Eutrophication in Aquatic Ecosystems....

Eutrophication is the over-enrichment of aquatic ecosystems with nutrients leading to too many nutrients stimulating the rapid growth of plants and algae, clogging waterways and sometimes creating blooms of toxic blue-green algae.  The result of this is that when the plants and algae die and decompose, they use up large amounts of oxygen (O₂). 

So the amount of oxygen that is available for fish and other aquatic species will be reduced. In extreme cases, it can lead to a completely oxygen-less aquatic environment that can support nothing except a few species of anaerobic bacteria. It also can kill fish and other aquatic life and reduce the aesthetic and recreational value or aspect of the lake.

The nutrients include nitrates found in sewage and fertilizers, and phosphates found in detergents and fertilizers. Human inputs of nutrients from the atmosphere and from nearby urban and agricultural areas can accelerate the natural eutrophication of lakes, a process called cultural eutrophication. Eutrophication is a persistent condition of surface waters and a widespread environmental problem. Some lakes have recovered after sources of nutrients were eventually reduced. 

In others, recycling of phosphorus from sediments enriched by years of high nutrient inputs causes lakes to remain eutrophic even after external inputs of phosphorus are decreased. Slow changes of phosphorus from over-fertilized soils may be even more important for maintaining eutrophication of lakes in agricultural regions. This type of eutrophication is not reversible unless there are substantial changes in soil management. 

Technologies for rapidly reducing phosphorus content of overly enriched soils, or reducing erosion rates, are needed to improve water quality. Excess phosphorus inputs to lakes usually come from sewage, industrial discharges, and runoff from agriculture, construction sites, and urban areas. Over time, many countries have regulated point sources of nutrients, such as municipal and industrial discharges. Nonpoint sources of nutrients, such as runoff from agricultural or urban lands, have replaced point sources as the driver of eutrophication in many regions.

Lake eutrophication has proven to be a stubborn environmental problem. Instead of alternating rules, many lakes remain eutrophic for extended periods of time. Causes of slow recovery, or non-recovery, from eutrophication are multiple and not really understood. Persistent eutrophication could be due to internal recycling from a large pool of phosphorus in sediments, which leads to alternative stable states. Prolonged release of phosphorus from enriched soils may also explain the persistent eutrophication.

Eutrophication can be avoided by using minimal required amounts of chemical fertilizers or still do away with them and use natural ones instead. Be sure not to have the fields close to the water bodies. Take extra care while using fertilizers during monsoons as due to run-off, they get transmitted to the water bodies. Then they can cause blockage of waterways, death of marine life and breakage of food chain.

Maintaining flat plains adjacent to rivers can also help to reduce nutrient-load in mouth water bodies; as when the river breaks its banks and floods, sediments and nutrients are deposited on the plains either side of the river is another innovative way that Eutrophication can be avoided.