Which of the following is identified as a cause of eutrophication?

Eutrophication is a process that involves the enrichment of water bodies with nutrients, primarily nitrogen and phosphorus, leading to excessive growth of algae and aquatic plants. The effluent from wastewater treatment facilities often contains high levels of these nutrients. When this effluent is discharged into rivers, lakes, or coastal waters without adequate treatment, it can significantly increase the nutrient levels in those ecosystems. This nutrient overload can trigger algal blooms, which not only deplete oxygen in the water as they decompose but also can release toxins that harm aquatic life and disrupt the overall ecological balance of the water body.

In contrast, while increased rainfall can lead to higher runoff and potential nutrient loading, it is not a direct cause of eutrophication. Instead, it can be a facilitator of runoff from agricultural areas or urban environments, where fertilizers and other organic matter may enter water bodies. Similarly, the destruction of wetlands can impact nutrient filtration and habitat stability but is not directly a cause of eutrophication itself. Runoff from industrial areas may contribute pollutants, but these generally differ from the nutrient-related causes of eutrophication. Hence, wastewater effluent stands out as a significant direct contributor to the eutrophication process due to its nutrient content.