Question

An oligotrophic lake is characterised by
A. great changes in water level
B. Long food chains
C. Low nutrient and little life
D. High nutrient levels and abundant flora and fauna

Answer 1

Hint: Lakes are the freshwater biomass. They are often large and deep upto 100 meters. They have permanent water. The lakes are mainly of different types; it depends on how much the plant life can give favour among these lakes: eutrophic and oligotrophic lakes.

Complete answer:
The lakes develop by different ways:
-As natural or manmade depressions filled with water
-As a result of glaciations
-As they cut off the acute bend of winding rivers. The lakes which are U shaped in nature are termed as oxbow lakes.

Oligotrophic lakes: These are the lakes which are deep with steep rocky sides and narrow littoral zones. They are very low in nutrients like in phosphorus, calcium and in the nitrogen. The lake is of very low productivity and very low nutrient contents. These lakes have very less amount of algal production and have clear water with high drinking quality in it. Therefore they support a few organisms. Their water is usually dark and very clear and deep water always contains the oxygen because there are very many organisms using it. Some lakes have saline as well as the brackish water like the Sambhar lake which is situated in Rajasthan. The brackish lakes are called oligotrophic lakes.
-Eutrophic lakes: are shallow lakes and are very nutritious and life-like. These lakes have low oxygen because decomposer organisms rapidly use it and metabolize the organic matter produced by other organisms. The Dal Lake of Kashmir is an example of Eutrophic lake.

Hence, the correct answer is option (C).

Note: The physical factors of a lake depend on the source of water, location, altitude, latitude and surrounding biome. The small lakes and the peripheral shallow parts of the large lakes have the physical factors forms of life almost similar to those found in the ponds. Other freshwater biomes are streams, rivers, ponds and marshes.