| Karstification is a kind of special geological processes occurring in the earth surface environment,and is closely related to the atmosphere,hydrosphere,biosphere.Because of its low temperature,sensitivity and biological characteristics in the geochemical process,the karst water DIC input is variable.As the main control factor of karst carbon sink,the water circulation influence on the karst carbon sink,and the carbon sequestration characteristics are different in different periods(large,high water period,normal water period and dry period).In addition to carbonate acid,anthropogenic sulfate(acid rain)on the weathering of carbonate rock can increase the DIC concentration in water,carbonate rock weathering caused by H2SO4 in essence is a process of net release of atmospheric CO2,must be deducted in the calculation of carbon sinks,which is of great significance to the study of the global carbon cycle,so sulfate carbonate weathering mechanism and its relationship with the regional carbon cycle in recent years has been a concern hot issues.The process of chemical weathering of sulfate sources mainly include gypsum dissolution,sulfide oxidation,atmospheric precipitation and anthropogenic emissions,the human activity can significantly accelerate basin chemical erosion,change the regional carbon cycle,the biogeochemical cycle of interference substances on the West River Basin.Atmospheric acid deposition(SO42-,NO3-and other acids of acid rain)ions in most from anthropogenic emissions of SO2 and NOX gas,so recently people pay more attention to the impact of atmospheric deposition on the chemical composition of stream.The acid rain in karst region of Southwest China is more prominent in Liuzhou area as the study area,set up three rain sampling points including Shatang(suburb)Liuzhou Meteorological Bureau and Liuzhou Environmental Protection Bureau,the samples are used for analysis of chemical characteristics of acid rain in Liuzhou city and acidic material sources,set up monitoring sections.in Liujiang River district Located in Liuzhou import and export,Lutang and Luowei,and central Liuzhou hydrologic station,the datas are used for analysis of the influence of sulfur source in precipitation on the regional carbonate weathering and carbon sequestrationThe results show that pH distribution range of annual precipitation in Liuzhou city is 4.16~6.61.The acid rain rate was 67.6%,mainly for the weak acid rain(5 < pH < 5.6)and heavy(4.5 < pH < 5),acid rain situation is still severe.Compared to 90 s,mainly acid ions concentration are significantly decreased,while desulfurization and dust removal measures also led to NH4+,Ca2+ concentration decline,so there was nosubstantial change in the value of pH,but the precipitation ion concentration and conductivity have fully proved effective governance of acid rain in Liuzhou.The change trend of acid rain frequency and pH value has obvious seasonal characteristics,acid rain is mainly concentrated in the winter and spring,which is same to the most southern areas of our country.The enrichment factor(EF)was used to analyze the main factors of precipitation,and the results showed that most of the 97.2% of the crust sources in K+ were obtained from the activities of wood combustion.CI-is significantly affected by human activities,mainly from local emissions,such as waste incineration,automobile exhaust emissions.SO42-is mainly from anthropogenic sources,accounting for 98.2%.SO42-is mainly due to the combustion of coal gas released by SO2 oxidation.NO3-accounted for 99.8% of anthropogenic sources,including fuel combustion,chemical reactions in the atmosphere,as well as automobile exhaust emissions,etc..Ca2+ and Mg2+ mainly as soil source,which is consistent with the study area karst area background,but human factors can also release amount of alkaline ions into the atmosphere,and is more severe relatively,such as the quarry stone mining process.Two relatively stable sources of water vapor in the study area: 1.southwest of Baise,Nanning and other mining industry developed or densely populated city,which is passed by most of the southwest airflow,especially in summer by the southwest monsoon,in almost all of the water vapor of acid rain air comes from southwest just arrived in Liuzhou through Nanning city,accounted for 44% in summer,the southeast air landing after Nanning city of southwest arrived in Liuzhou in autumn and winter;2.southeast of Guangdong Leizhou Peninsula and the Pearl River Delta region,air source from the Western Pacific through here directly arrived in Liuzhou or passed by Nanning city,accounted for 8% in summer,57% in autumn and 33% in winter.Compared to the adjacent acid rain area,the flow path of the precipitation of Guilin,the middle of the acid rain zone,such as Jiangxi,Hubei,Hunan,Anhui and other provinces of the densely populated areas of the industry did not directly affect the acid rain in Liuzhou.There is a good correlation between SO42-concentration change trend and rainfall in monitoring section of the Liuzhou hydrologic station,illustrating the contribution of SO42-is large,combining with the analysis of the ?34S-SO42-,the influence of human activities in the form of atmospheric deposition is bound to carbonate rock weathering and carbon sequestration in the river basin,compare the contribution of precipitation to the ions concentration of river between flood season and dry season,the contribution rose on dry season,the reason for this phenomenon may be human activity signals were diluted,or the weathering was strengthened,more products into the water and the relative contribution of sea salt source was reduced.The source of SO42-from precipitation is as high as 70%,In the flood season and dry season,the proportion of SO42-brought by artificial sources into the river reach 65.9% and 76.5% respectively,and the mean value is about.71.2%The proportion of sulfate weathering carbonate rock is 32%,and the ratio of anthropogenic sulfur source to carbonate rock in the basin is about 22.8%.The change of carbonate weathering rate and carbon sink rate compared to the carbonate sulfate in sulfuric acid,the calculation results show that the participation of acid rain,the weathering rate increased by 5.6%,carbon sink rate decreased by 19%,the proportion of SO42-by anthropogenic sulfur source is 71.2%,so the carbon sink rate caused byanthropogenic sulfur source was reduced by 13.53%. |
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