Question 30

B, C, and D indicate that human activity is negatively impacting a freshwater ecosystem.

Observations such as algal blooms, increased sediment loads, and the presence of nonnative fish species typically signal detrimental effects from human activities on freshwater ecosystems.

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

This observation generally suggests a healthy ecosystem, as a diverse range of aquatic insects indicates good water quality and a balanced food web. Therefore, this choice does not imply negative human impact.

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

Algal blooms are often the result of nutrient runoff from agricultural activities, such as fertilizers, which can lead to excessive growth of algae. This can deplete oxygen levels in the water, harming aquatic life, and serves as a clear indicator of negative human impact on freshwater ecosystems.

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

Increased sedimentation in rivers often results from deforestation, which removes vegetation that stabilizes soil. This can lead to erosion and negatively affect water quality and aquatic habitats, making this observation a strong indicator of human activity harming the ecosystem.

D) Nonnative fish are found in a lake.

The introduction of nonnative fish species can disrupt local ecosystems by outcompeting native species for resources, altering food webs, and introducing diseases. This observation is indicative of negative human impact, often resulting from intentional or unintentional introductions of species.

Conclusion

The presence of algal blooms, increased sediment loads, and nonnative fish species are significant indicators of human activities adversely affecting freshwater ecosystems. Each of these observations reflects changes in water quality and biodiversity that can result from agricultural practices, deforestation, and species introduction, highlighting the negative consequences of human interference in these environments.