What is eutrophication? Causes, effects and control. & Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems [BE21]

blog #21

What is eutrophication? Causes, effects and control. & Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems
by:  Francesca Scannone, Michael F. Chislock

November 3rd, 2016, 2013
eni, nature education 

“Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use”. The processes promoting eutrophication are fertilizers, the discharge of waste water into water bodies, as well as the reduction of self purification capacity of bodies of water (a.k.a the accumulation of sediments). Eutrophication, as shown below, is often characterized by a build up of algae because some factor necessary for photosynthesis is in greater availability than normal. The algae dies and accumulates at the bottom of the lake, where anaerobic organisms feed off the matter, however aerobic plants and animals are at risk of death as these conditions worsen. 

As a consequence of eutrophication, bodies of water will have increased levels of phosphorus and nitrogen. Those with limited availability of these nutrients environment are described as “oligotrophic” while one with high availability of these elements is called “eutrophic”; and a lake with intermediate availability would be called “mesotrophic”. Animals are harmed by the reduction in water quality, and humans are as well. Recreation may be banned in contaminated lakes. Past attempts at using herbicides to manage eutrophication have been proven unsuccessful, so today prevention techniques, (such as the removal of the nutrients that are introduced into water bodies) is used to prevent the worsening of these conditions. 

While eutrophication is a natural process anthropogenic activities have accelerated this process by excreting limiting nutrients, such as nitrogen and phosphorus, into waterways. Humans might intentionally add fertilizers to waters to enhance primary productivity in lakes therefore increasing the density and biomass fisheries. While doing so has economic benefits, it is not sustainable in the long term. Consequences include blooms of blue-green algae, tainted drinking water supplies, degradation of recreational opportunities, and hypoxia. The resulting damages in the U.S. alone amount to $2.2 billion annually. High rates of photosynthesis can deplete dissolved inorganic carbon and significantly raise pH levels during the day. Elevated pH can in turn ‘blind' organisms that rely on perception of dissolved chemical cues for their survival by impairing their chemosensory abilities. Furthermore, the poisonings of domestic animals, wildlife and even humans by blooms of toxic cyanobacteria have been documented throughout the world.