Effects of bioturbation on the fate of oil in coastal sandy sediments – An in situ experiment

Effects of bioturbation by the common lugworm Arenicola marina on the fate of oil hydrocarbons (alkanes and PAHs) were studied in situ during a simulated oil spill in a shallow coastal area of Roskilde fjord, Denmark. The fate of selected oil compounds was monitored during 120 d using GC–MS and bioturbation activity (feces production and irrigation) was measured regularly during the experiment and used as input parameters in a mechanistic model describing the effects of A. marina on the transport and degradation of oil compounds in the sediment. The chemical analytical data and model results indicated that A. marina had profound and predictable effects on the distribution, degradation and preservation of oil and that the net effect depended on the initial distribution of oil. In sediment with an oil contaminated subsurface-layer A. marina buried the layer deeper in the sediment which clearly enhanced oil persistence. Conversely, A. marina stimulated both the physical removal and microbial degradation of oil compounds in uniformly oil contaminated sediments especially in deeper sediment layers (10–20 cm below the surface), whereas the fate of oil compounds deposited in surface layers (0–5 cm) mainly was affected by removal processes induced by wave actions and other bioturbating infauna such as Nereis diversicolor, Corophium volutator and Hydrobia spp. present in the experimental plots.

Research highlights
► The fate of oil hydrocarbons were examined in an in situ experiment and with models.
► The fate of oil depends on oil distribution and presence of keystone bioturbators.
► When oil was added as a subsurface layer, bioturbation increased oil persistence.
► When oil was uniformly distributed, bioturbation increased oil removal.
► Bioturbation affect both the transport and biodegradation of oil hydrocarbons.