HR: 09:20h
AN: H41I-06    [Abstracts]
TI: Vegetation Disturbance in an Ecomorphodynamic Model of Tidal Marsh Response to Sea Level Rise.
AU: * Kirwan, M L
EM: mlk13@duke.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Box 90227, Durham, NC 27708 United States
AU: Murray, A
EM: abmurray@duke.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Box 90227, Durham, NC 27708 United States
AB: Vegetation enhances tidal marsh accretion by trapping inorganic sediment, providing a source of organic matter, and reducing channel erosion. We have previously developed a numerical model that couples biologically influenced platform accretion with hydrodynamically driven channel network erosion, and have used it to simulate marsh system response to sea level rise. In our model, increased inundation on the platform stimulates biomass productivity and therefore tends to increase deposition rates and resistance to channel bank erosion. In model experiments excluding vegetation effects, an increase in sea-level rise rate and consequent increases in erosion from tidal currents convert intertidal surfaces to subtidal surfaces that are incapable of supporting vegetation. However, in parallel experiments including vegetation effects, an intertidal platform persists. These preliminary model results suggest that vegetation promotes a metastable equilibrium, where tidal marshes accrete at the same rate of sea level rise when vegetation is intact, but are prone to rapid change following vegetation disturbance. In this contribution we present preliminary results of model experiments with temporally and spatially variable disturbance regimes and high rates of sea level rise. Vegetation is completely removed in single random cells, representing disturbed patches of 25 m². Experiments test the ecologic and geomorphic response to disturbances of 10, 50, and 75% of the vegetation on the marsh platform for durations of 1, 10, and 100 years. Bare surfaces accrete less rapidly than vegetated surfaces causing small ponds to form. The increased water depths represent potential increases in the tidal prism. Tidal creeks expand into adjacent cells where vegetation has been disturbed, and over time link ponds into elongated channel networks. Ponds far from the channel network are ephemeral features, filling in with sediment when vegetation growth resumes. Ponds incorporated into the channel network tend to be permanent. Disturbance regimes that remove many patches of vegetation over extended periods of time lead to widespread channel network expansion and permanent loss of vegetation. These model observations suggest that tidal marshes in regions of rapid sea level rise are highly susceptible to degradation following vegetation disturbance.
DE: 0476 Plant ecology (1851)
DE: 0497 Wetlands (1890)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 1813 Eco-hydrology
DE: 1825 Geomorphology: fluvial (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005