Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. This enrichment leads to an increase in the growth of aquatic plants, both macrophytes and phytoplankton, which in turn leads to an increase in the growth of invertebrates and fish species. There are two types of eutrophication: natural and cultural. Natural eutrophication is a very slow process in which nutrients, especially phosphorus compounds and organic matter, accumulate in water bodies. Cultural or anthropogenic eutrophication is the process that speeds up natural eutrophication because of human activity. Due to clearing of land and building of towns and cities, land runoff is accelerated and more nutrients such as phosphates and nitrate are supplied to lakes and rivers, and then to coastal estuaries and bays.
Eutrophication sets off a chain reaction in the ecosystem, starting with an overabundance of algae and plants. The excess algae and plant matter eventually decompose, producing large amounts of carbon dioxide. This lowers the pH of seawater, a process known as ocean acidification. Acidification slows the growth of fish and shellfish and can prevent shell formation in bivalve mollusks. The most conspicuous effect of cultural eutrophication is the creation of dense blooms of noxious, foul-smelling phytoplankton that reduce water clarity and harm water quality. Algal blooms limit light penetration, reducing growth and causing die-offs of plants in littoral zones while also lowering the success of predators that need light to pursue and catch prey. Eutrophic waters can eventually become “dead zones” that are incapable of supporting life.
Water resource managers routinely employ a variety of strategies to minimize the effects of cultural eutrophication, including diversion of excess nutrients, altering nutrient ratios, physical removal of algae, and reducing nutrient inputs. Pollution control and improved municipal, industrial, and agricultural practices could do much to curb the cultural eutrophication.
