U.S. GEOLOGICAL SURVEY DIGITAL DATA SERIES 37 Data from Selected U.S. Geological Survey National Stream Water-Quality Monitoring Networks (WQN) [This is the \DOCFILES\OVERVIEW.TXT file] BACKGROUND During the past 30 years, the U.S. Geological Survey (USGS) has operated two national stream water-quality networks, the Hydrologic Benchmark Network (HBN) and the National Stream Quality Accounting Network (NASQAN). In these networks, the USGS systematically monitored streams in watersheds throughout the United States to provide national and regional descriptions of stream water-quality conditions and trends and to improve our understanding of the effects of the natural environment and human activities on water quality. The HBN, consisting of 63 relatively small, minimally-disturbed watersheds, provides data for investigating naturally-induced changes in streamflow and water quality and the effects of airborne substances on water quality. NASQAN, consisting of 618 larger, more culturally-influenced watersheds, provides information for tracking water-quality conditions in major U.S. rivers and streams. The watersheds in both networks include a diverse set of climatic, physiographic, and cultural characteristics. Data from the networks have been used to describe geographic variations in water-quality concentrations, quantify water- quality trends, estimate rates of chemical flux from watersheds, and investigate relations of water quality to the natural environment and anthropogenic contaminant sources. Much of the historical water-quality data collected by the NASQAN and HBN and supporting documentation and quality-assurance information have been assembled in an easy-to-use format on two CD-ROMs. These data are collectively referred to as Water-Quality Networks (WQN). The data retrieval tools and ancillary information provided on the CD-ROMs allow for the efficient and proper use of WQN data. The CD-ROMs are designed to allow users to efficiently browse text files and retrieve data for subsequent use in user-supplied software including spread-sheet, statistical analysis, or geographic information systems. The data may be extracted from one of the CD-ROMs (the "DOS disc") using the supplied DOS-based software, and output in a variety of formats. This software allows the user to search, retrieve, and output data according to user-specified criteria. Alternatively, the ASCII form of the WQN data may be accessed on a second CD-ROM (the "ASCII disc") from user-supplied software including Web browser, spreadsheet, or word processor. CONTENTS OF THE WQN DATA BASE The WQN data base contains water-quality and streamflow data collected at 679 locations in the United States including 63 HBN stations from 1962-95 and 618 NASQAN stations from 1973-95 (two stations have belonged to both networks during the period of operations). The water-quality data includes a set of 63 physical, chemical, and biological properties analyzed during more than 60,000 stream visits using relatively consistent sampling and analytical methods. The water-quality data reflect sampling over a wide range of streamflow conditions. [Note that the number of water-quality analyses has changed over time because of changes in sampling frequency and the number of stations and water constituents; see the accompanying Open-File Report for details] Supporting information identifies and describes the water- quality and streamflow stations, water-quality constituents, and the methods, remarks, laboratories, sample collection agencies, and the laboratory measurement accuracy associated with the WQN data. The WQN data include the following: o Uniformly-sampled (i.e., semiannually to monthly) stream water-quality data for 63 physical, chemical, and biological properties (122 water constituents including the dissolved, suspended, and total forms). These data include physical/field measurements (e.g., temperature, instantaneous streamflow, pH, suspended sediment), major ions, nutrients, organic carbon, radiochemicals biological measurements (e.g., fecal bacteria, phytoplankton, and periphyton), and inorganic trace elements. With the exception of the periphyton data, which reflect substrate conditions, all measurements reflect conditions in the water column. o Daily mean records of streamflow for time periods corresponding to the water-quality data. These data can be used with the water-quality data to derive estimates of flux. o Water-quality and streamflow station attributes including drainage area, latitude, longitude, the dates of station operation, county, state, and hydrologic unit code (HUC) identifiers, and drainage basin population for 1990 and land-cover statistics for 1987. o The sample collection agencies, laboratories, and laboratory analytical methods associated with the stream water-quality data. In addition to national network documents describing these characteristics, information on the collection agencies, laboratories, and analytical methods have been stored in the water-quality digital data files on a frequent basis since the early to mid 1980s. o Laboratory quality-control data for 34 chemical constituents that can be used to evaluate the measurement bias and variability of national network stream water-quality data for the period 1985-95. The quality-control data were collected through the Blind Sample Program, a USGS program that regularly monitors the quality of laboratory analytical results through the use of stable, homogeneous standard reference water samples. o Documentation of changes in field and laboratory methods, constituent coverage, network operations, reporting conventions, and sample contamination that may affect the use and interpretation of WQN stream water-quality data. This includes USGS water- quality memoranda documenting national network operations and important changes in field and laboratory methods. o A report that discusses the history of the national networks, characteristics of the water-quality, streamflow, and quality- assurance data, and statistical methods for using laboratory quality- control data to evaluate the accuracy of stream water-quality measurements [The accompanying report is entitled "Data from Selected U.S. Geological Survey National Stream Water- Quality Monitoring Networks (WQN) on CD-ROM" by R.B. Alexander, A.S. Ludtke, K.K. Fitzgerald, and T.L. Schertz, U.S. Geological Survey Open-File Report 96-337.] o A bibliography of publications on national network field and laboratory methods, network characteristics, summaries and interpretations of network data at the national, regional, and local levels, and statistical and computer software methods that have been developed for use with data having characteristics similar to those of the national network data.