Collaborative Research: Biophysical alteration of wetland geomorphology in response to rising sea level

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Collaborative Research: Biophysical alteration of wetland geomorphology inresponse to rising sea levelOur objective is to examine the evolution of networks of tidal creeks in salt marshes asthey respond to rising sea level. We have documented rapidly growing creeks, incising into themarsh at 1-2 m per year, in coastal marshes throughout the South Atlantic Bight and in similarenvironments worldwide. Understanding the mechanisms driving the evolution of these drainagenetworks is crucial for predicting marsh responses to sea level rise under different conditions.The study will examine the physics of tidal flows and sediment erosion, while also consideringthe significant impact of marsh plants and animals (e.g. crabs) on these processes. Using acombination of field measurements, mesocosm experiments, and numerical modeling, we will 1)evaluate the physical mechanisms underlying sediment erosion in creeks, including variation inflow speed and processes changing the strength of the marsh soils, 2) test the hypotheses thatcrabs facilitate growth of creeks by loosening sediment through burrowing and removingstabilizing vegetation; and that hydrological conditions at creek heads are preferred by crabs, and3) develop a numerical model of creek evolution to test the importance of different parameterssuch as vegetation type, faunal density, tidal range and sediment supply on the morphologicalevolution of creeks. The model will help us to integrate our observations and generalize ourfindings over a range of conditions.Salt marshes provide valuable ecosystem services to humanity, but these productive habitats arethreatened globally by accelerating sea-level rise. Understanding the impact of sea-level rise onthe physical structure of a marsh is crucial to predicting both the response of marsh ecosystemsand the larger-scale morphological response of the coastline. The impact of increasing waterlevels on marshes depends on complex feedbacks between physical and biological processes.Initial studies of this issue focused on interactions between water depth and marsh elevation,which affect sediment deposition and plant growth. Recently, increasing attention is beingdirected towards the manner in which creek networks evolve as they respond to the largervolume of water they must convey during each tidal cycle at higher sea levels. The evolution ofcreek networks is a critical component of marsh response to sea-level rise, because creekmorphology affects the amount of water and sediment delivered to the marsh surface, and thedrainage of the marsh, and thus, the length of time the marsh is waterlogged. In turn, the floodingand drainage of the marsh influences the health of plants and animals in this ecologically vitalenvironment. The ability of creek networks to respond to increasing sea levels depends, in part,on how easy it is to erode the marsh surface, which depends on both sediment type, and onstabilization or loosening associated with flora and fauna. Uncovering the linkages betweengeology and biology will have bearing on the fields of geology, ecology and climatology, as wellas those interested in coastal protection and salt marsh evolution. The project will develop a newmodeling tool to examine response of marshes to sea-level rise, which will be broadly applicableto many salt marshes in the U.S. and globally.