Many studies showed that the carbon sink resulted from karst process is fast and stable, which compose the very important part of "Missing carbon sink". Different land-use patterns can affect the karst process by influence the soil properties. Commonly, with the land-use change from forest land to cultivated field the soil organic matter will reduce, the stability of soil structure get worse, the soil moisture retaining quality get down and the quantity of soil microbiology will diminish, all the above would affect the karst process.
This study took 6 different land-use patterns(Tilled land (code: Ha),Paddy field(St), Reforested land(Tu), Abandoned Land(Hu),Mixed Woodland with Chinese fir-bamboo(Sz) and Bamboo land(Zh))with the same geological backgrounds but different human influence intensity in Qingmuguan karst valley as a case study to determine the influence factors on karst processes. Standard limestone tablets were buried in the field to test the dissolution process rate. HOBO automatic weather station was located in the roof of local people's house to get the precipitation and temperature data. CO₂ content in different soil layers were tested by Gas-Tec CO₂ tester. Soil samples in different layers were taken back to laboratory to detect the pH value, the organic matter, soil moisture content, and soil bulk density.
The dissolution data from tablets showed that, firstly, the mean dissolution mass per unit area of different land-use patterns in different layers in Summer were 3.87 times than in Winter. The max mean dissolution mass changed from -80cm layer in Summer to -20--50cm layers in Winter. Secondly, the mean dissolution mass in these two land-use patterns Ha and St with strong human influence intensity (Abbr. HII) was higher than that inTu and Hu in which the HII get weaker, while that in Sz and Zh which had the weakest HII with the lowest mean dissolution mass. Also, the range between them was higher in summer with strong HII than that in winter.
Afteranalyzing the temperature(T), precipitation (P) and the soil physicochemical properties data, we can find that, there was a positive correlation between the change of dissolution mass with seasons and T,P which were the most important factors affecting the former. The soil CO₂ content can only play an important role on dissolution in summer which has more precipitation, and these two factors can react each other enough to form more carbonic acid so more carbonate tablets can be dissoluted. There was a negative correlation between soil organic matter and soil pH, and these two factors affected the dissolution jointly. They can influence dissolution greatest only in surface layer with high organic matter and low pH, while less in deeper layers. The influence of soil texture determined by soil bulk density and soil porosity on dissolution was bidirectional. The clay with good moisture retaining quality but bad permeability was benefit for the dissolution in winter for there was less precipitation that time, but bad in summer for there was no so much water pass through the soil, Hu was a good example of this. However, there was an oppose process in sandy soil with good permeability but bad moisture retaining quality, corresponded more dissolution in summer and less in winter, there was a good example of tilled land also. Additionally, the use of farmyard manure and chemical fertilizer which include NO₃^- and SO₄^2- can promote the dissolution process too. Above all, the results of this study can provide consultation for evaluate karst carbon sink more scientifically and accurately.