Water Quality Measurement  | Chemical Parameter

Lake Pend Oreille | Pend Oreille River

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. 

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. High nitrogen levels can cause increased plant and algae growth, which is sometimes associated with low dissolved oxygen (DO) levels, and increased temperature.

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 common sources of nitrate contamination in water are fertilizers, animal waste, and septic tanks. Nitrate in drinking water can cause temporary health issues, especially in infants under the age of 6 months. 

We measure the nitrate-nitrite of the water each time we collect data – once a month for five months out of the year (June – October). The bars represent the upper quartile (75% of the data taken at this site falls below this line), the median (or mid-point of the data) for each site, first quartile (25% of the data taken at this site falls below this line), and the box represents the middle 50% of the data. Please note that the data for this graph has been log-transformed for visual aid purposes. 

Use our interactive graph to check out all the data we have collected since 2012. Hover over a data point to see more information or try clicking on the name of a month to see all the data for just one month!

Some sources of nitrate-nitrite:

  • Sewage/failing septic systems
  • Fertilizers
  • Animal waste/agricultural runoff

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