What is the connection between excess phosphorus and water quality?

Since the late 1960s, point sources of water pollution have been reduced due to their ease of identification and the enforcement of the Clean Water Act in 1972. As water quality problems remain, attention is now being directed to controlling the contributions from agricultural nonpoint sources. Eutrophication has been identified as the main problem in surface waters having impaired water quality (U.S. EPA, 1996). Eutrophication restricts water use for fisheries, recreation, industry, and drinking due to the increased growth of undesirable algae and aquatic weeds and oxygen shortages that result from their death and decomposition. Recent outbreaks of the dinoflagellate Pfiesteria piscicida in the eastern U.S. have been linked to excess nutrients in affected waters. Neurological damage in people exposed to the highly toxic volatile chemical produced by this dinoflagellate has dramatically increased public awareness of eutrophication and the need for solutions.

Phosphorus inputs to fresh waters can accelerate eutrophication. Although nitrogen (N) and carbon (C) are also essential to the growth of aquatic biota, most attention has focused on P because of the difficulty in controlling the exchange of N and C between the atmosphere and water and fixation of atmospheric N by some blue-green algae. Thus, managing P inputs to control the most limiting factor is critical to reducing freshwater eutrophication.