 104,293 years of daily streamflow records from 3,936 streamflow-gaging stations in Ontario, Canada and the eight Great Lakes States of Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin to estimate base-flow index (BFI) and base flow. BFI ranged an average of 0.24 BFI depending on which hydrograph-separation method was used. BFI data from 959 selected streamflow-gaging stations with a combined 28,784 years of daily streamflow data were used to relate BFI to surficial geology and the proportion of surface water within the gaged watersheds. This relation was then used to derive estimates of BFI throughout the Great Lakes, Ottawa River, and upper St. Lawrence River Basins at a scale of 8-digit hydrologic unit code (HUC) watersheds for the U.S. and tertiary watersheds in Canada. This process was repeated for each of the six hydrograph-separation methods used. When applied to gaged watersheds, model results predicted observed base flow within 0.2 BFI up to 94 percent of the time. Estimates of long-term (length of streamflow record) average annual streamflow in each HUC and tertiary watershed were calculated and used to determine average annual base flow from BFI estimates. Possibilities for future study based on results from this study include long-term trend analysis of base flow and improving the scale at which base-flow estimates can be made.

Great Lakes Basin↗
USGS2006

Land-Cover Trends of the Central Basin and Range Ecoregion

The U.S. Geological Survey (USGS) Land Cover Trends research project is focused on understanding the amounts, rates, trends, causes, and implications of contemporary land-use and land-cover (LU/LC) change in the United States. This project is supported by the USGS Geographic Analysis and Monitoring Program in collaboration with the U.S. Environmental Protection Agency (EPA) and the National Aeronautics and Space Administration (NASA). LU/LC change is a pervasive process that modifies landscape characteristics and affects a broad range of socioeconomic, biologic, and hydrologic systems. Understanding the impacts and feedbacks of LU/LC change on environmental systems requires an understanding of the rates, patterns, and driving forces of past, present, and future LU/LC change. The objectives of the Land Cover Trends project are to (1) determine and describe the amount, rates, and trends of contemporary LU/LC change by ecoregion for the period 1973-2000 for the conterminous United States, (2) document the causes, driving forces, and implications of change, and (3) synthesize individual ecoregion results into a national assessment of LU/LC change. The Land Cover Trends research team includes staff from the USGS National Center for Earth Resources Observation and Science (EROS), Rocky Mountain Geographic Science Center, Eastern Geographic Science Center, Mid-Continent Geographic Science Center, and the Western Geographic Science Center. Other partners include researchers at South Dakota State University, University of Southern Mississippi, and State University of New York College of Environmental Science and Forestry. This report presents an assessment of LU/LC change in the Central Basin and Range ecoregion for the period 1973-2000. The Central Basin and Range ecoregion is one of 84 Level-III ecoregions as defined by the Environmental Protection Agency. Ecoregions have served as a spatial framework for environmental resource management and to denote areas that contain a geographically distinct assemblage of biotic and abiotic phenomena including geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. The established Land Cover Trends methodology generates estimates of LU/LC change using a probability sampling approach and change-detection analysis of thematic land-cover images derived from Landsat satellite imagery.

Scientific Investigations Report↗
USGS2003

Preliminary assessment of microbial communities and biodegradation of chlorinated volatile organic compounds in wetlands at Cluster 13, Lauderick Creek area, Aberdeen Proving Ground, Maryland

A preliminary assessment of the microbial communities and biodegradation processes for chlorinated volatile organic compounds was con-ducted by the U.S. Geological Survey in wetlands at the Cluster 13, Lauderick Creek area at Aberdeen Proving Ground, Maryland. The U.S. Geological Survey collected wetland sediment samples from 11 sites in the Lauderick Creek area for microbial analyses, and used existing data to evaluate biodegradation processes and rates. The bacterial and methanogen communities in the Lauderick Creek wetland sediments were similar to those observed in a previous U.S. Geological Survey study at the West Branch Canal Creek wet-land area, Aberdeen Proving Ground. Evaluation of the degradation rate of 1,1,2,2-tetrachloroethane and the daughter compounds produced also showed similar results for the two wetlands. How-ever, a vertical profile of contaminant concentra-tions in the wetlands was available at only one site in the Lauderick Creek area, and flow velocities in the wetland sediment are unknown. To better evaluate natural attenuation processes and rates in the wetland sediments at Lauderick Creek, chemi-cal and hydrologic measurements are needed along ground-water flowpaths in the wetland at additional sites and during different seasons. Nat-ural attenuation in the wetlands, enhanced biore-mediation, and constructed wetlands could be feasible remediation methods for the chlorinated volatile organic compounds discharging in the Lauderick Creek area. The similarities in the microbial communities and biodegradation pro-cesses at the Lauderick Creek and West Branch Canal Creek areas indicate that enhanced bioreme-diation techniques currently being developed for the West Branch Canal Creek wetland area would be transferable to this area.

Maryland↗
USGS1987

Hydrologic unit maps

A set of maps depicting approved boundaries of, and numerical codes for, river-basin units of the United States has been developed by the U.S . Geological Survey. These 'Hydrologic Unit Maps' are four-color maps that present information on drainage, culture, hydrography, and hydrologic boundaries and codes of (1) the 21 major water-resources regions and the 222 subregions designated by the U.S . Water Resources Council, (2) the 352 accounting units of the U.S. Geological Survey's National Water Data Network, and (3) the 2,149 cataloging units of the U.S . Geological Survey's 'Catalog of information on Water Data:' The maps are plotted on the Geological Survey State base-map series at a scale of 1 :500,000 and, except for Alaska, depict hydrologic unit boundaries for all drainage basins greater than 700 square miles (1,813 square kilometers). A complete list of all the hydrologic units, along with their drainage areas, their names, and the names of the States or outlying areas in which they reside, is contained in the report. These maps and associated codes provide a standardized base for use by water-resources organizations in locating, storing, retrieving, and exchanging hydrologic data, in indexing and inventorying hydrologic data and information, in cataloging water-data acquisition activities, and in a variety of other applications. Because the maps have undergone extensive review by all principal Federal, regional, and State water-resource agencies, they are widely accepted for use in planning and describing water-use and related land-use activities, and in geographically organizing hydrologic data . Examples of these uses are given in the report . The hydrologic unit codes shown on the maps have been approved as a Federal Information Processing Standard for use by the Federal establishment.

Water Supply Paper↗
USGS2020

Inundation exposure assessment for Majuro Atoll, Republic of the Marshall Islands using a high-accuracy digital elevation model

Majuro Atoll in the central Pacific has high coastal vulnerability due to low-lying islands, rising sea level, high wave events, eroding shorelines, a dense population center, and limited freshwater resources. Land elevation is the primary geophysical variable that determines exposure to inundation in coastal settings. Accordingly, coastal elevation data (with accuracy information) are critical for assessments of inundation exposure. Previous research has demonstrated the importance of using high-accuracy elevation data and rigorously accounting for uncertainty in inundation assessments. A quantitative analysis of inundation exposure was conducted for Majuro Atoll, including accounting for the cumulative vertical uncertainty from the input digital elevation model (DEM) and datum transformation. The project employed a recently produced and validated DEM derived from structure-from-motion processing of very-high-resolution aerial imagery. Areas subject to marine inundation (direct hydrologic connection to the ocean) and low-lying lands (disconnected hydrologically from the ocean) were mapped and characterized for three inundation levels using deterministic and probabilistic methods. At the highest water level modeled (3.75 ft, or 1.143 m), more than 34% of the atoll study area is likely to be exposed to inundation (68% chance or greater), while more than 20% of the atoll is extremely likely to be exposed (95% chance or greater). The study demonstrates the substantial value of a high-accuracy DEM for assessing inundation exposure of low-relief islands and the enhanced information from accounting for vertical uncertainty.

Majuro Atoll↗
USGS1989

Studies of geology and hydrology in the Basin and Range Province, Southwestern United States, for isolation of high-level radioactive waste - Basis of characterization and evaluation

The geologic and hydrologic factors in selected regions of the Basin and Range province were examined to identify prospective areas for further study that may provide isolation of high-level radioactive waste from the accessible environment. The six regions selected for study were characterized with respect to the following guidelines: (1) Potential repository media; (2) Quaternary tectonic conditions; (3) climatic change and geomorphic processes; (4) ground-water conditions; (5) ground-water quality; and (6) mineral and energy resources. The repository medium will function as the first natural barrier to radionuclide travel by virtue of associated slow ground-water velocity. The principal rock types considered as host media include granitic, intermediate, and mafic intrusive rocks; argillaceous rocks; salt and anhydrite; volcanic mudflow (laharic) breccias; some intrusive rhyolitic plugs and stocks; partially zeolitized tuff; and metamorphic rocks. In the unsaturated zone, the permeability and hydrologic properties of the rocks and the hydrologic setting are more important than the rock type. Media ideally should be permeable to provide drainage and should have a minimal water flux The ground-water flow path from a repository to the accessible environment needs to present major barriers to the transport of radionuclides. Factors considered in evaluating the ground-water conditions include ground-water traveltimes and quality, confining beds, and earth materials favorable for retardation of radionuclides. Ground-water velocities in the regions were calculated from estimated hydraulic properties of the rocks and gradients. Because site-specific data on hydraulic properties are not available, data from the literature were assembled and synthesized to obtain values for use in estimating ground-water velocities. Hydraulic conductivities for many rock types having granular and fracture permeability follow a log-normal distribution. Porosity for granular and very weathered crystalline rock tends to be normally distributed; porosity of fractured crystalline rock probably follows a log-normal distribution. The tectonic setting needs to prevent an increase in radionuclides to the accessible environment. Data on historic seismicity and heat flow, Quaternary faults, volcanism, and uplift were used to assess the tectonic conditions. Long-term late Cenozoic rates of vertical crustal movement in the Basin and Range province range from less than 2 meters per 104 years to greater than 20 meters per 104 years. Shortterm rates of vertical movement may be more than an order of magnitude greater, based on geodetic leveling. Changes in tectonic and climatic processes may potentially cause changes in hydrologic conditions and geomorphology that could affect the integrity of a deep, mined repository either adversely or beneficially. The transition from a full-glacial climate to the current interglacial condition has occurred within the past 15,000 years. Reconstructions of the last full-glacial climate indicate that, at that time, there was greater water availability for runoff and vegetation growth than there is now. Based on the increased water availability and depending on seasonal distribution of precipitation, on soil characteristics, on topography, and on other characteristics, ground-water recharge during the full-glacial climate is estimated to have been possibly 2 to 10 or more times the modern rate. During the full-glacial climate, more than 100 lakes occupied closed basins in the province. Any increase in ground-water recharge and refilling of Pleistocene lakes will tend to decrease the distance of ground-water flow and its time of travel. The unsaturated zone this zone is considered a potential host medium where the thickness is greater than 150 m will be decreased by these changes. In contrast, incision of streams and other geomorphic, tectonic, or climatically induced changes that lower the ground-water discharge level will tend to increase the thickness of the unsaturated zone. Aggradation in basinal troughs may either decrease or increase the thickness of the unsaturated zone. Aggradation in basins that causes the ground-water discharge level to rise will tend to decrease the thickness of unsaturated zone in the adjacent uplands; aggradation in basins where the ground-water discharge level remains the same or is lowered will increase the unsaturated thickness of basin fill. Records show that, throughout late Cenozoic time in the Basin and Range province, continued vertical crustal movements have tended to maintain mountain ranges and closed basins, whereas aggradation of the basins and erosion of the mountain ranges have tended to decrease the topographic relief. Maximum rates of denudation for small basins in areas climatically similar to the Basin and Range province are about 2 meters per 104 years. For sites unaffected by stream incision and scarp retreat, a conservative estimate of erosion affecting long-term changes in depth of burial would appear to be 2 meters per 104 years, or, equal to the long-term rate of vertical crustal movement where greater than 2 meters per 104 years. The response of the ground-water conditions to climatic and geomorphically induced boundary conditions is significant from the points of: (1) The potential maximum change in the ground-water flow system; (2) the time of response of the ground-water system; and (3) the present state of the ground-water system as a result of past changes. Effects of longterm climatic and tectonic changes on hydrologic and geomorphic conditions differ from area to area, and rates of change of geomorphic and hydrologic conditions may vary significantly. Therefore, sitespecific studies need to be made to assess the long-term integrity of deep, mined repositories.

Arizona, California, Idaho, Nevada, New Mexico, Te↗
USGS1997

Flood dependency of cottonwood establishment along the Missouri River, Montana, USA

Flow variability plays a central role in structuring the physical environment of riverine ecosystems. However, natural variability in flows along many rivers has been modified by water management activities. We quantified the relationship between flow and establishment of the dominant tree (plains cottonwood, Populus deltoides subsp. monilifera ) along one of the least hydrologically altered alluvial reaches of the Missouri River: Coal Banks Landing to Landusky, Montana. Our purpose was to refine our understanding of how local fluvial geomorphic processes condition the relationship between flow regime and cottonwood recruitment. We determined date and elevation of tree establishment and related this information to historical peak stage and discharge over a 112-yr hydrologic record. Of the excavated trees, 72% were established in the year of a flow >1400 m 3 /s (recurrence interval of 9.3 yr) or in the following 2 yr. Flows of this magnitude or greater create the necessary bare, moist establishment sites at an elevation high enough to allow cottonwoods to survive subsequent floods and ice jams. Almost all cottonwoods that have survived the most recent flood (1978) were established >1.2 m above the lower limit of perennial vegetation (active channel shelf). Most younger individuals were established between 0 and 1.2 m, and are unlikely to survive over the long term. Protection of riparian cottonwood forest along this National Wild and Scenic section of the Missouri River depends upon maintaining the historical magnitude, frequency, and duration of floods >1400 m 3 /s. Here, a relatively narrow valley constrains lateral channel movement that could otherwise facilitate cottonwood recruitment at lower flows. Effective management of flows to promote or maintain cottonwood recruitment requires an understanding of locally dominant fluvial geomorphic processes.

Montana↗
USGS2015

User guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R packages for hydrologic data

Evaluating long-term changes in river conditions (water quality and discharge) is an important use of hydrologic data. To carry out such evaluations, the hydrologist needs tools to facilitate several key steps in the process: acquiring the data records from a variety of sources, structuring it in ways that facilitate the analysis, processing the data with routines that extract information about changes that may be happening, and displaying findings with graphical techniques. A pair of tightly linked R packages, called dataRetrieval and EGRET (Exploration and Graphics for RivEr Trends), have been developed for carrying out each of these steps in an integrated manner. They are designed to easily accept data from three sources: U.S. Geological Survey hydrologic data, U.S. Environmental Protection Agency (EPA) STORET data, and user-supplied flat files. The dataRetrieval package not only serves as a “front end” to the EGRET package, it can also be used to easily download many types of hydrologic data and organize it in ways that facilitate many other hydrologic applications. The EGRET package has components oriented towards the description of long-term changes in streamflow statistics (high flow, average flow, and low flow) as well as changes in water quality. For the water-quality analysis, it uses Weighted Regressions on Time, Discharge and Season (WRTDS) to describe long-term trends in both concentration and flux. EGRET also creates a wide range of graphical presentations of the water-quality data and of the WRTDS results. This report serves as a user guide to these two R packages, providing detailed guidance on installation and use of the software, documentation of the analysis methods used, as well as guidance on some of the kinds of questions and approaches that the software can facilitate.

Techniques and Methods↗
USGS2013

Integrated hydrologic modeling of a transboundary aquifer system —Lower Rio Grande

For more than 30 years the agreements developed for the aquifer systems of the lower Rio Grande and related river compacts of the Rio Grande River have evolved into a complex setting of transboundary conjunctive use. The conjunctive use now includes many facets of water rights, water use, and emerging demands between the states of New Mexico and Texas, the United States and Mexico, and various water-supply agencies. The analysis of the complex relations between irrigation and streamflow supplyand-demand components and the effects of surface-water and groundwater use requires an integrated hydrologic model to track all of the use and movement of water. MODFLOW with the Farm Process (MFFMP) provides the integrated approach needed to assess the stream-aquifer interactions that are dynamically affected by irrigation demands on streamflow allotments that are supplemented with groundwater pumpage. As a first step to the ongoing full implementation of MF-FMP by the USGS, the existing model (LRG_2007) was modified to include some FMP features, demonstrating the ability to simulate the existing streamflow-diversion relations known as the D2 and D3 curves, departure of downstream deliveries from these curves during low allocation years and with increasing efficiency upstream, and the dynamic relation between surface-water conveyance and estimates of pumpage and recharge. This new MF-FMP modeling framework can now internally analyze complex relations within the Lower Rio Grande Hydrologic Model (LRGHM_2011) that previous techniques had limited ability to assess.

Conference Paper↗
USGS2010

Radar image and data fusion for natural hazards characterisation

Fusion of synthetic aperture radar (SAR) images through interferometric, polarimetric and tomographic processing provides an all - weather imaging capability to characterise and monitor various natural hazards. This article outlines interferometric synthetic aperture radar (InSAR) processing and products and their utility for natural hazards characterisation, provides an overview of the techniques and applications related to fusion of SAR/InSAR images with optical and other images and highlights the emerging SAR fusion technologies. In addition to providing precise land - surface digital elevation maps, SAR - derived imaging products can map millimetre - scale elevation changes driven by volcanic, seismic and hydrogeologic processes, by landslides and wildfires and other natural hazards. With products derived from the fusion of SAR and other images, scientists can monitor the progress of flooding, estimate water storage changes in wetlands for improved hydrological modelling predictions and assessments of future flood impacts and map vegetation structure on a global scale and monitor its changes due to such processes as fire, volcanic eruption and deforestation. With the availability of SAR images in near real - time from multiple satellites in the near future, the fusion of SAR images with other images and data is playing an increasingly important role in understanding and forecasting natural hazards.

International Journal of Image and Data Fusion↗
USGS2022

Water-budget accounting for tropical regions model (WATRMod) documentation

Regional groundwater recharge commonly is estimated using a threshold-type water-budget approach in which groundwater recharge is assumed to occur when water in the plant-root zone exceeds the soil’s moisture storage capacity. A water budget of the plant-soil system accounts for water inputs (rainfall, fog interception, irrigation, septic-system leachate, and other inputs), water outputs (runoff, evaporation, transpiration, and recharge), and changes in stored water during a specified time interval. Water budgets can be computed on any desired interval, including annual, monthly, daily, and subdaily intervals. In general, uncertainty in recharge estimates is expected to be lower using daily or subdaily intervals relative to monthly and annual intervals. Average recharge rates computed over a period of a year or multiple years are commonly determined from water budgets computed using a daily computation interval capable of capturing rainfall and land-cover changes during the period. This report documents the Water-budget Accounting for Tropical Regions Model, or WATRMod, code that can be used to estimate spatially variable, daily water-budget components in tropical-island and other appropriate settings. The purpose of this report is to provide descriptions of WATRMod’s (1) approach to computing a daily water budget, (2) represented processes, (3) limitations, and (4) execution procedure, input requirements, output files, and example files. The model computes a daily water budget for each hydrologically independent subarea within the overall study area. A subarea is defined by its climatic, soil, land-cover, and human-related (for example, adding irrigation or other water) characteristics. The water-budget model can represent processes including rainfall, fog interception, irrigation, septic-system leachate, direct recharge that bypasses the plant-soil system, runoff, canopy evaporation in forested areas, evapotranspiration, and groundwater recharge. The water-budget model can represent either one of the following different accounting orders: (1) accounting for loss of water by evapotranspiration before accounting for recharge, and (2) accounting for recharge before accounting for evapotranspiration. WATRMod’s limitations include: (1) uncharacterized, subdaily transient changes in water inputs and outputs from the plant-soil system, (2) unrepresented precipitation in the form of snow and sublimation, and (3) routing runoff from one subarea to an adjacent subarea that is not directly represented.

Hawaii↗
USGS2020

Assessment of rangeland ecosystem conditions in Grand Canyon-Parashant National Monument, Arizona

Sustainability of dryland ecosystems depends on the functionality of soil-vegetation feedbacks that affect ecosystem processes, such as nutrient cycling, water capture and retention, soil erosion and deposition, and plant establishment and reproduction. Useful, common indicators can provide information on soil and site stability, hydrologic function, and biotic integrity. Evaluation of rangeland health thus relies on describing the condition and sustainability of these individual, measurable, and observable indicators that are linked to important ecosystem processes. This report focuses on the ~200,000 acres of the Grand Canyon-Parashant National Monument that is administered by the National Park Service (NPS)—one of the largest NPS units where livestock grazing is a permitted land-use activity. Many ecosystems in the monument are characterized by a low degree of resilience to improper grazing because of low and variable precipitation. The monument is marked by a high degree of environmental heterogeneity, including a large elevation gradient, widely differing precipitation patterns, a diversity of geologic substrates, and unique combinations of plant species. The objective of this report is to (1) increase our understanding of the underlying landscape, soil, and climate setting factors that affect Grand Canyon-Parashant National Monument dryland ecosystem structure and function (also referred to as land potential) and (2) characterize the condition of monument ecosystems in relation to management concepts, such as rangeland health. Data were analyzed by elevation zone using both univariate and multivariate approaches. Survey results document the high level of diversity within the study area, including 15 unique soil taxa and 271 species of plants. We collected three new plant species for Grand Canyon-Parashant National Monument and 17 new species for the NPS portion of the monument. Results also document a strong association between rangeland health indicators and elevation, topographic setting, and soils. Soil factors found to explain important variation across plots include the amount of exposed bedrock, soil rockiness, soil texture (and associated hydrologic properties), and soil depth. We also found that dominant species turnover across elevation may represent species’ differences in adaptation to climates, including Larrea tridentata , Coleogyne ramosissima , and Artemisia spp. Bromus rubens is the most common invasive species of concern recorded in this study, but other common invasive species are Bromus tectorum , Erodium cicutarium , and Schismus arabicus . Correlations between an index of cattle use and indicators of rangeland health suggest that areas with high cattle use have increased bare ground, decreased ground cover, increased frequency of Schismus arabicus , decreased cover of Coleogyne ramosissima and Ephedra spp., and increased cover of Gutierrezia spp. The few strong correlations observed between indicators of vascular plant community cover or abundance and indicators of cattle activity support rangeland assessment and monitoring strategies that do not rely solely on plant-based indicators are needed. This work supports management of dryland ecosystems, including Grand Canyon-Parashant National Monument, using concepts of land potential. We conclude the report with recommendations on improving existing land-potential-based classification systems, associated interpretations, and methods for moving forward with a Grand Canyon-Parashant National Monument rangeland monitoring program.

Arizona↗
USGS2015

Instrumenting caves to collect hydrologic and geochemical data: case study from James Cave, Virginia

Karst aquifers are productive groundwater systems, supplying approximately 25 % of the world’s drinking water. Sustainable use of this critical water supply requires information about rates of recharge to karst aquifers. The overall goal of this project is to collect long-term, high-resolution hydrologic and geochemical datasets at James Cave, Virginia, to evaluate the quantity and quality of recharge to the karst system. To achieve this goal, the cave has been instrumented for continuous (10-min interval) measurement of the (1) temperature and rate of precipitation; (2) temperature, specific conductance, and rate of epikarst dripwater; (3) temperature of the cave air; and (4) temperature, conductivity, and discharge of the cave stream. Instrumentation has also been installed to collect both composite and grab samples of precipitation, soil water, the cave stream, and dripwater for geochemical analysis. This chapter provides detailed information about the instrumentation, data processing, and data management; shows examples of collected datasets; and discusses recommendations for other researchers interested in hydrologic and geochemical monitoring of cave systems. Results from the research, briefly described here and discussed in more detail in other publications, document a strong seasonality of the start of the recharge season, the extent of the recharge season, and the geochemistry of recharge.

Virginia↗