豫北山前平原深层地下水硫酸盐来源与污染途径的同位素示踪

Sources and Pollution Pathways of Deep Groundwater Sulfate Underneath the Piedmont Plain in the North Henan Province

豫北山前冲洪积平原深层地下水硫酸盐(SO_(4)^(2-))呈现持续增高趋势,但其机制仍不清楚.为探讨深层地下水SO_(4)^(2-)来源与污染机制,选择山前冲洪积平原不同赋存条件深层地下水作对比分析,借助水体水化学、氢氧同位素(δD_(H2O)和δ^(18)O_(H2O))、硫酸盐硫和氧同位素(δ^(34)S_(SO4)和δ^(18)O_(SO4)),示踪人类活动影响下深层地下水SO_(4)^(2-)的来源、污染途径及硫酸盐细菌还原过程.结果表明:深层地下水水化学、δD_(H2O)和δ^(18)O_(H2O)以及δ^(34)S_(SO4)和δ^(18)O_(SO4)组成月际变化相对稳定,但不同地点的地下水组成呈现显著空间差异.研究区未受人为影响的深层地下水SO_(4)^(2-)来源包括大气降水、黄铁矿氧化以及石膏溶解,且经历细菌还原作用;人为输入对深层地下水的影响表现为两种不同的途径和过程,一种是在山前补给区,因无显著的隔水层,在降水入渗和河水侧渗作用下,深层地下水显著受到人类活动来源硫酸盐(工业废水)影响.另一种是在排泄区,由于深层地下水过量开采导致地下水水位下降,上伏浅层咸水产生越流补给,造成深层地下水的SO_(4)^(2-)浓度显著增加.研究结果很好地揭示了焦作山前冲洪积平原深层地下水受污染的机制,为我们有效管理和保护深层地下水资源提供重要科学依据.

Deep groundwater sulfate in the piedmont alluvial plain in Jiaozuo had been increasing,however,the mechanism is still unclear.To illustrate the pollution mechanism of deep groundwater,deep groundwater in different hosting conditions was sampled to compare,and hydro‐chemical compositions,hydrogen and oxygen isotopes(δD_(H2O)andδ^(18)O_(H2O)),sulfate sulfur and oxygen isotopes(δ^(34)S_(SO4)andδ^(18)O_(SO4))were determined to constrain the sulfate sources,pollution pathways and sulfate bacterial reduction processes with the presence of anthropogenic activities.The results indicated that there were small variations of monthly hydro‐chemical and isotope compositions in respective deep groundwaters,but large spatial differences were found in the hydro‐chemical compositions of these deep groundwater.Sulfate in the undisturbed deep groundwater was mainly derived from atmospheric deposition,pyrite oxidation and gypsum dissolution,and the bacterial sulfate reduction obviously occurred;There were two kinds of pollution pathways and processes in the polluted deep groundwater.First was that in the piedmont where deep groundwater was recharged,due to no obvious aquifuge between them,the precipitation and river water containing industrial wastes could easily infiltrate into deep groundwater with the result of increasing sulfate concentrations.Second was that in the discharge zone,increased deep groundwater sulfate was related with leapfrog recharge from the above aquifer where sulfate was rich,and the leapfrog recharge was due to overwhelming deep groundwater pumping.Our results well illustrated the sulfate pollution mechanism in deep groundwater underneath the piedmont alluvial plain in Jiaozuo,and provided vitally scientific evidences on effective management and protection of deep groundwater source.