Characterizing the groundwater flow pathways and recharge sources of a desert inter-dune aquifer system by geophysical approaches and multiple isotopes (B, H and O)

Studies of groundwater hydrodynamics are rare in desert aquifer system due to its remote location, sparse population, low effort input, and limited field data, but necessary and vital for water security and environment protection. Hydro-meteorological conditions, subsurface electrical resistivity structure, and the chemical and isotopic (¹¹B/¹⁰B, ²H/H, and ¹⁸O/¹⁶O) compositions of groundwater and lake water in a desert inter-dune aquifer system were systematically investigated in order to delineate the origins and processes of groundwater flow. It was found that (1) two possible recharge mechanisms are possible to recharge the shallow sand dune aquifer, namely intensive rainfall infiltration and moisture-heat coupled transport; (2) the electrical resistivity tomography data show that salt lake water intrudes the ambient aquifer and interacts with fresh groundwater. The emergences of uptake of boron and increase of δ¹¹B in salt groundwater further stress the intrusion of salt lake water. (3) Dissolution of ¹⁰B in fresh groundwater leads to a shift of the δ¹¹B value from positive to negative along the flow path. Fresh groundwater streamlines originate from one place with high δ¹¹B value in solution to another place with low δ¹¹B value. Further referring to much high δ¹¹B value in local rainwater, it is suggested that the shallow lakeshore groundwater is probably recharged by local rainfall; (4) Combining with the flow field of lakeshore groundwater and, hydrogen and oxygen isotopic characteristics of groundwater and lake water, the desert lake water is considered to be mainly sustained by shallow lacustrine groundwater discharge.