Key Laboratory of Karst Dynamics, MNR & Guangxi, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin, 541004, China.
Department of Geological Sciences, University of Florida, Gainesville, FL, 32611, USA.
Environ Sci Pollut Res Int. 2019 Apr;26(11):11029-11041. doi: 10.1007/s11356-019-04456-z. Epub 2019 Feb 21.
Metabolic processes of the submerged aquatic community (photosynthesis and respiration) play important roles in regulating diel cycles of dissolved inorganic carbon (DIC) and sequestering carbon in a karst stream. However, little is known of whether diel DIC cycling occurs during rainfall in a karst groundwater-fed stream, even though this question is critical for the accurate estimation of what may be a major terrestrial carbon sink. Here, we measured diel variations of water chemical composition in a small karst groundwater-fed stream in southwest China during a rainfall event to assess the influences of rainfall and rising discharge on DIC diel cycling and the potential carbon sink produced by in-stream metabolism. Our results show that water chemical composition at the source spring (CK site) is relatively stable due to chemostatic behavior during rising discharge after a rainfall period. This site lacked submerged aquatic vegetation and, thus, had no diel variations in water chemistry. However, diel cycles of all hydrochemical parameters occurred at a site 1.3 km downstream (LY site). Diel variations in pH, DO, and δC were inversely related to diel changes in SpC, DIC, Ca, and pCO. These results indicated that diel cycling of DIC due to in-stream metabolism of submerged aquatic community was still occurring during elevated discharge from rainfall. We estimate the carbon sink through the in-stream metabolism of the submerged aquatic community to be 5.6 kg C/day during the studied rainfall event. These results imply that submerged aquatic communities in a karst stream can significantly stabilize carbon originating from the carbonate rock weathering processes in karst areas.
水生生物群落的代谢过程（光合作用和呼吸作用）在调节溶解无机碳（DIC）的昼夜循环和将碳固定在喀斯特溪流中起着重要作用。然而，对于喀斯特地下水补给溪流在降雨期间是否会发生昼夜 DIC 循环，人们知之甚少，尽管这一问题对于准确估计可能是一个主要陆地碳汇至关重要。在这里，我们在降雨事件期间测量了中国西南地区一个小型喀斯特地下水补给溪流的水化学组成的昼夜变化，以评估降雨和上升流量对 DIC 昼夜循环的影响以及溪流代谢产生的潜在碳汇。我们的结果表明，由于雨后上升流量期间的化学稳定行为，源泉水（CK 点）的水化学成分相对稳定。该点没有水生植物，因此水化学没有昼夜变化。然而，所有水化学参数的昼夜循环都发生在 1.3 公里下游的一个点（LY 点）。pH、DO 和 δC 的昼夜变化与 SpC、DIC、Ca 和 pCO 的昼夜变化相反。这些结果表明，由于淹没的水生生物群落的溪流内新陈代谢，在降雨引起的高流量期间仍在发生 DIC 的昼夜循环。我们估计，在研究的降雨事件中，通过溪流内的水生生物群落的碳汇为 5.6kgC/天。这些结果表明，喀斯特溪流中的水生群落可以显著稳定来源于喀斯特地区碳酸盐岩风化过程的碳。
