In this article we will discuss about the meaning, types and effects of eutrophication.
Meaning of Eutrophication:
Inorganic nitrates and phosphates in excess amount stimulate excessive plant growth in lake and reservoir. The plant deplete the oxygen content of water during night.
This leads to suffocation of fish and other aquatic life. The rapid algal growth (plant) leads to the diminishing of nutrient in the medium causing rapid decay of algae filament. The increased productivity of lake and stream water brought about nutrient enrichment is called Eutrophication.
Types of Eutrophication:
Eutrophication is mainly of two types:
1. Natural Eutrophication, and
2. Cultural Eutrophication.
1. Natural Eutrophication:
The process of lake aging characterised by nutrient enrichment is called natural eutrophication. During this process oligotrophic lake is converted into an eutrophic lake. 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 streams. Lake Mendota and Lake Washington have undergone rapid eutrophication due to man’s activities is possible.
Effects of Eutrophication:
Eutrophication causes several physical, chemical and biological changes which considerably deteriorate the water quality.
It creates the following effects:
1. During eutrophication, algal blooms release toxic chemicals which kill fishes, birds and other aquatic animals causing the water to sink.
2. Decomposition of algal blooms leads to oxygen depletion in water. Thus with a high CO, level and poor oxygen supply, aquatic organism begin to die and the clean water turns into stinking drain.
3. When O, level falls to zero (anaerobic zone), some bacteria drive oxygen through reduction of nitrates. On complete exhaustion of nitrate, oxygen may as a last resort be obtained by reduction of sulphate yielding hydrogen sulphide causing foul smell and putrefied taste of water.
4. Many pathogenic microbes, viruses, protozoa and bacteria etc. grow on sewage products under anaerobic conditions. It results into spread of fatal water-borne diseases such as polio, dysentery, diarrhoea, typhoid and viral hepatitis.
5. Algae and diatoms attain high degree of dominance due to over fertilization. Algae and rooted weeds interfere with the hydroelectric power, clog the filters, retard the water flow and affect water quality and water works.
6. Macrophytes, particularly Hydrilla, Potamogeton, Ceratophyllum and Myriophyllum assume high population densities making near shore and shallow regions unsuited for any purpose.
7. During eutrophication midge Chironomous plumosus and tubificid worms develop extremely high populations creating anaesthetic and economic problems in water bodies.
8. Phytoplankton communities are most sensitive to eutrophication. Investigations on lake Wisconsin showed that their population in eutrophic lake is smaller as compared to oligotrophic water.
9. The lake undergoing eutrophication may become oxygen deficient, destroying fish habitats leading to the elimination of several desirable aquatic species in water.
10. Prolonged eutrophic conditions lead to dystrophic state. The lake receiving huge amounts of organic matter from alloethonous source are called dystrophic. These lakes contain big flora and high amounts of humic acid while planktonic productivity is very low.
11. In India, Dal, Nagin, Loktak lake and Hussain sagar are seriously chocked by aquatic weeds affecting fisheries production, utility for aquatic flora and aesthetic value.
When sewage and agricultural run-off containing phosphates or other nutrients enter natural water bodies they cause over nutrition leading to eutrophication.
The latter is the process of providing a water body with nutrients for the aquatic life it supports.
A lake starts its life cycle as oligotrophic i.e. a clear body of water. With the introduction of nutrients through land run off and growth and decay of aquatic life, the lake collects a good amount of organic substances. Eventually, there is algae bloom when the lake becomes marsh or debris. The stage is eutrophic, when the lake become marsh or debris. The stage is eutrophic when the lack is filled with sediment while aquatic animals life will perish. It will then turn into dry land.
The rate of eutrophication strikes a balance between the production of aquatic life and its destruction by bacterial decomposition. Lakes can be protected from eutrophication only by providing measures for sewage treatment and preventing the sewage from entering the water bodies.