Wu Fei-Hong, Pu Jun-Bing, Li Jian-Hong, Zhang Tao, Li Li, Huang Si-Yu
Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China.
Key Laboratory of Karst Dynamics, Ministry of Land and Resources & Guangxi, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, China.
Huan Jing Ke Xue. 2017 Aug 8;38(8):3209-3217. doi: 10.13227/j.hjkx.201703138.
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 in the epilimnion and the average DIC concentration of 4.18 mmol·L at the bottom of the thermocline. The value of stable carbon isotope (δC) was more positive in the epilimnion than in the thermocline, where δC 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.
热分层导致水库水化学和水生生物具有显著的分层特征，进而影响水库中的生物地球化学循环。本研究旨在了解位于中国广西壮族自治区上林县的大龙洞水库（一个由岩溶泉补给的水库）的理化性质、溶解无机碳变化过程及其影响因素。2015年6月19日至21日，沿着水流方向设置了8个采样点。结果表明：①该水库夏季呈现明显的热分层现象。表层水和温跃层之间的物理和化学参数，如pH值和电导率（Spc）存在显著差异；②从表层到底层，溶解氧（DO）和叶绿素a（Chl-a）含量并非呈单一下降趋势，而是最大值出现在水面以下2.5米或5米处；③从表层到底层，溶解无机碳（DIC）浓度呈上升趋势，表层水的平均DIC浓度为2.03 mmol·L，温跃层底部的平均DIC浓度为4.18 mmol·L。稳定碳同位素（δC）的值在表层水比在温跃层更正，在温跃层中，δC随水深逐渐变为部分负值。这些结果的可能原因包括：①热分层导致不同水层的温度、水生生物分布以及代谢强度和方向存在显著差异；②表层水的DIC变化主要受碳酸盐沉淀过程和浮游植物光合作用的影响，从而影响DIC稳定同位素分馏。温跃层中的DIC主要受生物呼吸和有机物分解过程控制。
