Abstract

The word eutrophy means “nutrient rich.” In 1919, Nauman introduced the concepts of oligotrophy and eutrophy, distinguishing between oligotrophic lakes containing little planktonic algae and eutrophic lakes containing much phytoplankton. The eutrophication of aquatic ecosystems all over the world has increased rapidly during the last decade due to increased urbanization and, consequently, increased discharge of nutrient per capita. The most critical effect from an ecological point of view is the reduced oxygen content of the hypolimnion, caused by the decomposition of dead algae, particularly in the fall. It is recommended to set up mass balances for the nutrients to determine which nutrient is limiting the phytoplankton growth. For aquatic ecosystems with a high loading of wastewater, it is often nitrogen, because wastewater contains only three to three and one-half times as much nitrogen as phosphorus, and phytoplankton uses seven to eight times as much nitrogen as phosphorus for the growth. This does not imply that removal or reduction of nitrogen is the best management strategy, because it may be possible to remove phosphorus more effectively and at lower price, often by chemical precipitation of the wastewater. References to other entries that present various methods for elimination or reduction of the nutrients are given.