The effects of nitrogen (N), phosphorus (P) and plants on attenuation of applied South Louisiana Crude (SLC) to a Sagittaria lancifolia freshwater marsh were investigated under field conditions. Sixteen plots were established in the substrate and treatments were: (1) oil, no plants, no N and P; (2) oil, plants, no N and P; (3) oil, no plants, N and P and (4) oil, plants, N and P. SLC, N and P were applied, 21 m(-2), 10 g m(-2) and 4 g m(-2), respectively. Sediment cores were collected 2, 15 and 53 weeks after oil application and extracts were analyzed by GC/MS for target n-alkanes and polycyclic aromatic hydrocarbons (PAH). Results demonstrate N, P and S. lancifolia accelerated turnover or attenuation of SLC at 2 and 15 weeks. However only trace hydrocarbon concentrations were detected in the marsh soil after I year regardless of treatment, demonstrating relative rapid turnover at the oil rate used in this study. (C) 2003 Elsevier Ltd. All rights reserved.