土壤有机碳动态:风蚀效应

土壤风蚀是引起土壤退化最广泛的形式和原因之一。土壤风蚀对土壤碳动态的影响机制一方面是土壤风蚀引起土壤退化使土壤生产力下降,输入土壤的碳数量减少;另一方面是富含有机碳的细粒物质直接移出系统。风蚀土壤碳的去向包括:(1)就近沉积,(2)沉积于水渠和河流,输入水体;(3)以粉尘形式运移,在远离风蚀区的地域沉积;(4)氧化释放至大气。风蚀引起土壤碳的迁移和沉积不仅导致土壤有机碳在地域间的再分布,使土壤性状的空间异质性增加,也显著改变了土壤系统中碳矿化的生物学过程。土壤有机碳的保持可以促进团聚体的形成,使土壤物理稳定性增加,减缓风蚀。对易风蚀土地进行退耕还林还草、实行保护性耕作等措施可以有效增加土壤碳的固存。

Soil organic carbon dynamics:wind erosion effect

Soil erosion by wind, transport, and deposition occur over more than one third of the land surface of the earth and it is the most widespread form of soil degradation. Land area globally affected by wind erosion is 549 million ha, of which 296 Mha is severely affected. In China, the desertified land area induced by wind erosion and deposition has 36 9000 ha. Whereas the adverse effects of wind erosion on soil productivity and environment are widely recognized, soil organic carbon dynamics in wind erosion process, wind erosion-induced carbon fate and attendant emission of CO_2 into the atmosphere remain misunderstood. Soil erosion is an important process controlling soil carbon levels and distribution patterns in some arid and semiarid regions. Therefore, a sound understanding of soil carbon dynamics in wind erosion process is critical for quantifying component of the global carbon budget and identifying the contribution of carbon loss from the desertified land to atmosphere CO_2. This article reviews the current studies on the dynamics of soil organic carbon in relation to wind erosion. Soil erosion by wind depletes soil organic carbon (SOC) pool. First, wind erosion selectively removes the fine particles in the surface soil, leaving behind coarse sand. Secondly, it causes soil degradation, which in turn reduces soil productivity and the amount of C returning to the soil in plant residues. In addition, the physical processes of wind erosion and deposition drastically alter the biological process of C mineralization in soil landscape, and mineralization results in a net loss of C from the soil system to the atmosphere. Wind erosion and deposition redistribute considerable amounts of SOC, resulting in significant increase of spatial heterogeneity in SOC distribution at various scales, which indicates the extent of land desertification in some arid and semiarid regions. It is difficult to accurate estimate the fate of the eroded C in wind erosion process. There are four possibilities: (1) deposition onto nearby soil; (2) deposition in water bodies; (3) deposition in areas far from the erosion sites; (4) oxidation and release to the atmosphere. The redistribution of soil C in wind erosion process must be considered to assess the eroded C on the contribution of atmosphere CO_2. SOC facilitates the formation of soil aggregates, increase soil physical stability and improves soil structure, which in turn decrease the risk of wind erosion. Rational soil and crop management can significantly increase soil C sequestration. Thus the use of management practices that prevent or reduce soil erosion by wind such as returning desertified cropland to forest of grassland, conservative tillage and residues cover may reduce the risk of C loss and sequester C in soil.