江苏洋口港地区地下水的环境同位素组成及其形成演化研究

Study on the environmental isotope compositions and their evolution in groundwater of Yoco port in Jiangsu Province,China

江苏洋口港地区是江苏沿海开发重点建设的深水港区,水质优良的地下水是港区经济社会发展的重要基础.本研究利用近期获得的钻孔剖面地层对比数据资料,沿水文径流剖面分层采集水样,通过识别地表水、各含水层地下水的环境同位素(δD、δ^(18)O、~3H、^(14)C)组成指纹特征,以揭示研究区地下水的形成演化规律.结果表明,研究区浅层地下水主要来源于现代大气降水的入渗补给,大气降水在补给地下水过程中经历了明显的蒸发过程;研究区深层地下水的放射性^(14)C年龄主要为15000~26000 a,其稳定同位素δ^(18)O、δD值比现代降水低,是晚更新世末次冰期(大理冰期)的盛冰期降水入渗补给.地下水含水层的氘、氧、碳同位素分布具有明显的呈层性,随着地下水埋藏深度增加,地下水中的δD、δ^(18)O值呈下降趋势.浅层地下水与地表水水力联系紧密,可更新能力较强;深层地下水径流缓慢,总体上处于封闭-半封闭状态,可更新能力弱.江苏沿海平原天然地下水流动是自晚更新世末期以来,伴随着冰退、海平面上升而调整到目前的模式.末次盛冰期以来的自然地理及地质发展史,决定着研究区第四系地下水流系统的演变格局,现代人类活动加强了浅层与深层地下水之间的水力联系.研究在高强度开发地下水条件下的区域水文循环特征,可为沿海地区地下水演变机理和调控研究提供技术支持.

Yoco, as an important deep port, is an important construction in coastal area of Jiangsu Province. On the other hand, excellent water quality of groundwater is an important basis for regional economic and social development. Based on the recently acquired data of stratigraphic correlation of core section and systematic sampling, this research was conducted to study the formation and evolution of groundwater through identifying the fingerprints of environmental isotope compositions （ δD, δ18O, 3H, 14C ） in surface water and groundwater of each aquifer. The results show that shallow groundwater in the study area mainly originates from the precipitation, which has experienced significant evaporation in the recharge process. The 14C age of the deep groundwater mostly ranges from 15000 to 26000 a, and δ18O, δD is lower than those of modern precipitation. The deep groundwater may originate from the precipitation in colder weather condition during the glacial maximum of the Late Pleistocene （ Dali glacial）. The distribution of δD,δ18O and 14C shows an obvious strata variation in the groundwater, and the δD,δ18O decrease with the increase of the depth. The hydraulic connection is closely linked between the shallow groundwater and surface water and the shallow groundwater shows strong renewability, while the deep groundwater runoff is slow and shows weak renewability in the closed or semi closed state. The natural groundwater flow in the coastal plain of Jiangsu has being adjusted to the current status since the Late Pleistocene, with the changes of the ice retreat and the rising of sea-level. Since the last glacial period, the change of geological environment determines the evolution of the pattern of the Quaternary groundwater flow system, however, the hydraulic connection is strengthened between the shallow and deep groundwater by human activities. This research reveals the characteristics of hydrological cycle under the condition of high strength human activities, and may provide technical support to study the evolution mechanism and control of groundwater in coastal areas.