Potential for intrinsic and enhanced crude oil biodegradation in Louisiana's freshwater marshes

This study determined the intrinsic rates of biodegradation of Louisiana "s weet" crude oil (LSCO) in a Panicum hemitomon freshwater marsh using kineti c microcosm studies and verified the results in a large intact core study. In addition, the potential to enhance biodegradation using inorganic nutrie nt additions was determined. These freshwater marsh soils have high intrins ic rates of degradation (2.0%/day) for the measured alkane fraction (C11-C6 6) and even higher rates (6.8%/day) for the measured polycyclic aromatic hy drocarbon (PAH) fraction (naphthalene, methylated naphthalenes, phenanthren e, and methylated phenanthrenes). However, there were compound-specific eff ects with intrinsic rates of degradation highest for the smaller alkanes (C <15) (8.5-2.1%/day), while rates for longer chain alkanes (C>15) were much lower (0.7-1.2%/day). Results from the intact core study indicate that thes e rates are similar to those experienced in situ, with the exception of the PAH fraction, whose rate constants will be substantially lower than those determined in the kinetic study. Nitrogen (ammonium) was primarily the limi ting nutrient and increased degradation rate constants (2-3 fold). Few diff erences were seen between different classes of alkanes after fertilization. Critical nitrogen loading rates (amount needed to produce significant degr adation increases) were similar for both the microcosm and core study (2.2- 8.8 mg NH4+-N/g oil), while maximum rates of degradation were observed at h igher loading rates (22-44 mg NH4+-N/g oil). While crude oil degradation ca n be enhanced by fertilization, the benefits need to be weighed against the presence of high intrinsic biodegradation rates in these systems.