Effect of burrowing by the crab helice crassa on chemistry of intertidal muddy sedimentsa

Abstract

Abstract The chemical environment was measured in vertical and horizontal profiles of cores taken from intertidal sediments that are extensively burrowed by the mud crab Helice crassa. The crab burrows folded the thin (2–5 mm) oxic layer into the sediment, and the burrows appeared to have a strong influence on the concentrations of acid volatile sulfide (AVS), acid-extractable FeII (probably FeCO3 and FeS), FeIII (probably predominantly hydrous ferric oxide FeOOH), and MnII, III, IV and a modest effect on FeS2 but no effect on total organic carbon, total organic nitrogen, or acid-extractable zinc concentrations. The oxic layer was thinner in the burrows than on the sediment surface and showed some minor differences in solid-state chemistry, with higher FeOOH and lower FeS2 concentrations in the burrow walls. Acid volatile sulfide, FeCO3, and FeS2 were found in the oxic layers, presumably because of deposits from crab excavations of deeper anoxic sediments. The chemistry of the bioturbated profile was highly variable, not only because of existing burrows but also because of infilled abandoned burrows. The colors of the sediment profile were strongly related to the concentrations of FeII, AVS, FeIII, Mn, and FeS2. The implications of the observed sediment chemistry to the fate and bioavailability of contaminants is discussed.