EFFECT OF BIOTURBATION BY NEREIS SP, MYA-ARENARIA AND CERASTODERMA SPON NITRIFICATION AND DENITRIFICATION IN ESTUARINE SEDIMENTS

Three different sets of undisturbed sediment cores containing: Nereis sp. (polychaete, 2,000 ind. m(-2)), Mya arenaria (bivalve, 1,100 ind. m(-2)) or Cerastoderma sp. (bivalve, 1,100 ind. m(-2)) were incubated in the laboratory. Rates of oxygen consumption and denitrification wer e measured. Total denitrification rates were 8 +/- 4, 12 +/- 4, 13 +/- 6 and 40 +/- 20 mu mol N m(-2) h(-1) in control cores and cores conta ining Cerastoderma sp., Mya arenaria and Nereis sp., respectively. Den itrification was partitioned, by the N-15 isotope pairing technique, i nto the contribution from NO3- in the overlying water (dw) and from NO 3- generated within the sediment (dn). The polychaetes stimulated aero bic respiration, dw and dn rates similar to 2-times more than the biva lves. The effect of both bivalves on oxygen uptake, dw and dn processe s was similar. The bivalves stimulated dn more than dw, whereas the po lychaetes preferentially stimulated dw. The different irrigation mecha nisms used by the polychaetes and the bivalves were thought to be resp onsible for these different patterns of stimulation.