What is eutrophication primarily caused by?

Eutrophication is primarily caused by the addition of nutrients, particularly nitrogen and phosphorus, to aquatic systems. These nutrients often come from agricultural runoff, wastewater discharge, or industrial effluents. When these nutrients enter a water body, they can lead to an excessive growth of algae—a phenomenon referred to as algal blooms. While algal blooms can initially seem beneficial, they can result in various ecological problems, including reduced oxygen levels in the water as algae die off and decompose. This depletion of oxygen can be detrimental to fish and other aquatic life, ultimately harming the ecosystem's balance and health.

The other options, while related to aquatic systems, do not directly cause eutrophication. Increased sedimentation can impact water clarity and habitat but does not necessarily lead to nutrient over-enrichment. A deficiency of nitrogen is contrary to the process of eutrophication, which typically involves excess nitrogen or phosphorus. The removal of aquatic plants can alter the ecosystem but is not the primary driver of the nutrient overload that characterizes eutrophication.