Answer : Option A) Increased eutrophication caused by high levels of nitrogen and phosphorous increased nitrates.
Explanation : The major human influence on biogeochemical cycles is observed in the increased eutrophication these days. This eutrophication occurs because of presence of excess amount of nitrogen and phosphorus in the water bodies which increases the number of nitrates in it. The major cause is identified to be is nitrogen pollutants; which comes from the surface run-off from agricultural land, whereas most phosphorus pollution is found to be collected from households and industry, including phosphorus-based detergents.
This has drastically affected the biogeochemical cycles that exists in nature.