Title page for ETD etd-11072008-120338


Type of Document Dissertation
Author Steyer, Gregory Dean
Author's Email Address gsteye1@lsu.edu, gsteyer@usgs.gov
URN etd-11072008-120338
Title Landscape Analysis of Vegetation Change in Coastal Louisiana Following Hurricanes Katrina and Rita
Degree Doctor of Philosophy (Ph.D.)
Department Oceanography & Coastal Sciences
Advisory Committee
Advisor Name Title
Charles Sasser Committee Chair
Andy Nyman Committee Member
Jaye Cable Committee Member
John Day Committee Member
David Longstreth Dean's Representative
Keywords
  • marsh
  • disturbance
  • NDVI
  • land change
  • stressors
Date of Defense 2008-10-03
Availability unrestricted
Abstract
Investigations of hurricane disturbances on coastal vegetated communities are common, but relatively few are comprehensive across broad geographic regions. The 2005 hurricanes, Katrina and Rita, exposed Louisiana coastal landscapes to physical modifications and extensive and prolonged flooding, resulting in measurable physicochemical changes. This research used remote sensing and field investigations to regionally assess (1) porewater salinity and sulfide impacts to and recovery of coastal Louisiana vegetation communities, and (2) the importance of mineral sediment deposition on accretionary processes. Hurricane effects were most direct and prominent in eastern Louisiana from Katrina and western Louisiana from Rita, compared to central Louisiana exposed to indirect affects from Rita.

A coastwide analysis of moderate resolution imagery found over 4,714 km2 of the prestorm coastal wetland area experienced a substantial decline in vegetation density and vigor in October 2005, with the majority of persistent damage through November 2006 in the west (1,046 km2). In the east region, 91.8% of persistent damage was accounted for by conversion of marsh to new open water; whereas in the west region, 71% was associated with other vegetation stressors.

The physical landscape disruption in the east contributed to a high abundance of disturbance species in fresh and intermediate marsh from fall 2006 to fall 2007. Salinity and sulfide stress persisted throughout the west region, contributing to low vegetative cover, slow recovery of Spartina patens, and shifts towards more saline marsh classifications by fall 2007. Hydrologic barriers, including impoundments in the west, contributed to salinity and sulfide stress; however, these same structures facilitated trapping of mineral sediments delivered by Hurricane Rita, providing critical supplies of bulk sediment and nutrients. Large periodic sediment inputs partially compensate for reduced vertical accretion found in impounded marshes. However, management actions should endeavor to optimize organic matter production to support vertical accretion.

Two full growing seasons after the 2005 hurricanes, marshes directly impacted in the east and west regions were still recovering. Although vegetation cover values were approaching pre-hurricane levels, species composition is still indicative of a disturbance environment.

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