Question

Which of the following is the cause of Eutrophication?
(a) Increase in nutrients
(b) Increase in dissolved salts
(c) Reduction in dissolved oxygen
(d) Reduction in water pollution

Answer 1

Eutrophication is the process of enrichment of the aquatic ecosystem by human activities that adds nutrients like nitrogen and phosphorus to the water bodies, which leads to excessive algal population and lower biodiversity.

Complete step by step answer:
Eutrophication is a process which is mainly seen near the ocean areas where nutrients get into water bodies like lakes, ponds or oceans. Humans generally dump their waste into water bodies but what is wastage to humans can be good to plants or other creatures. For example, here, nutrients are the food for algae. Now, when it grows, it blocks sunlight from entering into the water bodies and it is very well known that plants need sunlight to make their food through the process of photosynthesis. Due to the lack of photosynthesis, plants die and the algae dies too. Now, Bacteria come into play and digest the dead plants using the oxygen left in the plants and give off carbon dioxide in return. Blocking of water surface does not let the fish and other wildlife to swim and they become unhealthy and eventually die due to lack of oxygen.
For option (a), Eutrophication is the result of excessive accumulation of nutrients like phosphorus and nitrogen. So, this option does not suit its definition.
For option (b), Eutrophication leads to increase in the amount of the total organic carbon and does not increase the dissolved salts.
For option (c), since Eutrophication leads to excessive growth of plant population so, there is a high content of the dissolved oxygen in the day time but at dark it is greatly reduced due to the respiration of the algae and other microorganisms which are the result of eutrophication. So, eutrophication leads to reduction in dissolved oxygen.
For option (d), over growth of plant algae, lack of free surface for movement of aquatic organisms, low intake of oxygen, all these lead to the degradation of the aquatic ecosystem and hence, lead to water pollution. So, this option is also incorrect

So, the correct answer is Option C.

Note:
Oligotrophic is the reverse process to the eutrophication process, in which water is less nutrient rich to support less algae growth. Oligotrophic water has very clean water with drinking purpose quality.