Eutrophication, Process, Sources and Consequences

 

Eutrophication

The word eutrophication is derived from Greek words "eu” meaning abundant and “trophi” meaning food or nutrient, thus eutrophication is defined as the enrichment of an eco-system with nutrients which results in the abnormal increase in the growth of aquatic organisms.

According to Nixon (1995) an increase in the supply rate of organic matter to an ecosystem is termed as eutrophication.

Eutrophication is an environmental problem caused by the load of nutrients especially nitrogen and phosphorous in aquatic ecosystem (Johnson et al., 2007, Donal et al., 2011, costa et al 2018)

According to Ospar 2003 the enrichment of water by nutrients causing an accelerated growth of algae and higher forms of plant life to produce undesirable distribution to the balance of organisms present in the water and to the quality of water concerned.

Process of Eutrophication

Nutrient loading causes a rapid elevation in primary production of phytoplankton which results in the change of physical chemical and biological characteristics of waterbodies to a great extent (dup et al., and Carneiro et al.,2014). In such an environment planktons grow very fast, this will create an imbalance in the food web which leads to high levels of plankton biomass in water bodies and they form a algal bloom all over the water body, on their death and decay the already existing organic load increase to a maximum amount now the water body start producing foul smell due to the action of anaerobic organisms on the organic waste which results in the liberation of certain harmful and toxic gases such as methane and hydrogen sulfide and hence produce a pungent smell , this changed state results in the depletion of dissolved oxygen,  to a great extent which ultimately leads to the death and change of flora and fauna of that very water body. With the passage of time the water body gets filled with remains of aquatic flora and fauna it settles down and the water body changes from its eutrophic state into wetlands or even dry land.

Sources of Eutrophication

The nutrients in a water body whether it is lake stream etc. enter through runoff, erosion, and leaching from agricultural fields where application of fertilizers, is practiced.

According to European Union Environmental Agency the source of nitrogen is runoff from agricultural lands whereas most phosphorous in waterbodies come from domestic and industrial activities

Some other activities associated with eutrophication include aquaculture, transportation of exotic species reservoirs in arid land  

Factors Favoring Eutrophication

Besides nutrients a number of physical factors play a great role in the development of eutrophication these include

• Contamination of water
• Temperature
• light
• Thermal stratification of stagnant water bodies
• Tidal effects

Limiting Factors

The limiting factors determine the growth of phytoplankton. Generally, phosphorus tends to be the limiting factor in in fresh water, nitrogen in large marine areas during summer and phosphorous in intermediate water bodies. The enrichment of water by nutrients can be of natural origin but human activities (cultural eutrophication) have enhanced it to a great extent.  

Indicators of Eutrophication

A variety of species acts as indicator species whose presence in any water body reflects eutrophication. Some of the common species are Duckweed, Yellow Water Lilly, Bur Reed, Common Reed, Cladophora glomeata etc.

Consequences of Eutrophication

There are a number of consequences associated with eutrophication

• Decrease in dissolved oxygen
• Increased biomass of aquatic flora and fauna especially phytoplankton and periphyton
• Variation in phytoplankton species composition to taxa that may be toxic or noxious population, similarly there is a shift in the zooplankton species as well
• Habitat destruction
• Esthetic degradation
• Loss of resources
• Loss of tourism
• Collapse of fisheries
• Human health implications
• Creation of dead zones
• Decrease in ecosystem resilience
• Hypoxia
• Tainted drinking water supply
• Elevated pH

Control of Eutrophication:

There are a wide range of strategies employed for the control of eutrophication. They fall under two broad categories traditional strategies and modern preventive techniques. In traditional one a number of methods were adopted like physical mixing, alteration of excess nutrients, use of herbicides and algaecides but these methods are quite unscientific, ineffective and risk loaded, because these may affect the non-target organisms which is a matter of concern. As far as the modern preventive techniques are concerned they are safe and ecofriendly these include

• removal of nutrients,
• removal of hypolymnetic water,
• treatment of waste water before discharging it into water bodies,
• in lake phosphorous precipitation,
• sediment dredging and phosphorous binding,
• reduction by flushing,
• bio manipulation,
• oxygenation of eutrophy water
• runoff from agricultural fields should be minimizes by crating barriers,
• use of phosphate free detergents should be encouraged,
• use of barley straw,
• introduction of exotic species into water bodies should be done after checking their adverse effect.