Differences in hydrogeochemistry between shallow and deep aquifers in the Baiyangdian basin, China

Groundwater is the dominant long-term water resource for agricultural irrigation and industrial production in the Baiyangdian basin, North China Plain. Groundwater and pore-water were investigated to evaluate chemical evolution and geochemical processes in shallow and deep aquifers. Results show that both shallow groundwater and shallow pore-water had higher TDS, Ca2+, Mg2+, SO42-, and HCO3- concentrations than deep groundwater and deep pore-water. Generally, concentrations of groundwater major ions were higher than those of pore-water in shallow aquifers, while they were slightly lower in groundwater than in pore-water from deep aquifers. Water isotopes showed the meteoric origin of groundwater and pore-water, although evaporation signature was traced in shallow groundwater. Shallow groundwater also experienced carbonate dissolution and silicate weathering. Silicate weathering and evaporite dissolution were the major hydrogeochemical processes in deep aquifers. This study indicated that deep groundwater has better water quality, but is vulnerable to contamination from shallow groundwater with high TDS and NO3- concentrations.