6.7: FotE - Eutrophication

Focus on the Environment (FotE)

EUTROPHICATION - NUTRIENT POLLUTION

Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the surface of a river, lake, etc., often because chemicals that are used to help crops grow have been carried there by rain. This short video explains the basic process.

Many lakes, streams, and other freshwater and marine environments naturally contain low concentrations of essential nutrients, such as nitrates and phosphates. In order to survive, the species living in these nutrient-poor waters must then be adapted to this natural nutrient scarcity. However, raw sewage, agricultural fertilizers, concentrated animal feeding operations, and industrial processes release large amounts of additional nitrates and phosphates into the environment, which are washed into the aquatic environment. Minor additions of essential nutrients stimulate plant growth, providing more food for organisms at higher trophic levels. However, at high concentrations, the system become subjected to nutrient pollution. Such nutrient pollution usually causes algal blooms and bacterial growth, resulting in the depletion of dissolved oxygen in water and causing substantial environmental degradation.

Some Major Sources of Nutrient Pollution

Farms - Large, industrial farms apply large amounts of chemical fertilizers to help their crops grow. Irrigation water or rain then washes this fertilizer into local waterways.

Raw Sewage - This can come from humans or from large livestock operations. Human and animal wastes contain large amounts of the chemical nutrients needed to feed algae blooms.

City Stormwater Drainage- City stormwater washes large amounts of nutrients from fertilizer application, pest wastes, and other sources into nearby waterways.

Industrial Wastes - Textile, Chemical, and Food Processing plants sometimes release wastes with large amounts of nutrients.

One of the worst outcomes of nutrient pollution is eutrophication. During eutrophication, surface algae grow so rapidly (known as an algae bloom) that it starts blocking sunlight from reaching aquatic organisms below the surface (Figure 11.2.4). Because each individual alga is short-lived, their rapid growth also adds large amounts of decaying matter to the environment. In response, decomposers that feed on the dead algae can become so abundant that they consume most of the water’s dissolved oxygen. Without oxygen and sunlight, aquatic plant and animal life may die off in large numbers. The resultant dead zones are sometimes visibly in the form of fish kills, with large numbers of dead fish floating on the surface of the affected water body. The organisms that die during this process is generally also toxic to humans because of bacteria build-up and other imbalances. Eutrophication is an increasingly common problem.

Figure 11.2.4: Eutrophication of a stream in China. (Felix Andrews, own work, CC BY 3.0 Wikimedia commons)

Material on this page used from wikipedia (eutrophication). CC BY-SA