甑皮岩洞穴遗址地下水的水-气界面H2S气体的产生机理

Production Mechanism of HS at the Water-air Interface of Groundwater at the Zengpiyan Cave Site

桂林甑皮岩洞穴遗址是我国新石器时代洞穴遗址的典型代表。污染物进入到以裂隙介质为主地下水所形成的还原环境后,其性质可能会改变从而侵蚀遗址文化层。本文通过采集地下水水-气界面的H2S和CH4气体,结合硫酸盐的硫同位素δ^34S-SO4^2-、溶解有机碳(DOC)、化学需氧量(COD)、硫酸盐还原菌(SRB)等指标,研究遗址地下水水-气界面侵蚀性气体H2S的产生机理。结果表明:甑皮岩水体SO4^2-浓度范围为0.57~131.00 mg/L,其空间分布不均匀,来源主要受到大气降水、硫化物矿物的氧化及微生物硫酸盐还原的影响;丰富的有机质为硫酸盐还原提供能量,DOC与COD浓度存在空间差异,高值均位于人类活动强烈的径流上游区;SRB普遍参与硫酸盐还原作用,气温、降水和有机质决定SRB数量在时空上表现为雨季>旱季、地表水>地下水;气温较高促进H2S的形成,SRB与环境的还原程度均影响H2S和CH4浓度。H2S性质不稳定易氧化为硫酸,若继续聚集将加剧遗址的化学侵蚀。建议增加污染物的运移和反应产物的监测,关注遗址的保存环境。

The Zengpiyan cave site in Guilin is a typical representative cave site of the Neolithic Age in China.When pollutants enter the reductive environment of fracture-based groundwater,their properties may be changed and thus they may erode the cultural layer of the site.In this paper,by collecting H2S and CH4 gases at the water-air interface of groundwater and analyzing sulfur isotopeδ^34S-SO4^2-,dissolved organic carbon(DOC),chemical oxygen demand(COD),sulfate reducing bacteria(SRB)and other indicators,the production mechanism of the corrosive gas H2S at the water-air interface of groundwater in the site was studied.The results showed that the concentration of SO42-in the water body of the Zengpiyan cave ranged from 0.57 mg/L to 131.00 mg/L,with an uneven spatial distribution,indicating that the effects from precipitation,oxidation of sulfide minerals and microbial sulfate reduction.The abundant organic matter provided enough energy for the sulfate reduction.The spatial distributions of concentrations of DOC and COD were different but their high values all showed in the upstream area of the runoff,which was affected strongly by human activities.Generally,SRB participated actively in the sulfate reduction,amounts of SRB trended as rainy season>dry season and surface water>groundwater,which was determined by temperature,precipitation and organic matter.The formation of H2S was promoted by higher temperature,SRB and degree of reduction environment affected concentrations of H2S and CH4.H2S is unstable and can be easily oxidized to sulfuric acid,which may aggravate the chemical erosion at the site if accumulated.It is suggested to increase the monitoring of pollutant transport and reaction products and to pay more attention to the preservation environment of the site.