Islands in the oil: Quantifying salt marsh shoreline erosion after the Deepwater Horizon oiling.

Qualitative inferences and sparse bay-wide measurements suggest that shoreline erosion increased after the 2010 BP Deepwater Horizon (DWH) disaster, but quantifying the impacts has been elusive at the landscape scale. We quantified the shoreline erosion of 46 islands for before and after the DWH oil spill to determine how much shoreline was lost, if the losses were temporary, and if recovery/restoration occurred. The erosion rates at the oiled islands increased to 275% in the first six months after the oiling, were 200% of that of the unoiled islands for the first 2.5years after the oiling, and twelve times the average land loss in the deltaic plain of 0.4%y(-1) from 1988 to 2011. These results support the hypothesis that oiling compromised the belowground biomass of the emergent vegetation. The islands are, in effect, sentinels of marsh stability already in decline before the oil spill.

Landscape-scale analysis of wetland sediment deposition from four tropical cyclone events.

Hurricanes Katrina, Rita, Gustav, and Ike deposited large quantities of sediment on coastal wetlands after making landfall in the northern Gulf of Mexico. We sampled sediments deposited on the wetland surface throughout the entire Louisiana and Texas depositional surfaces of Hurricanes Katrina, Rita, Gustav, and the Louisiana portion of Hurricane Ike. We used spatial interpolation to model the total amount and spatial distribution of inorganic sediment deposition from each storm. The sediment deposition on coastal wetlands was an estimated 68, 48, and 21 million metric tons from Hurricanes Katrina, Rita, and Gustav, respectively. The spatial distribution decreased in a similar manner with distance from the coast for all hurricanes, but the relationship with distance from the storm track was more variable between events. The southeast-facing Breton Sound estuary had significant storm-derived sediment deposition west of the storm track, whereas sediment deposition along the south-facing coastline occurred primarily east of the storm track. Sediment organic content, bulk density, and grain size also decreased significantly with distance from the coast, but were also more variable with respect to distance from the track. On average, eighty percent of the mineral deposition occurred within 20 km from the coast, and 58% was within 50 km of the track. These results highlight an important link between tropical cyclone events and coastal wetland sedimentation, and are useful in identifying a more complete sediment budget for coastal wetland soils.