A synthesis of the literature on impacts of oil on marshes was conducted as a joint project by the National Oceanic and Atmospheric Administration and American Petroleum Institute. The goal was to summarize the scientific literature and experience from past spills in a format that balances between too much detail and too many generalizations. Sufficient data were compiled for 32 oil spills and field experiments to generate recovery curves and identify influencing factors controlling the rate of recovery. Recovery was longest for spills with the following conditions: Cold climate (e.g., Metula, Arrow, Amoco Cadiz); sheltered settings (e.g., Metula, Arrow, Gulf War, Nairn pipeline, Mill River); thick oil on the marsh surface (e.g., Metula, Amoco Cadiz, Gulf War); light refined products with heavy loading (e.g., Florida, Bouchard-65, Exxon Bayway); heavy fuel oils that formed persistent thick residues (Metula, Amoco Cadiz, Gulf War); and intensive treatment (e.g., Aransas Pass, Amoco Cadiz, Golden Robin). Recovery was shortest for spills with the following conditions: Warm climate (e.g., many spills in Louisiana and Texas); Light to heavy oiling of the vegetation only; Medium crude oils; and Less-intensive treatment. For many spills, recovery occurred within 1-2 growing seasons, even in the absence of any treatment. The decision to conduct treatment operations in oiled marshes needs to be based on the best understanding of the likely tradeoffs. Recommendations are made for treatment based on the following oiling conditions: Free-floating oil on the water in the marsh; thicker oil (> 0.5 cm) on marsh surface; thinner oil (<0.5 cm) on marsh surface; heavy oil on vegetation; and light to moderate oil on vegetation.
