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Chinese Researchers Make Progress in Study of Cascade Hydropower Development Impacts on River Biogenic Elements
Post Time:2020-07-20Front:[ Large Medium Small ]

Funded by National Natural Science Foundation of China (Approval Nos. 91547206 and 51425902), the study of cascade hydropower development impacts on river biogenic elements yield fruitful results. This study is carried out by an international research team, comprised of CHEN Qiuwen and ZHANG Jianyun from Nanjing Hydraulic Research Institute, NI Jinren from Peking University, China, Jef Huisman from University of Amsterdam, the Netherlands, Stephen Maberly from Center for Ecology and Hydrology, UK, and Taylor Maavara from Yale University, USA. For a long time, it has been believed that high dams and large reservoirs significantly impede the flow of key biogenic elements such as carbon, nitrogen and phosphorus, thereby affecting downstream ecosystems.

There are some reports by the international community saying that the development of cascade hydropower on the Lancang River undermines the downstream water-sediment-nutrient situation and primary productivity, and affects the protein intake and right to life of residents in the downstream countries. However, there is no direct evidence to support these reports. In recent years, greenhouse gas emissions from reservoirs have led to doubts about the cleanliness of hydropower. So it is an important scientific issue of sustainable hydropower development to explore the impacts of cascade reservoirs on migration and conversion of key biogenic elements and their environmental effects.

Fig. 1 The conceptual mechanism for the stimulation of phytoplankton production and modification of nutrient export downstream by dams in the upper Mekong River

The research team finds that although the cascade hydropower development of the Lancang River partially intercepts the total nitrogen and total phosphorus, high dams and large reservoirs increase the hydraulic retention time and change the temperature field, thereby promoting the phytoplankton production and the succession of community structure in reservoirs. The accumulation of sedimentary organic matter and reservoir stratification lead to an oxygen-poor bottom. These biological and abiological factors together enhance the release of bioavailable phosphorus and the conversion of nitrate nitrogen to ammonia nitrogen, thus increasing the bioavailability of downstream nitrogen and phosphorus. A paper of the research results, titled Hydropower Reservoirs on the Upper Mekong River Modify Nutrient Bioavailability Downstream, was published online in the National Science Review on February 17, 2020. Link to the paper is This discovery has challenged the long-standing traditional understanding of the impacts of dam construction on river biogenic factors, and will help to serve the Lancang-Mekong geopolitical cooperation.

Fig. 2 Key nutrient processes during a reservoir life cycle

The team also clarifies the impacts of reservoir construction on the terrestrial and marine material fluxes of key biogenic factors, and reveals the potential impact mechanism of reservoirs from the perspectives of nutrients proportion change, greenhouse gas emission, change of nutrients status in a reservoir and downstream. Then the team proposes specific quantification methods and related suggestions for reservoir planning, construction and operation, which are reservoir scheduling shall be optimized to change hydraulic retention time and thus to control nutrients deposition and greenhouse gas emission. It is also advised to implement this idea throughout a reservoir’s life cycle. A paper of the research results, titled River Dam Impacts on Biogeochemical Cycling, was published online in Nature Reviews Earth & Environment on February 3, 2020. Link to the paper is The achievements provide a new perspective for global sustainable hydropower development and river ecological protection in the future.

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