Variation and rgulation mechanism of karst carbon sink in typical dolomite basin in recent 27 years：A case study of the Huangzhouhe basin in Shibing, Guizhou

The response mechanism of karst carbon sink to climate change and land use patterns remains controversial. Dolomites with higher solubility than limestone may have higher karst carbon sink potential. However， most previous studies tend to calculate the karst carbon sink value of limestone and ignore the contribution of dolomite to karst carbon sink. Therefore， this paper selects the Huangzhouhe dolomite basin in Shibing county， Guizhou Province as the research object which has developed a typical dolomite karst landform and has become a world natural heritage protected area. We quantitatively estimate the annual average karst carbon sink strength of the dolomite basin in 1990-1992， 2001-2003 and 2016-2018 by using the dolomite chemical equilibrium thermodynamic method derived from the dolomite dissolution equilibrium equation， with a view to estimating the dolomite karst carbon sink value and its response mechanism to the joint effect of climate change and land use. The results show that，（1） The average annual rainfall in the basin decreases with time， but the effective rainfall in the second period is the largest due to the difference in evapotranspiration， followed by the first period， and the effective rainfall in the third period is the smallest；（2）The basin is mainly forested land. With the gradual increase of human activities， paddy fields， dry land， and construction land continue to increase， but the growth rate of the latter two types of land has slowed down， and due to the environmental regulations of the World Natural Heritage Site， the overall vegetation coverage of the basin shows a trend of restoration；（3）The overall karst carbon sink intensity in the basin at different periods of time is the second period， the first period， and the third period， and the corresponding karst carbon sink values are 31.68， 33.40，27.93 t CO2·km-2·a-1，respectively. Among different types of land use， although the carbon dioxide partial pressure of natural land is higher than that of land used for human activities，natural forest land with higher vegetation coverage causes greater water loss，making dry land and paddy fields affected by human activities significantly higher.The karst carbon sink value reached 31.97-32.64 t CO2·km-2·a-1， while the karst carbon sink value of forest land and shrubland was relatively small， only 28.64-30.48 t CO2·km-2·a-1.According to the above analysis， we believe that climate change and land use jointly act on karst carbon sink， and the rainfall runoff effect dominated by climate change obviously masks the carbon dioxide effect， and the intensity of karst carbon sink may not increase with the positive succession of land use. Moreover， by comparing the calculation results of karst carbon sink in limestone basins under the same climatic conditions， although different calculation methods and basin areas will lead to certain differences in karst carbon sink values， dolomite karst carbon sink still have a large karst carbon sink potential. Therefore， in the calculation of global terrestrial karst carbon sink， the role of global dolomite karst carbon sink should be taken seriously.