中文摘要：

热分层导致水库内部水化学、水生生物分布等出现显著的分层特征,并影响了水库内部的生物地球化学循环过程.为掌握夏季热分层期岩溶水库水体理化性质和溶解无机碳变化过程及其影响因素,以岩溶地下水补给型水库广西上林县大龙洞水库为研究对象,于2015年6月沿水库流程方向在8个点位开展分层采样及监测.结果发现：（1）水库夏季存在明显的热分层现象,水体pH、电导率（Spc）等理化性质出现分层结构;（2）水体溶解氧（DO）与叶绿素a（Chl-a）浓度从表层至底层并没有呈现单一的递减趋势,而是在水面以下2.5 m或者5 m处达到最大值;（3）由表层至底层水体溶解无机碳（DIC）浓度整体上呈增加趋势,表层水体DIC平均浓度为2.03 mmol·L~（-1）,底层平均浓度为4.18 mmol·L~（-1）;其同位素（δ~（13）C_（DIC））在表水层偏正,在温跃层随水深增加逐渐偏负.分析认为：（1）由于夏季热分层效应,水库水体温度、水生生物的分布及新陈代谢的强度和方向在不同水层存在显著差异,致使水库水体理化性质、DIC均呈现垂向分层性特征;（2）DIC浓度变化在表水层主要受碳酸盐岩沉淀过程及浮游植物光合作用影响,进而影响水中DIC稳定同位素的分馏;在温跃层则主要由生物呼吸作用及有机质分解过程控制.

英文摘要：

Thermal stratification leads to significant stratification characteristics of hydrochemistry and aquatic organisms in reservoirs,and thus affects the biogeochemical cycle in the reservoir. This study aims to understand physico-chemical properties and dissolved inorganic carbon change processes and its factors in a karst groundwater-fed reservoir,Dalongdong Reservoir,located in Shanglin County,Guangxi Zhuang Autonomous Region,China. The eight sampling points were placed along the direction of the water flow on June 19-21,2015. The results show that：（1） The reservoir exhibited obvious thermal stratification in the summer. There were significant differences in physical and chemical parameters, such as pH and conductivity（ Spc） between the epilimnion and thermocline;（2） The dissolved oxygen（ DO） and chlorophyll a（ Chl-a） content from the surface to the bottom did not show a single decreasing trend,but the maximum value occurred 2. 5 m or 5 m below the surface;（3） From the surface to the bottom,dissolved inorganic carbon（ DIC） concentrations showed an increasing trend with the average DIC concentration of 2. 03 mmol·L~（-1）in the epilimnion and the average DIC concentration of 4. 18 mmol·L~（-1）at the bottom of the thermocline. The value of stable carbon isotope（ δ~（13）C_（DIC）） was more positive in the epilimnion than in the thermocline,where δ~（13）C_（DIC）gradually became partially negative with water depth. Possible reasons of these results include：（1） The significant differences in temperature,distribution of aquatic organisms,and strength and direction of metabolisms in different water layers due to thermal stratification;（2） The DIC variations in the epilimnion were mainly affected by the carbonate precipitation process and phytoplankton photosynthesis,thereby affecting the DIC stable isotope fractionation. DIC was mainly controlled by biological respiration and the organic matter decomposition process in the thermocline.