A 3-hectare lake in the American Midwest suddenly has succumbed to an algal bloom. What is the likely cause of eutrophication in freshwater ecosystems, such as this one?

Question

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The most likely cause of eutrophication in freshwater ecosystems, such as the 3-hectare lake in the American Midwest, is nutrient-rich runoff. This can occur when excess nutrients from sources such as fertilizers, animal waste, and sewage enter the water system, leading to an overgrowth of algae and ultimately an algal bloom. Increased solar radiation (A) may contribute to the growth of algae, but it is not the primary cause of eutrophication. Introduction of non-native tertiary consumer fish (B) may disrupt the ecosystem, but it is not the primary cause of eutrophication. Accidental introduction of a prolific culture of algae (D) may exacerbate the problem, but it is not the underlying cause. Iron dust blowing into the lake (E) may not necessarily contribute to eutrophication.

A 3-Hectare Lake in the American Midwest Suddenly Has Succumbed