Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

View Data for Nitrate in Streams View Data for Ecosystem Comparison, Nitrate in Streams

What Is This Indicator, and Why Is It Important? This indicator reports on the concentration of nitrate in representative streams in forested areas. Specifically, the indicator reports the percentage of streams with average nitrate concentrations in one of four ranges, for streams draining watersheds that are primarily forested.

Nitrate is a naturally occurring form of nitrogen and an important plant nutrient; it is often the most abundant of the forms of nitrogen that are readily usable by plants, including algae. Increased nitrate in streams that ultimately empty into coastal waters can lead to algal blooms in those waters, which can decrease recreational and aesthetic values and help deplete oxygen needed by fish and other animals (see the national nitrogen indicator and the hypoxia indicator). Elevated nitrate in drinking water can also cause human health problems.

Elevated amounts of nitrate in streams are a sign that inputs from human sources have increased or that that plants in the system are under stress. Nitrogen is a critical plant nutrient, and most nitrogen, including nitrate, is used and reused by plants within an ecosystem. Thus, in undisturbed forested ecosystems, there is relatively little “leakage” into either surface runoff or groundwater, and concentrations are very low. Elevated stream nitrate might come from land clearing, the use of fertilizer in the watershed, or from rain and snowfall (in the form of acid rain).

What Do the Data Show? Almost all forest stream sites (97%) had nitrate concentrations below 1 part per million (ppm), more than three-fourths had concentrations of less than 0.5 ppm, and more than half had concentrations of less than 0.1 ppm. Most streams in urban/suburban areas also have low average nitrate concentrations (less than 2 ppm), while farmland streams have the highest nitrate concentrations (see nitrate in farmlands streams and nitrate in urban and suburban streams). There is also a core national indicator for nitrogen (movement of nitrogen).

The federal drinking water standard for the protection of human health is 10 ppm of nitrate, which is exceeded only in agricultural areas (nitrate in farmlands streams and groundwater).