Environmental consequences of damming the mainstream Lancang-Mekong River: A review

Abstract Damming rivers to generate hydropower can help mitigate the world's energy crisis and reduce the risk of global climate change; however, damming can also produce enormous negative effects on the environment and ecosystems. The mainstream Lancang-Mekong River within China has been planned as one of the thirteen state hydropower bases. To date, there have been six operational dams along the mainstream Lancang River, and the 15 remaining dams of the proposed Lancang cascade will be completed in the next decades. In this paper, we examined several crucial environmental changes and ecological responses that have resulted from the construction and operation of the existing dams of the Lancang cascade. The current literature and observational data suggest that the commissioned dams have led to a decline in the flood season water discharge and annual sediment flux within China's borders, reservoir aggradations, and water quality degradation in the reservoirs, which has negatively affected riverine aquatic biological communities and fish assemblages. In contrast, the dams have only had small unfavorable effects on downstream environments and ecosystems outside of China. Because of the potential environmental and geopolitical risks of the Lancang cascade dams, a long-term basin-wide terrestrial and aquatic monitoring program is urgently required to ensure that regional sustainable development occurs in the Lancang-Mekong River Basin.