Eutrophication is a natural process, derived from the Greek word eutrophos meaning well nourished or enriched. This enrichment leads to other slow process referred to as natural aging of lakes. Eutrophication escalates rapidly, however when normally high amounts of nutrients from fertilizers, domestric and industrial wastes, urban drainage, detergents, animal wastes and sediments enter water streams.
Types of Eutrophication.
1. Natural eutrophication. The process of lake aging characterized by nutrient enrichment is called natural eutrophication. It permits the production of phytoplankton, algal blooms and aquatic vegetation including water hyacinth, aquatic weeds, water fern and water lettuce which in turn provide ample food for herbivorous zooplankton and fish.
2. Cultural Eutrophication. This process is generally speeded up by human activities, which are responsible for the addition of 80% nitrogen and 75% phosphorus to lakes and strams. In India, recreational value of Kashmir lakes is reduced while nainital lake is undergoing a rapid eutrophication as a result of sewage, domestic waste and detergent addition.
Effects of Eutrophication.
Eutrophication causes several physical, chemical and biological changes which considerably deteriorate the water quality.
• During eutrophication, algal bloom release toxic chemicals which kill fish, birds and other aquatic animals causing the water to sink.
• Decomposition of algal bloom leads to oxygen depletion in water.
• When O2 level falls to zero (anaerobic zone), some bacteria drive oxygen through reduction of natrates.
• Many pathogenic microbes, viruses, protozoa and bacteria etc. grow on sewage products under anaerobic conditions.
• Algae and diatoms attain high degree of dominance due to over fertilization.
• Macrophytes, particularly hydrilla, potamogeton, ceratophyllum and myriophy1-lum assume high population densities making near shore and shallow regions unsuited for any purpose.