污染地下水对桂林甑皮岩洞穴遗址的侵害

The cultural accumulation of Zengpiyan site in Guilin is located in the groundwater seasonal fluctuation zone of a cave-dominated karst aquifer. Being in an original groundwater environment of sulfate contamination, the site is found to have bearing more organic matter from domestic waste. It is deduced that bacterial sulfate reduction could probably occur, resulting in increasing risk of carbonate dissolution in the cultural accumulation. The project aims to reveal the mechanism of bacterial sulfate reduction in a cave-dominated karst aquifer, and to evaluate the impact of reduction products on relics protection. In consideration of pollutant migration and transformation in the aquifer are controlled by karst media, it is crucial to find the active moving pathways of solute transport because the contaminant plume is very heterogeneities in the aquifer. However, the common methods of hydrogeological tests and geophysical exploitation are limited for contaminant survey in karst aquifers. Therefore, a multi-layer monitoring and sampling technique will be used in the borehole to find active fractures and conduits, combining with high precision groundwater temperature logging and downhole CCTV surveys. Through these, we can understand the hydrodynamic condition and its biogeochemical environment in the aquifer, which is important to know the fate of contaminants. By means of SRB bacterial detection, hydrochemical analysis from multi-layer sampling, gas collection and testing for CO2 and H2S, the degree of bacterial sulfate reduction and the biomarker of organic matter degradation products are studied. Carbonate dissolution test in the field and simulation experiment with different scenarios are two ways to measure the carbonate dissolution rate and to evaluate the weathering capacity of contaminants. Overall this project tries to uncover the fate of sulfate and organic matter under the circumstance of anaerobic condition in karst aquifer, focusing on finding the function of H2S on the acceleration of carbonate dissolution. The results will provide a new view of risk assessment and prevention for karst groundwater pollution and strategies for protection, and new understanding in karst formation and cave enlargement. Likewise, it will be useful in risk assessment and early warning system for Zengpiyan cave relics protection, and it will be good references for other relics protection with the similar geological background.

甑皮岩古人类洞穴遗址文化层位于地下水的季节变动带中。在原富硫酸盐的地下水环境中，叠加生活污染带来的有机质，推测发生细菌硫酸盐还原，导致碳酸盐岩加速溶蚀的风险增大。本研究将揭示溶洞发育的岩溶含水层中细菌硫酸盐还原发生的机制，评估还原产物对遗址保护的影响。鉴于污染物的迁移和降解受到岩溶形态的控制，为此利用高分辨率地下水分层测温和钻孔电视成像技术，定位活跃裂隙管道并开展地下水分层监测，掌握控制污染物迁移转化的水动力条件和化学环境。通过含水层的SRB细菌检测、分层水化学分析、有机质组分分析以及CO2和H2S气体测试，研究硫酸盐还原程度和有机质降解产物的标志物。通过野外溶蚀试验和室内溶蚀模拟实验，探索硫酸盐还原对加速碳酸盐岩溶蚀的作用。研究结果不仅为岩溶地下水污染风险评价和防治提供新的视角,为岩溶形成或洞穴发育理论提供新认识，也将有助于建立遗址保护的风险评估方法，对类似地质条件区文物保护有参考价值。

甑皮岩古人类洞穴遗址文化层位于地下水的季节变动带中。在原富硫酸盐的地下水环境中，叠加生活污染带来的有机质，推测可能发生细菌硫酸盐还原，致使碳酸盐岩加速溶蚀的风险增大。本项目在综合前期已经开展水文地质钻探、物探和示踪试验的基础上，选取分别代表裂隙流、具有溶洞的管道流和开放程度高的洞穴水流进行地下水的物理-化学性质的在线监测。发现三种水流因地下水的滞留时间不同，地下水-地表水的交换程度不同，水化学性质差异明显。裂隙流为主的地下水常处于还原的环境，而具有溶洞的管道流为主的地下水处于氧化的环境，导致污染物的降解过程和产物不同。通过利用高分辨率地下水分层测温和钻孔电视成像技术，定位活跃裂隙管道并开展地下水分层监测，掌握控制污染物迁移转化的水动力条件和化学环境。通过对遗址洞穴内，以及管道流、裂隙流和洞穴水流的代表性水点的侵蚀性气体H2S和CO2、CH4的测试，发现在局部还原的条件下，地下水硫酸盐确实发生了还原作用，产生侵蚀性气体。H2S气体浓度在遗址洞穴内普遍最高，表明洞穴内相比密闭、潮湿的环境更有利于H2S气体的富集和氧化。溶洞发育的岩溶含水层中细菌硫酸盐还原发生的机制还通过地下水的硫酸盐还原细菌(SRB)的检测和有机质降解产物得以证实。裂隙介质水体中的溶解有机质(DOM)以结构比较简单的蛋白类物质为主，腐殖酸类物质的含量较少；而管道介质水体的DOM中结构复杂且较难降解的腐殖质含量较多，这与地下水运动的速度和管道介质中污染物的聚集有关。野外标准石灰岩溶蚀试验表明，87.2%表现为溶蚀状态，结合方解石、白云石的饱和指数分析，发现溶蚀不仅仅是碳酸造成的，其它酸(硫酸和有机酸)已经参与了碳酸盐岩的溶蚀作用。讨论了硫酸盐还原对碳酸盐岩溶蚀的作用的影响。研究结果不仅为岩溶地下水污染风险评价和防治提供新的视角,为岩溶形成或洞穴发育理论提供新认识，也有助于建立遗址保护的风险评估方法，对类似地质条件区文物保护有参考价值。