Emergy analysis for the upper Mekong river intercepted by the Manwan hydropower construction

Hydropower is a renewable and clean source of power generation. Building on its economic, technical and environmental benefits, hydropower generation has been given priority in most countries' development. However, hydropower construction is associated with undesirable side effects on the environment, of which dams block the natural processes of water environments via human intervention, significantly altering the structure and functioning of river ecosystems. In this paper, the Upper Mekong River intercepted by the Manwan hydropower station is selected as our case study. An ecosystem health evaluation was conducted to describe the condition of disturbed river ecosystems based on emergy. The pre-dam river ecosystem was set as a reference condition to compare the reservoir and downstream ecosystems separated by the dam to assess the blocking effects in terms of material and energy flows. Furthermore, a set of indicators based on emergy's environmental loading, blocking effects, and economic benefits were established to analyze the health status of the post-dam river ecosystem. The results indicated that dam construction improved the vigor of the upper stream ecosystem, as well as the organization ability and environmental capacity of both the upper and downstream ecosystems, whereas dam construction created negative impacts on the resilience of the whole ecosystem. This indicates that the river ecosystem still provided supporting services to human society but not to as sufficient an extent as it did before perturbation. Additionally, the blocking effects analysis revealed the obstruction of nutrients and sediments resulted in the eutrophication of the reservoir and posed a potential oligotrophic threat for the downstream ecosystem.