Excess nutrients promote excessive aquatic plant growth—eutrophication—which has been a serious problem in the watershed. Both nitrogen and phosphorus are used to indicate the potential for eutrophication. The overgrowth of algae and aquatic plants leads to large daily changes in dissolved oxygen and pH (acidity) levels, which affect fish survival. Eutrophication can also severely impair the enjoyment of the river’s scenery, use for recreation, and habitat for other species that live in or use the river. When it decomposes, it leads to a sewage-like smell. Nitrogen is generally considered the controlling nutrient for saltwater systems but can impact freshwater if phosphorus concentrations are also high, spurring the overgrowth of algae and aquatic plants.
Nitrate (NO3) scores are calculated based on a comparison with EPA Ecoregion XIV background statistics. Nitrate is used as a surrogate for Total Nitrogen because it represents the dominant portion of biologically available nitrogen in surface waters.