The Karst Features Research And Potential Calculation On Carbon Sink In The Basin Of Dalongdong Underground In The Hunan Province

Carbon cycle model has“missing sink”.The theory-the karstificationprocesses of carbon cycle-provides a new way finding “the missing sink”. TheMinistry of land and resources in2010launched the project that is potential studyon carbon sink from the side of geology in China,for estimating explicitly thefunction and intensity of carbon sink format-ting by the process of karstgeology.That could help our country obtain the active position when every countrynegotiate about the change in the climate.Meanwhile, find a method that wouldcalculate carbon sink accurately caused by karst water cycle though the theoryof carbon sink by karst process.On the other hand,through the project,we couldmaster the corrosion characteristics of carbonate using the method of fieldcorrosion experiment,and understand further the mechanism of carbonate rockcorrosing in karst process.Taking Dalongdong underground river basin in the Hunan Province as anexample,at the basement of the investigation,such as hydrologicalgeological,dynamic monitoring of flow and water chemistry, soil organic carbon,inorganic carbon and chemical component content, dynamic CO₂concentration in thesoil air, to analyse the water chemistry character-ristics of the system ofDalongdong underground river.And learn the regular of carbonate rock distributedin the basin, use the chemical runoff method and field corrosion method to calculatethe amount of carbon sink.The system of Dalongdong underground river has a typical double-layerstructure.Within the groundwater recharge process,the maior methods contentinjection, leakage and infiltration.The system has the natural flow state, andthe dynamic changes were large. The type of groundwater chemical is HCO₃-Ca, andrange of pH value is7～8.64. There is a good correlation ship between pH valueand groundwater. PCO₂in water was effected by the pH value, moreover controlledby the system of carbonate rock in the water. In the groundwater,Ca²⁺,Mg²⁺and HCO-3were more.The ion concentration reached the minimum in the rainy season.[Mg²⁺+Ca²⁺]/[HCO₃] ratios were between1and2, indicating the impact to crossingwas low from sulphuric acid in the River Basin. The average equivalent of [SO₄^2-]/[HCO₃]ratio is0.09.It was well belowed0.5,that is the theoretical value sulfuric acidattended carbonate rock corrosion.That indicated that the corrosion sulfuric acidnearly did not participate the crossion process in watershed of carbonate rocks.Dissolved inorganic carbon （DIC）changed with rainfall.When the rainfull is large,the content of DIC is low.The results about detection of organic carbon and other chemical componentsin soil displayed that content of organic carbon in the surface layer（0-20cm）content is higher than in the bottom （20-50cm）.In the surface layer, thevalue was1.764%,bottom1.014%.In shrub forest land,it was1.5%, higher than thatin the other land use types. SiO2is dominated in the chemical composition of soil,its content accounted for more than60%. Through monitoring the concentration ofCO₂in soil air, it increased with the, and when reach the biggest it would lowwith the increase of depth.The other, the concentration was4032.79ppm in winter,it was lowest,in summer it was highest,and come to18911.65ppm.The image showedthat the changed of concentration has the well relationship with seasonal variation.The corrosion rate of carbonate rock was quicker in50cm depth than in20cm.Andthe corrosion rate was fast in woodland than other land type,that illustrated thepositive succession of vegetation can speed up the process of karst erosion. Inaddition, the corrosion rate of limestone rock tableis quicker than that ofdolomite rock.The CO₂concentration could promote corrosion rate to corrose.It tookon an important role in the carbon cycle of soil.Because of the different of calculation methods between water chemical runoffmethod and field corrosion test method,the results on the carbon sink amount areobviously different.The calculated result of the former is12.55×10³t CO₂/a,thelatter is a34.89×102t CO₂/a. As the soil of basin was alkaline,the calculationresult of CO₂recovery amount was smaller.If using the standard limestone tocalculate basin CO₂recovery amount,it is47.96×10²t CO₂/a.That is larger thanthat calculated by the erosion of rocks distribution in the watershed.