CARBON BUDGET OF A VALLEY-TYPE CASCADE RESERVOIR IN THE UPPER MEKONG RIVER

Abstract

To evaluate the damming effect on carbon transportation, a carbon budget was constructed for a daily-operated hydroelectric reservoir, the Gongguoqiao Reservoir in the upper Mekong River. Different from any existing model, there was no sign of trophic upsurge from the flooded land that fuels up intense greenhouse gas emissions or any eutrophication caused by nutrient retention that accelerates carbon uptake in surface water since most of the nutrients in water was in a solid mode. When the rainfalls brought plenty of carbon in the rainy season, most of the particulate species were sequestered while the dissolved species were discharged directly to the downstream, allowing insufficient time for the decomposition of allochthonous DOC and limiting the production of carbon dioxide. Due to the high sedimentation rate and low carbon emission, the reservoir has been acting as a significant carbon sink.