Total Nitrogen

Water Quality Measurement  | Chemical Parameter

Lake Pend Oreille | Pend Oreille River

Nitrogen is an essential plant nutrient but in high quantities it can cause increased plant and algae growth, low dissolved oxygen (DO) levels, and increased temperature. Nitrogen in aquatic systems is found in many forms, including ammonia, nitrates and nitrites. Nitrogen sources include soil erosion, organic matter and debris, sewage and failing septic systems, fertilizers, animal waste, and agricultural runoff.

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Nitrogen is an essential plant nutrient but in high quantities can cause excessive plant growth. Microbial metabolism can decompose organic nitrogen (e.g., plants) into ammonia, which may be oxidized into nitrite then further oxidized to nitrate. All forms are soluble in water and are closely related.

Nitrogen has higher solubility in water than phosphorus (P) and quickly travels into rivers and streams. This property is one reason why phosphorus, rather than nitrogen, is the limiting nutrient for plant growth. When sampling for nutrients, it is advisable to include both phosphorus and nitrogen testing to determine the nitrogen to phosphorus ratio (N:P). The EPA mandates nitrogen and phosphorus limits through National Pollutant Discharge Elimination System (NPDES) permits, which are often based on the assessed ability for dilution by the receiving waters.

The most commonly-used methods to test nitrogen test for both nitrite and nitrate. Nitrate is a form of nitrogen that is more available to plants relative to other forms. Nitrite is a byproduct of ammonia oxidization, is unstable in aqueous environments, and is therefore rarely detectable. Detectable nitrite levels therefore may be indicative of an ammonia source. Total Kjeldahl Nitrogen (TKN) is the sum of organic nitrogen, ammonia, and ammonium in a water body. High TKN concentrations can indicate sewage and manure discharges are present in the water body.

Some sources of nitrogen

  • Soil erosion
  • Organic matter/debris (decomposing leaves & plants)
  • Sewage/failing septic systems
  • Fertilizers
  • Animal waste/agricultural runoff

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