【作者】 史婷婷；

【导师】 陈植华；

【作者基本信息】 中国地质大学 ， 地下水科学与工程， 2012， 博士

【副题名】以湖北香溪河流域为例

【摘要】 工业革命以来,人类活动将大量的以化石(煤、石油)形式固定的碳重新释放到大气中,使大气CO2浓度总体呈持续上升趋势。由此导致的全球变暖现象已经日益成为公众讨论的热点并且这种现象对人类赖以生存的环境的影响变得更为直接。自从发现“遗失碳汇的存在以来,碳循环领域的科学家从各个方面做了大量的工作对其进行合理解释和推测,与此同时,国内外众多学者关注岩石的风化过程,特别碳酸盐岩的岩溶过程在全球碳循环中的作用。碳酸盐岩是全球最大的碳库,与其它碳形态相比,其参与碳循环的速率较慢,因而在全球碳循环研究中,对碳酸盐岩的研究较少,甚至被忽略。但是,现代岩溶学研究成果表明,碳酸盐岩在积极的参与全球碳循环,且响应极其迅速。由于特殊的含水结构,岩溶水是全球最大的地下水体,并供给全球大约20%-25%人口作为饮用水源,其在全球水循环中占有重要地位。我国是岩溶大国,碳酸盐岩分布较广,分布面积达3,440,000km2,占国土面积1/3、全世界碳酸盐岩出露面积22,000,000km2的1/7。其形成年代古老,质地坚硬,且未受末次冰期的刨蚀,由于受新生代的地壳抬升影响而出露地表,再加上特殊的季风气候、雨热同期、岩溶作用非常强烈。由于水循环而伴随发生的岩溶作用也是造成碳酸盐岩化学风化、形成“碳汇”的重要途径。经过多国岩溶水文地质学家的共同努力,于1995-1999年间,执行了由我国科学家提出建议并组织的国际地质对比计划IGCP379"岩溶作用与碳循环(Karst processes and the carbon cycle)’项目,其研究表明,而全球由表层岩溶作用而回收的CO2量为2.2×108～6.08×108tC/a,说明岩溶作用一直在积极的参与着碳循环。然而,长期以来人们对全球变化主要归咎于人类本身,对自然调节的研究并不十分重视。哥本哈根联合国气候会议前“气候门”事件发生后,人们开始对IPCC报告提出质疑,并冷静思考自然因素在全球变化中的作用。鉴于此,2009年3月,中国地调局启动“全球变化的地质响应研究”项目,2010年3月,中国地调局又启动“我国地质碳汇潜力研究”,两项目均涉及到了岩溶作用过程中碳循环研究。国土资源部于2010年启动“我国地质碳汇潜力研究”项目,重新评估地质作用在碳汇中的作用及强度,为我国在国际科技竞争及气候变化谈判中处于主动地位提供有力数据,有重大的现实意义。另一方面,如何能利用岩溶碳汇机理精确计算由岩溶水循环而引起的碳汇量,可为全球碳循环模型的校正提供重要参数,具有重要的理论意义。本研究是对我国西南岩溶山区岩溶流域水循环及其碳汇机制的基础研究,为了阐明岩溶流域不同环境条件下岩溶水碳汇作用的强度及其控制因子,本文研究选择长江中游三峡库区内的香溪河岩溶流域作为研究对象,在对香溪河流域的水文地质条件进行详细调查的基础上,将香溪河流域划分为三大子流域以及干流区域(干流位于三峡库区回水区)进行对比研究,同时选取香溪河流域两个典型地下河系统作为地下水研究对象。自2010年9月至2011年12月逐季对三大子流域及干流地表水和两个地下河进行定期水化学取样分析,对香溪河流域的锶同位素组成(87Sr/86Sr)、溶解无机碳同位素组成(δ13CDIC)、氘、氧同位素组成(δD、δ18O)进行取样、测试分析,进而分析香溪河流域不同子流域和地下河系统在时间和空间上的岩溶碳汇量、碳汇效应的差异性及其各影响因素,得到了以下主要认识和结论：1、研究区水文地球化学特征受水文地质条件的控制,其次还受到气象条件、植被和土壤的影响。1)香溪河流域水化学类型的区域特征：南阳河和古夫河流域的水化学类型主要为HCO3-Ca-Mg型；高岚河流域以HCO3-Ca-Mg型水为主,在该子流域东南部出现HCO3-SO4-Ca-Mg型水；响水洞的水化学类型为HCO3-Ca-Mg型,响龙洞的水化学类型为HCO3-Ca型：说明受流域水文地质条件的影响较大。2)香溪河流域碳酸盐的溶解-沉淀平衡是控制其水化学稳定性的主导因素。流域大部分地区都处于方解石和白云石的饱和与过饱和状态,流域中上游地区溶解pC02均高于大气,而在干流靠近长江部分地区则接近甚至低于大气pC02,说明不断地进行脱气过程,向大气交换CO2,与干流水受三峡库区回水影响,水流滞缓,与大气交换时间过长有关。3)由环境同位素分析结果对流域内水循环方式得到如下认识：南阳河流域上游受(神农架林区)高山低温的特殊地形和气候等因素影响,水的来源不同,到中下游河水流量逐渐增大,流域内地下水流入河流,汇入地表水,不同的水源混合均匀,并且蒸发作用强烈；高岚河流域上游不同支流内的水源不同,到流域中下游,河水主要受高度效应和蒸发作用影响；响水洞(暗河出口)地下水的地下径流途径与滞留时间相对较长,地质环境封闭,水岩反应强烈;响龙洞(暗河出口)的地下径流途径相对较短,流速快,水岩作用弱。说明三大子流域和两个地下河系统的水循环过程存在差异。4)锶同位素组成分析结果也反映出：香溪河流域87Sr/86Sr组成主要来源于碳酸盐岩的风化或溶解,碳酸盐岩的风化对流域水体化学组成起主要控制作用,并且受硅酸盐矿物溶解对水化学组成的影响。其中,高岚河流域部分地区的锶同位素组成较高,反映出流域水化学受碎屑岩风化的影响显著,两个地下河明显受不同的岩性特征控制,响龙洞主要受石灰岩化学风化作用影响,响水洞则受石灰岩和白云岩风化作用的共同影响。说明在不同子流域内和地下河系统,存在不同类型化学风化过程。2、研究区岩溶碳汇的主控因子为水循环条件,土壤的影响因素不容忽视。1)香溪河流域的溶解无机碳(DIC, Dissolved Inorganic Carbon)在不同子流域和地下河中的含量特征为：暗河出口(响水洞和响龙洞)>高岚河流域(孔子河流域)>古夫河流域>南阳河流域>高岚河流域(夏阳河流域)。2)不同流域受水循环条件的控制程度不同：①南阳河流域DIC含量丰水期低于枯水期,受雨季降雨控制；②高岚河流域中孔子河流域DIC含量丰水期含量低于枯水期；而夏阳河流域DIC含量丰水期含量高于枯水期;③两个地下河：响水洞DIC含量明显枯水期高于丰水期,受流量影响显著,明显具有稀释效应；而响龙洞的DIC含量在枯水期和丰水期含量差别不大。3)香溪河流域地表水和地下水的DIC含量在整个流域的分布具有明显的区域差异特征,造成这种差异的主要原因为流域岩性和水文地质条件的影响：导致DIC含量高不仅与流域内碳酸盐岩出露的面积比例有关,还与不同时代地层碳酸盐岩的岩溶作用强度和时间,即水文地质条件有关。4)香溪河三大子流域和两个地下河DIC含量存在不同的季节性变化特征,与不同流域在不同水文季节受土壤CO2影响的程度不同有关：①南阳河和古夫河流域DIC主要来自于岩溶作用,受土壤CO2影响程度较小；②高岚河流域DIC除来源于岩溶作用外,还来源于大气、土壤中CO2的溶解。③两个地下河的DIC来源不同：响水洞DIC枯季明显主要来源岩溶作用,并且岩溶作用强度高,水岩相互作用时间长；响龙洞DIC在枯季和雨季除来源于岩溶作用外,还明显受到土壤和大气CO2的影响。这与响水洞和响龙洞的氘过量参数特征及水循环方式分析结果一致。3、以δ13CDIC稳定同位素为示踪指标,分析无机碳汇的来源和河流系统中碳的生物地球化学行为特征,判断在水循环产生的无机碳汇中大气(土壤)CO2和碳酸盐岩各自的贡献量。1)流域岩溶水中δ13CDIC值受季节性影响较为明显。在丰水期偏正而枯水期偏负,表明有机质分解作用、生物作用的重要影响。在不同季节,香溪河流域水中DIC浓度与δ13C呈负相关关系,与浮游植物的光合作用有关。2)香溪河流域水中的δ13CDIC的这种时空分布规律反映了受流域特征控制：①南阳河流域夏季和冬季水中DIC浓度与813C呈负相关关系,表明生物成因的DIC有较大影响,南阳河流域DIC较低,而813C值较高,明显反映区域碳酸盐岩地质特征；②古夫河和高岚河流域DIC含量较高,而813C值略低,则说明土壤二氧化碳对DIC的δ13CDIC贡献较大。3)两个地下河(响水洞和响龙洞)DIC含量均较高,说明两个地下河岩溶地质特征较为显著；而δ13CDIC值相差较大,响龙洞的δ13CDIC值在冬季和夏季均较小,响水洞的δ13CDIC值只在夏季较低,而冬季较高,和香溪河流域地表水的值接近。反映出,在夏季,两个地下河补给区植物根呼吸和土壤有机质氧化作用产生的无机碳贡献较高：在冬季,只有响龙洞的补给区仍受土壤中CO2气体的溶解驱使,碳酸盐系统不断发生反应和演化,具有较强的微生物活动。4)δ13CDIC与其距河口距离的相关关系反映不同流域特征差异明显：南阳河流域δ13CDIC与其距河口距离总体上呈正相关关系,而高岚河流域δ13CDIC与其距河口距离总体上呈负相关关系。说明光合作用可能为控制南阳河流域δ13CDIC值的重要因素,而高岚河流域上游矿山开采活动较多,沿途水流急、滞留时间短,汇入河道中的大量陆源有机碳分解缓慢并且快速汇入到下游段,而只有到了河口地段,因水流变缓、水量增大,大量陆源有机质才得以强烈分解,释放大量的轻碳,出现了沿河道向河口δ13CDIC变小、轻碳比率变大的趋势。5)运用13C质量平衡法和热力学平衡分馏法分别计算DIC来源贡献率,虽然结果有差异,但得到的结论一致,反映出南阳河流域和古夫河流域在枯水期水中的DIC更多地受来自于土壤CO2的影响；丰水期南阳河流域DIC主要来源于岩溶作用,高岚河流域DIC来源于岩溶作用外,还更多地来源于大气、土壤CO2的溶解。4、结合香溪河流域的岩石风化特征,将岩石化学风化碳汇量估算模型(GEM-CO2)和水化学平衡模式法进行分析对比后,应用于香溪河流域的岩溶碳汇量估算,其中,采用风化碳汇量估算模型(GEM-CO2)计算,香溪河流域岩石化学风化的年碳汇量为23665.7t/a,三大子流域的风化碳汇量分别占香溪河流域的22.217%,38.064%和34.085%；其中香溪河流域碳酸盐岩的碳汇量对香溪河流域岩石风化碳汇量的贡献率达到了99.03%,岩溶碳汇贡献最大,起主导性作用。研究区碳酸盐岩总的出露面积为2135.11km2,运用水化学平衡模式法估算香溪河流域2011年吸收CO2为65885.20t/a。香溪河流域各时代地层岩溶水CO2含量相差并不大,但各地层岩溶水CO2吸收模数却有较大差异,反映地下径流条件是一个关键因素,说明岩溶系统吸碳能力不但受水化学条件的影响,而且也受地下水动力条件的严格控制。5、通过分别对DIC与气象因素(温度和降雨量)、DIC与6大类影响因素(植被覆盖度、土地利用类型、坡度、土壤厚度、土壤类型和母岩岩性)分别进行定量的相关性分析,发现DIC除受气象因素影响,同时也受6大类影响因素影响,是多种因素共同作用的结果：土壤厚度不受季节影响,对碳汇贡献率差异无法判断;高植被覆盖区域和高陡边坡等区域主要受区域内的土地利用类型控制,分别受降雨和温度的影响,少数因子因为土地利用类型复杂的影响,表现出不受降雨和温度变化的影响,植被覆盖度越高其碳汇贡献率越高；士壤类型则受土壤本身特性影响,主要分为受降雨影响和不受季节影响两大类型,棕色石灰土的贡献率高于暗黄棕壤,其他土壤类型无法判断；母岩岩性中则分为变质岩受温度变化影响、其余受降雨影响两大类型,并且碳酸盐岩中,以寒武系中统奥陶系下统∈201、奥陶系中上统(02-3)、震旦系上统陡山沱组(Z3d)和元古界神农架群石槽河组(Pts)为主,整体表现出受降雨量影响的季节性变化特征,但其各亚类碳酸盐岩贡献率无法判断。论文的主要创新体现在：1、结合岩溶流域的特征分析结果,对不同环境条件下岩溶流域地表水和地下河系统的水循环过程中岩溶水碳汇作用的强度及碳汇机理进行分析和解释；并探讨植被、土壤等多种因素在岩溶水循环中及其碳汇过程中的作用；2、运用多项水化学指标和同位素组成特征,对流域地表水和地下水的碳汇强度和无机碳来源进行分析,并运用碳稳定同位素示踪碳汇的碳源,甄别水循环产生的碳汇中大气(土壤)CO2和碳酸盐岩各自的贡献量及其变化；3、运用岩石风化碳汇模型和水化学平衡模式法对香溪河流域岩石风化碳汇量进行估算,并评价岩溶碳汇量的贡献作用;4、将影响岩溶碳汇的多个可能影响因素与岩溶碳汇量(DIC)进行相关性定量分析,确定岩溶碳汇的影响因素。更多还原

【Abstract】 Since the Industrial Revolution, human activities with a large number of fossil (coal, oil) in the form of fixed carbon to re-release into the atmosphere, which has been lead to a continuing upward trend in atmospheric CO2concentration around the world. The resulting global warming has increasingly become a hot topic of public discussion and the environmental impact of this phenomenon on mankind’s survival becomes more direct. Since the discovery of the existence of "missing carbon sink" scientists in the field of carbon cycle have done a lot of work concerning all aspects to reasonably explain and speculate it.. At the same time, many scholars at home and abroad, pay close attention to the process of rock weathering, especially the role of carbonate rock karst in the global carbon cycle. Carbonate is the world’s largest carbon pool compared with other carbon forms. However, due to their slower rate of participation in the carbon cycle, and the research on carbonates in the global carbon cycle was less or even ignored. However, the modern karst study results indicate that the carbonate is actively involved in the global carbon cycle, and the response is extremely rapid. Due to the special structure of the aquifer, karst water is the world’s largest groundwater body, and supplies about20%-25%of the world’s population as a source of drinking water, and occupies an important position in the global water cycle. The distribution of carbonate rocks is wide in China, covering3,440,000km2, taking1/3of China’s total land area, and1/7of world’s carbonate rock outcrop area of22,000,000km2. However, for a long time, the global change is mainly attributable to human who does not attach great importance to the study of natural adjustment. People began suspecting the IPCC Report after he "Climate Gate" in the Copenhagen UN climate conference, and thinking calmly of the role of natural factors in global change. In view of this, in March2009. China Geology Survey Bureau started a "Geological Response Study on Global Change" project. In March2010, China Geology Survey Bureau also started "Research on China’s Geological Carbon Sequestration Potential". These two research projects involve with the karstification carbon cycle research. Description of the geological carbon sequestration in China has risen to the national strategic level, in which karst carbon sinks are an extremely important part.The Ministry of Land and Resources started "Research on China’s Geological Carbon Sequestration Potential" project in2010to reassess the role and strength of the geological carbon sinks, providing strong data for China’s driving position in the international science and technology competition and climate change negotiation to respond to global climate change, fulfill its international commitments as a responsible stakeholde, having great practical significance. In the other hand, how can we use the karst carbon exchange mechanism of carbon sequestration strength of China’s land area of karst, a more reasonable description of the mechanism of the karst process development, an accurate calculation of the amount of carbon sinks caused by the karst water circulation for the global carbon cycle, as well as the calibration of the model provide important parameters having important theoretical significance.This study is basic research of southwest China karst mountainous karst water cycle and its carbon sequestration mechanism. In order to clarify the karst water carbon sink strength of the role of the karst basin under different environmental conditions and its control factors, this study chose the Xiangxi River karst Watershed in Three Gorges reservoir area of middle reaches of the Yangtze River to study, based on the detailed investigation on the hydro geological conditions of the Xiangxi River Basin. The Xiangxi River Basin is divided into three sub-basins for which a comparative study has been made for the main stream region (main stream located in the backwater area of the Three Gorges reservoir area), and two typical underground river system were also selected for a groundwater study. From September2010to December2011, quarter by quarter, field water chemistry sampling and analysis were performed regularly for the three sub-basins, including the main stream of surface water and underground river. The strontium isotope (87Sr/S6Sr), dissolved inorganic carbon isotopic composition (δ13CDIC), deuterium and oxygen isotopic composition (δD of and δ18O) of the Xiangxi River Basin were sampled, tested and analyzed, and the Xiangxi River watershed sub-basins and underground river system and space on the karst carbon sequestration were then analyzed in a timely manner. Carbon sequestration effect of differences and the impact factors were analyzed to investigate the following key knowledge and conclusions:1. Hydro-geochemical characteristics are not only controlled by the hydro-geological conditions, but also influenced by weather, vegetation, and the soil.1) The regional characteristics of the type of water chemistry in Xiangxi River Basin:Water chemistry type of the Nanyang River and the Gufu River basin is HCO3-Ca.Mg type; the Gaolan River Basin is mainly HCO3-Ca.Mg type with HCO3-SO4-Ca-Mg type water in its southeast sub-basins; the Xiangshui Cave is HCO3-Ca Mg type; and the Xianglong Cave is HCO3-Ca type.2) Xiangxi River Basin’s carbonate dissolution-precipitation balance is the dominant factor in controlling the stability of the water chemistry. Most parts of the basin are saturated and over-saturated with calcite and dolomite, and the content of dissolved pCO2in middle and upper reaches of the Xiangxi river domain is higher than that of atmosphere; and in the main stream near the Yangtze River, the content of pCO2in the water is close to or even lower than that of atmosphere,. The water promotes CaCO3nucleation and solid phase precipitation through CO2degassing and exchanges with atmosphere for CO2by means of continuous degassing process. This is relevant to the over long time of exchange with atmosphere due to slow rate of river flow affected by backwater of the Three Gorges Reservoir.3) New understanding on the water cycle way within the Basin getting from analysis of the environmental isotope results:upstream water of Nanyang river basin is from different sources, subject to the special terrain and climate and other factors, like low temperature, in (Shennongjia Forest) mountains, and the middle and lower reaches of the river flow increased gradually, groundwater flowing into the river basin and mixing with the surface water with a certain amount of evaporation; Upstream tributaries of the Gao Lan River watershed are from different sources, and the middle and lower reaches of river basin is mainly affected by the altitude effect and evaporation; the underground runoff pathways and groundwater residence time of the Xiangshui Cave (underground river outfalls) are relatively long in a closed geological environment, having a strong water-rock reaction; the underground runoff pathways of the Xianglong Cave (underground river outfalls) are relatively short with fast rate of flow, having a weak water-rock interaction.4) From the analysis of the strontium isotope composition, we know that the87Sr/86Sr in Xiangxi River Basin comes mainly from the weathering or dissolution of carbonate rocks. The weathering of carbonate rocks plays a major role on the basin water chemistry composition which is also affected by the dissolution of silicate minerals. The strontium isotope composition in part of the Gaolan River Basin is higher, reflecting the significant impact of clastic weathering on water chemistry of the basin. Two underground rivers are significantly controlled by the different end members. The Xianglong Cave is near the limestone end member, while the Xiangshui Cave is affected by two end members, namely limestone and dolomite..2. The main control factor of karst carbon sink in the area is water cycle condition; but the impacts of the soil can never be ignored.1) The order of dissolved inorganic carbon (DIC) concentration in different sub basins and underground stream in Xiangxi River Basin from high to low is underground water outfall (Xiangshuidong and Xianglongdong)>Gaolan River Basin (Kongzi River Basin)> Gufu River Basin> Nanyang River Basin> Gaolan River Basin (Xiayang River Basin).2) The extent of different basins controlled by water cycle is various:①The DIC concentration of samples from Nanyang River Basin (except Honghua village) in wet season is less than it in dry season. It is controlled by rainfall in rainy season.②The DIC concentration of samples from Kongzi River Basin in Gaolan River Basin is not influenced by flows. Instead, the concentration in dry season is less than it in wet season. The DIC concentration of samples from Xiayang River Basin in wet season is higher than it in dry season; it is much affected by flows and rainfall capacity.③The concentration of DIC in Xiangshuidong and Xianglongdong, both underground stream, shows different characteristics in dry season and wet season. The DIC concentration of Xiangshuidong in dry season is obviously higher than it in wet season, reflecting that it is affected by flow. There is dilution effect distinctly. Meanwhile, there are fewer differences between the concentration of Xianglongdong in dry season and wet season; it is not affected by flow.3) The distribution of DIC concentration of surface water and groundwater in Xiangxi River Basin has obvious territorial difference due to the impact of basin lithology and hydrogeologic condition.①The DIC concentration of Kongzi River Basin in Gaolan River Basin is the most due to the high carbonatite proportion of area in Kongzi River Basin. The carbonatite proportion of area in Nanyang River Basin reachs up to79.82%, though the DIC concentration there is less. The runoff modulus of this kind of strata karst water is the highest, and the karst reaction is very intense. The DIC concentration improves because of the water-rock interaction over long term.②The carbonatite proportion of area is high in Nanyang River Basin, with Pts in the lead. Its proportion in carbonatite is43.73%. The proportions of∈1,∈2O1and Z3d are18.58%、13.15%and9.55%. The runoff modulus of strata karst water is relatively low, leading to less DIC concentration in this river basin. It reflects that high DIC concentration is related to not only the emersion area proportion of carbonatite in river basin but also the intense and time of carbonatite karstification in strata of different times, or hydrogeologic condition.③The DIC concentration of Xiayang River Basin in Gaolan River Basin is low. The main lithology is gneiss, marble and so on. It is quite different from the lithology of upper middle in Gaolan River Basin (Kongzi River Basin). The DIC is rooted in various rock chemical weathering type.4) The DIC concentration of3sub-basins in Xiangxi River Basin and2underground streams is range greatly in a water year, especially between a wet season and a dry season. It is related to the different effect of CO2in soil on the DIC concentration in different hydrological season.①The inorganic carbon concentration in wet season is lower than it in dry season. It is rooted in karstification, and is less affected by CO2in soil.②The inorganic carbon concentration in wet season does not decrease with the raising flow. It shows that DIC in water comes from not only karstification but also maybe the dissolution of CO2in air and soil.3. Using the stable isotope δ13CDIC as the indexes, this paper analyzed the source of the inorganic carbon sink and the biogeochemistry behavior characteristics of the carbon in the river system, judged the contribution of the atmosphere(soil) CO2and carbonate rocks in inorganic carbon sink during the water cycle;1)The value of δ13CDIC in the karst water is evidently influenced by season. In high water season, the value was more positive and in low water season, the value was more negative, which indicated the important affection of decomposition of organic matter and biological effect. In different seasons, there was a negative linear correlation between the DIC concentration and δ13C in the Xiangxi river basin, which was related to the photosynthesis of the phytoplankton:①The effect of photosynthesis surpass decomposition of organic matter and aquatic respiration, moreover, due to high temperature, the dissolving capacity of CO2was reduced, then the CO2was escaped from the river to the atmosphere, so that the DIC in river was decreased;②In the winter,δ13CDIC showed the negative correlation, accompanied by elevated DIC concentrations, lower water temperature, weakening of the photosynthesis, declining in production capacity of water, a lot of organic matter began to decompose, which lead to the negative changes of δ13CDIC while elevated DIC concentrations, due to lower water temperature, the dissolution capability of the water to atmospheric CO2was enhanced, which lead to an increase of DIC concentrations, coupled with poor rains, conspiring to make the DIC concentrations peaked.2) The temporal and spatial distribution of the δ13CDIC in Xiangxi River Basin reflects the basin river system dissolved inorganic carbon to form the nature of its source and sink characteristics related to the watershed characteristics and river hydrodynamic conditions. The DIC concentration and δ13C show a negative correlation in Nanyang River Basin water in summer and winter, which shows that the DIC of biogenesis has a principal effect, the DIC was low but the δ13C was high in Nanyang River Basin, which shows the geological characteristics of the regional carbonate significantly;②The DIC concentration was high but the δ13C was low slightly in Gufu River Basin and Gaolan River Basin, this shows that the soil CO2had a big contribution to DIC.3) There was a high DIC concentration in the two subterranean rivers (Xiangshui Cave and Xianglong Cave), which show the Karst geological features evidently of the two caves; but there was a large different in δ13CDIC, the value of δ13CDIC had a small negative correlation in winter and summer in Xianglong Cave, but in Xiangshui Cave, the value of δ13CDIC only lower in summer, while higher in winter, which was nearly the same with the value in surface water of Xiangxi River Basin. In summer, inorganic carbon contribution by plant root respiration and soil organic matter oxidation in the two underground river recharge area is higher; In winter, only the recharge area of Xianglong Cave is still driven by CO2gas dissolved in the soil carbonate system and continues to react and evolution, with a strong microbial activity.4) The value of δ13CDIC in Nanyang River Basin had a positive correlation with its distance from the mouth of the river generally, but in Gaolan River Basin, the situation was opposite. This showed that photosynthesis may be the important factor in control of the δ13CDIC value in Nanyang River Basin, due to the prosperous mining activities in Gaolan River Basin upstream, fast-flowing, short residence time, a large number of land-based sources of organic carbon, which imported in the river, decomposes slowly and quickly imported into the downstream segment. Only in the estuary location, a large number of land-based sources of organic matter was able to strongly decompose due to slowed water flow and increased amount of water, releasing a flood of light carbon, showing a trend that the δ13CDIC became smaller and lightweight carbon ratio became bigger along the road to the estuary. 5) Calculating the contribution rate of DIC sources by using13C mass balance and thermodynamic equilibrium fractionation, although the results were different, the overall trend was the same:the average ratio of three sub-basins derived from soil CO2were Nanyang River, Gufu River and Gaolan River in dry season, which reflected that the DIC of Nanyang River Basin and the Gufu River Basin water were more from the soil CO2in the dry season; the average ratio of the source of soil CO2in wet season were the Gufu River, Gaolan River and Nanyang River, the DIC in Nanyang River Basin in the wet season was more from karstification, also, the inorganic carbon in Gaolan river Basin in the wet season was from karstification, but the more came from the atmosphere and the dissolution of CO2in the soil.4. Combining the characteristics of the Xiangxi River Basin, petrochemistry weathering carbon sequestration estimation model (GEM-CO2) and water chemical equilibrium model method, after analysis and comparison, were applied to karst carbon sequestration estimates in the Xiangxi River Basin. Where, according to the calculation of the weathering carbon sequestration estimation Model (GEM-CO2), the carbon sequestration of Xiangxi River Basin under the process of rock chemical weathering is23665.7t/a, the three major sub-basins’weathering carbon sequestration accounted for22.217%,38.064%and34.085%. that of the Xiangxi River Basin respectively. The carbon sequestration of carbonate in Xiangxi River Basin contributes to99.03%of its rock weathering carbon sequestration, in which the karst carbon sequestration makes the greatest contribution, playing a dominant role. The total outcrop area of the carbonate rocks in the study area is2135.11km2. Estimating by using the water chemical equilibrium model, the Xiangxi River Basin in2011absorbs6.59×107kg CO2. The difference of karst water CO2content in various times of formation of the Xiangxi River Basin is not significant, but the CO2absorption modulus of karst water among all layers differs more significantly, reflecting that the underground runoff conditions is a key factor, and indicating that the carbon absorption capacity of the karst system not only affected by the water chemistry conditions, but also strictly controlled by the groundwater dynamic conditions.5. Quantitative correlation analysis on DIC and meteorological factors (temperature and rainfall), DIC and six categories of factors (vegetation cover, land use, slope, soil thickness, soil type and parent rock lithology) shows that DIC, in addition to meteorological factors, is also affected by the six categories of factors. It is a result of multiple factors.Through comparative analysis, we found that the thickness of soil is not subject to seasonal influence, and differences in the contribution rate can’t be determined. Regions with high vegetation cover and the high and steep slope are mainly affected by the type of land use,, respectively under the impact of rainfall and temperature.A small number of factors, being affected by the complex land use type, show no impact of rainfall and temperature changes,, the higher of the vegetation cover, the higher of their contribution rate. Soil type is mainly affected by soil characteristics itself, mainly divided into two types that are subject and not subject to seasonal impact., The contribution of brown calcareous soil is higher than yellowish brown soil. And the contribution rate of other soil types can’t be determined. With regard to the host rock lithology, metamorphic rocks are affected by temperature changes, and the remaining types are affected by rainfall. The carbonate rocks were subdivided into three types, mainly included①∈2O1, O, Z3d and Pts carbonate,②supplemented with P, and T, and③two carbonate subcategories, containing a small amount of Z2∈1and∈1. The overall performance of the main carbonate mainly affected by the seasonal variations of rainfall impact, but its sub-carbonate contribution rate can’t be judged.The main innovations:1. Combine the characteristics of karst watershed analysis results, the strength and mechanism of carbon sequestration of the karst water in the water cycle process of karst surface water and underground river system under different environmental conditions are analyzed and explained. And the role of vegetation, soil and other factors in the karst water cycle and the carbon sequestration process is probed.2. By using a number of hydrochemistry indicators and characteristics of isotopic composition, carbon sequestration strength of both surface water and groundwater and sources of inorganic carbon are analyzed. And using the carbon stable isotope, the carbon sources of carbon sequestration are traced, screening the respective contribution and change of atmospheric CO2and carbonate rocks to the carbon sequestration in the water cycle.3. Rock weathering carbon sequestration model and hydrochemistry balance method are used to estimate the carbon sequestration of rock weathering in the Xiangxi River Basin, and evaluate the the contribution of karst carbon sequestration.4. Quantitative analysis of correlation between multiple possible influencing factors and karst carbon sequestration (DIC) is performed to determine the influencing factors of karst carbon sequestration.更多还原