MEPS 164:179-188 (1998)  -  doi:10.3354/meps164179

The effect of bioturbation by the lugworm Arenicola marina on uptake and distribution of cadmium in sediment was assessed using laboratory sediment cores. Carrier-free ¹⁰⁹Cd was added to the water phase each day. Bioturbation (irrigation) was measured using bromide (Br^-) as a tracer for water movement. In cores without lugworms all Cd was found in the surface sediment where it continued to build up over 16 d of exposure. In cores containing lugworms a distinct peak of Cd was found both at the sediment surface and, after a few days, at the feeding pocket of the worm (10 to 15 cm depth). During the 16 d of exposure this subsurface peak broadened and eventually Cd was found in all depths from top to feeding depth of the individual worm. Compared to sediment cores without worms, the presence of lugworms more than doubled the rate of removal of Cd from water to sediment. This was attributed to an increased turnover of sediment (due to feeding activity), an increased sediment surface area (due to fecal casts, head shaft, tube and irrigation of the whole burrow) and an increased contact of Cd-labelled water with potential binding sites in the sediment due to irrigation. Exposure to 1 ppm Cd reduced the fractional rate at which lugworms removed Cd from the water (as % of Cd in the water). The total Cd flux to the sediment, however, was much greater due to the higher Cd concentrations in the water. Water fluxes estimated using Br^- as a solute tracer revealed a 10- to 20-fold increase in water exchange of the sediments when lugworms were present. This enhanced water flux was not affected by exposure of lugworms to 1 ppm Cd. The results indicate that the presence of bioturbating infauna influences both the uptake rates of trace metals in near-shore sediments and the distribution of those metals.

Arenicola marina · Cadmium · Irrigation · Bioturbation · Sediments