Groundwater storage depletion and contamination trade-offs under contrasting irrigation practices in drought-stressed Morocco

The Haouz Plain, Tensift basin, central Morocco. The Haouz region has undergone a clear trend toward aridification over the last four decades, with a severe drought from 2019 through 2025. This study investigates how contrasting irrigation practices influence groundwater quality and quantity using a multi-indicator approach combining tryptophan-like fluorescence (TLF), nitrate, microbial indicators (E. coli, S. enterica), stable isotopes (δ¹⁸O, δ²H), and tritium (³H). Traditional surface-water irrigation areas exhibit elevated TLF (up to 11.3 QSU), nitrate (>15 mg/L), and microbial contamination, indicating influence from wastewater and surface-derived inputs. Shallow water tables (<40 m) and high tritium (>3 TU) confirm recent recharge pathways facilitating contaminant migration. In contrast, modern drip-irrigated areas relying on intensive groundwater abstraction show limited contamination (TLF ≤0.9 QSU; nitrate mostly <20 mg/L; the absence of fecal coliforms), longer mean residence times (>60 years), extraction of older groundwater, and groundwater storage depletion. Results reveal a trade-off in dryland agricultural systems: traditional irrigation sustains recharge but increases vulnerability to contaminant transport, whereas modern irrigation limits contaminant propagation yet accelerates depletion of stored groundwater reserves. Wastewater infiltration may occur independently of irrigation practices, but abstraction intensity largely governs aquifer storage declines. Under intensifying drought conditions, sustainable groundwater management in the Haouz Plain requires integrated strategies combining optimized irrigation, controlled abstraction, and strengthened wastewater treatment and reuse. • Traditional irrigation sustains recharge but increases contamination risk. • Modern irrigation reduces contamination but accelerates aquifer depletion. • TLF enables rapid detection of wastewater contamination in groundwater. • Isotopes and tritium distinguish recharge sources and groundwater age. • Drought intensifies trade-offs between groundwater quality and quantity.