Sample Passage with questions and answers

The Eutrophication is the nutrient enrichment in a water body. A freshly formed body of water has a very low concentration of plant nutrients. Little plant life develops in such waters. Low primary production limits animal communities as well surface runoffs, wind borne dust and organic debris, excreta and exudates of animals which use water, slowly raise the nutrient content. Bacteria and cyanobacteria fix atmospheric nitrogen.

Phosphates in rocks and detritus at the bottom are solubilized by the microbial activity. In gradual stages the nutrient status of the water improves. A moderate population of plants, animals, aquatic fungi and other microorganisms develop. With the passage of time further nutrient enrichment occurs. Dense population of plants, phytoplanktons and animals now appears.

At this stage, the aquatic system becomes highly productive in terms of fish yield and other produce. Based on nutrient status and productivity an aquatic system can be classified into the following three types: The oligotrophic or water with poor nutrient status and productivity; the mesotrophic or water with intermediate or moderate nutrient status and productivity; and eutrophic or water with rich nutrient status with high productivity.

In some eutrophic waters dense population of plank tonic algae develops, water turns green followed by unpleasant odour referred to as water bloom.

Answer the following questions:

1. Write short note Eutrophication.

Ans. The process of again of a body of water by the growth of vegetation particularly algae, these plants flourish and then die, their decay using up the dissolved Oxygen of water with serious impairment of water quality, in lakes, rivers, harbors, and estuaries, the accumulation of nutrients.

2. What are results of Eutrophication?

Ans. In Eutrophication, algal bloom release chemicals which kill fish and other aquatic animals when oxygen fall to zero i.e., anaerobic zone same bacteria drive oxygen through reduction of nitrates on complete exhaustion of nitrate, oxygen may be last resort be obtained by reduction of sulphate yielding hydrogen sulphide (H^S) causing foul smell and bad taste of water.

3. Which are the organisms that fix up nitrogen?

Ans. Certain bacteria e.g. Azotobacter and blue-green algae e.g. Anabaena, Phizobium are able to fix nitrogen in association with cells in the roots of leguminous plants such as pear and beans, in which they form characteristic root nodules, cultivation of legumes is therefore one way of increasing soil nitrogen.

4. Name the types of Eutrophication.

Ans. Eutrophication is of two types.

(i) Cultural Eutrophication: St is due to human activities which are responsible for 80% nitrogen and 75% of phosphorous to streams and lakes.

(ii) Natural Eutrophication: It is due to natural activities/reasons.

5. What is water bloom?

Ans. An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a Small number of phytoplankton species are involved, and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells.