Lake Ecology
A lake is a large, stationary water body that is usually enclosed by land. It can vary greatly in its origin, hydrology, chemical characteristics, ecology, and depth.
Ageing of Lakes
- Lakes, like living organisms, undergo ageing.
- They originate through geological and geomorphological processes, collect water from runoff and underground discharge, and gradually accumulate mineral and organic matter.
- Over thousands of years, they fill up with sediments, leading to changes in morphology and function, eventually transforming into wetlands or terrestrial ecosystems.
Classification of Lakes
Lakes are classified in two major ways:
- Based on Salinity:
- Freshwater Lakes: Very low salt content.
- Brackish Lakes: Moderate salt levels.
- Saline Lakes: High salt concentrations.
- Based on Nutrient Content:
- Oligotrophic: Very low in nutrients, usually deep and oxygen-rich.
- Mesotrophic: Moderate levels of nutrients.
- Eutrophic: High nutrient content, shallow, and often oxygen-depleted in deeper zones.
General Characteristics of Oligotrophic vs. Eutrophic Lakes
| Sl. No | Parameter | Oligotrophic Lake | Eutrophic Lake |
|---|---|---|---|
| 1. | Aquatic plant production | Low | Eliminated due to eutrophication |
| 2. | Aquatic animal production | Low | Eliminated due to eutrophication |
| 3. | Nutrient content | Low | High |
| 4. | Oxygen in bottom layer (hypolimnion) | Present | Absent |
| 5. | Depth | Tend to be deeper | Tend to be shallower |
| 6. | Water quality for use | Good (suitable for domestic & industrial use) | Poor |
| 7. | Salinity or electrical conductance | Usually lower | Sometimes higher |
| 8. | Number of plant and animal species | Many | Fewer |
Lakes in India
- Natural lakes are relatively fewer and are mainly located in:
- Himalayan regions
- Floodplains of rivers like Indus, Ganga, and Brahmaputra
- Man-made water bodies are more common, especially in semi-arid and arid regions like Rajasthan and peninsular India.
- Example: Lake Sudarshan in Gujarat, built around 300 BCE in the Girnar region, is one of the oldest man-made lakes.