Integrated modeling of groundwater–surface water interactions to evaluate management strategies for the protection of the Anzali coastal wetland

Coastal wetlands are highly sensitive groundwater-dependent ecosystems whose sustainability is strongly influenced by groundwater–surface water interactions. The Anzali Wetland in northern Iran is hydraulically connected to the shallow Foumanat coastal aquifer and receives inflow from multiple rivers and tributaries. In this study, the integrated MIKE SHE–MIKE 11 modeling framework was applied to simulate coupled hydrological processes and evaluate the relative impacts of groundwater abstraction and river-flow variations on wetland sustainability. The model was calibrated and validated using hydrometeorological, groundwater-level, and river-discharge data, demonstrating satisfactory performance in reproducing regional hydrological dynamics. Four diagnostic stress-test scenarios were developed to assess the effects of groundwater abstraction (± 30%) and river-discharge variations (± 50%) under wet, normal, and dry hydrological conditions. The results showed that groundwater abstraction is the dominant factor controlling groundwater levels and wetland–aquifer hydraulic connectivity. A 30% increase in pumping caused groundwater-level declines of up to 1.38 m near the wetland and intensified downward hydraulic gradients, promoting seepage losses from the wetland toward the aquifer. In contrast, reducing pumping by 30% increased groundwater levels by up to 1.56 m and partially restored more favorable hydraulic conditions between the wetland and aquifer. Although river inflows contributed locally to groundwater recharge near hydraulically connected channels, river-discharge variations produced only localized effects and could not compensate for the regional impacts of groundwater abstraction. The findings demonstrate that sustainable protection of the Anzali Wetland depends primarily on sustainable groundwater management rather than on surface-water regulation alone, highlighting the need for integrated groundwater abstraction control and aquifer-recharge strategies under increasing climatic and anthropogenic stress.