Overview:

The U.S. Geological Survey (USGS) nutrient enrichment studies are planned and implemented through the National Water-Quality Assessment (NAWQA) Program. In 2001, the NAWQA Program began an intensive study of nutrient enrichment—elevated concentrations of nitrogen and phosphorus—in streams in agricultural basins across the Nation. Five study units were began in 2002 (Group 1), with three additional study units added in 2005 (Group 2).

This study is providing nationally consistent and comparable data and analyses of nutrient conditions, including how these conditions vary as a result of natural and human-related factors, and how nutrient conditions affect algae and other biological communities. This information will benefit stakeholders, including the U.S. Environmental Protection Agency (USEPA) and its partners, who are developing nutrient criteria to protect the aquatic health of streams in different geographic regions.

Objectives of the Nutrient Enrichment Study

1. Determine the total algal biomass and the abundance, type, and diversity of algal and aquatic invertebrate communities in streams with different nutrient conditions, watershed characteristics, habitat, climate, and other natural factors.
2. Determine the interrelations among nutrient conditions, algal communities, and stream metabolism, which is defined as the gain and loss in dissolved oxygen associated with photosynthesis and plant and animal respiration. Adequate levels of dissolved oxygen are critical to fish and other aquatic life.
3. Determine the transport, chemical transformation, and retention of nutrients (referred to as "nutrient cycling") in the water column and surrounding sediments, and resulting effects on biological communities in stream reaches. Such cycling differs in different geologic and hydrologic settings, and is controlled, in large part, by ground-water and surface-water interactions.
4. Determine the extent to which associations between nutrient conditions and biological communities occur over geographic regions that share common natural features, landscape characteristics, and biological communities.

Large-Scale Synoptic Studies

Streamflow, nutrient concentrations and other chemical characteristics, dissolved-oxygen concentrations, biological communities, and stream and riparian habitat are assessed at 25-30 sites within each Study Unit. Data from these one-time "snapshot" assessments will be used to define relations among nutrients, stream metabolism, and biological communities in diverse environmental settings (study objectives 1 and 2), and to aid in statistical analyses for regionalization of nutrient conditions (objective 4).

Small-Scale Process Studies

Processes controlling stream metabolism and nutrient cycling (which includes transport, transformation, and retention) are being assessed in a single stream reach within three of the five Study Units. These more detailed, small-scale studies will help to determine the effects of these processes on biological communities (objectives 1 and 2), and help to identify environmental settings that have chemical, physical, and biological characteristics associated with nutrient enrichment (objective 4)

National priority topics to be addressed in the second decade of NAWQA studies

• Effects of nutrient enrichment on stream ecosystems (NEET)
• Effects of urbanization on stream ecosystems (EUSE)
• Bioaccumulation of mercury in stream ecosystems (HG)
• Transport of contaminants to public-supply wells (TANC)
• Sources, transport, and fate of agricultural chemicals (ACT)