Impact of Arenicola marina (Polychaeta) on sediment sulfur dynamics

Sulfate reduction rates and various parameters related to the sulfur cycling were investigated in situ and experimentally by a mm approach in sediment surrounding burrows of the polychaete Arenicola marina. Sulfate reduction rates were immediately affected in a 5 to 15 mm-thick zone surrounding the tail shaft. Rates were depressed by 52% in the burrow wall and increased with distance towards ambient rates. Experimental use of artificially ventilated burrows showed that the reduction was mediated by introduction of oxygenated surface Water by irrigation, which suppressed possible stimulating effect of increase in organic carbon availability from mucus secretion by the worm. Furthermore, irrigation and sediment reworking by A. marina increased the content of biological reactive Fe(III) in the feeding funnel and in a narrow zone around the tail shaft, creating environments suitable for dissimilative Fe(III) reduction. Total reduced sulfide pools showed that reoxidation of reduced sulfide species occurred along the burrow and in the feeding funnel of A. marina. Reoxidation in the tail shaft region was mediated by irrigation, while the reduction in the feeding funnel probably occurred due to the combined effect of irrigation and sediment reworking. In general, A. marina has a great impact on sediment sulfur biogeochemistry, suggesting that bioturbation depresses sulfate reduction and increases the importance of Fe(Ill) as an electron acceptor in carbon oxidation. It is also indicated that A. marina reduces permanent burial of reduced sulfide and lowers the steady-state level of total reduced sulfide in the sediment.