环境地球化学国家重点实验室知识库

To assess the effects of river damming on dissolved inorganic carbon in the Jialing River, a total of 40 water samples,including inflow, outflow,and stratified water in four cascade reservoirs (Tingzikou,Xinzheng, Dongxiguan,Caojie) were collected in January and July, 2016. The major cations,anions, and delta ~(13)C_(DIC) values were analyzed. It was found that the dissolved compositions are dominated by carbonate weathering, while sulfuric acids may play a relatively important role during carbonate weathering and increasing DIC concentration. Different reservoirs had variable characteristics of water physio-chemical stratification. The DIC concentrations of reservoir water were lower in summer than those in winter due to the dilute effects and intensive aquatic photosynthesis,as well as imported tributaries. The delta~(13)C_(DIC) values in Tingzikou Reservoir were higher during summer than those in winter, which indicated that intensive photosynthesis increased the delta~(13)C_(DIC) values in residual water, but a similar trend was not obvious in other reservoirs. Except for in Xinzheng Reservoir, the delta~(13)C_(DIC) values in inflow and outflow reservoir water were lower than those in the surface water of stratified sampling in summer. For stratified sampling,it could be found that,in summer,the Tingzikou Reservoir delta~(13)C_(DIC) values significantly decreased with water depth due to the anaerobic breakdown of organic matter. The significant correlation (p < 0.01 or 0.05) between the DIC concentrations,the delta~(13)C_(DIC) values and anthropogenic species (Na~++K~+,Cl~-,SO_4~(2-)and NO_3~-) showed that the isotope composition of DIC can be a useful tracer of contaminants. In total, Tingzikou Reservoir showed lacustrine features, Xinzheng Reservoir and Dongxiguan Reservoir had "transitional"features, and Caojie Reservoir had a total of "fluvial" features. Generally,cascade reservoirs in the Jialing River exhibited natural river features rather than typical lake features due to characteristics of reservoir water in physiochemical stratification, spa- tiotemporal variations of DIC concentrations and isotopic compositions. It is evident that the dissolved inorganic carbon dynamics of natural rivers had been partly remolded by dam building.