Nutrient enhanced biodegradation of crude oil in tropical salt marshes

Tropical salt marshes in Louisiana are at risks of accidental oil spills and remediation of these ecosystems is mainly limited to natural biodegradation due to physical sensitivity of the ecosystems. This study investigated both intrinsic and nutrient enhanced rates of crude oil degradation in core studies. In addition, loading rates of nitrogen and optimal porewater nitrogen concentrations were determined. Nitrogen additions increased biodegradation rates of some alkanes and polycyclic aromatic hydrocarbons (PAHs). Addition of NH₄⁺-N increased zero-order mineralization constants of labeled hexadecane and phenanthrene up to 15.4-19.2% (Fourchon marsh) and 56.2% (Ugly Shack Bayou marsh) and rates of total carbon dioxide production up to 14.0-33.1% (Fourchon marsh) and 3.0% (Ugly Shack Bayou marsh), respectively. Efficient biodegradation of crude oil was achieved when NH₄⁺ was applied at the loading rate of 28.3-56.6 g N m^-2 producing porewater concentration at the level of 80-450 mg NH₄⁺-N L^-1. No significant lag time was observed indicating that nitrogen application directly stimulates biodegradation of crude oil in tropical salt marshes in Louisiana.