Shallow Groundwater of Poyang Lake Area

Abstract

Two main types of the shallow groundwater are identified in the Poyang Lake area. Groundwater of red earth refers to the HCO$_{3}$-Ca-Na type, has low TDS values (25–130 mg/L) and is mainly slightly acidic (pH varies from 4.5 to 6.6). Due to active water exchange, this groundwater type is in equilibrium with kaolinite and hydroxides, which give the kaolinite weathering crust a reddish shade. Such groundwater develops mainly on sites with a hilly topography, which contributes to the formation of active water exchange. Within agricultural landscapes, where the water exchange rate decreases, there is the shallow groundwater with higher TDS values (160–600 mg/L) and pH values (6.3–7.7) in comparison with the groundwater associated with red earth. The equilibrium with minerals in this case shifts toward montmorillonites and illite due to new stage of water-rock interaction established. It is worth to note, that due to influence of anthropogenic factors relatively high concentrations of pollutants were identified both in the shallow groundwater associated with red earth and groundwater of agricultural landscapes. Prevailing pollutants are NO$_{3}{}^{-}$, Cl${}{-}$ and SO$_{4}{}^{2-}$. This pollution leads to an increase in TDS values up to 800 mg/L and a change in the groundwater chemical type to Cl–NO$_{3}$, NO$_{3}$, SO$_{4}$–HCO$_{3}$, SO$_{4}$–Cl–HCO$_{3}$ by anionic composition and K–Na–Ca, Ca–K, Ca–Na–K by cationic composition.