DENITRIFICATION IN ESTUARINE SEDIMENT STIMULATED BY THE IRRIGATION ACTIVITY OF THE AMPHIPOD COROPHIUM-VOLUTATOR

Sediment with different densities of Corophium volutator (Pallas), ranging from 0 to 19 800 ind. M-2, were incubated in laboratory microcosms, and rates of oxygen uptake, denitrification and nitrate ammonification were determined from sediment-water fluxes. The measured processes were stimulated differently by C. volutator; oxygen uptake, denitrification of NO3- from nitrification within the sediment, and denitrification of NO3- from the overlying water were enhanced 2-, 3- and 5-fold respectively in the presence of 19 800 ind. m-2. This differential stimulation was explained by the different characteristics of diffusional solute transport at the sediment-water interface and mass transfer of water into the burrows where 02 and NO3- was depleted. Denitrification rates were calculated by using the N-15 isotope pairing technique. The applicability of the 15N isotope pairing technique for measuring coupled nitrification-denitrification in bioturbated sediment was confirmed in a test incubation with different levels of (NO3-)-N-15 added to microcosms with 12 000 C. volutator ind. m-2.