Animal wastes contain significant quantities of nutrients, particularly nitrogen and phosphorus. The primary potential problems include excessive nitrogen and phosphorus in surface waters, and nitrate in groundwater. Nitrogen in manure occurs in different forms, including ammonia, nitrate, and organic forms such as amines and proteins. Nitrogen and phosphorus can enter the environment through runoff, soil infiltration, and percolation into groundwater, and ammonia can volatize with subsequent redeposition on surface waters and land.
In surface waters, excessive phosphorus and nitrogen can lead to eutrophication, algal blooms, fish kills, reduced biodiversity, objectionable tastes and odors, growth of toxic organisms (e.g., toxins from blue-green algae), increases in organic matter content (e.g., DBP precursors), and resulting increased drinking water treatment costs.
Nitrogen can convert to nitrate as it passes through the vadose (unsaturated) zone, and nitrate transports readily through soils into groundwater. Consumption of nitrate can cause methemoglobinemia (blue baby syndrome) in infants, as well as spontaneous abortions and increased incidence of stomach and esophageal cancers (USEPA, 2003a). The USEPA drinking water MCL for nitrate is 10 mg/L as N. In soil systems, phosphorus tends to bind to soil particles until the phosphorus content of soils build up, leading to phosphorus surface export and subsurface loss (Sharpley et al., 1999; Mallin et al., 2003).
Information on the source, fate, and transport of phosphorus and nitrogen in the agricultural environment, as well as applicable BMPs, are provided in the following sources: