Nutrient enrichment and criteria

Nuisance plant growth is noted in streams across the nation because of elevated concentrations of nutrients. In fact, concentrations of phosphorus exceeded the USEPA desired goal for phosphorus for preventing nuisance plant growth in streams (0.1 parts per million) in about 75 percent of agricultural and urban streams sampled by the NAWQA Program. It is difficult and premature, however, to attempt a national summary of the effects of eutrophication because methodologies are limited for deriving criteria based only on nutrient concentrations. In recognition of these limitations, USEPA, in collaboration with USGS and other federal agencies, and state agencies, is developing a strategy to evaluate aquatic plant growth and to develop an understanding of stream nutrient dynamics, stream habitat (including shading and temperature), turbidity, and algal-growth processes.

We will work with states and tribes to develop a methodology for deriving criteria, as well as developing criteria where data are available, for nitrogen and phosphorus runoff for lakes, rivers, and estuaries by the year 2000. We intend to develop such criteria on a regional basis using scientifically defensible data and analysis of nutrients, such as those available from the USGS. We will assist states and tribes in adopting numerical nutrient criteria as water-quality standards by the end of 2003 (Robert Cantilli, Nutrients Criteria Coordinator, USEPA, U.S. Geological Survey Circular 1225, 1999).

NAWQA also works with individual states on nutrient standards and criteria.

State of Louisiana—USGS works with the Louisiana Department of Environmental Quality to develop nutrient criteria using NAWQA information on chlorophyll a in the Acadian-Pontchartrain Basins. According to Louisiana Department officials, "The largest, most consistent source of chlorophyll a data for Louisiana comes from NAWQA sites.”

State of Texas—NAWQA data for nutrients collected in the Trinity River Basin are used by the Trinity River Authority to develop nutrient criteria for streams.

Factors affecting nutrient enrichment

NAWQA information is used to assess factors affecting eutrophication, both regionally and locally.

Mississippi River Basin and the Gulf of Mexico— NAWQA scientists participate in a multi-agency effort, coordinated by the White House Committee on Environmental Natural Resources (CENR), to assess nutrient enrichment, eutrophication, and the effects of hypoxia (low oxygen conditions) in the Gulf of Mexico. Specifically, NAWQA is modeling sources and transport of nutrients using a spatially referenced computer model throughout the Mississippi River watershed. The model tracks the sources (including point sources, fertilizer, livestock wastes, nonagricultural land, and atmospheric deposition) and movement of nutrients in individual stream reaches across the watershed. The effort has demonstrated key roles that hydrology and natural processes play in the transport of nutrients to, and eutrophication in, the Gulf of Mexico. Specifically, closer proximity of nitrogen sources to large streams and rivers increases the transport of nutrients to the Gulf. This is because nitrogen is not removed as readily in the large streams and rivers by natural processes as in the smaller tributaries and is, therefore, much more likely to reach a coastal area if it originates close to a larger river. As a result, some watersheds in the Mississippi River Basin are much more significant contributors of nitrogen to the Gulf of Mexico than others, despite similar nitrogen sources or similar distances from the Gulf.

State of North Carolina—NAWQA findings are used by the North Carolina Department of Environment and Natural Resources to help control excessive nutrients and resulting algal blooms, fish kills, and Pfiesteria incidents in the Neuse and Tar-Pamlico Rivers. For example, the findings led to the implementation of buffers in the Neuse River, which proved to effectively reduce nutrient runoff to the surface water. In addition, NAWQA research on the role of organic matter in streambed sediment in removing nitrate from ground water in some areas of the Coastal Plain has allowed the State to prioritize its efforts in streams where elevated nitrate is not as easily removed under natural conditions.

The St. Croix National Scenic Riverway (NSR) was established in 1968 under the National Wild and Scenic Rivers Act. In the early 1990’s continued development and usage of the St. Croix River concerned water resource managers about the impact on water quality. Research from the NAWQA Program provided evidence that nutrient loading from the tributaries was increasing the rate of eutrophication in Lake St. Croix, a sink of the St. Croix River Basin. In response to these threats, a cooperative agreement was signed in 1993 by the National Park Service, the Minnesota Department of Natural Resources, the Wisconsin Department of Natural Resources, and the Minnesota Pollution Control Agency. To date, the partnership that was formed (St. Croix Basin Water Resources Planning Team) has relied heavily on data from NAWQA to implement a protection strategy for the St. Croix River (Pam Davis, Coordinator, St. Croix Basin Water Resource Planning Team, March 2001).