Assessing groundwater salinity and nitrate variability due to drought in Mahdia's aquifers

ABSTRACT In Mahdia, a coastal arid region in eastern Tunisia, the overexploitation of groundwater (GW) has caused a significant decline in GW levels, increasing the risk of seawater intrusion and surface pollutant infiltration. This study assesses GW contamination by analyzing nitrate concentrations and salinity variations in wet and dry years using long-term data (1998–2016) from 37 shallow GW wells. Geostatistical analyses reveal strong spatial dependence of contamination, with higher salinity and nitrate levels during dry years. A reduced range of influence in the semi-variogram models during dry years suggests the need for denser GW monitoring networks to minimize spatial uncertainty. Findings of this study indicate that GW pollution is driven by the combined effects of excessive fertilizer use, insufficient wastewater treatment, industrial discharges and seawater intrusion. To address these challenges, an integrated water management strategy is required, particularly during drought periods. Strengthening regulatory frameworks for fertilizer use, improving wastewater treatment infrastructure and enforcing stricter controls on industrial discharges are essential for mitigating pollution. Furthermore, promoting precision irrigation and the cultivation of salt-tolerant crops can help sustain agricultural productivity while reducing GW overexploitation, a key driver of seawater intrusion. Continuous monitoring is critical for data-driven GW management and ensuring long-term sustainability.