Biologically‐controlled multiple equilibria of tidal landforms and the fate of the Venice lagoon

TLDR

Tidal landscapes exhibit multiple equilibria and transitions, raising the question of whether impending geomorphological shifts can be anticipated—a concern of ecological, cultural, and socio‑economic importance amid global tidal environment decline. The authors introduce a coupled tidal physical–biological model to quantitatively predict the fate of tidal landforms, illustrated using five centuries of Venice lagoon observations. The model links vegetation type, benthic biofilm disturbances, sediment availability, and sea‑level changes to drive bio‑geomorphic evolution. The model reproduces historical observations and predicts that Venice lagoon salt marshes may disappear within the next century under high sea‑level rise scenarios.

Abstract

Looking across a tidal landscape, can one foresee the signs of impending shifts among different geomorphological structures? This is a question of paramount importance considering the ecological, cultural and socio‐economic relevance of tidal environments and their worldwide decline. In this Letter we argue affirmatively by introducing a model of the coupled tidal physical and biological processes. Multiple equilibria, and transitions among them, appear in the evolutionary dynamics of tidal landforms. Vegetation type, disturbances of the benthic biofilm, sediment availability and marine transgressions or regressions drive the bio‐geomorphic evolution of the system. Our approach provides general quantitative routes to model the fate of tidal landforms, which we illustrate in the case of the Venice lagoon (Italy), for which a large body of empirical observations exists spanning at least five centuries. Such observations are reproduced by the model, which also predicts that salt marshes in the Venice lagoon may not survive climatic changes in the next century if IPCC's scenarios of high relative sea level rise occur.