Tan Zeli, Leung L Ruby, Li Hong-Yi, Tesfa Teklu, Zhu Qing, Huang Maoyi
Pacific Northwest National Laboratory, Richland, WA, USA.
Department of Civil and Environmental Engineering, University of Houston, Houston, TX, USA.
Glob Chang Biol. 2020 Apr;26(4):2642-2655. doi: 10.1111/gcb.14982. Epub 2020 Feb 7.
Realistic representation of land carbon sink in climate models is vital for predicting carbon climate feedbacks in a changing world. Although soil erosion that removes land organic carbon has increased substantially since the onset of agriculture, it is rarely included in the current generation of climate models. Using an Earth system model (ESM) with soil erosion represented, we estimated that on average soil erosion displaces 5% of newly fixed land organic carbon downslope annually in the continental United States. In the lower Mississippi river basin and the Cascades, the fraction can be as large as 40%. About 12% of the eroded organic carbon is eventually exported to inland waters, which is equal to 14% of the simulated net carbon gain by terrestrial ecosystems. By comparing the eroded organic carbon export to rivers with the particulate organic carbon export to oceans, we demonstrated that a large fraction of the carbon export to rivers could have been mineralized in inland waters. Importantly, with a direct comparison of eroded and exported soil organic carbon and land net carbon uptake, we found that ESMs that ignore soil erosion likely offset the erosional carbon loss by increasing heterotrophic respiration implicitly. But as soil erosion and heterotrophic respiration respond differently to a warming climate, this unrealistic compensation would lead to biased predictions of future land carbon sink.
在气候模型中对陆地碳汇进行现实的表征对于预测不断变化的世界中的碳气候反馈至关重要。尽管自农业开始以来，导致陆地有机碳流失的土壤侵蚀显著增加，但目前这一代气候模型中很少将其纳入考虑。使用一个包含土壤侵蚀表征的地球系统模型（ESM），我们估计在美国大陆，土壤侵蚀平均每年将5%新固定的陆地有机碳向下坡方向转移。在密西西比河下游流域和喀斯喀特山脉地区，这一比例可能高达40%。约12%被侵蚀的有机碳最终被输送到内陆水域，这相当于陆地生态系统模拟净碳增益的14%。通过比较河流中被侵蚀有机碳的输出与海洋中颗粒有机碳的输出，我们证明了大量向河流输出的碳可能已在内陆水域矿化。重要的是，通过直接比较被侵蚀和输出的土壤有机碳以及陆地净碳吸收量，我们发现忽略土壤侵蚀的地球系统模型可能通过隐含地增加异养呼吸来抵消侵蚀造成的碳损失。但由于土壤侵蚀和异养呼吸对气候变暖的响应不同，这种不现实的补偿将导致对未来陆地碳汇的预测出现偏差。
