In Situ Burning and Ecological Recovery in an Oil-Impacted Phragmites australis Tidal Freshwater Marsh at Delta National Wildlife Refuge, Louisiana

ABSTRACT In situ burning of oiled marshes is a response method that can be more effective and less damaging to the marsh environment than more intrusive manual and mechanical methods, given appropriate conditions for burning. In situ burning has been examined for a variety of oiled marsh types and vegetation species; however, little to no published data are available for in situ burning of oiled Phragmites australis marshes (common reed, Roseau cane). In late May 2014, a pipeline spill occurred in Delta National Wildlife Refuge, Louisiana, releasing an estimated 4,200 gallons of South Louisiana crude oil into a semi-permanently flooded Phragmites tidal freshwater marsh located on the Mississippi River Delta. Due to the remote location, degree of oiling, and difficulty of oil removal within the dense vegetation, an in situ burn was conducted in early June 2014 while the marsh was flooded. In order to examine the effectiveness and environmental effects of in situ burning for this marsh type, and ecological recovery over time, we monitored oiling conditions and ecological metrics for more than two years, comparing sites from three oiling/treatment classes: (a) reference (not oiled or burned), (b) oiled-and-not-burned, and (c) oiled-and-burned. The burn was effective in rapidly removing much of the gross oiling from the marsh, and also reduced residual oiling on the marsh vegetation. Oil concentrations in marsh soils were initially elevated in the oiled-and-burned sites, but were similar to reference conditions and below background levels after three months. Initial oiling and burning drastically affected the marsh vegetation and a common marsh invertebrate; however, overall ecological recovery was relatively rapid and habitat quality in terms of native plant species composition and wildlife value was enhanced by burning at a local scale, at least for several years. Based on these findings, in situ burning appears to be a viable response option to consider during future spills in marshes with similar plant species composition, environmental setting, and oiling conditions.