Early Warning Signals for Rate-induced Critical Transitions in Salt Marsh Ecosystems

Abstract

Intertidal ecosystems are important because of their function as coastal protection and ecological value. Sea level rise may lead to submergence of salt marshes worldwide. Salt marshes can exhibit critical transitions if the rate of sea level rise exceeds salt marsh sedimentation, leading to a positive feedback between reduced sedimentation and vegetation loss, drowning the marshes. However, a general framework to recognize such rate-induced critical transitions and predict salt marsh collapse through early warning signals is lacking. Therefore, we apply the novel concept of rate-induced critical transitions to salt marsh ecosystems. We reveal rate-induced critical transitions and new geomorphic early warning signals for upcoming salt marsh collapse in a spatial model. These include a decrease in marsh height, the ratio of marsh area to creek area, and creek cliff steepness, as well as an increase in creek depth. Furthermore, this research predicts that increasing sediment capture ability by vegetation would be an effective measure to increase the critical rate of sea level rise at which salt marshes collapse. The generic spatial model also applies to other intertidal ecosystems with similar dynamics, such as tidal flats and mangroves. Our findings facilitate better resilience assessment of intertidal ecosystems globally and identifying measures to protect these ecosystems.