Question

A lake with an inflow of domestic sewage rich in organic waste may result in
(a)Drying of the lake very soon due to algal bloom
(b)An increased production of fish due to lot of nutrients
(c)Death of fish due to lack of oxygen
(d)Increased population of aquatic food web organisms

Answer 1

Hint: A lake rich in domestic sewage nutrients will lead to eutrophication and cause the environment to become rich in nutrients and pollutants. This also affects the aquatic organisms.

Complete answer:
The natural aging of a lake by nutrient enrichment such as nitrogen, phosphorus, and domestic sewage is introduced by streams draining into the lake. These in start might seem nothing to the aquatic habitats at first but as time passes by might create a problem. It can cause algal blooms and other aquatic plants which will overcrowd the area and plants compete for sunlight, space, and oxygen. The biodegradable organic matter coming from the domestic sewage is decomposed by bacteria and other microorganisms. They multiply by using these organic substances and a lot of dissolved oxygen is consumed by the microorganisms involved in biodegradation of organic matter. There is competition as even other organisms need oxygen and this leads to a sharp decline in dissolved oxygen. This causes the mortality of fish and other aquatic creatures.
So, the correct answer is option ‘Death of fish due to lack of oxygen’.

Note: Reducing these kinds of elements from the water bodies should be a key concern about a sustainable solution. Cleanup measures have been set up and most are a success. In the mid-1970s Finnish phosphorus removal measures were started and have targeted rivers and lakes polluted by industrial discharges. Oyster reefs remove nitrogen from the water column reducing the harmful algal blooms. Fertilizers and chemical compounds should be reduced. It was found that organically fertilized fields significantly reduce harmful nitrate leaching compared to modern fertilized fields. But recent studies say organic fertilizers have more harmful effects.