河流碳输移及其对流域环境要素的响应机制

River systems are important linkages between the land, atmosphere and the ocean, playing a critical role in the global carbon cycle. Recent studies show that the total carbon reaching inland waters is estimated at 5.7 Pg per year (1P=10^15). Of the carbon originated from terrestrial ecosystems, however, only 0.9 Pg is finally discharged into the oceans through fluvial export. This implies that more than 80% of the carbon is buried in sediments on landscape or biogeochemically processed and degassed into the atmosphere as greenhouse gases. Furthermore, human activities, dam construction and land use changes in particular, have significantly altered riverine carbon cycling. Understanding these human-induced impacts on riverine carbon transport is of paramount importance for riverine carbon cycle and beyond. Based on the Jinghe River catchment on the Loess Plateau, this proposal is aimed to elucidate its riverine carbon export processes. By means of extensive field sampling and lab analyses tailored for this catchment, this proposal will systematically investigate the changes in lateral delivery of riverine carbon and quantify CO2 evasion across water-air interface. In addition, the underlying mechanisms will be explored in association with hydrologic and geomorphologic information, and the resulting biogeochemical implications will be discussed. The expected results will definitely deepen our understanding of riverine carbon export on the Loess Plateau and more importantly, shed light on regional carbon budget assessments.

作为陆地生态系统与海洋、大气之间相互联系的重要纽带，河流在全球碳循环过程中意义重大。近年的研究表明对于每年自陆地生态系统进入内陆水体的5.7 Pg碳来说，只有0.9 Pg碳最终经河流系统输送进入海洋。这意味着>80%的碳被埋藏在内陆水体或经氧化分解而进入大气。另外，人类活动(特别是库坝建设和土地利用)也深刻地影响河流系统原有的碳输移规律。因此，探讨其影响机理对于理解河流碳输移过程具有重要意义。通过选取黄土高原典型流域泾河作为研究对象，本项目拟较为深入地分析其河流碳输移过程。采用野外实测和室内分析相结合的手段，以整个流域为研究单元，开展时空尺度上的高频率野外采样并结合水文、地貌资料，系统地探讨其河流碳输移过程及地貌环境因子和人类活动对其的作用机制，并评估其在河流碳循环研究中的生物地球化学意义。本研究将深化对黄土高原地区河流碳输移过程的认识，为更准确地评估区域碳收支平衡提供数据支持和理论基础。

本研究围绕流域环境因子和人类活动对河流碳循环的影响，选取了黄土高原地区土壤侵蚀极为严重的泾河和窟野河流域作为研究对象，通过开展涉及时空尺度的野外采样和室内分析，并结合长期的径流、泥沙、植被和气候数据，系统地探讨了其河流碳循环过程特征；明确了流域岩性特征对水体溶解CO2分压（pCO2）的控制；阐述了主要人类活动（如水库/淤地坝建设、城镇废水排放等）对河流横向碳输移及水-气界面CO2和CH4温室气体排放速率的影响。由于进入河流系统的碳主要来源于陆地生态系统，本研究结果还改进了针对大气-陆地生态系统的区域碳源/碳汇收支平衡评估；丰富和完善了干旱-半干旱地区水体生态系统碳输移对相应的陆地生态系统净碳收支平衡的潜在影响。因此，本研究结果有助于推动河流碳循环研究的理论发展；同时也有助于更准确地评估区域尺度上的碳收支平衡。已在地学和环境科学国内外主流期刊上发表论文8篇，其中SCI论文7篇。培养硕士研究生1名。