Hydropower dam impact on the environment and livelihood in the Mekong river basin

Hydropower is a renewable energy source, but can have huge impacts on freshwater ecosystems, fisheries, and flood dependent agriculture. New hydropower dams have already threatened some of the world’s most ecologically diverse river basins such as the Amazon, the Zambezi and the Mekong. They may partially dehydrate the landscapes and influence the surface and the groundwater systems. River dynamics may suffer major modifications, particularly in runoff distribution change. There may also be an increase in the erosive capacity of the river, linked to the decrease in sediment load as a result of reservoir sedimentation. Environmental hazards may include remobilization of sediment contamination, nutrient input reduction, reservoir eutrophication, groundwater organic carbon contamination. Ecological impacts may include loss of forests and wildlife habitats, loss of species populations and the degradation of upstream catchment areas due to inundation, loss of aquatic biodiversity, including upstream and downstream fisheries, and loss of the services of downstream floodplains, wetlands, riverine, estuarine and adjacent marine ecosystems. In the Lower Mekong Basin, at least twelve potential mainstream hydropower developments are currently being considered by private sector developers. Hydropower development adversely affects the productivity of agriculture by degrading or depleting a number of natural resources that constitute vital agricultural inputs. An estimated fifty percent of the Mekong’s annual sediment load is derived from the Chinese section of the Mekong Basin. The construction of the Yunnan cascade therefore poses a disproportionately large threat to the supply of nutrients downstream. Hydropower development may harm Mekong agriculture by reducing the availability of clean freshwater. Downstream from the hydropower dam, water quality is reportedly more turbid than before the dam is built, due to increased riverbank erosion that results from fluctuating river levels. Hydropower development has recently reduced the supply of fish stocks in the Mekong Basin. Major impacts on fisheries include: physical barrier to migration, fish habitats degradation and destruction.