Studying groundwater flow systems is important for water resources
management, for pollution prevention and for maintaining the ecological
balance in arid and semi-arid areas. Systematic geophysics and
hydrogeological investigations allow us to define the thickness of the
Quaternary sedimentary layer, the lateral boundary of the groundwater
system, and the depth and basement of water circulation.
Hydrogeochemistry and environmental isotopes are used to gain insights
into the recharge process, water-rock interactions, hydraulic
characteristics and groundwater retention time and to identify
groundwater flow systems at all levels in the Aksu River Basin. Owing to
the dissolution of carbonate and gypsum minerals and evaporites, cation
exchange between Ca 2+ (Mg 2+) and
Na + (K +), and the
evaporation-concentration effect, concentrations of specific ions (SO
4 2-, Cl -, Na
+) and [total dissolved solids](javascript:;)
(TDS) gradually increase along the flow direction and decrease with
depth (indicating that they belong to different groundwater flow systems
(GFSs)). Furthermore, interpretation of stable isotope concentrations
such as δ 18O values suggests different degrees of
depletion in the horizontal and vertical directions. Combined with the
unique structural framework (namely the Wensu uplift, Wushi sag, and
Awat sag), the particle size variation of loose sediments and the
distribution and aggregation of phreatic water with high F and As and
soil salinization show the existence of the surface-ground water
interaction and the distribution pattern of multiple local GFSs. The
vertical zonation of 3H and 14C
isotope concentrations and estimates of groundwater
[residence](javascript:;) time (modern to 24000 years) further
illustrate the hydrodynamic cycle of the local and regional GFSs. The
hydrodynamic and hydrochemical characteristics confirmed the
distribution of GFSs and the complex mixing relationships between GFSs
in the Aksu River Basin under the tectonic conditions since the Neogene
in the South Tianshan Mountains.