Causes of observed temporal variability of nutrient fluxes from a southern Australian marine embayment

Abstract

Benthic chambers were used to measure temporal differences of sediment–water column flux of dissolved oxygen (DO), ammonium, nitrite plus nitrate, phosphate, silicate and total carbon dioxide (TCO₂) in Port Phillip Bay. Three clear and three dark benthic chambers were deployed between October 1994 and January 1996 at each of three sites: near the outflow of a major sewage treatment plant, near the mouth of a river and in the deep centre of the bay. Analysis of variance indicated that chamber type did not significantly affect magnitude of flux for the majority of deployments. Water temperature at the time of deployment had a significant effect on the fluxes of DO, TCO₂ , NH₄ , and SiO₄ at the central bay site and for all fluxes at the other two sites. There was a relationship between TCO₂ flux in the sediment and C production in the water column (r² = 0.6552). The denitrification efficiency at the central bay site was usually >80% at all times, and altered by ~30% seasonally at the other two sites. It is likely that the effect of water temperature on a suite of biological processes is the predominant source of temporal variation in these benthic fluxes.