Abstract

A study of zinc complexation in Lakes Manapouri and Hayes revealed that zinc speciation in both lakes is dominated by its complexation to natural organic ligands. In Lake Manapouri, dissolved zinc concentrations increased from 0.9 nM in surface waters to ~1.4 nM at depth. Ligand concentrations for this lake were relatively uniform with depth, with values ranging between 2.9 and 4.2 nM. A similar ligand concentration was measured for Lake Hayes, which had a surface zinc concentration of 0.46 nM. Conditional stability constants (log K) for the complexation of zinc to these ligands were high,with values ranging between 10.0 and 11.1. Calculated free Zn ²⁺ concentrations for both lakes were in the low picomolar range (5—48 pM). Such low free Zn ²⁺ levels may limit the growth of some phytoplankton in both lakes.