黄土坡面有机碳流失对土壤分离-输移-沉积过程的响应机制

The soil organic carbon loss from the slopes is the basis for studying the effects of soil erosion on the carbon cycle. However, there is still no unified understanding and systematic theoretical explanation on how soil detachment-transport-deposition processes affect the soil organic carbon loss characteristics on the slopes. This project is based on the field observational experiments which will be conducted on the different bare runoff plots with Huangmian soil on the Loess Plateau. In this project, the traditional soil erosion research methods will combine with 7Be tracer techniques and the dynamic processes of soil erosion will be considered. Differences and variations in organic carbon characteristics (content, enrichment, composition, and mineralization) of soil from the eroded surface soil and of sediments from splashing erosion, interrill erosion, rill erosion, interrill and rill erosion and sediment deposition on the slope will be systematically analyzed under different slope gradient, slope length and rainfall. The loss characteristics of soil organic carbon on the slope will be illuminated. The effects of rainfall, runoff, sediment particle sorting, and different erosion sub-processes on the organic carbon loss from the slope will be clarified. The key influence factors on organic carbon characteristics in eroded surface soil and loss sediment from the slope will be determined. The response mechanisms of soil organic carbon loss from the slopes to soil detachment-transport-deposition processes will be revealed. The project will further deepen the research on the mechanism of organic carbon loss from the slopes, and provide basic supports for clarifying the potential impact of soil erosion on the dynamic changes of soil carbon pools, carbon budgets and the establishment of carbon cycle dynamic models.

坡面土壤有机碳流失研究是研究土壤侵蚀对碳循环影响的基础，然而目前对坡面土壤分离-输移-沉积过程如何影响有机碳流失还缺乏统一的认识和系统的理论解释。本项目基于黄土高原黄绵土分布区不同类型坡耕地裸露径流小区原位监测试验，将传统土壤侵蚀研究方法与Be-7示踪技术相结合，从土壤侵蚀发生发展的动力过程出发，系统分析不同坡度、坡长、降雨条件下坡面溅蚀、细沟间侵蚀、细沟细沟间混合侵蚀和沉积的泥沙中及侵蚀界面表层土壤中有机碳特性(含量、富集、组分及矿化)的差异及变化规律，阐明坡面有机碳流失特征，明确降雨、径流、泥沙颗粒分选及不同侵蚀子过程对坡面有机碳流失的影响，辨析引起侵蚀界面表层土壤中和泥沙中有机碳特性变化的关键因子，揭示坡面有机碳流失对土壤分离-输移-沉积过程的响应机制。该项目将进一步深化坡面有机碳流失机理的研究，为阐明土壤侵蚀对土壤碳库动态变化和碳收支的潜在影响及碳循环动力模型的建立提供基础支撑。

土壤侵蚀作为影响碳循环的主要环节，但在坡面土壤分离-输移-沉积过程方面关于坡面有机碳流失机理的研究仍较少，各侵蚀子过程对坡面有机碳流失特征的影响还缺乏统一的认识。本项目通过对黄土高原典型黄绵土不同类型坡耕地裸露径流小区进行多年连续原位监测，结合室内人工模拟降雨试验，系统分析不同坡度、坡长、降雨及覆盖条件下坡面溅蚀、片蚀和沉积泥沙中及侵蚀界面中有机碳特性的差异及变化规律，明确降雨参数、径流参数、泥沙颗粒分选及不同侵蚀子过程对坡面有机碳流失特征的影响。结果表明：（1）溅蚀量随平均雨强增加而增加，侵蚀表土与溅蚀泥沙中有机碳含量均呈SOC>MOC>POC。不同坡度及降雨特征下的有机碳及其组分变化没有一致性规律。侵蚀表土与溅蚀泥沙中SOC、MOC、POC富集规律与侵蚀土壤颗粒富集规律具有一致性。（2）不同雨强条件下的片蚀泥沙有机碳及组分随坡度的变化不一。不同孔径网格覆盖下的产流量、产沙量、各有机碳流失量与富集比均小于裸坡，SOC与MOC含量随网格孔径增大而增加，POC反之，而不同植被盖度下各有机碳组分与裸坡则相差不大。侵蚀泥沙颗粒富集情况与SOC、MOC、POC富集规律较为一致，但与总有机碳、易氧化及难氧化有机碳间关系复杂。（3）单位面积径流量随输移距离增加而减少，泥沙量则波动变化。各坡长下的有机碳及其组分含量无显著差异。各有机碳与降雨参数间的关系随输移距离而不同，其富集特征而与泥沙颗粒分选一致。（4）对于溅蚀过程，侵蚀量是影响溅蚀有机碳迁移的主要因子，降雨因子为间接影响。对于片蚀过程，地形因子对碳含量影响最大，而坡面侵蚀特征对有机碳流失量的影响则最大。不同组分有机碳含量在不同侵蚀过程下存在一定差异，以POC对于片蚀较为敏感，以MOC对于溅蚀较为敏感，主要受分散前后的泥沙颗粒影响。该项目将进一步深化坡面有机碳流失机理的研究，为阐明土壤侵蚀对土壤碳库动态变化和碳收支的潜在影响提供基础支撑。