基于^(222)Rn的马莲河下游地下水补给河水空间差异特征研究

A study of the spatial variation in groundwater discharge to river using ^(222)Rn in the lower reaches of the Malian River

河水和地下水转化关系的定量评价是流域水资源量管理和合理利用的基础。在西北内陆马莲河流域下游开展氡同位素示踪,利用河水222Rn通量模型评价了地下水沿河排泄强度。结果表明:地下水222Rn活度高于河水1个数量级,潜流带水222Rn活度受河水、地下水混合作用及沉积物氡释放影响。马莲河下游均为白垩系环河组地下水排泄补给河水,累计排泄量4.5 m3/s,占河流流量的73.2%。排泄强度存在空间变异,上段及下段为地下水强排泄区,中段作用强度较低。模型不确定性主要受地下水端元、潜流带输入及气体逸散系数三个因素控制,222Rn示踪方法在地下水补给河水型地区较为适用。

Quantifying groundwater-river interactions is critical for protection and management of water resources.Radon was utilized as a tracer to determine the distribution of groundwater discharge in the lower reaches of the Malian river in northwestern China.A mass balance model for river 222 Rn is established and it provides a detailed longitudinal profile of the groundwater discharge rates.The results show that groundwater 222 Rn activities are almost 1 order of magnitude higher than those of river water and the 222 Rn activity in the hyporheic zone water is governed by the mixing with groundwater and river water and 222 Rn inputs from sediments,which indicates that the groundwater from the Cretaceous aquifer discharged to the Malian river in the whole sections of the lower reaches with a total of 4.5 m 3/s,accounting for 73.2%of the total river flux.The discharge rates vary spatially along the river length with higher rates in the upper and lower reaches,while a weaker interaction exists in the middle sections.The groundwater discharge resulting from the model is subject to several uncertainties including variability in groundwater 222 Rn activity,uncertainties of 222 Rn inputs from the hyporheic zone and gas transfer coefficient.Despite the uncertainties of the model,when correctly applied,the 222 Rn tracer method can provide detailed information on the spatial distribution of groundwater discharge,especially in the gaining rivers.