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Nutrients are a potential concern for aquatic life

U.S. Geological Circular 1225--The Quality of Our Nation's Waters--Nutrients and Pesticides


Nitrogen and phosphorus have different effects on aquatic plant growth in freshwater and saltwater. Eutrophication of freshwater streams generally results from high phosphorus concentrations. In contrast, excess nitrogen, and nitrate in particular, can lead to algal blooms in coastal waters. The USEPA suggests a desired goal of 0.1 mg/L total phosphorus for freshwater streams, but there are no national criteria established for nitrogen concentrations to control excessive aquatic plant growth in coastal bays and estuaries.

Average annual and average monthly concentrations of un-ionized ammonia did not exceed USEPA aquatic-life criteria for most streams sampled. Exceptions include an agricultural stream affected by upstream wastewater treatment plant effluent in the San Joaquin-Tulare Basins and two urban streams, one in the South Platte River Basin and another in the Nevada Basin and Range. The urban streams, which are in relatively arid climates and exceeded the criteria year-round, also received effluent from wastewater treatment plants.


Eutrophic conditions were noted in some streams across the Nation because of elevated concentrations of nutrients. For example, the average annual concentration of total phosphorus in 57 percent of all streams sampled was greater than the USEPA desired goal of 0.1 mg/L for preventing nuisance plant growth in streams. In addition, about 75 percent of agricultural and urban streams exceeded this goal. It is difficult and premature, however, to attempt a national summary of eutrophication effects because of limited available methodologies for deriving criteria based only on nutrient concentrations. Moreover, the uncertainty regarding how nutrient contamination of streams harms aquatic life and affects nuisance plant growth does not lessen the value of accurate information for management of our Nation's streams. A strategy, spearheaded by the USEPA in collaboration with other Federal and State agencies, is underway to evaluate excessive aquatic plant growth, such as algae, in surface water. This strategy includes an understanding of stream nutrient dynamics, stream habitat (including shading and temperature), turbidity, and algal-growth processes.

Study-basin boundary
Un-ionized ammonia concentrations exceeded USEPA criteria for protection of aquatic life in Las Vegas Wash, Nevada, downstream from wastewater treatment plant discharges. Concentrations in all samples collected from April 1993 to April 1995 exceeded the criteria. The median ammonia concentration downstream from wastewater treatment plant discharges was more than 100 times the median value upstream from the discharges. Downstream ammonia concentrations decreased fivefold during 1996-97, following full implementation of tertiary treatment of wastewater, and USEPA criteria probably are no longer exceeded at this site.


"As part of the Clean Water Action Plan, the Vice President called upon USEPA to accelerate development of nutrient water-quality criteria for beneficial ecological uses in every geo-graphic region in the country. 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

Total phosphorus

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In April 1994, total phosphorus concentrations in the South Platte River exceeded the USEPA desired goal for preventing plant nuisances (0.1 mg/L) in a 150-mile reach downstream from Denver, Colorado.

Photo by Larry J. Puckett

Large amounts of nitrate enter the Chesapeake Bay from the Susquehanna River. Nitrate concentrations in the Susquehanna River at Harrisburg, Pennsylvania, generally were less than 2 mg/L. However, these concentrations, when multiplied by the large flows of the Susquehanna River, contribute large amounts of nitrate to Chesapeake Bay (especially compared with other rivers entering the bay) and provide enough nitrate to stimulate algal growth and affect the bay ecosystem.


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