Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 579, Issue -, Pages 1343-1355Publisher
ELSEVIER
DOI: 10.1016/j.scitotenv.2016.11.132
Keywords
Carbon sequestration; Dissolved inorganic carbon; In-stream metabolism; Aquatic phototrophs; Diel cycle; Karst system
Categories
Funding
- National Natural Science Foundation of China [41572234, 41202185, 41402324]
- Special Fund for Basic Scientific Research of Chinese Academy of Geological Sciences [YYWF201636]
- Key Research & Development Fund of Ministry of Science and Technology of China [2016YFC0502501]
- Guangxi Natural Science Foundation [2016GXNSFCA380002]
- Special Fund for Public Benefit Scientific Research of Ministry of Land and Resources of China [201311148]
- Geological Survey Project of CGS [DD20160305-03]
- US NSF [EAR-0938369, EAR-0853956]
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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 CO2 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, Ca2+, delta C-13(DIC)) 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 1.3 km downstream (LY site). Diel variations in pH, DO, and delta C-13(DIC) were inversely related to diel changes in SpC, DIC, Ca2+ and pCO(2). 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(2), Ca2+ and delta C-13(DIC), with gross primary production (GPP) dominating in day and ecosystem respiration (ER) dominating at the night. Absence of in-stream metabolism at CK enhances CO2 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-streammetabolismof SAC to be 73 t C km(-2) a(-1), 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 CO2 evasion. (C) 2016 Elsevier B.V. All rights reserved.
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