Wetland Dynamics and Morphological Changes due to Hurricane-induced
Sediment Deposition
Abstract
Wetlands are endangered ecosystems that provide valuable services to
society and contribute to maintaining biodiversity in low-lying areas.
Hurricanes, among other stressors such as sea level rise (SLR) and
anthropogenic activities, alter wetland dynamics and shape coastal
morphology by redistributing sediments in estuaries and bays. Hurricane
forcing plays a key role in sediment deposition and erosion within
coastal wetlands and their surroundings; hence maintaining marsh
elevation relative to SLR as well as eroding the edge of marsh
platforms. In this study, we reconciled observed spatiotemporal patterns
of wetland coverage change from multi-source remote sensing imagery with
hydrodynamic simulations of both average and extreme(hurricane-like)
scenarios in Mobile Bay, AL, USA. To account for sediment deposition and
erosion in coastal wetlands, we constructed ‘generic’ LiDAR-derived
digital elevation models (DEMs) corrected for wetland elevation errors
(vertical bias) and used them as a proxy of historical DEMs. We then
associated changes in wetland elevation and coverage to inundation
duration and estimated the likelihood of wetlands to be either fully
exposed or inundated in both scenarios. Results indicated that the
likelihood of sediment deposition peaks between 4-h and 7-h of
inundation for both average ande xtreme conditions. The likelihood of
erosion for average conditions peaks between 11-h and 16-h, whereas that
of extreme conditions is highly dependent on hurricane forcing
characteristics and peaks around 6-h in the case of Hurricane Ivan
(Sep/2004) and 21-hfor Hurricane Katrina (Aug/2005). Results revealed
that Hurricane Ivan and Katrina had a two-sided effect on Mobile Bay’s
coastal wetlands: (i) erosion along shorelines and marsh edges due to
extreme coastal water levels and strong winds, and(ii) sediment
deposition in landward direction due to both hurricane-induced sediment
deposition and fluvial sediment input. We acknowledge that, next to
hurricane forcing, an increase in sea levels could also affect sediment
dynamics and so alter coastal morphology and compromise wetland
survivability.