Natural erosion on oil on rocky shores in non-tidal areas

Abstract

One year of weathering effects on oil on rock surfaces has been studied on four different shores in the archipelago of Stockholm, northern Baltic Proper (non-tidal). The test shores are exposed in different ways to waves and drift-ice and their slopes are either flat or steep. In order to study the natural weathering, spots of heavy fuel oil (No. 5) were applied at different levels above the mean water level. After 12 months of weathering, the moderately high and the highly exposed rocks were almost free from oil between the mean water level and 5 m above. In contrast, significant weathering only occurred up to 0·5 m above the mean water level on the less exposed and flat sloping rock. Furthermore, the less exposed rock with high inclination was free of oil only at the mean water level.

The results from this study show that natural weathering can remove oil from certain levels on rocky shores in less than a year even in non-tidal areas like the Baltic.