Salt marshes are coastal ecosystems of critical importance that provide fundamental ecosystem services and represent important indicators of environmental change. Their temporal and spatial evolution is in fact governed by feedbacks between physical and biological processes, whose dynamics can be severely impacted by changes in environmental forcings, such as rates of relative sea level rise and sediment supply. While the crucial role of interacting physical and biological processes on salt-marsh emergence and survival is indeed well established, a fascinating question that deserves further scrutiny is whether or not one can unravel the signatures of the interaction between physical and biological processes in salt-marsh landscapes, and furthermore detect landscape features that would not have emerged in the absence of such interactions.
Here we use field observations and a spatially explicit biomorphodynamic model to analyze vegetation and topographic patterns developed over salt marshes in the Venice Lagoon and furthermore address, through numerical simulations, the impact of natural and human-induced changes in the environmental forcings on salt-marsh biogeomorphic patterns.
Results/Conclusions
The analysis of field data collected at different spatial scales, such as ancillary field surveys of vegetation cover and soil elevation, airborne and satellite remote sensing observations of salt-marsh vegetation patterns coupled with a digital terrain model obtained by LiDar data and the results of the biomorphodynamic model, emphasize that zonation patterns usually observed in salt-marsh landscapes, are indeed biogeomorphic patterns emerging from the interplay between physical and biological processes. Salt-marsh plants act as landscape-constructors by actively and directly altering, and contributing to shape, the tidal environment. The landscape-constructing role of marsh plants emerges from the multi-modal frequency distributions of marsh elevations, that show to be the signature the interplay between physical and biological processes. Model simulations analyzing the effects of changes in bio-geomorphic patterns induced by varying environmental forcings and plant characteristics, show that marsh responses are highly spatially dependent. Changes in sediment supply most directly affect biogeomorphic patterns of marsh portions closest to the channel network, whereas relative sea level changes tend to affect the marsh platform as a whole. Interestingly, we observe that if, on the one hand, environmental forcings can lead to changes in biodiversity through the disappearance of one or more vegetation species, on the other hand, the number of species that actively tune salt-marsh landscapes influences salt-marsh response to changes in the forcings and marsh ability to face such changes.