Which of the following can cause eutrophication of surface waters?

Eutrophication of surface waters is primarily caused by the excessive accumulation of nutrients, particularly phosphorus. When phosphorus enters water bodies through runoff from agricultural fields, urban areas, and wastewater, it stimulates the overgrowth of algae, leading to algal blooms. These blooms can deplete oxygen in the water as they decay, resulting in hypoxic conditions that are harmful to aquatic life.

Phosphorus is often the limiting nutrient in freshwater systems; therefore, its addition can significantly increase productivity. This process disrupts the balance of the aquatic ecosystem, leading to adverse effects like fish kills and loss of biodiversity. While nitrogen can also contribute to eutrophication, phosphorus is generally regarded as the primary driver in freshwater systems, making it the key nutrient of concern for eutrophication.