Groundwater Contamination Processes in Depleting Alluvial Aquifers, Haouz Plain Morocco

This study examines the effects of groundwater depletion on salinity and nitrate contamination in a detritic unconfined alluvial aquifer. Over the past five decades, the aquifer has transitioned from shallow groundwater (<20 m) in the 1970s to predominantly deep groundwater (>40 m) due to significant water table declines. Groundwater analysis reveals moderate contamination, with nitrate levels highest in shallow zones but detectable at all depths. Dominant hydrochemical processes influencing salinity include rock weathering, halite dissolution, and reverse ion exchange.  
The Haouz Plain, located in central Morocco, covers a significant area within the Tensift Basin. Characterized by an arid to semi-arid climate, it is a center of intensive agricultural and industrial activities, making its water resources highly susceptible to contamination risks.
The thick unsaturated zone formed by water table decline has mitigated surface-borne contamination and reduced evapotranspiration impacts. However, vertical flow dynamics induced by pumping have allowed younger, nitrate-rich groundwater to mix with older, deeper groundwater. Tritium dating indicates that nitrate in deep groundwater likely originates from historical fertilizer use, highlighting the long-term legacy of agricultural practices on water quality.  
Continued aquifer depletion poses serious risks. Pumping deep groundwater could mobilize salts, increasing salinity. Moreover, contaminants accumulated in the thick unsaturated zone could migrate downward over time or with increased recharge, further degrading groundwater quality. These findings emphasize the vulnerability of depleted aquifers to salinization and nitrate contamination, underscoring the need for sustainable groundwater management strategies.  

Keywords: Pollution, irrigation, hydrochemistry, salinity, quality.