Water bodies, like all living things, age with time. This ageing process is referred to as "eutrophication" in lakes. Algal bloom (excessive growth of planktonic algae) occurs when huge levels of nutrients are present in water. Lakes age as a result of this. This article will explain to you Ageing of Lakes which will be helpful in preparing the Environment syllabus for the UPSC Civil service exam.

Ageing of Lakes - Concept

• Lakes are formed as a result of diverse geological and geomorphic events, and they 'grow' over time to change their morphological and functional properties before eventually falling.
• Lakes derive their water from surface runoff (and sometimes groundwater discharge), as well as various chemical compounds and mineral matter eroded from the earth.
• Ageing occurs over millennia as the lakes gather mineral and organic debris and gradually fill up.

Natural Ageing of Lakes or Natural Eutrophication

• Ageing of lakes happens naturally in many situations, with erosional materials transported in by tributary streams, materials deposited directly from the atmosphere, and materials created inside the lake itself filling in over geologic time.
• In the beginning, the cold, clean water of a young lake does not support much life.
• However, over time, streams flowing into the lake introduce nutrients like nitrogen and phosphorus, which promote aquatic organisms growth.
• Eutrophication is the term used to describe this biological enrichment of a lake's water that causes it to age naturally.
• Eutrophication is a natural process that takes hundreds to thousands of years in a lake. Lake ageing is another term for natural eutrophication.
• Plant and animal life begin to develop as the lake's fertility rises, and organic remains begin to accumulate on the lake's bottom.
• As silt and organic debris accumulate over time, the lake becomes shallower and warmer.
• Warm-water organisms have now replaced cold-water ones. Marsh plants establish themselves in the shallows and gradually fill in the original lake basin.
• The lake eventually generates enormous quantities of floating vegetation swamp and eventually converts to land.

Natural Eutrophication or Natural Ageing of Lakes

Cultural Eutrophication

• Humans can hasten the process of eutrophication by rapidly adding excess nutrients and sediment, causing the lake to change trophic states in a matter of decades.
• Because it is caused by humans, this type of eutrophication is known as cultural eutrophication.
• Agriculture, animal feedlots, factories, and urban areas all contain high concentrations of nutrients. During heavy rains or through direct storm sewers, these nutrients wash into lakes.
• The increased nutrients cause algal blooms, increased plant growth, and overall poor water quality, making the lake less suitable for recreation.
• Furthermore, soil eroded by tree and vegetation removal washes into lakes, filling them in and making the bottom mucky.
• The percent littoral area (the area of the lake shallow enough for light to reach the bottom) increases as the lake shallowens, resulting in even more plant growth.

Cultural Eutrophication

Natural Lakes in India

• Natural lakes (which are relatively few in India) are mostly found in the Himalayan region, on the floodplains of the Indus, Ganga, and Brahmaputra rivers.
• Tens of thousands of water bodies have been built over millennia in the semi-arid and arid regions of western and peninsular India.
• Lake 'Sudarshan' in Gujarat's Girnar area was possibly India's oldest man-made lake, dating back to 300 BC.
• Lakes are also classified according to their water chemistry. They are classified as freshwater, brackish, or saline lakes based on their salinity levels (similar to aquatic ecosystem classification).
• They are classified as Oligotrophic (very low nutrients), Mesotrophic (moderate nutrients), and Eutrophic based on their nutrient content (highly nutrient rich).
• Because of nutrients derived from their surroundings or organic wastes entering them, the vast majority of lakes in India are either eutrophic or mesotrophic.

Young Lakes

Young lakes are referred to as the Oligotrophic Lakes. Young lakes have the following characteristics:

• Shorelines that slope down to the water's edge.
• Along the shore, there are mostly conifer trees (pine).
• They are deep and abruptly drop off.
• The majority of the bottom is rocky.
• The water is exceptionally clear.
• There aren't many aquatic weeds there.
• They have a high proportion of oxygen.
• Cold-water fish such as trout, steelhead, whitefish, and salmon inhabit them.
• Lake Superior in North America is an example of oligotrophic lakes.
• The shorelines of oligotrophic lakes erode and become less steep over thousands of years.
• More plant life arises on the coast and in the water as the rocks on the lake's bottom grind against each other, forming sand. The lake now reaches the next stage of ageing.

Oligotrophic Lake

Middle-aged Lakes

Middle-aged lakes are referred to as the Mesotrophic Lakes. Middle-aged lakes have the following characteristics:

• Shorelines are less steep.
• Oak, maple, and ash are among the coniferous and deciduous trees found here.
• The bottom is primarily sand, which is the result of rock erosion and weathering.
• On the shoreline, there are a few aquatic weeds and many flora.
• On average, they are shallower than oligotrophic lakes.
• The water remains crystal pure.
• Bass, perch, and bluegill, for example, can be found in both cold and warm water.
• Lake Michigan in North America is an example of mesotrophic lake.
• Mesotrophic lakes absorb nutrients from fallen, decomposed deciduous tree leaves, dead shoreline plants, decaying aquatic vegetation, and the remnants of fish and other water organisms after thousands of years.
• Silt and sediment accumulate on the lake's bottom near the shore. The lake now ages significantly.

Mesotrophic Lake

Old Lakes

Old lakes are referred to as the Eutrophic Lakes. Old lakes have the following characteristics:

• Shorelines are typically flat and gentle.
• Along the coast, there are mostly deciduous trees and a lot of shoreline flora.
• When compared to lakes with a sandy or rocky bottom, they are usually fairly shallow.
• In waters deeper than 30 feet, there is very little oxygen.
• Organic matter and single-celled planktonic algae have coloured the water, making it murky.
• Heavy weed growth in the water.
• There are few, if any, cold-water fish. In old lakes, however, bass, panfish, pike, and carp thrive.
• The inland lakes are the best examples of eutrophic lakes.
• All lakes have a natural tendency to fill up and become land.

Eutrophic Lake

Conclusion

After a few thousand years, the lake in general will continue to become shallower in the middle, as more shoreline erodes into the water, trees fall into the water, leaves, dust, and dirt blow in, weeds grow thicker and spread further into the lake, die, decay, and add to the bottom. Thus a lake finally remains no more as a result of the ageing process. We call bodies that were previously lakes by a variety of names. Bogs, swamps, and marshes are all names for them.