Diel-scale variation of dissolved inorganic carbon during a rainfall event in a small karst stream in southern China
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 δ13CDIC were inversely related to diel changes in SpC, DIC, Ca2+, and pCO2. 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.
KeywordsDissolved inorganic carbon Rainfall Diel cycle Carbon sink In-stream metabolism Karst stream
Special thanks are given to Wen Liu and Xue Mo for their help in field and lab works. Heartfelt thanks are also given to Qiang Zhang for his YSI and ISCO autosampler instruments.
The study is financially supported by National Natural Science Foundation of China (No. 41572234, No. 41202185, No. 41702271), the Special Fund for Basic Scientific Research of Chinese Academy of Geological Sciences (YYWF201636), the Guangxi Natural Science Foundation (2016GXNSFCA380002, 2017GXNSFFA198006), the Geological Survey Project of CGS (DD20160305-03), and the Special Fund for Basic Scientific Research of Institute of Karst Geology (No. 2017006).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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