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Which THREE of the following observations most likely indicate that human activity is negatively impacting a freshwater ecosystem?

Rationale

An algal bloom occurs in a pond near a farm, the sediment load of a river near a deforested area increases, and nonnative fish are found in a lake.

These observations indicate negative impacts from human activities, such as agricultural runoff, deforestation, and the introduction of nonnative species, which can disrupt the natural balance of freshwater ecosystems.

A (A variety of aquatic insect species are found in a stream.) YOUR ANSWER

The presence of a diverse range of aquatic insect species generally suggests a healthy ecosystem, as it indicates good water quality and proper habitat conditions. This observation does not imply negative human impact; rather, it may suggest that the ecosystem is functioning well.

B (An algal bloom occurs in a pond near a farm.) CORRECT

Algal blooms are often stimulated by nutrient runoff—particularly nitrogen and phosphorus—from agricultural activities. This excess nutrient input leads to eutrophication, which can deplete oxygen levels in the water and harm aquatic life, indicating a negative impact on the freshwater ecosystem.

C (The sediment load of a river near a deforested area increases.) CORRECT

Deforestation typically leads to increased erosion, resulting in higher sediment loads in nearby rivers. This can smother aquatic habitats, reduce light penetration, and disrupt the growth of aquatic plants, thus negatively affecting the ecosystem's health.

D (Nonnative fish are found in a lake.) CORRECT

The introduction of nonnative fish species, often due to human activities such as fishing or aquarium releases, can lead to competition with native species for resources. This can disrupt the ecological balance and lead to declines in native fish populations, indicating a negative impact on the ecosystem.

Conclusion

The observations of algal blooms, increased sediment loads, and the presence of nonnative fish highlight significant human-induced disturbances in freshwater ecosystems. These factors contribute to the degradation of water quality and biodiversity, emphasizing the need for sustainable practices to protect these vital habitats.

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