华北平原地下水演化地史特征与时空差异性研究

Geohistory Characteristics and Temporal-Spatial Diversity of Groundwater Evolution in North China Plain in Holocene

近万年以来华北平原地下水演化经历了百年、千年尺度的早全新世增雨、中全新世多雨和晚全新世干旱频发过程,地下水净补给与降水、蒸发及径流之间水分通量随之变化,并且在时空上呈现明显的差异性。基于全新世以来华北平原浅部地下水循环演化过程中水量均衡,280～350mm年降水量是阈值。当小于该阈值时,地下水系统呈现负均衡;现阶段不是区域地下水净补给最少时期,而是处于全新世多年平均水平。目前,华北平原区域地下水位不断下降是人类耗用地下水的强度远超过自然水循环的更新能力所致,急需规范人类用水行为。

The evolution of regional shallow groundwater in North China Plain over the past 12000 years has gone through three stages,i.e.,the increasing precipitation in early Holocene,abundant precipitation in middle Holocene and frequent drought in late Holocene on the scale of hundred or millennial years.In these stages,the rate of water fluxes among net recharge of the regional shallow groundwater and precipitation surface runoff and land evaporation varies with the precipitation.The variation of the rate obviously shows temporal-spatial diversity,which serves as a natural geographical condition.The recharge of groundwater is sufficient in the rainy period,and is less in the rainless period of the regional hydrologic circulatory course so that the groundwater level and the sea surface tend to decline.The latent capacity of utilizing groundwater is variable,which depends on the land processes of the regional hydrologic circulation.The land processes are adjusted so that the utilization ratio rises.The system of the regional shallow groundwater is in the negative balance if the average precipitation in the studied period is less than 280～350 mm.The main recharge period of groundwater is sufficient from 8.0 to 3.5 kaB.P.The precipitation is the key factor,which causes the evolution of regional groundwater in North China Plain.The coefficients of the relationship between regional groundwater evolution,precipitation surface runoff and land evaporation change continuously with the evolution of the regional hydrologic circulation in periodicity.Therefore,the adhering to the principle of water circulation together with the optimal adjustment of surface water is beneficial to the sustainable utilization of groundwater resources.