不同土地利用方式土下岩溶溶蚀速率及影响因素

以重庆中梁山为例,通过野外埋放标准溶蚀试片、土壤CO2收集装置和进行亮蓝染色示踪试验,测试不同土地利用方式下不同土层碳酸盐岩溶蚀速率、土壤CO2浓度、土壤溶解性有机碳(DOC)含量及土壤含水量、土壤pH值和孔L隙度等性质,探讨不同土地利用方式土下溶蚀速率差异及其影响因素.结果表明不同土地利用方式对土壤理化性质产生影响,形成特定的岩溶微环境,进而影响土下不同层次的岩溶作用:土壤CO2浓度是影响林地和草地旱季土下溶蚀速率的重要驱动力；土壤含水量和供水能力是影响旱季不同土地利用方式溶蚀速率的关键因素；菜地产生的酸性物质较多,土壤pH值最低,其平均溶蚀速率高于林地；土壤DOC随水下渗迁移性强,是林地土下50 cm处溶蚀速率高于土下20 cm处的原因之一.该文为西南岩溶区土下岩溶机理、岩溶碳汇提供理论依据和数据参考.

Dissolution rate under soil in karst areas and the influencing factors of different land use patterns

The unique karst ecosystem of Southwest China is an example of a typical vulnerable ecosystem and key eco-region in China. Rocky and soil desertification in the karst environment are two of the most serious problems, and unsuitable land use patterns will intensify the desertification. Increasing attention has been paid to the impact of land-use types on karst processes and consequently to investigate the best way to restore the ecosystem in rock and soil desertification areas, it is necessary to study the influences of changes in the soil environment on karst processes under different land use patterns. Soil physical and chemical variations result from land cover, and the resulting special karst micro-environments could intensively affect karst processes under different land use patterns. A case study was conducted at Mt. Zhongliang, Chongqing, in order to analyze and investigate the dissolution rate in a karst area and the factors which influence it under different land use patterns. Standard limestone tablets were buried in the field, soil CO₂ collection devices were set up, and tracer experiments using a bright blue dye were carried out. The dissolution rate of carbonate rocks, soil CO₂ concentrations, and dissolved organic carbon (DOC) contents were measured in different soil layers at depths of 20 cm and 50 cm, as well as land use patterns and soil properties, such as moisture, porosity and pH. The average contents of soil DOC from the highest to lowest were in the order: woodland>grassland>vegetable land. There was a significant difference in soil DOC content in the upper soil horizon (0-20 cm) between woodland and vegetable land, as well as in the lower horizon (20-50 cm) among woodland, vegetable land and grassland. The diversity of soil water content and porosity indicates that woodland and grassland are beneficial for maintaining water content. Use of the dye indicated an obvious distribution of soil preferential flow in woodland and grassland, but not in the vegetable land. Soil CO₂ concentrations and pH values at 50 cm depth were higher than at 20 cm, and were present in the order: grassland>woodland>vegetable land. Woodland and grassland have greater vegetation coverage, more plant residues, and greater microbial activity, which may be the reason for the variations in soil physical and chemical properties under the different land use patterns. The study showed that soil physical and chemical properties were affected by different land use patterns, forming special karst micro-environments and resulting in different karst processes in different soil layers. Dissolution rates in the dry season were in the order: grassland>vegetable land>woodland. Soil CO₂ concentration is an important driving force affecting the dissolution rate in woodland and grassland during the dry season; soil moisture and water-supplying capacity are key factors influencing the dissolution rate under the different land use patterns in the dry season; the average dissolution rate in the vegetable land is higher than that in the woodland as more acid materials are produced in the vegetable land which has the lowest pH; the DOC of soil has a strong transforming ability with water infiltration, which is one of the reasons why the dissolution rate of forest land 50 cm beneath the soil is higher than that at 20cm. This research provides a theoretical basis and data reference for the mechanism of karst dissolution and the karst carbon sink in southwestern China.