Total Nitrogen

What is Total Nitrogen?

Total Nitrogen is a measurement of how much elemental nitrogen in various molecular formations is present in the water. Total Nitrogen is measured as a concentration in milligrams per liter (mg/L). Nitrogen enters nontidal freshwater streams and rivers from organisms that naturally live in and around the water and through discharges of various sources of water pollution, such as sewage overflows, industrial discharges, and stormwater runoff containing animal waste and fertilizers, among other nitrogen-rich substances in the watershed.

Why is Total Nitrogen important?

Nitrogen is an essential element for cellular formation of plant, bacteria and animal life. As a limiting nutrient, excess levels of nitrogen and phosphorus in nontidal freshwater streams and rivers can drive rapid population “blooms” of bacteria and algae populations, which can have serious impacts on other aquatic and human life. These algae and bacteria blooms may secrete toxins harmful to fish and humans, and, when algae blooms die and are decomposed by bacteria, levels of dissolved oxygen can rapidly decline. These excess levels of nitrogen and phosphorus are often discharged to receiving tidal waters from watershed rivers and streams before they can contribute to algae blooms occurring within the rivers and streams.

How do we measure Total Nitrogen?

Total Nitrogen is measured through the collection of a water sample for analysis by a laboratory. We collect a water sample from halfway between the water’s surface and river bottom at each station, store samples on ice, and deliver samples the same day to the laboratory for analysis. We assess the Total Nitrogen data using numeric thresholds of ≤0.64 mg/L (Piedmont Streams and Rivers) and ≤0.82 mg/L (Coastal Plain Streams and Rivers), as established by the University of Maryland Center for Environmental Science’s EcoCheck Program for the assessment of the ecological health of nontidal freshwater streams and rivers in the Chesapeake Bay watershed.