Eutrophication Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Eutrophication is the process by which a body of water, usually a lake, becomes over-enriched by nutrients. The nutrients may comprise nitrates, phosphates, and or ammonia. The result is often an increase in the photosynthesis and growth of aquatic plants, particularly algae, followed by a decrease in plant and animal diversity. In more severe cases, dissolved oxygen within lakes may decrease to the extent that fish and aquatic plants die.

Eutrophication can be a natural process that is associated with the aging of a lake. This occurs through the erosion of mineral-rich bedrock or soil into the water. However, many more causes can be attributed to human impacts and this is sometimes referred to as cultural eutrophication.

Cultural eutrophication stems from various sources; one of the main causes is intensive agricultural practices, where both inorganic and organic fertilizers may either drain or be leeched into a lake. Many inorganic fertilizers are high in nitrates, which is a particularly damaging cause of eutrophication. The drainage of organic manure is also a potentially damaging factor, particularly given the high level of waste that is associated with intensive farming.

One of the most prominent drivers of eutrophication in contemporary agriculture comes from intensive livestock production in confined animal feedlot operations (CAFOs). Here, large numbers of animals are kept in small facilities where wastes are sluiced to holding ponds or tanks, sometimes unlined, and frequently vulnerable to flooding. During major rain events, organic nutrients can overwhelm nearby watersheds, resulting in massive eutrophication and large-scale fish kills.

Human settlements may, either directly or indirectly, also contribute to eutrophication. This is primarily through an increase in wastewater from treated sewage. More indirectly, recreational activities such as boating can also contribute to eutrophication through increasing the turbidity of a lake and bringing polluted sediments into suspension. Industrial discharges may also lead to eutrophication.

There are severe economic and social consequences to eutrophication. Lakewater may become undrinkable by humans, which, in turn, may cause the depopulation or abandonment of settlements that have limited access to transportable water or access via a well to underground water. Cattle and other animals drinking tainted water may die, an occurrence that has been reported in both Africa and Australia. Toxic secretions from some algae may be absorbed by fish, particularly shellfish, which are consumed by humans and have caused fatal poisoning.

In addition to drinking and agriculture, many lakes are also used for recreational tourism, although the processes associated with eutrophication may lead to a decline in recreational activities. Boating, swimming, and fishing have been negatively impacted in various areas as water quality changes to a much less aesthetically pleasing appearance and or smell. Boating and fishing may be hindered by the associated excessive growth of aquatic plants. The decline in the diversity of fish species may negatively impact recreational fishing. The result of one or more of these has affected property prices and settlement patterns as tourism shifts to less-affected water sources.

One well-studied area where eutrophication has both occurred and subsequently combated is in the Norfolk Broads in eastern England. The Norfolk Broads are a system of very shallow lakes and interconnecting rivers that are surrounded by marshes and fens. The lakes themselves are artificial, created through the excavation of peat and then subsequent flooding of the ensuing depressions in the 14th and 15th centuries. Problems started to occur in the first half of the 20th century, when water weeds began growing in open water areas. Sediment cores from the area show that the increase in the phosphorous content in the Norfolk Broads correlates readily with increases in both local human populations and farming activity and resulted in the loss of invertebrate and fish diversity and a reduction in aquatic plant and bird populations. Measures to combat the increased phosphorous began in 1977. Major sewage treatment works were especially singled out so that on one river the amount of discharged phosphorous was reduced by 90 percent. However, downstream of these major sewage treatment works, levels were only reduced by 50 percent. This discrepancy is most likely because motor boats that use the river created waves that brought the phosphorous-rich sediment, which had accumulated during previous years, into suspension. Even with the phosphorous reduction, the Norfolk Broads did not convert back to the desired status before eutrophication.

The levels of land use required to get phosphorous to the required levels would not be sustainable. Therefore, other measures need to be incorporated into the process, such as the encouragement of grazing zooplankton through the partial and temporary removal of fish populations.

Bibliography:

Andrew Goudie, The Human Impact on the Natural Environment (Blackwell Publishers Ltd., 2000);
David Harper, Eutrophication of Freshwaters (Chapman & Hall, 1992);
Henderson-Sellers and H.R. Markland, Decaying Lakes The Origins and Control of Cultural Eutrophication (John Wiley & Sons, 1987).