Key Laboratory of Karst Dynamics, MLR & Guangxi, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, China.
Key Laboratory of Karst Dynamics, MLR & Guangxi, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin 541004, China.
Sci Total Environ. 2017 Feb 1;579:1343-1355. doi: 10.1016/j.scitotenv.2016.11.132. Epub 2016 Nov 29.
Atmospheric carbon sequestered in karst systems through dissolution of carbonate minerals is considered to have no net effect on long-term regional and global carbon budgets because precipitation of dissolved carbonate minerals emits CO back to the atmosphere. Even though recent studies have implied that rapid kinetics of carbonate dissolution coupled with the aquatic photosynthetic uptake of dissolve inorganic carbon (DIC) could facilitate a stable atmospheric C sink in karst rivers and streams, little is known about the magnitudes and long-term stability of this C sink. To assess in-stream biogeochemical processes and their role on stream C cycling, we measured diel cycles of water characteristics and chemical composition (temperature, pH, DO, SpC, DIC, Ca, δC) in a groundwater-fed karst stream in southwest China. Our results show no diel variations at the groundwater discharge point (CK site) due to the absence of a sub-aquatic community (SAC). However, all hydrochemical parameters show significant diel cycle 1.3km downstream (LY site). Diel variations in pH, DO, and δC were inversely related to diel changes in SpC, DIC, Ca and pCO This result indicates that in-stream metabolism (photosynthesis and respiration) of SAC controls diel variations in stream water chemistry. Significant diel cycles of net ecosystem production (NEP) influences in-stream diel fluctuation of pH, DO, SIc, DIC, pCO, Ca and δC with gross primary production (GPP) dominating in day and ecosystem respiration (ER) dominating at the night. Absence of in-stream metabolism at CK enhances CO degassing from stream to the atmosphere, which is estimated to be 3-5 times higher than at LY. We estimate the carbon sink through in-stream metabolism of SAC to be 73tCkma, which is around half the rate of the oceanic biological pump. These results imply in-stream photosynthesis sequesters DIC originating from karst weathering and controls CO evasion.
岩溶系统中通过碳酸盐矿物溶解固定的大气碳被认为对长期区域和全球碳预算没有净效应，因为溶解碳酸盐矿物的沉淀会将 CO 释放回大气中。尽管最近的研究表明，碳酸盐溶解的快速动力学与溶解无机碳（DIC）的水生光合作用吸收相结合，可能在岩溶河流和溪流中形成稳定的大气 C 汇，但人们对这个 C 汇的规模和长期稳定性知之甚少。为了评估溪流中的生物地球化学过程及其对溪流碳循环的作用，我们测量了中国西南地区一条地下水补给的岩溶溪流的昼夜水特性和化学成分（温度、pH 值、DO、SpC、DIC、Ca、δC）变化。我们的结果表明，由于缺乏水下生物群落（SAC），在地下水排泄点（CK 点）没有昼夜变化。然而，所有水化学参数在 1.3km 下游（LY 点）都显示出显著的昼夜变化。pH 值、DO 和 δC 的昼夜变化与 SpC、DIC、Ca 和 pCO 的昼夜变化呈反比。这一结果表明，SAC 的溪流内代谢（光合作用和呼吸作用）控制着溪流水化学的昼夜变化。净生态系统生产力（NEP）的显著昼夜变化影响了 pH 值、DO、SIc、DIC、pCO、Ca 和 δC 的溪流内昼夜波动，其中总初级生产力（GPP）在白天占主导地位，生态系统呼吸（ER）在夜间占主导地位。CK 点没有溪流内代谢，增强了 CO 从溪流向大气的排放，估计比 LY 点高 3-5 倍。我们估计 SAC 溪流内代谢的碳汇为 73tCkma，约为海洋生物泵速率的一半。这些结果表明，溪流内光合作用固定了源自岩溶风化的 DIC，并控制了 CO 的逸出。
