【作者】 曹敏；

【导师】 袁道先；

【作者基本信息】 西南大学 ， 自然地理学， 2012， 硕士

【摘要】 重庆的岩溶地区蕴藏着丰富的地下水资源,岩溶地下河水资源量达47.77亿m3/a。由于岩溶地区特殊的水文地质结构造成了其固有的环境脆弱性,土层薄,地表污染物质很容易通过落水洞等岩溶形态进入岩溶含水层或者地下河系统,导致严重污染。特别是随着人类活动对自然干扰的增加,居民生活、生产过程产生的废水增加,在未经处理的情况下排入河道。本研究以重庆南山老龙洞流域为例,利用水化学和C、S、Sr同位素探讨自然与人为因素对地下河系统水化学组成的影响。老龙洞地下河系统对外界环境变化反应敏感,主要补给为大气降水来源,其水文变化过程反映了岩溶管道系统的特征,即补给、排泄迅速,动态变化强烈。流域的大气降水主要集中于4-9月,为地下水的丰水期,在这期间,水化学离子(如Ca2+、Sr2+、SO42-、PO43-)浓度高于旱季。流域内大气降水的水化学类型为Ca-SO4-HCO3型,桂花湾和赵家院子表层岩溶泉的水化学类型分别为Ca-HCO3-SO4、Ca-Mg-HCO3-SO4型,而地下河水化学类型为Ca-HCO3-SO4型,反映了下三叠统嘉陵江组和中三叠统雷口坡组碳酸盐岩地层对地下水水化学特征的控制。地下河水水化学介于表层岩溶泉、雨水和污水的水化学之间,反映了各种补给来源的影响。表层岩溶泉与地下河水的污染来源存在明显区别,表层岩溶泉的NO3-离子明显高丁地下河和地表污水,而其它离子浓度一般是地下河水和污水高于表层岩溶泉。岩溶地下水化学特征的形成受到地质作用、大气降水和士地利用方式等的综合影响。污水的水化学类型为Ca-Na-HCO3型,反映了人类活动影响下地表水的水化学特征。通过对一场降雨的监测,提取了对水质累积贡献大于86%的4个主成分,分别代表地质岩性背景、城市污水、水土流失和硝化作用。第一主成分主要包括是Ec、Ca2+、Mg2+、HCO3-,反映了碳酸盐岩(灰岩、白云岩)溶蚀对地下河水质的贡献,这与研究区中下三叠系地层中的碳酸盐岩地层中灰岩、白云岩含量较高有关。第二主成分与K+和PO43-密切相关,反映城市污水排放的贡献。第三主成分与全Fe、全Mn、Al3-和流量正相关,反映了降雨造成的地下河流域内地表的水土流失状况。第四主成分与NO3-显著正相关,归结为硝化作用的影响。降雨条件下,重庆南山老龙洞流域岩溶地下水中DIC浓度平均值低于旱季。平均DIC浓度：污水(467.8mg/L)>赵家院子岩溶泉(346.6mg/L)>地下河水(306.5mg/L)>桂花湾表层岩溶泉(292.5mg/L)。碳同位素最高值出现在春夏季,与其它地区观测到的夏季旺盛的生物活动影响下的同位素值偏轻的现象相反。岩溶地下水中δ13CDIC与DIC浓度没有明显关系,表明其来源复杂并受到多种因素控制。水化学计量关系证明硝酸和硫酸参与了溶蚀碳酸盐岩,并且使得地下水中δ13CDIC偏正。桂花湾泉和赵家院子泉的δ13CDIC均值分别为-12.2‰和-12.4‰。地下河C同位素的变化范围为-13.3‰～4.8‰,均值为-9.8‰。污水的δ13CDIC值最高,平均值为-9.6%。老龙洞的δ13CDIC值月变化特征与S1基本一致。由于其DIC来源不同,两个表层岩溶泉的碳同位素值明显低下地下河和污水。地下河中Sr2+浓度和87Sr/86Sr比值分析表明地下河中Sr2+主要来自于碳酸盐岩溶蚀,而人类活动产生的Sr同位素比值跟碳酸盐岩溶蚀的Sr同位素比值也接近。通过对87Sr/86Sr和PO43-相互关系的进行分析,发现人类活动,特别是城市污水排放和农业化肥的施用会使得87Sr/86Sr升高。但是具体的机理还有有待进一步研究。δ34S特征表明岩溶地下水中的SO42-具有多种来源。大气降水属于硫酸型酸雨,SO42-含量较高。地下河中SO42-明显受到降水和人类活动的影响。更多还原

【Abstract】 Karst region abounds in groundwater, providing a large amount of4.77billion m3/a water resources for local people. Due to the fragile hydrogeologic structure of karst, it leads to intrinsic vulnerability of environment with a lack of protective soil which can prevent contaminants derived from surface activities entering the karst aquifers and subterranean stream. Especially, in a case of urbanization, the increasing waste gas and waste water discharged from the residential areas are pouring into the groundwater system to contaminate the system. In this study, a case from the Laolongdong Subterranean stream system in Chonging, China, was chose, targeting the effects of groundwater from natural and anthropogenic factors based on hydrochemistry and C、S、Sr isotopes in the process of urbanization.The Laolongdong subterranean system responds quickly to outside environmental changes. The variations of hydrological processes showed characteristics of karst conduits that both the recharge and discharge were strongly dynamic. Precipitation is the main recharge of karst groundwater. The rainfall in study area always appears in April to September. In this period of time, the discharge of groundwater is much larger than the opposing seasons and concentrations of Ca2+、Sr2+, SO42-、PO43-also showed the similar trends to the discharge.The hydrochemistry of precipitation is Ca-SO4-HCO3, two springs showed a type of Ca-HCO3-SO4and Ca-Mg-HCO3-SO4respectively, whereas the subterranean stream presented a type of Ca-HCO3-SO4, which reflects the dominance of carbonate rocks. The hydrochemistry of Laolongdong subterranean stream stays in the midst of three end-members, namely, epikarst springs, rainwater and sewage water, which suggest contributions of multiple recharges. Thus, the formation of karst groundwater is affected by geological processes, precipitation and changes of land use. Domestic water showed a type of Ca-Na-HCO3. Four principal components which amount to86%of accumulated contribution were extracted to represent geological or lithologic backgrounds, domestic sewage water, soil erosion and nitrification, separately. The first component, related to Ec, Ca2+, Mg2+, HCO3-, illustrates contributions from the dissolution of carbonate rocks. The second component, related to K+and PO43-, showed contributions from discharge of domestic sewage water. The third component is highly connected to total Fe, total Mn, Al3+and discharge, which demonstrates the soil erosion attacked by precipitation. The fourth one was only correlated to NO3-, showing contribution from nitrification process.Attributed to the dilution processes of raining, DIC concentrations of groundwater were lower in high-flow season than in low-flow season, specificly, domestic sewage water (467.8mg/L)> Zhaojiayuanzi Spring (346.6mg/L)> Laolongdong subterranean stream (306.5mg/L)> Guihuawan Spring (292.5mg/L). The highest carbon isotopes took place in the spring and summer, which was different from previous reports that carbon isotopes tend to be light in summers because of the influence of the active biological processes in soils. There was no significant relationship between δ13CDiC and DIC, indicating they were originated from multiple sources and controlled by different factors.It was proved that nitric acid and sulfuric acid took part in dissolving carbonate rocks, which leads to heavy carbon isotopes. The range of carbon isotopes in subterraneam stream was from-13.3‰to-4.8‰with an average value of-9.8‰. While in the two springs, the average values of carbon isotopes were-12.2‰and-12.4‰, respectively, much lighter than the subterranean stream.Sr is mainly originated from the dissolution of carbonate rocks based on analysis of Sr2+concentration and87Sr/86Sr ratios. However, anthropogenic-originated Sr had similar rang of87Sr/86Sr ratios, which may elevate87Sr/86Sr ratios in groundwater. Even though we observed that elevated87Sr/86Sr ratios could be attributed to some anthropogenic activities, some further evidences should be introduced to support this.Features of δ34S showed that there were many sources to contribute to concentrations of SO42-Especially, local precipitation was acid with high concentration of SO42-and a sulphur-bearing seam of coal as well as anthropogenic activities, such as fertilizing, could make contributions to SO42-of karst groundwater.更多还原