Ecological Effects of Water Pollution

Ecological Effects of Water Pollution

	Ecological Effects of Water Pollution Minamata disease This disease is caused by mercury poisoning. The disease first occurred in Minamata, a small town in Japan and the primary cause was mercury which was released as a byproduct of the plastic industry. Mercury poisoning occurred in marine animals and this led to death of birds, cats and dogs which ate marine animals like fish, crabs and shell fish. Initial symptoms of Minimata disease include numbness of lips, limbs and tongue.
Impairment of motor nerve system, deafness and blurring of vision. The disease then progresses to brain dysfunction. Mortality of plankton and fish Chlorine which is added to water to control growth of algae and bacteria may persist in streams to cause mortality of plankton and fishes. Reduced productivity Intensive agriculture increases the amount of silt in lakes and rivers. Silts prevent penetration of light and thus reduces primary production. Siltation is a phenomenon by which gills of fishes are deposited with silt. This causes heavy mortality among fishes. Red tide When coastal waters are enriched with nutrients of sewage, dinoflagellates multiply rapidly and form a bloom. This is referred to as 'Red tide'. These blooming dinoflagellates liberate toxic metabolic byproducts which result in large scale death of marine fishes.
Biological oxygen demand Sewage enriches water systems with nutrients. This causes rapid growth of plankton and algae which leads to oxygen depletion in water. Biological oxygen demand (BOD) is the amount of oxygen required by microorganisms in water. BOD is higher in polluted water. Increased BOD lowers the content of dissolved oxygen in water causing suffocation and death of aquatic flora and fauna.
Methaemoglobinema Nitrates used in fertilisers enter the intestine of man through drinking water, where it is converted into nitrites. Nitrite is absorbed in the blood where it combines with haemoglobin to form methaemoglobin. Methaemoglobin cannot transport oxygen. This leads to suffocation and breathing trouble especially in infants. This disease is called methaemoglobinema.

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