光照水库溶解无机碳变化及其来源解析

河流拦截筑坝形成蓄水河流，逐渐向“湖泊型”生态系统演化，加强了生物地球化学循环并进一步影响水体碳循环.为了更准确地进行全球碳循环的预算并预测碳循环变化，必须确定对河流系统产生影响的碳来源.因此，通过测定库区水体c（DIC）（DIC为溶解性无机碳）及其δ13C（稳定碳同位素），分析了DIC的主要来源及其影响因素.结果表明:①水体c（DIC）为1.80~5.02 mmol/L，而δ13C_DIC（溶解性无机碳的稳定碳同位素）为-7.45‰~-1.26‰.c（DIC）与EC（电导率）、TA（总碱度）均呈正相关，与水温呈负相关.表水层δ13C_DIC与c（DIC）、TA均呈正相关，与EC在入库河流处呈负相关；而滞水层δ13C_DIC与EC、pCO₂（二氧化碳分压）、TA、c（DIC）均呈正相关.②水平方向上，表水层各指标变化明显，TA、EC、SIc（方解石饱和指数）和c（DIC）整体上呈降低趋势，δ13C_DIC从上游至下游逐渐偏正，受碳酸盐矿物溶解影响显著；垂直方向上，热分层和化学分层现象对水的碳循环产生了显著影响.有机质分解在深水层释放大量CO₂致使c（DIC）、pCO₂逐渐升高及δ13C_DIC逐渐降低，c（DIC）及其δ13C在整个水柱上存在显著的空间异质性.研究显示，光照水库DIC的来源主要有两种，即生物源的土壤CO₂和有机物呼吸产生的溶解CO₂形式的DIC源、碳酸盐矿物风化所产生的碳酸氢盐形式的DIC源. 

Analysis of Source and Change of Dissolved Inorganic Carbon in Guangzhao Reservoir

The interception of dams on rivers turns rivers into impoundment rivers, gradually evolving into 'lake' ecosystems, strengthening the biogeochemical cycle, and further affecting the carbon cycle process of the water bodies. In order to more accurately budget for the global carbon cycle and predict changes in the carbon cycle, it is important to identify the carbon sources that have an impact on the river systems. The main sources and controlling factors of dissolved inorganic carbon (DIC) in the reservoir were analyzed by measuring the concentration of c(DIC) and its δ13C (carbon stable isotope). The results showed that: (1) The c(DIC) of the reservoir was in the range of 1.80-5.02 mmol/L, while the δ13C_DIC(stable carbon isotope of dissolved inorganic carbon) was in the range of -7.45‰ to -1.26‰. c(DIC) was positively correlated with EC (electrical conductivity) and TA (total alkalinity), and negatively correlated with water temperature. The δ13C_DIC of the epilimnion was positively correlated with c(DIC) and TA in the whole reservoir area, but negatively correlated with EC in the inflow river, while δ13C_DIC was positively correlated with EC, pCO₂ (partial pressure of carbon dioxide in water), TA and c(DIC) in the bottom water. (2) In the horizontal direction, the indexes in the epilimnion changed obviously along the river. TA, EC, SIc (saturation indices for calcite) and c(DIC) showed a decreasing trend on the whole, while the δ13C_DIC gradually increased from upstream to downstream, which was significantly affected by the dissolution of carbonate minerals. In the vertical direction, thermal stratification, and chemical stratification had a significant impact on the carbon cycle of the reservoir. The decomposition of organic matter released a large amount of CO₂ in the hypolimnion, which resulted in the increase of c(DIC) and pCO₂ with the increase of water depth, but δ13C_DIC gradually decreased. c(DIC) and its δ13C showed significant spatial heterogeneity in the whole vertical profile. This study shows that there were two main sources of c(DIC) in Guangzhao Reservoir: soil CO₂ from biological sources and DIC sources in the form of dissolved CO₂ produced by organic matter respiration, and DIC sources in the form of bicarbonate produced by weathering of carbonate minerals.