Answer to Question 1
Beginning in 2001, the EPA began publishing water quality nutrient criteria aimed at preventing and reducing the eutrophication that impacts so many bodies of water. The agency listed its recommended criteria for causative factorsnitrogen and phosphorusand criteria for response factors: chlorophyll as a measure of phytoplankton density and a measure of water clarity. The EPA divided the country into ecoregions and determined criteria levels deemed appropriate for the specific region. Like the other water quality criteria, the nutrient criteria are provided as targets for the states as they address their water pollution (and especially eutrophication) problems.
Answer to Question 2
In nature, apart from human impacts, eutrophication is part of the process of aquatic succession, discussed in Chapter 4 . Over periods of hundreds of thousands of years, bodies of water are subject to gradual enrichment with nutrients. Thus, natural eutrophication is a normal process. Wherever nutrients come from sewage-treatment plants, poor farming practices, urban runoff, and certain other human activities, humans have inadvertently managed to vastly accelerate the process of nutrient enrichment. The accelerated eutrophication caused by humans is called cultural eutrophication.
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