What consequence can come from excessive nutrient runoff?

Excessive nutrient runoff can lead to significant disruptions in aquatic ecosystems. When nutrients, particularly nitrogen and phosphorus, wash off agricultural fields into nearby waterways, they can cause eutrophication, which is the over-enrichment of water bodies. This process results in excessive growth of algae, leading to algal blooms that deplete oxygen in the water when they die and decompose. This oxygen depletion can create dead zones where aquatic life cannot survive, disrupting the balance of the ecosystem and harming fish and other aquatic organisms.

In contrast, the other options highlight outcomes that are not associated with excessive nutrient runoff. Extended drought periods are climate-related and not a direct result of nutrient runoff. Enhanced crop yield and improved soil health typically result from careful nutrient management and balanced fertilization rather than excessive runoff, which can actually degrade soil quality and reduce agricultural productivity in the long term. Thus, the most relevant consequence of excessive nutrient runoff is indeed the disruption of aquatic ecosystems.