Impact Of Land-use Patterns Upon Karst Processes In Typical Karst Mountain

Previous studies on karst processes was always focused on karstification intensity and its variation under different geological settings,climatic and hydrologic conditions in the view of macroscale,and considering changes of CO₂ density driving krast processes in a certain area,or the contribution of carbonate rock weathering to the atmospheric CO₂ sink.It has been recognized that intensity of karst processes could be largely affected by soil's physical and chemistry properties. Less attention was paid to the impact of land-use types on karst processes in mountain area.These properties are closely related to types of land cover.Filed dissolution test of standard limestone tablets,carried out in the karst regions of Bitan spring which located on 800m elevation and Shuifang spring which located on 2100m elevation in Jinfo mountain of Chongqing,in rainy season and dry season of 2006-2007,where five types of land-use and six test sites were encountered. Almost all the typical land-use types occurred in the small study area,so the present study is also typical and representative.There is the special weather which its beginning with mid-July 2006 that little rain and high temperature had being for more than 40 days in Chongqing.The results showed that the corrosion ratio was some difference between the rainy season and dry season,and at different elevations is quite different that corrosional ratio in Shuifang spring is more quicker than that of in Bitan spring during the test time,revealed that limestone dissolution was related to corrosion speed of the soil,and the soil's corrosion speed was different with land-use types in study area.Moreover,it was also found that the soil's corrosional ratio was different at different elevation for the same land-use type.At the six test sites,different land-use patterns affect the soil physical and chemical properties of soil organic matter content in particular,resulting in the karst process,six tests corrosion speed under the soil have great differences.Soil profile dissolution of the rainy season ranked as follows:bamboo forest land of Shuifang spring(133.41mg)>forest of Shuifang spring(88.14mg)>meadow of Shuifang spring(75.29mg)>forest of Bitan spring (20.44mg)>shrub of Bitan spring(13.68mg)>tilled land of Bitan spring(5.16mg);Six tests soil profile dissolution of the dry season ranked as follows:forest of Shuifang spring(58.40mg)> meadow of Shuifang spring(49.63mg)>bamboo forest land of Shuifang spring(43.48mg)>forest of Bitan spring(14.75mg)>shrub of Bitan spring(7.15mg)>tilled land of Bitan spring(6.65mg).This study further found that except basic factors controlling karstification,such as rainfall,the temperature and CaCO₃ content in soils,CO₂ density and organic content within soil were other two particular factors in the study area.Dissolution process is controlled remarkably by soil organism in forest,shrub and tilled land of Bitan spring,the higher the organism content is and the less the pH value is,the higher the dissolution rate is.And the dissolution rate affected mainly by soil CO₂ in bamboo forest and meadow of Shuifang spring,it has imperceptible relativity with organism content. But forest of Shuifang spring's dissolution rate affected by both of soil CO₂ and soil organism.Six soil tests under different land-use patterns of Shuifang spring and Bitan spring in Jinfo mountain have a larger differences in soil fertility,the difference type-use patterns of the same soil profile fertility status have some differences,and the soil fertility of the same type-use pattern at different altitude also have a big difference.Six soil tests under different land-use patterns of Shuifang spring and Bitan spring in Jinfo mountain under the soil organic matter content by the addition of calcium rich environmental impact, the state of vegetation and use of soil test have a high content of organic matter and decreased with soil depth,but also displayed the full nature reserves,protected areas and non-protected areas of the border differences,six test points average content of organic matter in soil profile arranged in descending order:forest of Shuifang spring> bamboo forest land of Shuifang spring>meadow of Shuifang spring>forest of Bitan spring>shrub of Bitan spring >tilled land of Bitan spring.Six soil tests under different land-use patterns of Shuifang spring and Bitan spring in Jinfo mountain under the soil nitrogen contents are all high level nitrogen content,and the total nitrogen content and available nitrogen in soil have the same descending order that are:forest of Shuifang spring>bamboo forest land of Shuifang spring>meadow of Shuifang spring>forest of Bitan spring>shrub of Bitan spring >tilled land of Bitan spring.Six soil tests under different land-use patterns of Shuifang spring and Bitan spring in Jinfo mountain have a high content of phosphorus in the soil.The available phosphorus and total phosphorus content in six measurement soil points is not associated with each other obviously,the average total phosphorus content of the soil profiles in descending order is:forest of Shuifang spring>meadow of Shuifang spring>bamboo forest land of Shuifang spring>tilled land of Bitan spring>shrub of Bitan spring>forest of Bitan spring.And the available phosphorus of soil in descending order is:forest of Shuifang spring>bamboo forest land of Shuifang spring >tilled land of Bitan spring>meadow of Shuifang spring>forest of Bitan spring >shrub of Bitan spring.Six soil tests under different land-use patterns of Shuifang spring and Bitan spring in Jinfo mountain under the soil potassium have a less level of a state 5 in national levels,all of the average soil profile tests' total potassium in the soil is 5.07 g·kg^-1;the soil total potassium content of six tests points in descending order is:bamboo forest land of Shuifang spring>meadow of Shuifang spring>tilled land of Bitan spring>shrub of Bitan spring>forest of Bitan spring>forest of Shuifang spring.And the available potassium content of six tests points in descending order is:bamboo forest land of Shuifang spring>forest of Bitan spring>meadow of Shuifang spring>shrub of Bitan spring>forest of Shuifang spring>tilled land of Bitan spring.The study area of six test points in Shuifang spring and Bitan spring are located in the main national nature reserve area in Jinfo mountain,from the karst system dynamics perspective,there are a rich vegetation and a higher coverage,therefore,the karst vegetation in Jinfo mountain contribute to the growth and development of karst ecosystem stability and the improvement of the state,and karst ecosystem stability is conducive to regional growth of the vegetation - soil system too.