Why do we need to rejuvenate our lakes?

How are lakes formed?

Lakes are formed where there is depression in the landscape. It is localized in a basin, surrounded by land apart from rivers and other outlets that are fed. Lakes are distinct from lagoons and are larger than ponds.

Life Cycle of Lakes

Image from Vermont Lay Monitoring Program Manual

Once lakes are formed, they do not stay the same just like how humans go through phases like teenage, youth, maturity, old age and then die. Lakes slowly die/ disappear when the sediments settle in the lake. The aging of the lake could take over hundreds or thousands of years but with human influence it could just take a few decades. The plants, microbes and algae die. The warm upper layer of the lake decomposes the plants and sinks in the basin. The lake becomes smaller and smaller in size and eventually becomes a mash land and the lake dries up. 

A lake is usually classified in following possible cases: 

Oligotrophic lakes: They are pristine lakes where the ecosystem is naturally undisturbed by human activities and unspoiled its beauty. Oligotrophic lakes are characterized by high water clarity, low nutrient concentration (low on Phosphorus and Nitrogen), low algae growth, and minimum level of aquatic plants. The oxygen levels in these lakes are high in oxygen levels throughout the water column. Since there is low algal growth, the light penetration is deep and there is low decomposition. Since there is less decomposition, the oxygen doesn’t get used up. 

Mesotrophic Lakes – These lakes have clear water and beds submerged with aquatic plants, medium level of nutrients (Phosphorus and Nitrogen) and increasing levels of algae and weeds growing. These lakes have clear water but will have algal blooms in summer. These lakes behave differently in summer, they separate into layers. The top layer of the lake becomes warm from the sun and contains algae. While, at the bottom layer the remains cool and may be depleted by oxygen in the mid-summer. This happens because as the algae and other organisms die and sink at the bottom. Since water in the bottom and surface do not mix, oxygen cannot be replenished. During this time, the fishes move to the upper layer. 

Eutrophic Lakes – Eutrophication is a natural process where the oxygen levels in the lake decrease due to pollution and industrialization. Eutrophication is a state where the lake becomes toxic with high levels of nitrogen and phosphorus and they are silted heavily. There is low water clarity, high levels of aquatic plant growth, and high nutrients. The oxygen levels in the lake are very low for any ecosystem to survive. 

Hyper Eutrophic Lakes – There is very low/ no water clarity, highly rich in nutrients and depleted of oxygen. Lack of oxygen causes the fish to die and makes it not suitable for any ecosystem to live.  

Stresses on Lakes 

Stresses on the lakes have caused impairment of the lakes. Lakes occupy just a fraction of the landscape but they are a major source of surface water bodies in urban cities. Over the years due to population, urbanization and industrialization etc… water bodies are exploited. Water bodies are used for resource provision i.e drinking, washing & irrigation, regulating services like flood and drought management, cultural services like religious practices and historic values. However these water bodies are sensitive to environmental stress.   

Lake restoration is an act/method/process/steps undertaken for revival of a lake. These refer to the methods taken inside and outside the lake. Lake restoration activities are done mostly to battle eutrophication. Eutrophication leads to loss of biodiversity.  

Benefits of rejuvenation of lakes: 

1. Acts as a natural reservoir, it increases the storage of water

2. It constitutes natural biodiversity by maintaining the quality of water and atmospheric temperature. 

3. It increases the Ground water level. 

4. It controls erosion of soil and reduces the risk of flood. 

5. The lake is home to flora and fauna, the lake becomes a place of recreation for people around.  Lakes are the most valuable sources which maintain the temperature and support the ecosystem.

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