Nitrogen or #nitrate contamination of drinking and surface water poses serious health risks, and can result from agricultural runoff in rivers. It is often associated with algal blooms as well. Also see the topic #phosphate. ## Nitrogen: Nitrates, Nitrite, Ammonia, & Ammonium (moved from the [Common Water Contaminants page](/common-water-contaminants)) Nitrates, Nitrite, Ammonia, & Ammonium are all "fixed" forms of nitrogen available to living organisms, and represent different stages of nitrogen in the [nitrogen cycle.](https://en.wikipedia.org/wiki/Nitrogen_cycle) Nitrogen is a major limiting nutrient in plant growth-- when nitrates occur in large quantities in water from fertilizers, manure, or sewage runoff, they can cause algal blooms that create dead zones. Nitrates have also been linked to increased risks of [cancer, and complications with a number of diseases, including asthma](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1310926/). The EPA limits drinking water concentrations of Nitrates to 10mg/L or lower, however, health threats can occur even at those levels. Ammonia (NH3) and ammonium ion (NH4+) are related chemically by an acid / base reaction: `NH3 + H+ <=> NH4+` The equilibrium between ammonia and ammonium is pH dependent, with the two species being at the same concentration only under fairly alkaline conditions, pH = 9.25. At neutral pH, the concentration of free NH3 is less than 1% that of NH4+. Since this is the case, the concentration of ammonia is usually not significant and can be determined from the concentration of ammonium and the pH. **** ## Questions Questions can be either frequently asked questions, or "next step" challenges we're looking to solve. [questions:nitrogen] ## Activities [activities:nitrogen] ...