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At least 523 records · Page 29Linked to original sources
USGS2011

Spatially pooled depth-dependent reservoir storage, elevation, and water-quality data for selected reservoirs in Texas, January 1965-January 2010

The U.S. Geological Survey (USGS), in cooperation with Texas Tech University, constructed a dataset of selected reservoir storage (daily and instantaneous values), reservoir elevation (daily and instantaneous values), and water-quality data from 59 reservoirs throughout Texas. The period of record for the data is as large as January 1965-January 2010. Data were acquired from existing databases, spreadsheets, delimited text files, and hard-copy reports. The goal was to obtain as much data as possible; therefore, no data acquisition restrictions specifying a particular time window were used. Primary data sources include the USGS National Water Information System, the Texas Commission on Environmental Quality Surface Water-Quality Management Information System, and the Texas Water Development Board monthly Texas Water Condition Reports. Additional water-quality data for six reservoirs were obtained from USGS Texas Annual Water Data Reports. Data were combined from the multiple sources to create as complete a set of properties and constituents as the disparate databases allowed. By devising a unique per-reservoir short name to represent all sites on a reservoir regardless of their source, all sampling sites at a reservoir were spatially pooled by reservoir and temporally combined by date. Reservoir selection was based on various criteria including the availability of water-quality properties and constituents that might affect the trophic status of the reservoir and could also be important for understanding possible effects of climate change in the future. Other considerations in the selection of reservoirs included the general reservoir-specific period of record, the availability of concurrent reservoir storage or elevation data to match with water-quality data, and the availability of sample depth measurements. Additional separate selection criteria included historic information pertaining to blooms of golden algae. Physical properties and constituents were water temperature, reservoir storage, reservoir elevation, specific conductance, dissolved oxygen, pH, unfiltered salinity, unfiltered total nitrogen, filtered total nitrogen, unfiltered nitrate plus nitrite, unfiltered phosphorus, filtered phosphorus, unfiltered carbon, carbon in suspended sediment, total hardness, unfiltered noncarbonate hardness, filtered noncarbonate hardness, unfiltered calcium, filtered calcium, unfiltered magnesium, filtered magnesium, unfiltered sodium, filtered sodium, unfiltered potassium, filtered potassium, filtered chloride, filtered sulfate, unfiltered fluoride, and filtered fluoride. When possible, USGS and Texas Commission on Environmental Quality water-quality properties and constituents were matched using the database parameter codes for individual physical properties and constituents, descriptions of each physical property or constituent, and their reporting units. This report presents a collection of delimited text files of source-aggregated, spatially pooled, depth-dependent, instantaneous water-quality data as well as instantaneous, daily, and monthly storage and elevation reservoir data.

Texas↗
USGS2002

Digital Bathymetric Model of Mono Lake, California

In 1986 and 1987, Pelagos Corporation of San Diego (now Racal Pelagos) undertook a bathymetric survey of Mono Lake in eastern California for the Los Angeles Department of Water and Power (DWP). The result of that survey was a series of maps at various scales and contour intervals. From these maps, the DWP hoped to predict consequences of the drop in lake level that resulted from their diversion of streams in the Mono Basin. No digital models, including shaded-relief and perspective-view renderings, were made from the data collected during the survey. With the permission of Pelagos Corporation and DWP, these data are used to produce a digital model of the floor of Mono Lake. The model was created using a geographic information system (GIS) to incorporate these data with new observations and measurements made in the field. This model should prove to be a valuable tool for enhanced visualization and analyses of the floor of Mono Lake.

Miscellaneous Field Studies Map↗
USGS1995

Historical Landsat data comparisons: illustrations of the Earth's changing surface

The U.S. Geological Survey's (USGS) EROS Data Center (EDC) has managed the Landsat data archive for more than two decades. This archive provides a rich collection of information about the Earth's land surface. Major changes to the surface of the planet can be detected, measured, and analyzed using Landsat data. The effects of desertification, deforestation, pollution, cataclysmic volcanic activity, and other natural and anthropogenic events can be examined using data acquired from the Landsat series of Earth-observing satellites. The information obtainable from the historical and current Landsat data play a key role in studying surface changes through time. This document provides an overview of the Landsat program and illustrates the application of the data to monitor changes occurring on the surface of the Earth. To reveal changes that have taken place within the past 20 years, pairs and triplicates of images were constructed from the Landsat multispectral scanner (MSS) and thematic mapper (TM) sensors. Landsat MSS data provide a historical record of the Earth's land surface from the early 1970's to the early 1990's. Landsat TM data provide land surface information from the early 1980's to the present.

Report↗
USGS2008

Total mercury, methylmercury, methylmercury production potential, and ancillary streambed-sediment and pore-water data for selected streams in Oregon, Wisconsin, and Florida, 2003-04

Mercury contamination of aquatic ecosystems is an issue of national concern, affecting both wildlife and human health. Detailed information on mercury cycling and food-web bioaccumulation in stream settings and the factors that control these processes is currently limited. In response, the U.S. Geological Survey (USGS) National Water-Quality Assessment Program (NAWQA) conducted detailed studies from 2002 to 2006 on various media to enhance process-level understanding of mercury contamination, biogeochemical cycling, and trophic transfer. Eight streams were sampled for this study: two streams in Oregon, and three streams each in Wisconsin and Florida. Streambed-sediment and pore-water samples were collected between February 2003 and September 2004. This report summarizes the suite of geochemical and microbial constituents measured, the analytical methods used, and provides the raw data in electronic form for both bed-sediment and pore-water media associated with this study.

Oregon, Wisconsin, Florida↗
USGS2016

Identify potential lock treatment options to prevent movement of aquatic invasive species through the Chicago Area Waterways System (CAWS)

Introduction The Illinois River is a primary tributary of the Mississippi River, connecting with the Mississippi at Grafton, Illinois. The headwaters of the river are at the confluence of the Des Plaines and Kankakee Rivers in eastern Grundy County, Illinois. Approximately 273 miles long, it runs through the heart of Illinois and is the connection between the Mississippi River and Lake Michigan in the Great Lakes basin. Because of this connection, there is concern about the potential for introduced aquatic species in one basin to migrate through this connection into the other basin. A prime example of this are the Asian carps, which were introduced into commercial fishing ponds in Arkansas in the 1970s and, following escape, are now making their way up the Mississippi, Illinois, and Missouri Rivers. Options are being investigated to minimize or prevent non-native aquatic species from invading either basin through the Illinois River connection and eventually having detrimental impacts on the basin into which they migrate. The Illinois River has a series of locks and dams that are used to facilitate the navigation of commercial and recreational shipping from Chicago to Beardstown, Illinois. One option under consideration is to develop a lock treatment process that stops aquatic invasive species from entering (and moving through) the Chicago Area Waterway System (CAWS), while at the same time not unduly impeding the movement of barges and other boat traffic between Lake Michigan and the Mississippi River. The purpose this report was to evaluate the feasibility of using chemical and (or) physical treatments to determine if a sufficiently efficacious option could be used to prevent aquatic invasive species from being transported through the locks. Approximately 30 chemical and physical control options were evaluated on the basis of nine factors ranging from viability for use on a large scale, rapid lethality, human health effects, and potential damage to lock structures and vessel hulls. Compatibility of the various options was also evaluated to assess the possibility that options could be combined to enhance efficacy. Engineering requirements were not considered as part of this evaluation. The available information suggests that hot water at 43 °C and ozone are the most feasible options.

Chicago Area Waterway System↗
USGS2008

TerraLook: GIS-Ready Time-Series of Satellite Imagery for Monitoring Change

TerraLook is a joint project of the U.S. Geological Survey (USGS) and the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) with a goal of providing satellite images that anyone can use to see changes in the Earth's surface over time. Each TerraLook product is a user-specified collection of satellite images selected from imagery archived at the USGS Earth Resources Observation and Science (EROS) Center. Images are bundled with standards-compliant metadata, a world file, and an outline of each image's ground footprint, enabling their use in geographic information systems (GIS), image processing software, and Web mapping applications. TerraLook images are available through the USGS Global Visualization Viewer (http://glovis.usgs.gov).

Fact Sheet↗
USGS2014

Model documentation for relations between continuous real-time and discrete water-quality constituents in Indian Creek, Johnson County, Kansas, June 2004 through May 2013

Johnson County is the fastest growing county in Kansas, with a population of about 560,000 people in 2012. Urban growth and development can have substantial effects on water quality, and streams in Johnson County are affected by nonpoint-source pollutants from stormwater runoff and point-source discharges such as municipal wastewater effluent. Understanding of current (2014) water-quality conditions and the effects of urbanization is critical for the protection and remediation of aquatic resources in Johnson County, Kansas and downstream reaches located elsewhere. The Indian Creek Basin is 194 square kilometers and includes parts of Johnson County, Kansas and Jackson County, Missouri. Approximately 86 percent of the Indian Creek Basin is located in Johnson County, Kansas. The U.S. Geological Survey, in cooperation with Johnson County Wastewater, operated a series of six continuous real-time water-quality monitoring stations in the Indian Creek Basin during June 2011 through May 2013; one of these sites has been operating since February 2004. Five monitoring sites were located on Indian Creek and one site was located on Tomahawk Creek. The purpose of this report is to document regression models that establish relations between continuously measured water-quality properties and discretely collected water-quality constituents. Continuously measured water-quality properties include streamflow, specific conductance, pH, water temperature, dissolved oxygen, turbidity, and nitrate. Discrete water-quality samples were collected during June 2011 through May 2013 at five new sites and June 2004 through May 2013 at a long-term site and analyzed for sediment, nutrients, bacteria, and other water-quality constituents. Regression models were developed to establish relations between discretely sampled constituent concentrations and continuously measured physical properties to estimate concentrations of those constituents of interest that are not easily measured in real time because of limitations in sensor technology and fiscal constraints. Regression models for 28 water-quality constituents were developed and documented. The water-quality information in this report is important to Johnson County Wastewater because it allows the concentrations of many potential pollutants of interest, including nutrients and sediment, to be estimated in real time and characterized during conditions and time scales that would not be possible otherwise.

Kansas↗
USGS2013

Assessment of groundwater quality data for the Turtle Mountain Indian Reservation, Rolette County, North Dakota

The Turtle Mountain Indian Reservation relies on groundwater supplies to meet the demands of community and economic needs. The U.S. Geological Survey, in cooperation with the Turtle Mountain Band of Chippewa Indians, examined historical groundwater-level and groundwater-quality data for the Fox Hills, Hell Creek, Rolla, and Shell Valley aquifers. The two main sources of water-quality data for groundwater were the U.S. Geological Survey National Water Information System database and the North Dakota State Water Commission database. Data included major ions, trace elements, nutrients, field properties, and physical properties. The Fox Hills and Hell Creek aquifers had few groundwater water-quality data. The lack of data limits any detailed assessments that can be made about these aquifers. Data for the Rolla aquifer exist from 1978 through 1980 only. The concentrations of some water-quality constituents exceeded the U.S. Environmental Protection Agency secondary maximum contaminant levels. No samples were analyzed for pesticides and hydrocarbons. Numerous water-quality samples have been obtained from the Shell Valley aquifer. About one-half of the water samples from the Shell Valley aquifer had concentrations of iron, manganese, sulfate, and dissolved solids that exceeded the U.S. Environmental Protection Agency secondary maximum contaminant levels. Overall, the data did not indicate obvious patterns in concentrations.

North Dakota↗
USGS2024

Environmental DNA reveals invasion of Puerto Rican waterways by non-native Clarias catfish

The Sharptooth walking catfish ( Clarias gariepinus ) is native to parts of the Middle East, Asia, and Africa but is one of the world's most invasive freshwater fish species. The species’ ability to invade is partly due to its ability to breathe atmospheric oxygen, thereby avoiding hypoxia or poor water quality in receiving waterbodies; further, it can crawl over moist land to disperse to new systems. In 2018, two individuals purported to be Sharptooth walking catfish were collected and identified within the Canal de Patillas, a canal in the Guayama municipality in southeastern Puerto Rico. Several other specimens were also collected the following year. Given that this invasion was in its infancy, environmental DNA (eDNA) surveillance was employed as a rapid and efficient surveillance tool to help delineate the extent of this invasion. Water samples were collected and analyzed for Clarias eDNA from 66 sites encompassing a wide range of habitats in canals, lakes, and a river surrounding the area where they were first reported. Using eDNA-metabarcoding, we detected Clarias eDNA at 40 of the 63 sites throughout the sampled waterbodies. Furthermore, our molecular analysis indicated that the Whitespotted Clarias ( C. fuscus ) is the likely invader, and the original specimens, classified as C. gariepinus , were misidentified based on the use of morphological rather than genetic features for species classification. Environmental DNA surveillance indicated that the distribution of Clarias catfish in this system is substantially more extensive than previously documented. These findings suggest that additional survey efforts could help determine the invasion's full spatial extent and leading edge to inform the scope and scale of any potential management responses.

Puerto Rico↗
USGS2000

High flow and riparian vegetation along the San Miguel River, Colorado

Riparian ecosystems are characterized by abundance of water and frequent flow related disturbance. River regulation typically decreases peak flows, reducing the amount of disturbance and altering the vegetation. The San Miguel River is one of the last relatively unregulated rivers remaining in the Colorado River Watershed. One goal of major landowners along the San Miguel including the Bureau of Land Management and The Nature Conservancy is to maintain their lands in a natural condition. Conservation of an entire river corridor requires an integrated understanding of the variability in ecosystems and external influences along the river. Therefore, the Bureau of Land Management and others have fostered a series of studies designed to catalogue that variability, and to characterize the processes that maintain the river as a whole. In addition to providing information useful to managers, these studies present a rare opportunity to investigate how a Colorado river operates in the absence of regulation.

Colorado↗
USGS2009

Using a coupled groundwater/surfacewater model to predict climate-change impacts to lakes in the Trout Lake watershed, Northern Wisconsin

A major focus of the U.S. Geological Survey’s Trout Lake Water, Energy, and Biogeochemical Budgets (WEBB) project is the development of a watershed model to allow predictions of hydrologic response to future conditions including land-use and climate change. The coupled groundwater/surface-water model GSFLOW was chosen for this purpose because it could easily incorporate an existing groundwater flow model and it provides for simulation of surface-water processes. The Trout Lake watershed in northern Wisconsin is underlain by a highly conductive outwash sand aquifer. In this area, streamflow is dominated by groundwater contributions; however, surface runoff occurs during intense rainfall periods and spring snowmelt. Surface runoff also occurs locally near stream/lake areas where the unsaturated zone is thin. A diverse data set, collected from 1992 to 2007 for the Trout Lake WEBB project and the co-located and NSF-funded North Temperate Lakes LTER project, includes snowpack, solar radiation, potential evapotranspiration, lake levels, groundwater levels, and streamflow. The timeseries processing software TSPROC (Doherty 2003) was used to distill the large time series data set to a smaller set of observations and summary statistics that captured the salient hydrologic information. The timeseries processing reduced hundreds of thousands of observations to less than 5,000. Model calibration included specific predictions for several lakes in the study area using the PEST parameter estimation suite of software (Doherty 2007). The calibrated model was used to simulate the hydrologic response in the study lakes to a variety of climate change scenarios culled from the IPCC Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Solomon et al. 2007). Results from the simulations indicate climate change could result in substantial changes to the lake levels and components of the hydrologic budget of a seepage lake in the flow system. For a drainage lake lower in the flow system, the impacts of climate change are diminished.

Conference Paper↗
USGS2013

Electron donor concentrations in sediments and sediment properties at the agricultural chemicals team research site near New Providence, Iowa, 2006-07

The concentrations of electron donors in aquifer sediments are important to the understanding of the fate and transport of redox-sensitive constituents in groundwater, such as nitrate. For a study by the U.S. Geological Survey National Water-Quality Assessment Program, 50 sediment samples were collected from below the water table from 11 boreholes at the U.S. Geological Survey Agricultural Chemicals Team research site near New Providence, Iowa, during 2006-07. All samples were analyzed for gravel, sand (coarse, medium, and fine), silt, clay, Munsell soil color, inorganic carbon content, and for the following electron donors: organic carbon, ferrous iron, and inorganic sulfide. A subset of 14 sediment samples also was analyzed for organic sulfur, but all of these samples had concentrations less than the method detection limit; therefore, the presence of this potential electron donor was not considered further. X-ray diffraction analyses provided important semi-quantitative information of well-crystallized dominant minerals within the sediments that might be contributing electron donors.

Iowa↗
USGS2009

Using a coupled groundwater/surface-water model to predict climate-change impacts to lakes in the Trout Lake Watershed, northern Wisconsin

A major focus of the U.S. Geological Survey’s Trout Lake Water, Energy, and Biogeochemical Budgets (WEBB) project is the development of a watershed model to allow predictions of hydrologic response to future conditions including land-use and climate change. The coupled groundwater/surface-water model GSFLOW was chosen for this purpose because it could easily incorporate an existing groundwater flow model and it provides for simulation of surface-water processes. The Trout Lake watershed in northern Wisconsin is underlain by a highly conductive outwash sand aquifer. In this area, streamflow is dominated by groudwater contributions, however, surface runoff occurs during intense rainfall periods and spring snowmelt. Surface runoff also occurs locally near stream/lake areas where the unsaturated zone is thin. A diverse data set, collected from 1992 to 2007 for the Trout Lake WEBB project and the co-located and NSF-funded North Temperate Lake LTER project, includes snowpack, solar radiation, potential evapotranspiration, lake levels, groundwater levels, and streamflow. The time-series processing software TSPROC (Doherty 2001)was used to distill the large time series data set to a smaller set of observations and summary statistics that captured the salient hydrologic information. The time-series processing reduced hundreds of thousands of observations to less than 5,000. Model calibration included specific predictions for several lakes in the study area using the PEST parameter estimation suit of software (Doherty 2007). The calibrated model was used to simulate the hydrologic response in the study lakes to a variety of climate change scenarios culled from the IPCC Fourth Assessment Report of the Intergovernmental Panel of Climate Change (Solomon et al. 2007). Results from the simulations indicate climate change could result in substantial changes to the lake levels and components of the hydrologic budget of a seepage lake in the flow system. For a drainage lake lower in the flow system, the impacts of climate change are diminished.

Wisconsin↗
USGS2019

Groundwater and surface-water data collection for Mason County, western Washington, 2016–18

Groundwater levels and surface water flow measurements were collected from August 2016 to September 2018 to provide the Mason Conservation District and other stakeholders with basic knowledge of existing water resources in Mason County, Washington. Additionally, the data were collected with the intent of contributing to informed decision making about groundwater use, management, and conservation throughout the county and for future inclusion in a groundwater model. Data were collected and compiled for 130 sites—110 wells and 20 miscellaneous surface-water discharge sites. In the spring of 2016, field reconnaissance was conducted to locate suitable locations for baseflow discharge measurements to be used for estimating groundwater contribution to surface flow. In the summer of 2016, a field inventory of wells was conducted to acquire locational data and to assess the suitability of the wells for inclusion in a monthly groundwater-level monitoring network. Groundwater levels were measured bimonthly in the 64 wells over 2 years. Streamflow measurements were conducted two times each summer during two summers for each of the 20 surface water sites.

Washington↗
USGS2021

Methods of data collection and analysis for an assessment of karst aquifer systems between Albany and Buffalo, New York

The U.S. Geological Survey, in cooperation with the New York State Department of Environmental Conservation, catalogued aquifers and closed depressions in a karst-prone area between Albany and Buffalo, New York to provide resource managers information to more efficiently manage and protect groundwater resources. The New York State Department of Environmental Conservation has been working with the agricultural industry to raise awareness of karst aquifer contamination susceptibility and how to reduce effects on surface water and groundwater resources, especially in karst areas. There is also a need to make industries, State and local regulators, planners, and the public aware of New York’s karst resources to properly protect and manage these resources and the quality of surface water and groundwater that flows through the karst aquifer. Publicly available geospatial data were identified, collated, and analyzed for a region of karst terrain extending from Albany to Buffalo. The region was divided into 10 subareas. A series of geospatial datasets were assembled to determine the location and extent of karstic rock; bedrock geology and depth to bedrock; average water-table configuration; surficial geology; soil type, thickness, and hydraulic conductivity; land cover; and closed depressions in the land surface. Repeated glaciation and recession across New York have left the landscape pockmarked with closed depressions, which may or may not be related to the underlying bedrock. Closed depressions in areas where carbonate or evaporite karst are present are of primary concern to this study because of the increased potential of karst aquifer contamination from focused recharge. Closed depressions present in areas not associated with karst bedrock can also be evaluated to better understand their ability to transmit surface water to the groundwater system. Information on closed depressions can be used to develop land-management plans to protect local and regional water resources.

New York↗
USGS2018

Annual and approximately quarterly series peak streamflow derived from interpretations of indirect measurements for a crest-stage gage network in Texas through water year 2015

In 2006, the U.S. Geological Survey (USGS), in cooperation with the Texas Department of Transportation, began collecting annual and approximately quarterly series peak-streamflow data at streamflow-gaging stations in smallto medium-sized watersheds in central and western Texas as part of a crest-stage gage (CSG) network, along with selected flood-hydrograph data at a subset of these stations. CSGs record the peak stage during storm events, which is the maximum gage height (elevation of water surface above a local vertical datum), at each CSG station. Established and widely used indirect methods of peak streamflow estimation and interpretation, such as culvert-flow, slope-area, and flow-over-road methods, are used in conjunction with peak gage height data to create the database of peak streamflow described herein. The CSG network is focused on hydrology of small- to medium-sized watersheds in central and western Texas because additional streamflow data for this semiarid to arid study area will eventually provide for more statistical information and presumably reduced uncertainty in regional regression equations or other regionalized statistical methods for peak-streamflow frequency estimation at ungaged locations. The database of annual and approximately quarterly peak streamflow is published through USGS ScienceBase and described in this report.

Texas↗
USGS1975

National Cartographic Information Center Newsletter No. 1

This is the first of what we hope will become a continuing series of quarterly NCIC newsletters. You, the reader, are encouraged to make comments, offer praise or criticism as the occasion warrants, send in suggestions, and contribute information or articles. In this issue, we plan to present information on NCIC's operating concepts, systems, and data base and several data acquisition notes. We also have a few words on our future plans along with a brief article on our current microfilming program and a general organizational chart designed to introduce our key personnel. We realize that with such a large amount of basically introductory material our first issue is going to be a bit on the heavy side. Bear with us now and we promise a more traditional format with a lighter editorial touch in the future.

Newsletter↗
USGS2002

Analysis of nitrate (NO3-N) concentration trends in 25 ground-water-quality management areas, Idaho, 1961-2001

In Idaho, drinking-water supplies are pumped from relatively shallow ground-water zones where water quality has great potential for degradation by land- and water-use activities. One indicator of water quality, and one of the most widespread contaminants in Idaho ground water related to land and water uses, is dissolved nitrate. In December 2000, the U.S. Geological Survey, in cooperation with the Idaho Department of Environmental Quality, began a study to compile and assess nitrate data for ground water in 25 ground-water-quality management areas in Idaho. The primary objective of the study was to determine whether statistically significant trends in ground-water concentrations were discernible. Data included ground-water analyses but not analyses of water from springs, drains, or thermal water sources. A total of 8,465 nitrate analyses were compiled from 2,931 wells in the 25 priority areas; analyses dates ranged from June 1961 to February 2001. A time-period comparison was used to assess general trends in nitrate concentrations within individual priority areas. A time-series comparison was used to assess trends in nitrate concentrations from selected wells in each priority area. In time-period assessments, general trends in an area were evaluated by compiling nitrate data for selected time intervals to determine whether the population distributions were significantly different between one period and another. Data within each priority area were sorted into decades— 1970s, 1980s, and 1990s—for long-term trend assessment. The 1990s data also were divided into sets of selected years corresponding to Statewide Ambient Ground-Water Quality Program sampling cycles—1991 through 1994, 1995 through 1998, and a partial cycle, 1999 through 2000—for shortterm trend assessment. Data were analyzed by summary statistics, boxplots, and the Mann- Whitney statistical test. Long-term increasing trends in nitrate concentrations were evident for 6 of 25 priority areas, and long-term decreasing trends were evident for 4 of 25 areas. Short-term increasing trends were evident for 7 of 25 areas, and a short-term decreasing trend was evident for only 1 area. No long-term nitrate trends were evident for 7 of 25 areas, and no shortterm trends were evident for 15 of 25 areas. Data were insufficient for long-term trend assessment in 8 areas and for short-term assessment in 2 areas. Time-series trend analyses were conducted on data from wells with 7 or more nitrate analyses and longest periods of record, at least 10 years between oldest and most recent analyses. Because long-term records were available for so few wells and well construction data were not available for several of these wells, time-series analyses were not helpful to the nitrate trend assessment study. Trend results may be strongly affected by well construction, hydrogeologic environments, and changes in density and areal distribution of wells and analyses. The utility of nitrate trend assessments in priority areas would be improved by more consistent and specific well location descriptions between agencies; well construction and major water-yielding zone information to accompany the water-quality data for each well; and addition of historical nitrate data to data bases, particularly analyses prior to about 1990. Investigations of the possible effects of changing priority area boundaries and time periods on both long-term and short-term trend assessments are needed. Addition of these kinds of information would allow assessment of trends associated with hydrology and geology of each area and would provide a much stronger basis for trend assessment than currently possible.

Idaho↗