托福综合写作

📖 阅读文章

The construction of large-scale hydropower dams has long been considered a cornerstone of sustainable energy development. Proponents argue that dams provide clean electricity, flood control, and water storage, making them essential for growing economies. However, a closer examination reveals that the environmental and social costs of such projects often outweigh their benefits. This essay will outline three major drawbacks of large dams. First, dams disrupt river ecosystems by blocking fish migration and altering sediment flow, which can lead to the collapse of native species and degradation of downstream habitats. For example, the construction of the Aswan High Dam in Egypt drastically reduced nutrient-rich silt reaching the Nile Delta, causing a decline in sardine fisheries and coastal erosion. Second, reservoirs created by dams are significant sources of greenhouse gases, particularly methane, due to the decomposition of submerged vegetation in low-oxygen conditions. Studies have shown that tropical reservoirs can emit more carbon per kilowatt-hour than fossil fuel plants when accounting for land-use changes. Third, the displacement of local communities is a serious social issue. Large dam projects often force thousands of indigenous and rural people to relocate without adequate compensation, leading to cultural disruption and economic hardship. The Sardar Sarovar Dam in India displaced over 300,000 people, many of whom faced prolonged legal battles and inadequate resettlement. These three points demonstrate that despite their apparent benefits, large dams impose unacceptable ecological and social burdens.

🎧 听力讲座

The reading presents a pessimistic view of large dams, but its arguments are based on outdated or incomplete evidence. Let’s examine each point. First, regarding fish migration and sediment flow, modern dam designs now incorporate fish ladders and bypass systems that allow passage for many species. Moreover, sediment management techniques, such as controlled flushing, can mimic natural flood cycles and restore downstream habitats. The Aswan Dam example ignores that subsequent adaptive measures have partially revived fisheries through artificial nutrient supplementation. Second, the claim about methane emissions is exaggerated. Recent life-cycle assessments show that while some tropical reservoirs do emit methane, the global average is lower than the reading suggests, especially when compared to coal or natural gas. Furthermore, new turbine technologies can capture methane from reservoirs and convert it to energy, reducing net emissions. Third, displacement is a genuine concern, but the reading fails to acknowledge that modern dam projects, particularly in developed countries, now follow stringent environmental and social impact assessments, including free, prior, and informed consent of affected communities. In many cases, resettlement packages include land-for-land compensation and livelihood restoration programs. Thus, the lecture argues that with proper planning and technological innovation, many of the alleged disadvantages can be mitigated or avoided entirely.