Trace metal and major ion concentrations in Lakes Hayes and Manapouri

The major ion (Na+, K+, Mg2+, Ca2+, Sr2+, Cl-, SO42-, alkalinity, reactive Si) and trace metal (Cu, Zn, Fe, Mn, Cd and Pb) compositions of Lakes Hayes and Manapouri have been studied on five occasions throughout the seasonal cycle and depth range of each lake. In L. Manapouri, seasonal changes in bo th major element and trace metal concentrations were negligible and almost within the precision of analytical methods, indicating a highly uniform wat er composition. Major element concentrations were extremely low by global s tandards, in most cases below the 1% percentile level for global fresh wate rs. By contrast, the much shallower L. Hayes exhibited much higher major el ement concentrations, close to the global mean. In addition, this lake show ed a clear anoxic sub-surface layer during summer, in which concentrations of the redox-active metals Fe and Mn became very high. Evidence of surface water utilisation of reactive Si, and deeper water scavenging of Cu, were b oth found in this lake.