Bioremediation of an experimental oil spill in a coastal Louisiana salt marsh

The massive oil release from the Deep Water Horizon disaster has reemphasized the need to remediate oil impacted marshes. Due to the physically fragile nature of salt water marshes, bioremediation is often proposed as an appropriate technology and nutrient amendment is often proposed as a means of accelerating biodegradation of crude oil. However, no information is currently available concerning the efficacy of in situ nutrient amendments in Gulf Coast salt marshes. An experimental crude oil spill (142 l over 100 m2) was conducted to evaluate the efficacy of nitrogen amendment to stimulate bioremediation in a Spartina alterniflora dominated Louisiana salt marsh. A randomized complete block design with replication (n=10) was utilized to test the hypothesis that additions of fast-release ammonium nitrate (60 g N/m ²) and slow-release urea (30 gN/m ²) fertilizers could enhance biodegradation of selected crude oil components in the marsh. Crude oil degradation was monitored by analyzing sediment samples for branched and unbranched alkanes over the 180-day study period. The compound/hopane ratio was used to correct for nonbiological losses. No consistent statistically significant effect of fertilizer addition on degradation rates was observed, despite success in increasing the porewater ammonium and NaCl-extractable ammonium over the time frame of the trial. Intrinsic pseudo-first order degradation rates of alkanes in all plots were substantial (0.003-0.008 day ^-1). Existing, background levels of N did not appear to limit biodegradation rates in Spartinadominated salt marshes. These results suggest that nutrient amendments will not be successful in stimulation biodegradation of crude oil in these systems.