Short-term weathering rates of buried oils in experimental sand columns over north-temperate temperature range.

Abstract

Petroleum residues are degraded (weathered) at different rates, depending on various conditions. Degradation in slicks generally has time scales of days to weeks for loss of low molecular weight alkanes and aromatics. This largely involves physical processes of wind-driven evaporation, and dissolution into the water column. Weathering in homogeneously oiled surface sediments, not having the benefit of evaporation, has time scales of months to years. Tidal submergence and temperature can influence this significantly. For example, Prudhoe Bay crude oil in sediments placed in trays on the bottom of a near-arctic bay showed virtually no weathering. Here we report on weathering rates and qualitative changes of oils, buried within constantly submerged and irrigated sandy beach sediments for up to 11 mon. Such conditions occur when coastal stranded oil becomes buried subtidally, or becomes mixed into intertidal beach sediments below the water table. Experimental conditions included continuous sea water irrigation, indigenous microbial populations, and continuous complete submergence. For preliminary microbial incubation and weathering results, see Thorpe et al. (1986). We expected that oil degradation within sandy sediments would be comparatively slow, as organic material and nutrients are more limited, thereby limiting microbial activity. Lower temperatures and submergence also should limit the weatheringmore » process.« less