Water diversion projects negatively impact lake metabolism: A case study in Lake Dazong, China

Water diversion projects are one of the major tools for counteracting water resource shortage in China. Many diversion projects aimed at diverting water from the Yangtze River or other rivers. This study, using one of the lakes receiving Yangtze River water as a case study, illustrated how nutrient, O₂, and N₂ fluxes across the sediment-water interface (SWI) changed with increasing nitrate loads during in situ benthic chamber incubation. Increasing nitrate loads in the overlying water caused complex changes in the SWI fluxes. Furthermore, responses of the SWI fluxes to increasing nitrate loads were largely driven by season. Dissolved inorganic carbon (DIC), ammonium (NH₄⁺), CO₂, and N₂ fluxes increased with enhanced nitrate loads, likely induced by stimulated anaerobic mineralization. DIC had a stronger response to nitrate additions in late summer versus in winter. Nitrate influxes were enhanced by increasing nitrate loads in winter and showed a similar but stronger response in summer, with a shift from sediment release to influx. Sediment oxygen consumption decreased with increasing nitrate loads in both late summer and, especially, winter. Nitrate addition may have changed the proportions of aerobic and anaerobic respiration, i.e., nitrate competed with O₂ as an electron acceptor. With increasing nitrate loads, anaerobic respiration was strengthened in the dark benthic chamber. Water diversion from the heavily polluted Yangtze River to Lake Dazong may be disadvantageous for controlling eutrophication, especially during the summer.