No abstract

The U.S. Geological Survey (USGS) is committed to providing the Nation with reliable scientific information that helps to enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the Nation's water resources is critical to ensuring long-term availability of water that is safe for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife. Population growth and increasing demands for water make the availability of that water, measured in terms of quantity and quality, even more essential to the long-term sustainability of our communities and ecosystems. The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support national, regional, State, and local information needs and decisions related to water-quality management and policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed to answer: What is the quality of our Nation's streams and groundwater? How are conditions changing over time? How do natural features and human activities affect the quality of streams and groundwater, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. From 1991 to 2001, the NAWQA Program completed interdisciplinary assessments and established a baseline understanding of water-quality conditions in 51 of the Nation's river basins and aquifers, referred to as Study Units (http://water.usgs.gov/nawqa/studies/study_units.html). National and regional assessments are ongoing in the second decade (2001-2012) of the NAWQA Program as 42 of the 51 Study Units are selectively reassessed. These assessments extend the findings in the Study Units by determining water-quality status and trends at sites that have been consistently monitored for more than a decade, and filling critical gaps in characterizing the quality of surface water and groundwater. For example, increased emphasis has been placed on assessing the quality of source water and finished water associated with many of the Nation's largest community water systems. During the second decade, NAWQA is addressing five national priority topics that build an understanding of how natural features and human activities affect water quality, and establish links between sources of contaminants, the transport of those contaminants through the hydrologic system, and the potential effects of contaminants on humans and aquatic ecosystems. Included are studies on the fate of agricultural chemicals, effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment on aquatic ecosystems, and transport of contaminants to public-supply wells. In addition, national syntheses of information on pesticides, volatile organic compounds (VOCs), nutrients, trace ...

To improve understanding of the factors affecting pesticide occurrence in ground water, patterns of detection were examined for selected herbicides, based primarily on results from the National Water-Quality Assessment (NAWQA) program. The NAWQA data were derived from 2,227 sites (wells and springs) sampled in 20 major hydrologic basins across the USA from 1993 to 1995. Results are presented for six high-use herbicides--atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), cyanazine (2-[4-chloro-6-ethylamino-1,3,5triazin-2-yl]amino]-2-methylpropionitrile), simazine (2-chloro-4,6-bis-[ethylamino]-s-triazine), alachlor (2-chloro-N-[2,6-diethylphenyl]-N-[methoxymethyl]acetamide), acetochlor (2-chloro-N-[ethoxymethyl]-N-[2-ethyl-6-methylphenyl]acetamide), and metolachlor (2-chloro-N-[2-ethyl-6-methylphenyl]-N-[2-methoxylethyl]acetamide)--as well as for prometon (2,4-bis[isopropylamino]-6-methoxy-s-triazine), a nonagricultural herbicide detected frequently during the study. Concentrations were <1 microg L(-1) at 98% of the sites with detections, but exceeded drinking-water criteria (for atrazine) at two sites. In urban areas, frequencies of detection (at or above 0.01 microg L(-1)) of atrazine, cyanazine, simazine, alachlor, and metolachlor in shallow ground water were positively correlated with their nonagricultural use nationwide (P < 0.05). Among different agricultural areas, frequencies of detection were positively correlated with nearby agricultural use for atrazine, cyanazine, alachlor, and metolachlor, but not simazine. Multivariate analysis demonstrated that for these five herbicides, frequencies of detection beneath agricultural areas were positively correlated with their agricultural use and persistence in aerobic soil. Acetochlor, an agricultural herbicide first registered in 1994 for use in the USA, was detected in shallow ground water by 1995, consistent with previous field-scale studies indicating that some pesticides may be detected in ground water within 1 yr following application. The NAWQA results agreed closely with those from other multistate studies with similar designs.

Information on the amount and distribution of pesticide compounds used throughout the United States is essential to evaluate the relation between water quality and pesticide use. This information is the basis of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program studies of the effects of pesticides on water quality in 57 major hydrologic systems, or study units, located throughout the conterminous United States. To support these studies, a method was devised to estimate county pesticide use for the conterminous United States by combining (1) state-level information on pesticide use rates available from the National Center for Food and Agricultural Policy, and (2) countylevel information on harvested crop acreage from the Census of Agriculture. The average annual pesticide use, the total amount of pesticides applied (in pounds), and the corresponding area treated (in acres) were compiled for the 208 pesticide compounds that are applied to crops in the conterminous United States. Pesticide use was ranked by compound and crop on the basis of the amount of each compound applied to 86 selected crops. Tabular summaries of pesticide use for NAWQA study units and for the Nation were prepared, along with maps that show the distribution of selected pesticides to agricultural land. Information on agricultural pesticide use is available from several national and state pesticide use surveys and reports, along with a variety of research reports on specific crops or states. The type and detail of data that are reported varies widely between federal and state programs, making it difficult to rely on a single source for complete information. Three examples of such programs are the U.S. Department of Agriculture's (USDA) National Agricultural and Statistics Service (NASS), the Census of Agriculture, and the state of California's Department of Pesticide Regulation. The NASS provides state summaries of pesticide use annually for major field crops, which include corn, wheat, soybeans, cotton, potatoes, and, in selected years, peanuts, rice, sorghum, and tobacco. NASS conducts a second survey that targets specialty crops, alternating yearto-year between vegetables (even-numbered years) and fruit and nut crops (odd-numbered years). The NASS data are based on a statistical sample of farms in states that account for at least 80 percent of United States production for a specific crop. Summaries of the average application rates of major pesticide ingredients and the percentage of crop area (in acres) treated are published annually by NASS. In comparison, the United States Census of Agriculture conducts a survey every 5 years of all farms within the United States that have an annual farm income of $1,000 or more. This enumeration includes information on the type, quantity, and cost of agricultural chemicals used on each farm. The data, reported by county, include the number of farms and the number of acres on which broad classes of chemicals are used (for example, herbicides and insecticides). In contrast, the Ca...

Landsat multispectral-scanner data have been used to map irrigated cropland for determination of water use from the High Plains aquifer. Water-use estimates have provided one critical element in a groundwater flow model being developed by the U.S. Geological Survey. Information on irrigeited acreage and water use is needed to evaluate the effects of agricultural development on the High Plains aquifer. The High Plains aquifer is the primary source of water for one of the Nation's major agricultural areas covering about 174,000 square miles within parts of eight States. Several methods for determining irrigated acreage were evaluated. Digital analysis of Landsat data proved to be the most suitable approach and was used in a two-phase effort to map irrigated acreage for both the 1978 and 1980 growing seasons. The first phase, a test of analysis procedures, used 1978 Landsat data to map the majority of the High Plains. The test used a cluster-analysis technique to derive acreage estimates of irrigated cropland, nonirrigated cropland, and rangeland using 35 summer Landsat scenes. Based on the first-phase test results, several modifications were made to streamline and improve analysis techniques for the second-phase mapping of irrigated cropland using 1980 Landsat data. The analysis of 1980 data used a ratio technique to analyze the 59 spring and summer Landsat scenes required to provide acreage estimates for the major irrigated crops on the High Plains. Acreage estimates of irrigated cropland, nonirrigated cropland, and rangeland were aggregated to form a data base containing about 174,000 grid cells measuring 1 minute of latitude by 1 minute of longitude. Percentages for each land-use type were calculated and combined with sampled irrigation-application rates to compute estimates of irrigation water use for the groundwater flow model. An estimated 17,980,000 acre-feet of ground water was pumped from the High Plains aquifer during the 1980 growing season to irrigate 13,700,000 acres. To verify the reliability of the irrigated-acreage estimates used to calculate water use, an accuracy evaluation was conducted for the 1980 mapping of irrigated cropland using a multistage random-sampling method. The statistical evaluation confirmed that Landsat data and simple analysis techniques can provide an efficient tool for mapping irrigated cropland for the High Plains. However, availability of suitable Landsat scenes is required to provide a complete inventory of irrigated cropland. The techniques used to map irrigated cropland for the High Plains should be applicable to similar areas of the Western United States.