Rate-induced critical transitions in tidal marsh ecosystems

Abstract

Salt marshes are important coastal ecosystems because of their function as coastal protection and their ecological relevance. Many salt marshes in the world are threatened by an increasing rate of sea level rise. Because of a positive feedback loop between sedimentation and vegetation growth, salt marshes can exhibit a rate-induced critical transition induced by sea level rise. However, a general framework for analysing salt marsh collapse in terms of creek patterns and vegetation productivity is still lacking. In this thesis, a spatial and a non-spatial salt marsh model are analysed in terms of ecosystem stability and the presence of rate-induced early warning signals. This research shows a higher suspended sediment concentration and growth of plants which are better at capturing sediment increases salt marsh stability for high rates of sea level rise. Furthermore, it is concluded spatial processes do not have an influence on the rate of sea level rise at which the rate-induced critical transition occurs. Lastly, several early warning signals are identified for salt marsh collapse, most notably an increase in auto-correlation and variance, as well as a decrease in creek edge steepness and total salt marsh area. A better understanding of the factors influencing salt marsh stability and ecosystem behaviour close to its tipping point can help policy makers to better assess vulnerability of salt marshes around the world and identify potential measurements to protect these ecosystems.