Nitrates
Nitrogen, a nutrient found in both fresh- and saltwater environments, is an essential component for the growth of aquatic plants. In aquatic ecosystems, nitrogen is commonly found as a component of nitrate (NO3-), nitrites (NO2-), or ammonia (NH3). Nitrate, an oxidized form of nitrogen, is typically the most stable form of nitrogen, as well as the form our class measured throughout the year. Our class measured nitrate levels in milligrams/liter.
Interpreting Nitrate Levels
Though nitrates are a necessary food source for algae, an excess of nitrate levels can negatively impact a river ecosystem. High amounts of nitrates can cause an overabundance of al growth. High nitrate levels, when combined with high phosphate levels, can also cause a dramatic increase in algal growth known as eutrophication. As the algae bloom, it begins to inhibit other aquatic plants and block out sunlight, preventing photosynthesis. Once the algae begin to decompose, it strips the water of its dissolved oxygen; a condition called anoxia. Anoxia can be toxic to warm-blooded animals and fish at concentrations of 10mg/L or higher.
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Healthy rivers typically have nitrate levels below 10 mg/L. Levels ranging from 10 mg/L to 40 mg/L are usually indicators of poor water quality. In healthy rivers, some nitrates found in the surface water is typically less than 1 mg/L; in wastewater treatment effluent, levels can get as high as 30 mg/L. In addition to wastewater treatment effluent, other sources of nitrates include agricultural runoff (usually containing nitrogen-rich fertilizers), septic system leakage, animal manure, and industrial discharges that contain corrosion inhibitors.
Testing Protocol
Using a Vernier probe specific to nitrate testing, we measured the nitrate levels of the ten bottled samples taken at each site. Nitrate probes require pre-soaking for 30 minutes in a high (100 mL) concentration solution before use. Typically, our class soaked one probe before heading into the field, and packed an additional probe as a backup. Once arriving at the field, the probe required calibration using the high (100 mL) and the low (1 mL) concentration solutions. Throughout the year, our class encountered several issues with the nitrate probes, often because the tip of the probe had become slightly unscrewed from the base. Other issues were suspected to be the result of aging/faulty equipment. We recommend that new membrane tips be replaced twice during the school year.