Zinc speciation in Lakes Manapouri and Hayes, New Zealand

A study of zinc complexation in Lakes Manapouri and Hayes revealed that zin c speciation in both lakes is dominated by its complexation to natural orga nic ligands. In Lake Manapouri, dissolved zinc concentrations increased fro m 0.9 nM in surface waters to similar to1.4 nM at depth. Ligand concentrati ons for this lake were relatively uniform uniform with depth, with values r anging 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. Conditio nal stability constants (log K) for the complexation of zinc to these ligan ds 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 Zn2+ levels may limit the growth of some phytoplankton in bo th lakes.