Tidal marsh stability in the face of human impacts and sea level rise

Monday, 15 December 2014
Matthew L Kirwan, Virginia Institute of Marine Science, Gloucester Point, VA, United States
Coastal populations and marshes have been intertwined for centuries, where humans both influence and depend on the enormous ecosystem services that marshes provide. Although marshes have long been considered vulnerable to climate change, recent work identifies fascinating feedbacks between plant growth and geomorphology that enable them to actively resist sea level rise. Here, we will review existing literature and provide new data to examine how humans alter these feedbacks. Measurements of accretion and elevation change suggest that most marshes will survive present day sea level rise rates by building vertically. Numerical models predict that these marshes will survive moderate accelerations in the rate of sea level in places where dams do not limit sediment delivery to the coast. However, these results also suggest that marsh survival under faster accelerations in sea level will depend on their ability to migrate inland. Marsh transgression into uplands is influenced not only by topography, but also by human land use and decisions to harden shorelines. Preliminary numerical model experiments will be used to explore how basic biophysical and anthropogenic drivers determine whether sea level change will lead to marsh loss (erosion+drowning > transgression), marsh expansion (transgression > erosion), or dynamic equilibrium (transgression = erosion).