Hydrochemical and isotopic interpretation of interactions between surface water and groundwater in Delingha, Northwest China

•The local water is mainly recharged by precipitation in the mountainous area.•There is a close interaction between phreatic groundwater and Bayin river.•Hurleg Lake is recharged by Bayin River and phreatic groundwater.•Lianshui River receives groundwater and discharges into Tuosu Lake.•The interaction between phreatic groundwater and surface water shows spatial variability.