Nitrate in Groundwater | Sustainability Indicators

What is it?

Human alteration of nutrient cycles has resulted in many watersheds being highly enriched in certain elements, specifically nitrogen, phosphorus, and/or sulfur. Among other reasons, this is frequently a result of agricultural practices which use nitrogen and phosphorus enriched fertilizers to increase crop yield (Vitousek et al. 1997a, Vitousek et al. 1997b) or sulfur-based fungicides, which subsequently wash into the riverine systems. Nutrients (nitrogen and phosphorus) were consistently one of the top pollutants on the CWA Section 303(D) Lists to Congress Reports beginning in the early 1990’s, but “excess” concentrations of nutrients vary by waterbody type, climate, geologic areas, and other local risk cofactors (e.g., degraded riparian). Therefore, Nutrient Criteria cannot be developed as a single number for the U.S., or CA, due to variability in background conditions and the role of other risk co-factors which affect nutrient processing within ecosystems. California does have a threshold for drinking water nitrate of 10 mg/L (ppm) in surface and groundwater sources.

Why is it important?

Human alteration of nutrient cycles has resulted in many watersheds being highly enriched in certain elements, specifically nitrogen, phosphorus, and/or sulfur. Among other reasons, this is frequently a result of agricultural practices which use nitrogen and phosphorus enriched fertilizers to increase crop yield (Vitousek et al. 1997a, Vitousek et al. 1997b) or sulfur-based fungicides, which subsequently wash into the riverine systems. Nutrients (nitrogen and phosphorus) were consistently one of the top pollutants on the CWA Section 303(D) Lists to Congress Reports beginning in the early 1990’s, but “excess” concentrations of nutrients vary by waterbody type, climate, geologic areas, and other local risk cofactors (e.g., degraded riparian). Therefore, Nutrient Criteria cannot be developed as a single number for the U.S., or CA, due to variability in background conditions and the role of other risk co-factors which affect nutrient processing within ecosystems. California does have a threshold for drinking water nitrate of 10 mg/L (ppm) in surface and groundwater sources.

What can Influence or Stress Condition?

Nitrogen is one of the most essential elements for plant reproduction and growth, so the amount of available nitrogen can strongly limit plant productivity. At first glance, nitrogen limitation may be counterintuitive, since 78% of the atmosphere is composed of nitrogen gas (N2). Yet N2, and most forms of nitrogen found in terrestrial ecosystems, is not directly available to plants. Plants therefore rely on nitrogen fixing organisms to transform N2 into bioavailable forms. Consequently, although nitrogen is abundant, many natural systems are nitrogen limited. To get around this limitation, humans developed the Haber-Bosch process to artificially produce bioavailable nitrogen that can be used in fertilizers to increase productivity in cultivated crops. Fertilizers must be continuously reapplied because crops take up some the added nitrogen, and leaching causes the movement of nutrients out of the topsoil via entry into groundwater or storm-water runoff. As this nitrogen moves into nearby waterways, it can accumulate and at higher than natural concentrations. Through these processes along with other sources such as urban effluent and atmospheric deposition, humans have roughly doubled the amount of fixed nitrogen, and this alteration may have drastic consequences for ecological systems (Houlton).

Target or Desired Condition

For nitrate we used 10 ppm for a target for poor condition (score = 0).