Akey feature of estuaries is
low light conditions and high productivity
salt water and fresh water
frequent algal blooms
little or no vegetation

c Option (2)

Explanation: Estuaries refers to those coastal area water bodies where the river water flows over and meets the sea water. It is the region where there is presence of high sunlight and maximum productivity. The nutrient content is very high here and presence of excess nutrients lead to the formation of the algal blooms. It has a rich biodiversity where the water appears to be brackish in color and salty in taste but comparatively lesser than the ocean water.

Thus the correct answer is option (2).

compost can be added to topsoil as a:

pesticide