Effect of Bioturbation byNereissp.,Mya ArenariaandCerastodermasp. on nitrification and denitrification in estuarine sediments

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Abstract
Three different sets of undisturbed sediment cores containing: Nereis sp. (polychaete, 2,000 indo m-2), Mya arenaria (bivalve, 1,100 indo m-2) or Cerastoderma sp. (bivalve, 1,100 ind. m-2) were incubated in the laboratory. Rates of oxygen consumption and denitrification were measured. Total denitrification rates were 8 ± 4, 12 ± 4, 13 ± 6 and 40 ± 20 µmol N m-2 h-1 in control cores and cores containing Cerastoderma sp., Mya arenaria and Nereis sp., respectively. Denitrification was partitioned, by the 15N isotope pairing technique, into the contribution from NO3 in the overlying water (dw) and from NO3 generated within the sediment (dn). The polychaetes stimulated aerobic respiration, dw and dn rates – 2-times more than the bivalves. The effect of both bivalves on oxygen uptake, dw and dn processes was similar. The bivalves stimulated dn more than dw, whereas the polychaetes preferentially stimulated dw. The different irrigation mechanisms used by the polychaetes and the bivalves were thought to be responsible for these different patterns of stimulation.