Trace metals and the productivity of shelf waters off north west Australia

Abstract

Oceanographic measurements on the North West Shelf of Australia indicated that nutrient enrichment was derived from a combination of terrestrial run-off and interaction with the sediments. There was no evidence for upwelling. In situ fluorescence measurements suggested that the phytoplankton biomass was low and did not increase in regions of nutrient enrichment. On the continental shelf, the concentrations of copper, nickel and cadmium were typical of unpolluted waters and by using a reverse- phase high performance liquid chromatography absorbent (SEP-PAK), about 20% of the copper was found to be organically bound with smaller amounts of organically bound nickel, zinc and iron and even less organically bound cadmium, chromium and manganese. The copper-complexing capacity of the surface waters (5-10 nM) was comparable to the total concentration of trace metals liable to form organic complexes so that the trace metal speciation may change markedly with small changes in trace metal concentration or complexing capacity. Calculations show that the concentration of free copper ions is too low to have any adverse affects on the biota and it is suggested that the productivity of the water may be affected by the limited bioavailability of essential trace metals.