BIOTURBATION BY NEREIS SP AND ITS EFFECTS ON THE PHOSPHATE FLUX ACROSS THE SEDIMENT-WATER INTERFACE IN THE PALMONES RIVER ESTUARY

The effects of Nereis sp. on the flux of dissolved phosphate across the sediment-water interface has been studied in Palmones River estuary using benthic flux-chambers and intact cores. Diffusive fluxes of phosphate were calculated from pore water gradient concentration and compared with those obtained from benthic chambers experiments. The high abundance of Nereis in the upper sediment layers appears to play an important part in the dissolved oxygen profiles in the overlying water, but had no effect on the redox potential. A negative relationship was found between the Nereis abundance and the phosphate gradient; this gradient ranged between 40-mu-mol 1(-1) cm-1 with 340 Nereis individuals m-2 and 20-mu-mol 1(-1) cm-1 with 900 Nereis individuals m-2. The ratio of the in situ flux to the flux gradient concentration for dissolved phosphate increased with the abundance of Nereis (from 1.7 at low abundance to 5.8 at high abundance).