Observations on nitrate, phosphate and silicate in Cleveland Bay, northern Queensland

Abstract

Results of a year-long study of nitrate, phosphate and silicate concentrations at a station in Cleveland Bay are reported. Silicate concentrations in local rivers were consistently high and in the sea were greatly increased during the wet season. Silicate was not considered to be limiting to phytoplankton growth during the year. Nitrate and phosphate concentrations were generally low and not strongly correlated with salinity. They were, however, strongly correlated with Secchi disc transparency changes throughout the year. indicating that release of nutrients occurred during periods of bottom sediment resuspension. Nutrient enrichment experiments with seawater showed that only addition of nitrogen stimulated phytoplankton growth. although addition of nitrogen plus phosphorus gave maximum growth. The results suggest an unusual system in which the chemical and biological processes in the lagoon waters of the Great Barrier Reef are coupled to benthic processes by intermittent, wind-driven bottom resuspension events.