Integrating Aquatic and Terrestrial Carbon Fluxes to Assess the Net Landscape Carbon Balance of a Highly Erodible Semiarid Catchment
Lishan Ran, Xuhui Wang, Si‐Liang Li, Yuanyuan Zhou, Y. Jun Xu, Chun Ngai Chan, Nufang Fang, Zhongbao Xin, Hongxun Shen
Abstract
Abstract The magnitude of the carbon (C) sink due to terrestrial primary production may be overestimated if the C losses through fluvial networks are not properly accounted for. In this study, we hypothesize that terrestrial‐aquatic C transfers represent a major loss of the terrestrial C sink in semiarid catchments. To test the hypothesis, we assessed the net landscape carbon balance (NLCB) of a highly erodible catchment on the semiarid Chinese Loess Plateau by compiling terrestrial net ecosystem productivity (NEP) estimates and aquatic fluxes of downstream C export, emission of CO 2 and CH 4 , and C burial. Our results showed that, despite the severe erosion and strong C mobilization, this catchment was a net C sink (NLCB = 48.3–54.8 Mg C km −2 year −1 ). Downstream C export at catchment outlet and evasion of CO 2 and CH 4 only offset terrestrial NEP by 7.7%–8.5% due largely to low flow discharge and small water surface area of the stream network. Furthermore, C burial in reservoirs played a considerable role, reducing an additional 7.5%–8.3% of the NEP. Altogether, approximately 84% of the net terrestrial C production was stored within the catchment. Our study reveals that semiarid catchments with widespread erosion and low terrestrial production remain a net C sink, although the magnitude is lower than those found in other climate zones. Our study further advocates the need to integrate terrestrial‐aquatic C transfer into a comprehensive net C balance accounting at the landscape scale. Ignoring the aquatic C loss will cause biased estimates of the overall C sink strength.