Colorado NASQAN

1. Purpose and Objectives: Since 1995, the National Stream Quality Accounting Network (NASQAN) of the USGS, has focused on monitoring the water quality of some of the nation’s largest rivers, including the Colorado. NASQAN operates a network of 39 stations where the concentration of a broad range of chemicals, including pesticides and trace elements, and stream discharge are measured. From these data, source contaminants can be identified; contaminants can be routed through the river system to determine gains and losses; and the amount of contaminants delivered to receiving waters— such as estuaries and reservoirs—can be estimated. NASQAN data provide information on the influence of large-scale environmental processes and human activities on these rives that serve as drinking-water supplies, navigational routes, recreational areas, and biological habitats.

2. Funding: Since the NASQAN project involves the nation’s four largest rivers-- Mississippi, Colorado, Rio Grande, and the Columbia—it would be difficult to compute an estimate for a single river. However, the network, or the NASQAN overall, gets about $5 million annually.

3. Partners: USGS

4. Description and Background: NASQAN today, is markedly different from the program that was operated before 1995. NASQAN was begun in 1973 to provide nationally comparable information on water quality. Consistent with the design of the national streamflow-gauging network, water quality measurements were made at stations at the downstream end of most hydrologic accounting units; hence, the term accounting in the network name. More than 500 stations sampled on a monthly basis for suspended sediment, major ions (such as sulfate and chloride), trace elements (such as lead), nutrients (such as nitrate), sanitary indicators (such as fecal chloroform), and limited biological information (such as chlorophyll-a). These data were intended to provide general purpose information on the status and trends of water quality.

5. Methodology of Sampling: NASQAN stations are sampled frequently enough to characterize variations in chemical and sediment concentrations that occur during a year, particularly the variation that occurs between low and high lows, during different seasons of the year, and during different hydrologic regimes—such as periods when snowmelt dominates river discharge. By sampling a river under these different conditions, the amount of material that passes a station, known as the mass-flux of a constituent (expressed as tons per day), can be reliably determined by multiplying the concentration of a constituent by the stream discharge. Constituent mass fluxes can be compared among stations and across spatial scales. For example, yields of contaminants (in tons per sq. mi.) can be compared between stations; gains or losses in a river reach can be determined between any two stations; and amounts of materials delivered to a reservoir or estuary can be calculated. The ability to determine these three values—source, transport, and delivery of constituents—enables a broad range of scientific and policy issues to be addressed.

6. Status: The Program is Ongoing.

7. U.S. Contacts: Charles Heywood, USGS, (505) 262-5351; Fax: (505) 262-5298 Albuquerque, NM

For more complete information, see the USGS NASQAN website: http://water.usgs.gov/public/nasqan