Integrating remote sensing and functional traits to elucidate estuarine common reed beds decline driven by soil salinity and anoxia

Reed beds play essential roles in wetland ecosystems, acting as natural filters and providing critical habitat for freshwater, estuarine, and marine species. However, increasing saltwater intrusion and soil anoxia caused by ongoing sea-level rise are affecting the integrity and functionality of these communities. This study aimed to assess the functional response of Phragmites australis (common reed) in a river delta in the North Adriatic Sea along a soil stress gradient assessing its functional trait variation and scaling these patterns via Sentinel-2 remote sensing in order to detect long-term ecosystem trends. Results showed that high soil salinity and anoxic conditions significantly reduced plant height and stem density, while leaf traits such as specific leaf area (SLA) remained unchanged, indicating a conservative adaptive strategy of the studied population. Plant height was able to clearly depict a plant growth trade-off under harsh environmental conditions showing solid positive relationships with the vegetation index used (Inverted Red-Edge Chlorophyll Index (IRECI), R2 = 0.81), enabling the remote assessment of stress-induced changes. Satellite imagery analysis from 2017 to 2024 revealed an 11.3 % loss of reedbed cover, primarily in areas increasingly affected by marine influence. These findings suggested that rising sea levels and reduced freshwater inputs accelerated reedbed degradation in the Northern Adriatic Sea lagoons. The integration of functional ecology and remote sensing provided a powerful approach to monitoring wetland dynamics and assessing climate change impacts on coastal ecosystems.