Nutrients in Stormwater FAQs
Nutrients in the form of nitrogen and phosphorus are naturally-occurring elements in aquatic systems. In excess, nitrogen and phosphorus can have serious negative impacts on water systems and human health.
Nitrogen is a common element in all organic materials and in many inorganic industrial chemicals. Nitrogen is found as organic nitrogen (e.g. decaying plants and animals, and food products), urea, ammonia, nitrite, nitrate, and nitrogen gas. Our atmosphere contains 80% nitrogen.
Nitrogen changes forms continually in the environment following the nitrogen cycle. In biological systems such as forests, stormwater media filters, and waterways, nitrites and nitrates are continually produced by micro-organisms as organic nitrogen is broken down as a part of the nitrogen cycle.
Phosphorus occurs naturally in animal feces and decaying plant and animal matter. In a balanced ecosystem, plants can process and utilize nutrients from these sources. Nitrogen and phosphorus become pollutants when human activities such as fertilization in agriculture or large animal yards increase the nutrient load to the point where the ecosystem cannot keep pace.
Highly soluble, nutrients in concentrations that can be harmful to the environment can get into stormwater runoff from a variety of sources:
- nitrogen in the form of nitrate (NO3-) and nitrite (NO2-) — common in fertilizer
- ammonium ion (NH4+) — often originating from animal urine
- phosphorus in the form of phosphate (PO43-) — from laundry detergent, animal feces and animal urine
Excess fertilizer that is not taken up by plants is transported into water bodies through both groundwater and surface water flows. Nutrients in fertilizer can be transported in both solid and dissolved states. High concentrations of nitrogen and phosphorus are also found in animal feces.
Dishwashing detergent is a common source for phosphorus entering the aquatic environment. Most dishwashing detergent is four to eight percent phosphate by weight which is about the same fraction as household fertilizers.[v] In the United States, the use of phosphorus in laundry detergent has been limited since the early 1970s.[vi]
Nutrients should be removed from stormwater discharge because high nutrient loads in waterbodies (“eutrophication”) can cause nuisance or toxic algae blooms.[i] Eutrophication and associated algae blooms decrease dissolved oxygen, light and habitat available for other aquatic species.[iii] Threats to human health include seafood contamination and bacteria from sewage and animal waste.[ii]
Various nutrients including nitrogen, phosphorus, and organic nutrients are removed through the activity of microorganisms in the filter media, and by enhanced sorptive filtration to trap the nutrients within the filter media. Further reduction can be achieved using additional sorptive media types for these dissolved pollutants. The Aquip passive media filter and the Purus polisher combined to offer an advanced level of nitrate removal from stormwater prior to discharge to help facilities meet benchmarks or NALs. Learn more about our stormwater media filtration and polishing technologies.