Nutrient pollution is a form of water pollution that occurs when excessive amounts of nutrients, primarily nitrogen and phosphorus, enter rivers, streams, lakes, wetlands, estuaries, groundwater, or coastal waters. While these nutrients are essential for the growth of plants, algae, and aquatic organisms, excessive concentrations disrupt natural ecological processes and degrade water quality.
In stormwater management, nutrient pollution is most often associated with runoff that carries fertilizers, grass clippings, leaves, pet waste, agricultural wastes, eroded soil, septic system discharges, and other nutrient-containing materials into storm drains and surface waters. Because stormwater systems typically discharge directly to receiving waters with little or no treatment, nutrients can be transported rapidly from developed landscapes into aquatic ecosystems.
The two nutrients of greatest concern are:
Nitrogen (N), which may be present as nitrate, nitrite, ammonia, or organic nitrogen compounds. Nitrogen is highly mobile in water and can contaminate both surface water and groundwater.
Phosphorus (P), which is commonly attached to soil particles or present in dissolved forms. Phosphorus is often the limiting nutrient in freshwater systems, meaning even relatively small increases can trigger excessive algal growth.
Excess nutrient inputs can cause a process known as eutrophication, in which nutrient enrichment stimulates rapid growth of algae and aquatic plants. As these organisms die and decompose, bacteria consume dissolved oxygen from the water. This can lead to hypoxia (low oxygen levels) or even anoxia (complete oxygen depletion), creating conditions that can result in fish kills and the loss of aquatic habitat.
Common impacts of nutrient pollution include:
Major sources of nutrient pollution include agricultural runoff, urban stormwater runoff, wastewater treatment plant discharges, septic system failures, atmospheric deposition from fossil fuel combustion, animal waste, and fertilizer applications to lawns, landscapes, and cropland.
Stormwater management practices designed to reduce nutrient pollution include bioretention systems, bioswales, vegetated swales, constructed wetlands, infiltration practices, riparian buffers, street sweeping, erosion and sediment controls, fertilizer management programs, and public education efforts aimed at preventing nutrients from entering stormwater runoff. These practices reduce nutrient loading by promoting infiltration, filtration, plant uptake, soil adsorption, and microbial transformation processes.
In summary, nutrient pollution is the over-enrichment of water bodies with nitrogen and phosphorus, typically from human activities, resulting in excessive plant and algal growth, degraded water quality, ecological imbalance, and harm to aquatic life. It is one of the most widespread and significant water quality challenges addressed by modern stormwater management programs.