Dynamics of heat transport across sediment deposited hyporheic zone inside reservoirs following hydropower production

摘要

Heat transport through hyporheic zones is critical for many temperature-sensitive biogeochemical processes and survival of aquatic organisms. Water storing and releasing in the reservoir are often made to modify hydropower production, which may cause hydrological variation and alter heat transport regime across the hyporheic zone inside the reservoir. In this study, we investigated heat transport across the hyporheic zone within a sediment deposited bar inside a hydropower reservoir on the mainstream of the upper Mekong River. Hydrothermal dynamics in the hyporheic zone following hydropower production were analyzed by monitoring changes of water level and temperature using automatic monitoring wells. Results showed that hydropower production induced water level fluctuations, enhanced hyporheic exchanges and thereby accelerated heat transport across the bar. The hyporheic zone was a heat source for the reservoir water regardless of the time of the year. In summer, heat transport from the bar hyporheic zone to the reservoir was strong (0.50 × 10~8-10.28 × 10~8 J m~(-1) d~(-1)) and mainly occurred through near-surface sediment layer (0-0.5 m), which was attributed to active hyporheic exchanges and strong solar radiation. In winter, heat transport was weak (0.01 × 10~8-1.01 × 10~8 J m~(-1) d~(-1)) and mainly occurred in sediment bottom layer (< 1.0 m) with limited energy inputs from microbial activities. This study adds to our understanding of hydrothermal dynamics in hyporheic zones under flow regulations by dams.