喀斯特地区不同岩土组构对岩溶碳通量的影响

Influence of different rock-soil fabrics on carbonate weathering carbon sink flux in karst regions

我国南方喀斯特地区岩石裸露率高、土层浅薄且分布不均,这种特殊的岩土组构如何影响水文过程对于准确估算岩溶碳通量具有重要意义。水化学径流法是计算流域尺度岩溶碳通量的常用方法,其中流域面积和流量作为2个重要参数在喀斯特地区往往难以准确获取。在普定喀斯特生态系统观测研究站设计了一组岩土比(1∶1和4∶1)和一组土层厚度(5,20,100 cm)共计5种岩土组构的模拟试验场。通过一个完整水文年的流量和水化学监测,定量研究了岩石裸露率和土层厚度对水文过程以及岩溶碳通量的影响。研究结果表明,5个模拟试验场岩溶碳通量平均值为(17±3)gC/m^(2)/a,受渗漏量控制,雨季(5-10月)约占95%;岩石裸露率(2组岩土组构之间)对渗漏量的影响可达14%,且随着岩石裸露率增加,入渗系数也相应增加;土层厚度对渗漏量的影响仅在1%~2%之间。此外,对8个野外流域观测数据的分析发现,入渗系数与岩溶碳通量的相关性最为显著,说明入渗系数是喀斯特地区不同岩土组构地质背景影响和控制岩溶碳通量的主要因素,同时这种影响可能随降雨量变化而变化,即入渗系数并非常数。

The karst areas in southern China are characterized by a high rock exposure ratio and shallow and unevenly distributed soil layers.How this special geotechnical fabric affects the hydrological process is of great significance for the accurate estimation of carbonate weathering carbon sink flux.Hydrochemical runoff is a commonly used method for calculating carbonate weathering carbon sink flux at the watershed scale,and basin area and discharge,as two important parameters,are often difficult to accurately obtain in karst areas.To overcome this problem,we designed a rock-soil fabric simulation test site,including different rock-soil ratios(1∶1 and 4∶1)and soil thicknesses(5,20,100 cm)at the Puding Karst Ecosystem Research Station,Chinese Academy Sciences.The effects of rock exposure and soil layer thickness on hydrological processes and carbonate weathering carbon sink flux were quantitatively studied by monitoring the flow and hydrochemistry during a hydrological year.The results show that the average carbonate weathering carbon sink flux is 17±3 gC/m^(2)/a,which is controlled by the leakage amount and accounts for 95% in the rainy season(from May to October);The influence of the rock exposure ratio(between the two groups of rock fabric)on the leakage amount is up to 14%,and the infiltration coefficient increases with increaseing of rock exposure ratio;The effect of the soil layer thickness on seepage is only 1%-2%.In addition,it is found that the correlation between the infiltration coefficient and carbonate weathering carbon sink flux is the most significant by analysis the observed data of 8 field basins from previous studies.The infiltration coefficient is the main factor affecting and controlling the carbonate weathering carbon sink flux,which is due to the geological background of different rock and soil fabrics in the karst area.At the same time,the influence may change with the rainfall variation,that is,the infiltration coefficient is not constant.