Assessing the groundwater dependence of valley bottom wetlands in coal-mining environment using multiple environmental tracers, Mpumalanga, South Africa

Globally, increased stress on water resources and associated ecosystems is reported. Reducing overdependence on a single water resource grows, with growing global interest on hydrological cycle interactions, impacts of land uses and impacts of these interactions on dependant ecosystems. Through a case study, groundwater exchanges between wetlands and shallow unconfined aquifer and the impact of these exchange flows on water quality in a coal-mining area were investigated. Multiple techniques were applied to assess spatiotemporal dynamics of aquifer–wetland interactions in coal-mining environments. Water level measurements in piezometers and boreholes provided insights in groundwater flow and groundwater–surface water exchange fluxes in wetlands. The potentiometric surface was towards the two wetlands during the study period. Strong GW–SW connectivity was indicated through similarities in hydrochemical and stable isotope tracers, while the quality of sampled waters was suitable for ecosystems and use in agriculture. Water types were dominated by Na, Ca and HCO3−, while introduction of Al and SO4− was indicative of impacts of mine water in the northern wetland. Stable isotope ratios in all sampled waters clustered along the GMWL, suggesting the primary source of water was rainfall and indicated connectivity. Although groundwater-monitoring guidelines in coal-mining areas are available, these protocols lack emphasis on monitoring GW–SW interaction and impacts of mine operations on such interactions in these areas remains lacking. Findings of this study indicate that by incorporating GW–SW interaction monitoring as part of established mine monitoring protocols, unintended impacts of mine operations on related water bodies within mining environments can be avoided.