| "Global warming" and "greenhouse gas emission" has increasingly become the focus of discussion in society today, December 2009,7th to 18 th, the fifteenth conference of the parties of the UN climate change conference mainly considered the human factors on the impact of climate change in Copenhagen conference, but without enough attention on geological effects in carbon abatement process. Allogenic water has low carbonate saturation index, PH value, hardness, and strong erosiveness, which plays a special role in the karst landform and caves development. Allogenic water can accelerate the karst development, which is beneficial to the water cycle, promoting the dissolution of carbonate rocks, improving transfer speed and strength of the carbonate.Whether allogenic water can improve the carbonate in fixing carbon and increase geological carbon sink reserves or not, at present, nobody has done related research.Finding out whether allogenic water can raise carbon sink potential is one important problem to be solved so as to scientific and accurately calculate global carbon sink.This thesis selects Maocun subterranean river as study site, which is in Lingchuan county about 30km of Guilin, based on fully investigating climate, geomorphology, geological and hydrological geological data and combining with previous research results of the research region, taking detailed hydrogeology survey. Having a complete hydrological observation and sampling analysis of Maocun subterranean river, by measuring hydrological, water chemical parameters and 8I3C of study areas to reveal the dynamic mechanism between allogenic water and karst carbon sink, DIC concentration and space-time change characteristics of DIC sources in order to find out the role of the allogenic water in carbon emission reduction. Putting the carbonate briquettes and specimens in Xiao Longbei (allogenic water), Bianyan, She Gengyan, San Wanquan and Bei Diping, using imported MEM-Micro-erosion meter imported from Australia to measure the carbonate erosion rate. In the field, using the Multi 350i portable water chemistry analyzer produced by WTW company of Germany to measure conductivity. pH value and water temperature. Using calcium ion kit (Germany, Aquanmerck) to titrate Ca2'and HCO3" concentration in water, (accuracy of 0.1 mg/L and 0.1mmol/L). And collecting water samples for the ion. cation and carbon isotope analysis. Finally, collecting and analyzing data by Origin, Sufer, Spss software.Through the above research, the main conclusions are as followings:1. There are different hydrogeochemical features between karst water and allogenic water, carbonate saturation index trend to plus, while pH shows rising tendency from upstream to downstream in the study area, Sic of Xiao Longbei is less than 0, far from saturation, which has strong erosion; when enter the karst area, after a distance of water-rock interaction, Sic attains saturation, hydrochemical index variation are controlled by geological background and karstification intensity.2. The erosion ability of allogenic water is greater than karst water erosion ability, carbonate erosion rate of allogenic water and karst water is inverse with calcite saturation index (Sic) and dolomite saturation index (Sid). Carbonate erosion rate is influenced by hydrodynamic conditions and carbonate saturation index together, carbonate rock erosion rate:allogenic water> karst water, Rainy season> dry season.3.The variation range ofδ13CDIC is-10.31～-15.48%。, rainfall contributes little to DIC of Maocun subterranean river,however, hydrothermal conditions and stratigraphic lithology and soil biogenic CO2 are the dominant contribution of DIC; In addition, isotope fractionation, land uses, cover and fertilizer types can also affectδ13CDIC change of study area.4. Rainfall promotes the increase of karst carbon sink, karst carbon sink increases about 2 times after rainfall, the atmospheric CO2 consumed by karstification of Karst areas have significant seasonal variation, generally,the karstification carbon sink of rainy season is greater than the dry season; Karst carbon sink intensity is not only controlled by CO2 content, but also influnced by runoff of watershed, karst carbon sink significantly increased after heavy rainfall, the karst area has a great carbon sequestration remit potential.5. Allogenic water promotes karstification, when allogenic water (Xiao Longbei) enteres into Maocun subterranean river, DIC increases to 3.67 mmol/L from 0.2 mmol/L, from September 7, 2010 to March 22,2011, the carbon sink of XiaoLongbei allogenic water increased by3.04×105 gC from 3.82×104gC when it enters the outlet of Maocun subterranean river, carbon sink increased 8 times from upstream to downstream of the study area.
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