AQUEOUS CHEMISTRY OF MAJOR IONS AND TRACE-METALS IN THE TAKAKA-COBB RIVER SYSTEM, NEW-ZEALAND

Concentrations of major ions (Na+, K+, Ca2+, Mg2+, Cl-, SO42-), total alkalinity (TA), 4 silicate (Si) and trace metals (Zn, Cu, Pb, Cd) hav e been investigated in the Takaka-Cobb River system at the northernmos t extremity of the South Island, New Zealand. The range in concentrati ons of major ions, Si and TA was large, with Ca2+ and TA dominating. S ome waters in the upper catchment were close to saturation with respec t to calcite, reflecting limestone dissolution both in the upper Takak a River and in an associated spring system. Dissolved trace metals exh ibited different behaviour, with constant or increasing concentrations upriver, especially in the Cobb Valley. Low concentrations found in t he upper Takaka River suggest that limestone weathering makes a minor contribution to concentrations of trace metals. The Cobb River exhibit ed much higher concentrations, implying that the differing composition s of rock types and soils within the separate catchments exercise impo rtant controls on trace metals.