Contribution of clay-aquitard to aquifer iron concentrations and water quality

The contribution of aquitards to aquifer water quality can be pronounced but is rarely considered. The aims of this study were to delineate the spatial distribution of iron in a shallow aquitard-aquifer system within Jianghan Plain (JHP) of central China and to identify the origin of high iron within aquifers. Infiltration, hydraulic gradients and sediment chemistry influence the distribution of iron in the aquitard pore water which has a significant effect on the underlying aquifer. Chemical equilibrium modeling of pore water was used to simulate chemical processes influencing aquifer chemistry and determined the possible precipitation of FeCO₃, FeS minerals (FeSx) and Fe-oxides (representing hydroxides, oxyhydroxides, and oxides of ferric iron). We presented a conceptual chemical-physical scenario to explain the observed Fe distributions: (1) Increasing iron concentrations with low-level sulfide in aquitard pore water. (2) Increasing iron concentrations with low-level sulfide in aquitard pore water underlying ponded water. (3) Decreasing iron concentrations with high-level sulfide in aquitard pore water. In combination, our findings illustrate the influence of aquitards on aquifer chemistry using Fe within the Jianghan Plain as an example.