Dispersion of spilled oil in freshwater systems: Field trial of a chemical dispersant

The impacts of oil and dispersed oil on freshwater ecosystems were examined in afield experiment conducted as part of the Freshwater Oil Spill Research Program. In July 1985, 3 m³ of Normal Wells crude oil were spilled on each of two fen lakes. The slick on one lake was treated with the dispersant Corexit 9550. Corexit 9550 was effective in removing the oil from the water surface even though wave energy was very low. The oil or dispersed oil had little detectable short or long term impact on all water quality parameters measured, or on the microbial populations and activities in the water column and sediments of both lakes. Untreated oil caused more damage than the dispersed oil to floating aquatic plants and the shoreline vegetation, but new growth within the affected areas was observed one month after treatment. Seasonal regrowth of vegetation in all areas affected by the treatments appeared normal. Our results suggest that the best response to oil contamination in isolated fen lakes is no action at all. However, floating oil or oil washed ashore could pose a significant threat to indigenous wildlife or its habitats. Under these conditions, chemical dispersion may prove to be an effective alternative when conventional control and recovery measures are not feasible.