Seasonal Monitoring of Hydrocarbon Degraders in Alabama Marine Ecosystems Following the Deepwater Horizon Oil Spill

Abstract

Following the Deepwater Horizon explosion and crude oil contamination of a marsh ecosystem in AL in June 2010, hydrocarbon-degrader microbial abundances of aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated seasonally. Surface sediment samples were collected in October and December of 2010 and in April and July of 2011 along 40–70-m transects from the high tide to the intertidal zone including Spartina alterniflora-vegetated marsh, seagrass (Ruppia maritima)-dominated sediments, and nonvegetated sediments. Alkane and total hydrocarbon degraders in the sediment were detected, while PAH degraders were below detection limit at all locations examined during the sampling periods. The highest counts for microbial alkane degraders were observed at the high tide line in April and averaged to 8.65 × 105 of cells/g dry weight (dw) sediment. The abundance of alkane degraders during other months ranged from 9.49 × 103 to 3.87 × 104, while for total hydrocarbon degraders, it ranged between 5.62 × 103 and 1.14 × 105 of cells/g dw sediment. Pore water nutrient concentrations (NH 4 + , NO 3 − , NO 2 − , and PO 4 3− ) showed seasonal changes with minimum values observed in December and April and maximum values in October and July. Concentrations of total petroleum hydrocarbons in sediments averaged 100.4 ± 52.4 and 141.9 ± 57.5 mg/kg in January and July, 2011, respectively. The presence of aerobic microbial communities during all seasons in these nearshore ecosystems suggests that an active and resident microbial community is capable of mineralizing a fraction of petroleum hydrocarbons.