Anthropogenic Aquifer Recharge Effect on Groundwater Resources in an Agricultural Floodplain in Northeastern Tunisia: Insights from Geochemical Tracers and Geophysical Methods

In this study, geochemical tracers and geophysical methods were combined to assess the anthropogenic aquifer recharge (AAR) processes within a small floodplain in Mornag plain, NE of Tunisia. From a regional viewpoint, the aquifer is one of the most exploited because of the intensive agricultural and industrial activities in the region. Based on geochemical data and hydrodynamic observations, stream–aquifer connection was evidently proven. An AAR from the saline effluent rejected in the dry channel (the Wadi) was detected in the downstream area of the Wadi El Hma plain. Isotopic tracers ( 18 O and 2 H) were effective tools to clarify the recharge processes in relation to the hill dam to detect the signature of the effluent near an installed check dam. Electrical resistivity tomography (ERT) profiles were performed in the most salinized part of the plain in order to highlight the role of the Wadi in AAR. ERT provided clear images of low resistivity horizons longitudinally and transversely to the Wadi. Because groundwater is mainly used for irrigation in the Wadi El Hma plain, an assessment of its suitability for irrigation was performed based on a multi-criteria decision analysis, which revealed that, except the hill dam water and upstream groundwater, the remaining zones of the aquifer are providing water classified as doubtful to unsuitable for irrigation. The results of this work highlight the water sustainability threat in the region and would warn decision-makers to control the Wadi runoff and preserve it against any pollution source since it constitutes the principal inlet of any AAR.