GED Science TestEarth and Space ScienceMedium
A city planner is evaluating the long-term impact of constructing a large dam on a major river. Which of the following is the most significant long-term consequence for the regional ecosystem due to altered water flow and sediment transport?
- AEnhanced oxygen levels in river water immediately below the dam.
- BIncreased biodiversity in upstream reservoir areas.
- CReduced risk of flooding in downstream areas.
- DChanges in delta formation and coastal erosion downstream.
Show answer & explanationAnswer & explanation
Correct answer: D. Changes in delta formation and coastal erosion downstream.
Dams trap sediments, preventing them from reaching downstream areas. This lack of sediment alters natural delta formation and increases coastal erosion, which is a significant long-term ecological impact.
Why the other options are wrong
- A. Water released from deep reservoirs can be oxygen-depleted, not enhanced, negatively affecting downstream aquatic life.
- B. Reservoirs often lead to a decrease in native biodiversity, replacing riverine species with lacustrine ones.
- C. While dams reduce flooding risk immediately downstream, this is a short-term benefit, and the question asks for long-term ecological consequences.
Dam Environmental Impacts
Large dams significantly alter river ecosystems by changing water flow, temperature, and sediment transport, leading to various environmental consequences.
- Block fish migration routes.
- Alter downstream temperature and oxygen levels.
- Reduce sediment delivery to deltas and coastlines, increasing erosion.
Memory trick: Dams Disrupt Downstream Deltas Dramatically.