Hydrological exchanges and Organic Matter dynamics in highly vulnerable tidal wetland ecosystems at the land-ocean interface

Occupying a critical interface between the land and the sea, tidal wetlands are amongst the most ecologically valuable and economically important ecosystems on Earth, but also especially vulnerable to human pressures and climate change. These rich in biodiversity and highly productive ecosystems are hot spots of biogeochemical transformations, consistently exchanging Organic Matter with adjacent estuarine waters through tidal flushing. Here we discuss new results on the amount and directions of biogeochemical exchanges at the tidal wetland-estuary interface. Detailed microbial and photochemical degradation experiments and high resolution bio-optical observations in tidal freshwater and salt marsh systems of the Eastern US coast provide insights on the quality and fate of the organic compounds exported from tidal marshes and their influence on near-shore biological processes, biogeochemical cycles and optical variability. Impacts of anthropogenic activities and resulting air-pollution are also discussed. High resolution model runs were performed using the Community Multi-scale Air Quality (CMAQ) model, to examine atmospheric composition along the shoreline where processes such as sea and bay breeze circulations often favor the accumulation and air-deposition of atmospheric pollutants, impacting biogeochemical processes in sensitive tidal wetland ecosystems.