Metal — organic interactions in sea water: an ecosystem experiment

Abstract

A model plankton ecosystem was used to study the interactions of trace metals and organic compounds over a 10-day period during a phytoplankton bloom. Six bags of 1200–1 capacity were filled with coastal sea water. Three bags were spiked with copper (78, 157 and 314 nM) and one with copper (4.57 μM) plus nitrilotriacetic acid (10 μM). Samples were analysed for total dissolved copper, zinc, iron, nickel and manganese. The copper complexing capacity, determined by a method based on competition with Chelex-100 resin, was found to be essentially the same (35 nM) in all bags and independent of time. Organically bound complexes of copper (18% of the total), zinc (7%), nickel (4%) and iron (2%) were isolated by adsorption on Sep-Pak cartridges. The metal—organic complexes, were analysed on a liquid chromatograph interfaced to a multichannel atomic fluorescence detector. Organic complexes of zinc, iron and nickel were formed even in the presence of a large excess of copper. The organic and metal—organic compounds isolated by Sep-Pak cartridges became more polar as the bloom progressed.