What effect does excessive nutrient loading have on aquatic ecosystems?

Excessive nutrient loading, particularly from sources like agricultural runoff, septic systems, and wastewater discharges, introduces high levels of nutrients such as nitrogen and phosphorus into aquatic ecosystems. This can trigger a rapid increase in the growth of algae, known as algal blooms. While these blooms can initially seem beneficial by providing additional food for some aquatic life, they can be detrimental to the overall ecosystem health.

As the algae grow and eventually die, their decomposition consumes a significant amount of dissolved oxygen in the water. This depletion of oxygen can create hypoxic conditions, where there is insufficient oxygen for fish and other aquatic organisms to survive. Consequently, this can lead to fish kills and a decline in the overall biodiversity of the ecosystem, as sensitive species are unable to thrive in these conditions.

In contrast, the other choices describe outcomes that are not associated with excessive nutrient loading. For example, promoting biodiversity and enhancing water clarity are typically results of balanced nutrient levels rather than excessive amounts. Similarly, while decreased habitat availability may occur due to other environmental stresses, it is not a direct consequence of nutrient loading in the same way that algal blooms and oxygen depletion are.