What environmental impacts have been reported for the Three Gorges Dam?

• A. Emissions, erosion, and earthquakes
• B. Improved wildlife habitat
• C. No significant environmental impact
• D. Increase in forest cover

Answer: (A)

Large dams can bring energy and flood control benefits, but they also bring notable environmental problems that researchers have documented for the Three Gorges Dam. One major impact is emissions from the reservoir: when large areas are flooded, submerged vegetation and organic matter decompose anaerobically, releasing methane and other gases that contribute to atmospheric greenhouse gases. Another clear issue is changes in erosion and sediment dynamics: the dam traps a lot of sediment, which alters how sediment is carried downstream, leading to erosion of riverbeds and banks downstream and affecting habitats and navigation, while upstream shoreline areas can experience instability as water levels rise. A third concern is potential seismic activity related to the added weight of the large body of water and changes in pressure on faults in the region, with some studies noting increased microseismicity after filling. Taken together, these environmental effects—emissions from the reservoir, changes in erosion and sediment transport, and possible earthquakes—reflect the kinds of impacts reported for the dam. Positive changes like improved wildlife habitat or forest cover are not supported by the broad body of evidence, and claiming no significant environmental impact would overlook the documented changes in the river system and local ecosystems.