地质科技通报 (May 2022)
Influence of different rock-soil fabrics on carbonate weathering carbon sink flux in karst regions
Abstract
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/m2/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.
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