Soil hydrosaline dynamics with depth and time in actively water-managed Mediterranean coastal wetlands

Mediterranean coastal wetlands provide key ecosystem services but are increasingly threatened by hydrological alterations and climate change. Surface soil salinity is commonly identified as the main driver of plant distribution, yet its effects are strongly modulated by soil water dynamics. This comprehensive study investigates how the combination of active freshwater management, using former agricultural channels, and landscape position is associated with hydrosaline dynamics and vegetation differentiation on 9 plots in a Mediterranean saltmarsh in Southern France. Soil salinity was measured at multiple depths during three campaigns over two years, and soil water content was monitored every three weeks over six months in plots under prolonged (PWS), temporary (TWS) or no water supply (NWS). As PWS plots were located closer to the main channel, management and landscape position are partly confounded in this observational design; results are therefore interpreted as associations. Salinity profiles differed among management types: PWS plots had homogeneous, moderately saline profiles, whereas TWS and NWS plots showed salinity increasing with depth. TWS plots were less saline than NWS plots despite similar distances to the main channel, so proximity alone does not explain these differences. Differences among campaigns were small, suggesting long-term processes. Soil drying cycles differed among plots and were related to recharge indicators rather than vegetation type. Vegetation mosaic was the result of the combined action of water management and landscape position. These results suggest that long-term management outcomes may depend on landscape position and subsurface hydrology, which should both be integrated in restoration planning for Mediterranean wetlands under increasing water scarcity.