1. Engineering Research Center of Eco-environment in Three Gorges Reservoir Region, Yichang 443002, China; 2. Collge of Hydraulic and Environmental Engineering, China Three Gorges University, Yichang 443002, China; 3. Jiaxing Water Resources & Hydroelectric Prospecting & Design Research Institute Co, Ltd, Jiaxing 314001, China; 4. Three Gorges Base Development Co, Ltd, Wuhan 430074, China
Abstract：This study investigates the temporal and spatial variabilities of hydro-chemistry in Xialaoxi, a typical karst river in Yichang, Hubei Province, via biweekly sampling and monitoring at multiple sites in the main stream and tributaries throughout one year. The rock weathering rate, carbon sink flux, and carbon sink in the watershed were estimated using the forward model and the chemical runoff method. The results show that Mg2+, Ca2+, and HCO3-mainly came from the weathering and dissolution of carbonate rocks, and their concentrations were closely related to the dilution effect of the flow and decreased along the main channel, with lower concentrations in the wet season comparing to the dry season. Na+, K+, Cl-,NO3-, SO42- in water were from anthropogenic input, thus their concentrations increased dramatically in the densely populated downstream and in the seasons with intense human activities. The estimated rock weathering rate, carbon sink flux, and carbon sink amount in the catchment were 71.83t/(km2·a), 5.31×105mol/(km2·a), and 6.96×107mol/a, respectively. The carbon sink flux of Xialaoxi is as the same magnitude order as that of medium and large karst rivers, and higher than that of non-karst rivers and the world average, which can be attributed to the high coverage of carbonate rocks within the watershed and relatively warm and humid climatic conditions. Therefore, it indicates that karst streams under subtropical monsoon climate are an important “missing carbon sink”.
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