Fish mortality increases with influx of nutrients in a fresh-water body' write two reasons. How will the influx of nutrients affect the BOD level of this water body?

Explanation

Fish mortality increases with influx of nutrients in a fresh water body due to the following reasons:
(i) Nutrients like phosphates and nirates overstimulate the growth of algae. Which decrease the dissolved oxygen in water body leading to fish mortality. Decomposing remains of fish further decrease oxygen levels in water leading to further fish mortality, setting up a vicious circle.
(ii) In a young fresh lake, water is cold and clear but wish influx of nutrients algal growth increases making the lake shallower and warmer leading to increased fish mortality. The influx of nutrients primarily phosphates and nitrates leads to excessive algal growth or accelerated eutrophication. This algal growth leads to rapid depletion of the dissolved oxygen in the water body causeing a rise in BOD levels.