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Wetland Dynamics and Morphological Changes due to Hurricane-induced Sediment Deposition
  • David Fernando Muñoz Pauta
David Fernando Muñoz Pauta
The University of Alabama

Corresponding Author:[email protected]

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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.