Eutrophication

The nutrient-enrichment of the lakes promotes the growth of algae, aquatic plants and various fauna. This process is known as natural eutrophication.
Similar nutrient enrichment of lakes at an accelerated rate is caused by human activities such as discharge of waste waters or agricultural runoff and the consequent ageing phenomenon is known as cultural eutrophication.
Greek word – Eutrophia means adequate & healthy nutrition. 
•    Eutrophication is a syndrome of ecosystem, response to the addition of artificial or natural nutrients such as nitrates and phosphates through fertilizer, sewage, etc that fertilize the aquatic ecosystem. 
•    It is primarily caused by the leaching of phosphate and nitrate containing fertilisers from agricultural lands into lakes or rivers.
•    The growth of green algae in the lake surface layer is the most common indication of Eutrophication. 
•    Excess nutrients cause algae to grow massively on the water surface. This thick layer blocks sunlight from reaching plants below. 
•    Plants need sunlight for photosynthesis which produces oxygen in the ecosystem. Without light, oxygen production stops. Normal air diffusion provides little oxygen which is not enough to sustain the entire aquatic ecosystem.
•    Water already low in oxygen due to overcrowding by organic overload.
•    Oxygen levels are further depleted by decomposer microorganisms consuming dead algae in the water. 
•    Due to reduced oxygen level, fishes and other aquatic organism suffocate and they die. 
•    The anaerobic conditions can promote growth of bacteria which produces toxins deadly to aquatic organisms, birds and mammals. 
•    All this eventually leads to degradation of aquatic eco system and death of its organisms.  
•    It often leads to change in animal and plant population & degradation of water & habitat quality.
General Characteristics of a Eutrophic Lake :
1.    Aquatic plant production is less or completely eliminated.
2.    Aquatic animal production is less or completely eliminated.
3.    Aquatic plant nutrient flux is high.
4.    Oxygen in the hypolimnion (bottom layer) is low.
5.    Depth of the lake reduces – shallow lakes are formed.
6.    Overall water quality turns poor.
7.    Biodiversity of the aquatic system reduces. 
Lake restoration techniques : Eutrophication can be managed by various techniques such as
1.    Flushing with nutrient-poor waters. 
2.    Deep water abstraction. 
3.    On-site Phosphorus elimination by flocculation/flotation with water backflow, or floating Plant NESSIE with adsorbents. 
4.    On-site algae removal by filters and P-adsorbers. 
5.    On-site algae skimming and separator thickening. 
6.    Harvest of fishes and macrophytes. 
7.    Sludge removal