Vegetation recovery in an oil-impacted and burned Phragmites australis tidal freshwater marsh

Abstract

In-situ burning of oiled marshes is a cleanup method that can be more effective and less damaging than intrusive manual and mechanical methods. In-situ burning of oil spills has been examined for several coastal marsh types; however, few published data are available for Phragmites australis marshes. Following an estimated 4200gallon crude oil spill and in-situ burn in a Phragmites tidal freshwater marsh at Delta National Wildlife Refuge (Mississippi River Delta, Louisiana), we examined vegetation impacts and recovery across 3years. Oil concentrations in marsh soils were initially elevated in the oiled-and-burned sites, but were below background levels within three months. Oiling and burning drastically affected the marsh vegetation; the formerly dominant Phragmites, a non-native variety in our study sites, had not fully recovered by the end of our study. However, overall vegetation recovery was rapid and local habitat quality in terms of native plants, particularly Sagittaria species, and wildlife value was enhanced by burning. In-situ burning appears to be a viable response option to consider for future spills in marshes with similar plant species composition, hydrogeomorphic settings, and oiling conditions. In addition, likely Phragmites stress from high water levels and/or non-native scale insect damage was also observed during our study and has recently been reported as causing widespread declines or loss of Phragmites stands in the Delta region. It remains an open question if these stressors could lead to a shift to more native vegetation, similar to what we observed following the oil spill and burn. Increased dominance by native plants may be desirable as local patches, but widespread loss of Phragmites, even if replaced by native species, could further acerbate coastal erosion and wetland loss, a major concern in the region.

Keywords: Ecological recovery; In-situ burning; Oil spill; Phragmites australis; Sagittaria spp.; Scale insect damage; Tidal freshwater marsh.