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A short-term acute poisoning of the neurotoxin anatoxin-a, produced by an HAB of Anabaena, was the likely cause of death for a Wisconsin teenager in July 2002.
EPA’s 2000 National Water Quality Inventory showed that, of the U. water bodies assessed, 47 percent of rivers, 53 percent of lakes, and 52 percent of estuaries were polluted or threatened.
In 19, nutrients and siltation (sedimentation) were among the top five causes of impairment for streams, rivers, lakes, ponds, reservoirs, and estuaries.
The causes of nutrient enrichment can be categorized into two main sources: point source pollution (i.e., from a pipe) and non-point source (i.e., diffuse) pollution.
As all streams, lakes, reservoirs, and estuaries receive water from their respective watersheds (area of land that drains into a water body), any upstream or up-watershed sources of pollution can become pollution sources to the receiving water body.
In the United States, the point source release of plant (and algae) nutrients, phosphorus and nitrogen, into the environment is controlled by the National Pollutant Discharge Elimination System (NPDES), a provision of the Clean Water Act.
Although the NPDES program has achieved much improvement in nutrient pollution control, recent assessments of the nation’s water quality have shown continued water quality degradation caused by these nutrients (e.g., a 1999 U. Geological Survey study showed that the nation’s median stream phosphorous concentration was still greater than the 0.100 mg L-1 threshold for reduced phytoplankton growth), demonstrating a need to manage both point and non-point sources of nutrient pollution. Environmental Protection Agency (EPA) studies have shown that in a natural forested area, 40 percent of rainwater returns to the atmosphere through evapotranspiration, 50 percent filters into subsurface flow, and 10 percent runs off the land surface into a receiving water body.
Both nutrient enrichment and siltation can lead to eutrophication, but in many cases, the nutrient enrichment and siltation caused by human manipulation of the environment can be prevented or minimized through the use of best management practices (BMPs).
However, even though safe drinking and recreational waters are social necessities, a lack of understanding of causes and effects of pollution often inhibits stakeholder investment in BMPs.
In marine ecosystems, this phenomenon is seen in the Gulf of Mexico’s “dead zone,” where nitrogen from the Mississippi and Atchafalaya Rivers stimulates high rates of algal growth in the upper water layers, which cause oxygen depletion in the underlying waters.
Nutrient enrichment has also been cited as the cause of coral reef destruction, degrading both the ecological and recreational value of these marine resources.