Remotely sensed MODIS fire detections were used to examine wildfire variability from 2003-2011 in southeast Louisiana, and to determine if the Deepwater Horizon oil spill and hurricanes may have impacted fire frequency and intensity. Despite low wildfire detection rates, around 60% for fires at least 1 km2 or greater, the MODIS fire product provided a consistent and reliable source of wildfire data. As a result of Hurricane Katrina, wildfire detection frequencies doubled their average numbers during the fall of 2005 in inland areas and during the spring of 2006 in inland and coastal marsh areas. Strangely enough, the oil spill may have contributed to lower fire frequencies in the summer of 2010 and spring of 2011 inland. Neither hurricane Katrina nor the oil spill were found to have an effect on fire intensity, and the spatial distribution of wildfires remained relatively constant over the study area after both disasters.

Cette thèse présente l’étude de la signature sédimentaire des submersions marines de tempête, dans le domaine rétrolittoral. Cette signature peut être extrêmement variable principalement en fonction des paramètres météo-océaniques menant à la submersion, de la morphologie de l’avant-côte et du domaine rétrolittoral et du disponible sédimentaire. Premièrement, l’étude de dépôts de washover mis en place lors de l’hiver 2013-2014, au sud de l’île d’Oléron, particulièrement énergétique en terme de climat de vagues, via une approche couplant processus hydrodynamiques et sédimentologie, a permis (1) de mettre en évidence l’importance des ondes infragravitaires, sur une côte dissipative à caractère macrotidal, dans le déclenchement de l’overwash de la barrière et la mise en place de washovers ; et de (2) proposer un nouveau modèle de faciès des dépôts de washover mis en place par des ondes infragravitaires combinées à la marée haute. Deuxièmement, la caractérisation de la signature sédimentaire des submersions marines en domaine rétrolittoral plus distal a montré que dans le contexte morphologique des marais de Charente-Maritime, les apports extrêmement faibles de sédiments en provenance du domaine continental, entre deux évènements de submersion marine, empêche la distinction des différents niveaux de submersion. Cependant cette étude a permis de valider des proxies tels que la microfaune ou l’isotopie de la matière organique pour l’identification de niveaux de submersion marine, permettant en partie de pallier aux limites inhérentes à l’anomalie granulométrique généralement utilisée. Cette étude a aussi permis la mise en évidence d’une variabilité dans la signature sédimentaire des submersions marines entre deux marais géomorphologiquement contrastés et plus ou moins exposés aux houles en provenance de l’océan. / This thesis presents the study of the sedimentary signature of marine submersions triggered by storms, in the back barrier area. This signature can be extremely variable mainly according to the meteo-oceanic parameters leading to the submersion of the back barrier area, the morphology of the nearshore, shore and back barrier area, and sediment availability. Firstly, the study of washover deposits emplaced during the winter of 2013-2014 on the southern end of the Oléron Island, characterized by an exceptional wave climate, via a coupled hydrodynamical and sedimentological approach, allowed us to (1) highlight the importance of infragravity waves, on macrotidal and dissipative coasts, in triggering the overwash and emplace washover deposits ; and (2) to suggest a new facies model of washover deposits emplaced by infragravity waves combined to high tides. Secondly, the characterization of the sedimentary signature of marine submersions in the distal part of the back barrier area showed that in the morphological context of the Charente-Maritime coastal marshes, the extremely limited amounts of sediments in provenance from the continent, between two submersion events, prevent the distinction of the different marine submersion sedimentary layers. Nevertheless, this study allowed validating new proxies as microfauna and organic matter isotopy for the identification of marine submersion sedimentary signature, allowing to work independently of the granulometric anomaly proxy and its known limits. This study also allowed evidencing the variability in the sedimentary signature of marine submersions in geomorphologically contrasted marshes and that this variability was linked to the ocean waves exposure.

This study uses the storm surge sediment beds deposited by Hurricanes Audrey (1957), Carla (1961), Rita (2005) and Ike (2008) to investigate spatial and temporal changes in sedimentation rates on the McFaddin National Wildlife Refuge in Southeast Texas. Fourteen sediment cores were collected along a transect extending from 90 to 1230 meters inland from the Gulf Coast. Storm-surge-deposited sediment beds were identified by texture, organic content, carbonate content, the presence of marine microfossils, and Cesium-137 dating. The hurricane-derived sediment beds are marker horizons that facilitate assessment of marsh sedimentation rates from nearshore to inland locations as well as over decadal to annual timescales. Near the shore, on a Hurricane Ike washover fan, where hurricane-derived sedimentation has increased elevation by up to 0.68 m since 2005, there was no measurable marsh sedimentation in the period 2008-2014. Farther inland, at lower elevations, sedimentation for the period 2008-2014 averaged 0.36 cm per year. The reduction in sedimentation in the period 2008-2014 on the nearshore part of the marsh is likely due to reduced flooding in response to increased elevation from hurricane storm surge sediment deposition. These results provide valuable knowledge about the sedimentary response of coastal marshes subject to storm surge deposition and useful guidance to public policy aimed at combating the effects of sea level rise on coastal marshes along the Gulf of Mexico.