Cascade Reservoirs Drive Dissolved Organic Carbon Dynamics in the Lancang River

Abstract

There has been much debate about the potential effects of cascade reservoirs on nutrient retention. Dissolved organic matter (DOM) is an important nutrient in aquatic environment. Here, through a survey of source to leave-boundary section of Lancang River in June and November of 2017-2018, our results show that weak spatiotemporal variations were observed for dissolved organic carbon, whereas sediment organic carbon was remarkably higher in reservoir reach. DOM in LCR was mainly charactered by higher humification degree from terrestrial source. The larger HRT in reservoir reach resulted in the increased phytoplankton densities, thus brought about the sedimentation of autochthonous organic matter, manifesting higher contribution rates of algal source. The construction of hydropower reservoirs triggers a series of changes to DOM, including lower HIX, higher BIX and higher FI. All the DOM parameters (DOC, BIX and SUVA254) were positively fitted with the reservoirs age, while BIX was negatively correlated with the dam height, HRT and reservoir capacity. A unique fluorescent fraction C5 appeared in the reservoir reach, which was were significantly related with dGHG, especially for CO2 and N2O, while BIX was significantly and positively correlated with dCH4. As a clean energy, the priority application of high dam reservoirs was suggested for the development of hydro-electric power, which can weaken the adverse impact.

Keywords: Dissolved Organic Matter, Reservoir, Distribution, EEM, Greenhouse gas