Nutrients are required for growth and production by all plants and naturally cycle in the environment. Nutrients are also a leading cause of water quality impairment in groundwater, lakes, springs, rivers, and coastal waters. Excess nutrients can stimulate excessive algae growth, often referred to as algal blooms. An overabundance of algae can lead to low dissolved oxygen concentrations in the water for aquatic animals, decreased light availability for rooted submerged aquatic vegetation, and alteration of the natural flora and fauna. In spring waters, one nutrient associated with algal abundance is nitrate. Nitrate is a form of nitrogen naturally occurring in the environment, and is commonly found in fertilizer, and animal and human wastes (septic tanks and municipal wastewater). Once nitrogen is in the landscape and converted to the nitrate form, it will completely dissolve in water and move easily with water to aquatic ecosystems, where it can cause undesirable effects.
A nitrate molecule (NO3) consists of 1 nitrogen atom and 3 oxygen atoms, and there are several ways to measure nitrate. Nitrate concentrations are sometimes calculated using the weight of the entire nitrate molecule (usually reported as mg/L of NO3 or NOx) and some use the weight of just the nitrogen portion of the nitrate molecule (specified as nitrate-nitrogen usually in mg/L NO3-N or NOx-N). The nitrogen reported by SRWMD are nitrate-nitrogen concentrations. The use of the "x" in NOx indicates the measurement includes nitrite (NO2) in the analysis. Nitrite is typically present as a very small fraction of NOx, and is also bioavailable and contributes to pollution issues.
The Florida Department of Environmental Protection (FDEP) has developed numeric criteria for nutrients as targets to limit algal growth and maintain healthy surface waters. For clear water streams, such as spring runs, the criterion for nitrate is 0.35 mg NOx-N/L. For reference, this criterion is shown on the nitrate concentration graph as an orange line. This criterion will be used as a restoration goal for efforts intended to reduce nitrogen loading to springs from human sources.
High nitrate levels can also create human health concerns. The Federal drinking water standard for nitrate is 10 mg NOx-N/L. Concentrations above this can cause methemoglobinemia, or "blue baby" syndrome. Note that humans are much less sensitive to nitrate than our springs. For information about health risks related to nitrate, please visit the Florida Department of Health website (http://www.floridahealth.gov/).