BENTHIC NUTRIENT RECYCLING IN PORT-PHILLIP BAY, AUSTRALIA

Benthic chamber measurements of the reactants and products involved wi th biogenic matter remineralization (oxygen, ammonium, nitrate, nitrit e, phosphate, silicate, TCO2 and alkalinity) were used to define solut e exchange rates between the sediment and overlying water column of Po rt Phillip Bay, Australia. Measurements at various sites throughout th e bay, conducted during the summers of 1994 and 1995, indicate that th e variability in flux values within a site is comparable to year-to-ye ar variability (+/-50%). Four regions of the bay were distinguished by sediment properties and the northern region was identified as having 3-30 times greater nutrient regeneration rates than the other regions. Benthic recycling accounted for 63 and 72% of the annualized N and P input, respectively, to the entire bay as determined by summing benthi c, dissolved riverine, atmospheric and dissolved effluent sources. How ever, bay-wide sedimentary denitrification accounted for a loss of 63% of the potentially recyclable N. This fraction is higher than many ot her coastal regions with comparable carbon loading. Denitrification ef ficiency is apparently not enhanced by benthic productivity nor by bio -irrigation. The rate of bio-irrigation is negatively correlated with denitrification efficiency. Bio-irrigation was studied using radon-222 and CsCl spike injection chamber measurements. Radon fluxes from sedi ments in Port Phillip Bay were enhanced over the diffusive flux by 3-1 6 times. The modelled rate of loss of Cs from chamber water was positi vely correlated with radon flux enhancement results. Both methods iden tify regions within Port Phillip Bay that have particularly high rates of non-diffusive pore-water overlying water solute exchange. (C) 1998 Academic Press Limited.