- It is a natural process, which has been derived from the Greek word ‘eutrophos’ that means well-nourished or enriched.
- This enrichment leads to other slow processes which is called as “natural aging of lakes”.
- C.H Weber described eutrophication as nutrient rich conditions that is used to determine the flora of German peat bogs as eutrophe, mesotrophe and oligotrophe.
- It is a phenomenon through which a nutrient rich bog in a shallow depression changes to leached bog that is deficient in nutrients.
- Springs, streams, bog or lakes are categorized as oligotrophic (barren), mesotrophic and eutrophic on the basis of various contents like phosphorus, nitrogen and calcium.
- Eutrophication escalates rapidly, when abnormally high amounts of nutrients from fertilizers, domestic and industrial wastes, detergents, urban drainage, animal wastes and sediments get mixed with water streams.
Image source: netsolwater
Types of eutrophication
- Eutrophication is mainly classified into two types. They are:
a) Natural eutrophication
- The process of aging of lake which is characterized by nutrient enrichment is called natural eutrophication.
- During this process, oligotrophic lake is converted into a eutrophic lake.
- It permits the production of phytoplankton, algal blooms and aquatic vegetation which also includes water hyacinth, aquatic weeds, water fern and water lettuce that provide ample food for herbivorous zooplankton and fish.
b) Cultural eutrophication
- This process is generally speeded up by human activities.
- They are responsible for the addition of 80% nitrogen and 75% phosphorus to lakes and streams.
Effects of Eutrophication
- Eutrophication causes several physical, chemical and biological changes which deteriorates the quality of water.
- It creates the following effects:
1. During eutrophication, toxic chemicals are released by algal blooms which kill fish, birds and other aquatic animals causing the water to sink.
2. Decomposition of algal bloom depletes the oxygen level in water. Thus, with a high CO% level and poor oxygen supply, aquatic organisms begin to die which turns the clean water into a stinking drain.
3. Hydrogen sulphide is yielded by reduction of sulphate causing foul smell and putrefied taste of water.
4. Algae, diatoms and rooted weeds show dominance by interfering hydroelectric power, clogging the filters, retarding the water flow and affecting the quality of water and water works.
5. Fatal water borne diseases such as polio, dysentery, diarrhoea, typhoid and viral hepatitis spread as many pathogenic microbes, viruses, protozoans and bacteria grow on sewage products under anaerobic condition.
6. Macrophytes, particularly Hydrilla, Potamogeton, Ceratophyllum, and Myriophyllum gain high population densities which make near shore and shallow region 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.
9. The lake becomes oxygen deficient, destroying fish habitats leading to the elimination of several desirable aquatic species in water.
10. Prolonged eutrophication results to “dystrophic sate”. The lake receiving huge amounts of organic matter from alloethonous source is called dystrophic. These lakes contain bog flora and high amounts of humic acid which causes decrease in the planktonic productivity.
Control of eutrophication
Several technical devices along with prevention of further in flow of effluents have been used to control eutrophication. For example,
- The waste water must be treated before discharging it into water streams to limit the nutrient value.
- Recycling of nutrients can be checked through harvest.
- Removing nitrogen and phosphorous at the source, division of nutrient rich waters from the receiving bodies and dilution of these elements can minimize the eutrophication process.
- Algal blooms after death and decomposition should be removed.
- Disruption of algal food web stimulates bacterial multiplication.
- Physico-chemical methods like precipitation, nitrification, de-nitrification, electro-dialysis, reverse osmosis and ion-exchange methods can be adopted to remove dissolved nutrients like phosphorous and nitrogen.
Eutrophication and its type