Eutrophication is the process in the nutrients of waters and the resultant sudden increase in algal production. Eutrophication is basically a natural phenomenon which gets enhanced through the agricultural activities. Generally the lakes or ponds have only limited quantities of nutrients for algal growth. Hence, there won’t be much algal growth in the olden days. The present day agriculturists for the sake of mass productivity of agricultural yields make use of variety of minerals and fertilizers. The rain causing natural loss dissolves as well as carry the nutrients to the water body’s. Thus the water bodies (lakes, ponds and rivers) are having good nutrient contents favourable for the algal growth. Besides agricultural nutrients, other sources also help in the sudden growth of vegetation in lake.
Rain fall and urban and rural run off
The rainfall naturally increases the fertility due to its contamination with varying amount of atmospheric nutrients such as nitrogen, ammonia and phosphorus. The rain water collects huge quantities of natural organic matter as well as synthetic fertilizers and goes in to the river or lake.
Agricultural run off
The rain water not only carry the natural organic manures but even the fertilizers that is in the broken stage which can be absorbed by the organic vegetation very easily.
The domestic sewage has a huge amount of nitrogen and phosphorus which are essential nutrients for vegetation. These sewages are diverted into lakes or rivers.
Some of the industrial wastes possess plant nutrients in enormous quantities. The wastes get into the river or lake that makes the aquatic flora to flourish.
The eutrophicaion process pollutes the rivers and lakes and makes the water not useful for drinking or washing purposes. The eutrophication produces a sudden growth of algae in one cycle and in another cycle the algae die and decompose. In the meantime, the locked nutrients are again available for fresh algae growth. Thus there will be a continuous chain process of the large growth of algae and its death and decay which makes the lake highly polluted. The dissolved oxygen content of the water will be considerably increased. The decay of the algae at one stage causes bacterial action and produces foul smell and taste to water. The increase in oxygen and carbon-dioxide in water lowers the pH of water which makes the carbonate precipitation.
The algal growth give shelter to several undesirable insects including mosquitoes. Moderate level of eutrophication is beneficial to fish production. But severe eutrophication will be hindrance for the production of edible fish. Only certain hard variety of fishes with low economic value only can thrive in the conditions of lake or river.
- The first step towards the control of eutrophication is to divert the nutrient bearing flows away from lakes in order to keep them free from nutrients.
- The organic wastes should be given tertiary treatment to remove nutrients present in the organic matter.
- When water level of lakes are low, the fishes and aquatic vegetation should be periodically removed to bring down the nutrient content of the lakes.
- The sediments of the lakes can be covered with suitable plastic material so that the sediments working as store house at the bottom and periodically released to the upper sediments is stopped.
- The anaerobic conditions can be lowered by controlling the conditions such as dissolved oxygen, pH, temperature, phosphorus, nitrogen etc.
- By making use of chemical treatment such as precipitating phosphorus compounds.
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