半干旱岩溶区土壤次生碳酸盐比例及对岩溶碳汇计算的影响

摘要

定量评价半干旱岩溶区土壤次生碳酸盐比例和来源有助于认识土壤系统影响岩溶作用的机理。选取山西晋中盆地西南，吕梁山东侧的半干旱岩溶区马跑神泉小流域为研究对象，通过对林地、退耕地、灌丛地土壤剖面进行分层取样并测定碳酸盐含量及其δ13 C、CO 2浓度及其δ13 C 值，分析其随深度的变化规律和控制因素；并结合研究区碳酸盐岩的δ13 C 值计算3个剖面各层土壤次生碳酸盐所占比例。研究结果表明：3个土壤剖面的碳酸盐含量、CO 2浓度在0~50 cm 土层随深度增加而增加，在50~70 cm 土层随深度增加而减少；土壤碳酸盐δ13 C 值、δ13 CCO2值在0~50 cm 土层随深度增加而偏负，在50~70 cm 土层随深度增加而偏重；土壤碳酸盐含量及其δ13 C 值主要受次生碳酸盐比例控制，而土壤 CO 2及其δ13 CCO2值在上层主要受大气 CO 2和土壤有机质分解生成的 CO 2共同影响，下层还受土-岩界面岩溶作用过程制约；退耕地、林地、灌丛剖面次生碳酸盐所占比例的均值分别为52%、42%和32%，证实北方半干旱岩溶区土壤中存在原生碳酸盐向次生碳酸盐转化过程。%Quantitative evaluation of proportion and source of pedogenic carbonates in karst area with semiar-id environment have contributed to understand the mechanism of soil system affecting karst process,which has great significance in karst carbon cycle research.Soil samples were collected from soil profile of forest land,abandoned farmland and brushland,in a typical small watershed in semi-arid area,southwest of Jinzhong basin,Shanxi Province,China,for analysis of content andδ1 3 C of soil carbonates,content andδ1 3 C of CO 2 and δ1 3 C of parent rocks,hence to explore their variation with depth and controlling factors,and quantify ratio of pedogenic carbonates in soil carbon.Results show that in the upper layer(0 to 50 cm),the content of soil carbonates and CO 2 increase with depth,while the δ1 3 C of soil carbonates and CO 2 decrease with depth.In the lower layer (50-70 cm),the content of soil carbonates and CO 2 decrease with depth,and the δ1 3 C of soil carbonates and CO 2 increase with depth.The content and δ1 3 C of soil carbonates are mainly controlled by pedogenic carbonates proportion,while the content and δ1 3 C of CO 2 are mainly affected by at-mospheric CO 2 and soil CO 2 generated by organic matter decomposition in the upper layer,and impacted by karst process in soil-rock interface in the lower layer.The average proportion of pedogenic carbonates is 52%,42%,32% for abandoned farmland,forest land and brushland,respectively.This paper confirmed that the lithogenic carbonates can transform to pedogenic carbonates in north karst area with semiarid envi-ronment.