The Holocene influence on the future evolution of the Venice Lagoon tidal marshes

The resilience of marsh ecosystems to expected sea-level rise is determined by a complex interplay of organic and inorganic sedimentation dynamics. Marshes have formed over past centuries to millennia and consist of extremely reactive bodies with sediments that can experience high compaction. Here we provide a quantification of the degree to which the past history of a salt marsh can affect its long-term evolution. A dataset of elevation dynamics was established in the Venice Lagoon (Italy) and interpreted using a physics-based model of deposition and large consolidation of newly deposited material. We found that the fate of low-lying tidal landscapes over the next century of accelerating sea-level rise will be highly dependent on compaction of soft, recently deposited soils. Our results imply that a sedimentation rate twice the present rate will be needed to counterbalance the expected sea-level rise. Holocene compaction in the Venice Lagoon, Italy, highlights the importance of soil properties and deposition rate in predicting the evolution of tidal marshes, according to numerical model simulations calibrated with 20 years of observations.