CSDMS 2013 annual meeting poster Andrea DAlpaos
Biologic-Geomorphic feedbacks that sculpt tidal landscapes
Marco Marani, Duke University South Carolina, United States. marco.marani@duke.edu
Abstract:
Tidal systems are biogeomorphic systems of great relevance, providing important ecosystem services and coastline protection against storms. The dynamics of these systems, currently threatened by the acceleration in the rate of global sea level rise (SLR) and the decrease in sediment supply, are governed by complex interactions between hydrological, ecological, and geomorphological processes. How do salt-marsh ecosystems respond to changes in the environmental forcings? What is the role physical and biological processes and of their interactions through eco-geomorphic feedbacks in controlling salt-marsh dynamic response to these changes and the existence of possible equilibrium states? To address these important issues and improve our understanding of the chief eco-geomorphic processes controlling salt-marsh response to current changes, we have developed a suite of eco-morphodynamic models accounting for complex two-way interactions between ecological and geomorphological processes. We find that vegetation crucially affects the equilibrium marsh elevation, marsh resilience to accelerations in SLR rates, and the morphological features of salt marsh channels. As soon as the platform is colonized by vegetation, plants crucially affect the local hydrodynamic circulation, favor channel incision, enhance particle settling by a reduction of turbulence levels within the canopy, promotes trapping sediment, and provides organic material. Model results suggest that highly productive and sediment-rich marshes will approach new equilibrium states in response to changes in the rate of SLR faster than sediment-poor or less productive marshes. Moreover, marshes exposed to large tidal ranges are more stable, and therefore more resilient to changes in the rate of SLR, than their microtidal counterparts. We also find that marshes are more resilient to a decrease rather than to an increase in the rate of SLR, and they are more resilient to a decrease rather than to an increase in sediment availability. Our modeling approaches emphasize that biological and physical interactions are crucial in determining the observed spatial patterns in the biological and in the geomorphic domains. The existence of feedbacks between physical and biological processes affects the evolutionary trajectories of saltmarsh ecosystems, and the reversibility of such trajectories, thus highlighting the importance of accounting for biogeomorphic feedbacks to obtain realistic representations of the system dynamics in response to climatic changes.
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