Eutrophication of lakes results from addition of mainly _________________.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Nitrogen and Phosphorous
Nitrogen and phosphorus are the limiting nutrients for algal growth. When fertiliser runoff, sewage and detergents load a lake with nitrates and phosphates, algae bloom, die and decompose; the decomposition consumes dissolved oxygen and the water body turns anoxic. That nutrient enrichment is eutrophication.
Bicarbonate, sulfate, calcium, sodium, iron and nickel change the hardness, salinity or toxicity of water, but they do not drive the nutrient enrichment that defines eutrophication.