Salt Marsh Sediment Biogeochemical Response to the BP Blowout

The impact of the blowout on salt marshes was investigated by observing the biogeochemistry in salt marsh sediments along the Gulf Coast. High sulfide levels due to hydrocarbon loading, increased microbial activity, and microbial community shifts can lead to plant browning and mortality. Sediment biogeochemical processes that degrade enriched carbon pools through sulfate reduction are primarily responsible for the biodegradation of spilled hydrocarbons. An assessment of the impact of contamination on salt marshes at Skiff Island, LA, and Cat Island, Marsh Point, and Saltpan Island, MS, was achieved through sediment electrode profiling, microbial community profiling, and quantification of hydrocarbon contamination, which captured the spatial sedimentary biogeochemical response that affects salt marsh productivity. At western locations (Skiff and Cat Islands), total petroleum hydrocarbons (TPHs) ranged from 2183 to 2996 mg kg, which was more than double the TPH concentration observed at eastern locales. At eastern study locations (e.g., Marsh Point), sedimentary pore-water HS concentrations were higher (maximum value = 231 mg L) and detected further up in the sediment column than at western locales (e.g., Skiff Island). Similarly, anaerobic and aerobic microbial activity, as measured by C substrate utilization profiles and well-color development, was as high or higher at eastern locations as compared with western locations. These results indicate that other factors besides location or degree of contamination, perhaps sedimentary dynamics and physical processes specific to each marsh, should be considered when determining salt marsh response to hydrocarbon contamination.