Aqueous chemistry of major ions and trace metals in the Takaka–Cobb River system, New Zealand

Abstract

Concentrations of major ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl-, SO 4 2–), total alkalinity (TA), silicate (Si) and trace metals (Zn, Cu, Pb, Cd) have been investigated in the Takaka–Cobb River system at the northernmost extremity of the South Island, New Zealand. The range in concentrations of major ions, Si and TAwas large, with Ca²⁺ and TAdominating. Some waters in the upper catchment were close to saturation with respect to calcite, reflecting limestone dissolution both in the upper Takaka River and in an associated spring system.

Dissolved trace metals exhibited different behaviour, with constant or increasing concentrations upriver, especially in the Cobb Valley. Low concentrations found in the upper Takaka River suggest that limestone weathering makes a minor contribution to concentrations of trace metals. The Cobb River exhibited much higher concentrations, implying that the differing compositions of rock types and soils within the separate catchments exercise important controls on trace metals.