Lakes and reservoirs transform, emit, and bury carbon that is exported from land and are thus significant components of terrestrial carbon budgets. Their significance is often assessed by integrating these water bodies into terrestrial primary production. However, the transfer of inorganic carbon (IC) is likely a sticking point for these integrations because IC is not part of net ecosystem production. Here we integrated carbon evasion and organic carbon (OC) burial in a lake in the context of inorganic and OC cycling in a karst catchment from a system perspective. The lake emitted carbon dioxide (CO2) and buried OC at rates of 1.0 ± 0.2 and 0.9 ± 0.2 g C m−2 a−1, respectively, approximately equaling 13% and 11% of catchment net ecosystem production, respectively. These proportions represent significant influences on terrestrial carbon budgets, given an organic origin. However, catchment carbon export is dominated by IC that is derived from carbonates dissolved by soil CO2. Lake CO2 evasion accounts for less than 0.1% of soil CO2 efflux, suggesting little potential in significantly altering terrestrial carbon budgets. This comparison indicates the significance of aquatic CO2 evasion, requiring an adjustment of terrestrial carbon budgets to recognize their dependence on carbon origins. The significance may be overstated if inorganic origin is ignored. Our study suggests that a careful reassessment of the significance of CO2 evasion and OC burial in freshwater ecosystems to local and global carbon budgets, with full consideration of their sources, is necessary and pressing.
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This research was supported by the National Key Research and Development Program of China (2016YFA0601003) and the National Natural Science Foundation of China (91547117, 41373137, and U1612442).
All the data obtained in 2013 and 2015 are listed in Appendix as supporting information, and the data for 2001 to 2004 are available in Wang et al. (2015).
Lu, Weiqi; Wang, Shilu; Yeager, Kevin M.; Liu, Fang; Huang, Qiangsheng; Yang, Yuxue; Xiang, Peng; Lü, Yingchun; and Liu, Chong-qiang, "Importance Considered Organic Versus Inorganic Source of Carbon to Lakes for Calculating Net Effect on Landscape C Budgets" (2018). Earth and Environmental Sciences Faculty Publications. 12.