Interaction between surface water and groundwater revealed by multi-tracer and statistical approaches in the Baiyangdian Lake watershed, North China Plain

The surface water/groundwater-continuum flow system is investigated through an intensive field survey downstream of the Baiyangdian Lake watershed, North China Plain. Oxygen and hydrogen isotope and chemical analyses are conducted on surface water, shallow groundwater, and deep groundwater and the results are processed by applying principal component and cluster analyses. The surface water of the Fu River, Tang Reservoir, and Baiyangdian Lake is strongly affected by anthropogenic influence, resulting in high nitrate-ion concentration, a distinct sodium-sulfate water-type derived from industrial wastewater, and enriched stable isotopic compositions due to accumulated evaporation, respectively. In some areas, shallow groundwater shows close chemical and isotopic affinity to surface water, indicating that surface water recharges to shallow groundwater. Deep groundwater shows lower chemical and isotopic signals than surface water and shallow groundwater. However, a slightly high nitrate-ion concentration is observed in some samples of deep groundwater, suggesting a partial communication between shallow and deep aquifers.