From UPSC perspective, the following things are important :
Prelims level : Periyar River, Eutrophication
Mains level : Riverine water pollution in India
- There has been continued discolouration of water in the Periyar River turning into pitch black.
What caused discolouration?
- The discolouration was due to the poor quality of water as a result of eutrophication.
- When excessive nutrients reach the waterbody, it leads to algal bloom.
- A few days later, algae die and decay, resulting in a foul smell and discolouration of water.
- Water in some reaches of the river system has been stagnant. Reduced water flow in the system has added to the deteriorating water quality.
- Huge quantities of organic load in the form of sewage from nearby townships are regularly reaching the river system.
What is Eutrophication?
- Eutrophication is the response to the addition of nutrients such as nitrates and phosphates naturally or artificially, fertilizing the aquatic ecosystem.
- Algal blooms are the consequence of Eutrophication.
- Eutrophication occurs naturally due to deposition of nutrients [such as in depositional environments] carried by flood waters. It takes over centuries for eutrophication to occur naturally.
- Phytoplankton (algae and blue-green bacteria) thrive on the excess nutrients and their population explosion covers almost entire surface layer. This condition is known as algal bloom.
- Oxygen in aquatic ecosystem is replenished by photosynthetic aquatic plants. Algal Blooms restrict the penetration of sunlight resulting in death of aquatic plants, and hence restricts the replenishment of oxygen.
- The oxygen level is already depleted due to the population explosion of phytoplankton.