Nitrate (NO₃) and Nitrite (NO₂)
Nitrite and nitrate are sources of nitrogen (N), an important nutrient for plants and algae. As ammonia (NH₃) is broken down by bacterial action, nitrite is formed and is then converted to the more stable, much less toxic nitrate through a process called "nitrification."

Nitrate and Nitrite in Water
The typically low natural levels of nitrate in surface water can be supplemented with nitrate from human sources. Nitrate from the fertilizer not taken up by crops in fields and grass in lawns can enter water bodies in runoff. Nitrate can also enter water bodies from wastewater discharge or runoff from feedlots. Once in the water, nitrates can stimulate excessive plant and algae growth. Decomposition of the plant and algal material by bacteria can deplete dissolved oxygen (DO), adversely impacting fish and other aquatic animals.

As early as 1940, it was recognized that consuming waters with high nitrate levels contributed to methemoglobinemia ("blue baby" syndrome). This condition, usually in infants, impairs the ability of blood to carry oxygen. The U.S. Environmental Protection Agency (EPA) National Primary Drinking Water Standards require that nitrate nitrogen not exceed 10 mg/L in public water supplies. Nitrite, much more toxic than nitrate, is regulated at a level not to exceed 1.0 mg/L in public water supplies.

Nitrate and Nitrite in the Red River
Nitrate is regulated to protect human health as well as aquatic environments. The Minnesota Pollution Control Agency (MPCA) uses the EPA limits of 10 and 1.0 mg/L for nitrate and nitrite nitrogen, respectively, in drinking water supplies. The North Dakota Department of Health (NDDH), on the other hand, has established what it intends as an interim guideline limit of 1.0 mg/L nitrate nitrogen. NDDH is reserving the right to review this standard after additional study and to set specific limitations for constituents that cause excessive plant growth in surface water. NDDH states that in no case shall the standard for nitrate nitrogen ever exceed 10 mg/L for any waters used as a municipal or domestic drinking water supply.

Trends
The graph below shows measured nitrate + nitrite concentrations expressed as nitrogen in the local stretch of the Red River from July 2001 through June 2002. Even with higher levels in the summer, attributed in part to runoff from fields and urban green spaces, the nitrate-nitrite concentrations in the river water were below the federal regulatory limits set for human consumption even before entering the local water treatment plant.

Graph of nitrate + nitrite concentrations (mg/L) expressed as nitrogen for the Red River in the Fargo-Moorhead metro area for the period July 2001 through June 2002.