Journal of the Royal Society of New Zealand abstracts

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Geochemical cycling of major and minor elements in the Taieri River and Waipori River catchments

Jonathan P. Kim, Keith A. Hunter^*

Department of Chemistry, P.O. Box 56, University of Otago, Dunedin, New Zealand.

^*Author for correspondence.

The concentrations of the major ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, SO4^2-, total alkalinity AT and dissolved silica SiO2) and the dissolved trace metals Cu and Zn have been determined in the combined catchments of the Waipori and Taieri Rivers, in Otago, New Zealand. In general, the concentrations of the major ions were low, and were similar to levels observed in other uncontaminated rivers in the South Island. However, elevated concentrations of Na⁺, Cl^-, Ca²⁺, HCO3^-, with mole ratios characteristic of seawater, were found in the lower catchment, indicating intrusion of sea salts by tidal mixing. Significant inputs of nutrients, Zn, and, to a lesser extent, Cu, resulting from sewage effluent of the Mosgiel treatment plant, were observed at some periods during a time series of samples collected over a 20-month period. Estimates, based on the data, of the annual flux of nutrients and trace metals to the lower Taieri River catchment from this source indicate that the treatment plant contributes approximately 45% of the nutrients NO3^-, PO4^3-, and dissolved Zn. This implies that the recent closure of this treatment plant should result in a significant improvement in the water quality of the lower Taieri River.

Keywords  major ions; trace metals; geochemical cycling; New Zealand; Taieri; Waipori; river

R00052 Received 7 September 2000; accepted 5 March 2001

(c) Journal of The Royal Society of New Zealand,

Volume 31, Number 4, December 2001, pp 745-762

PDF file of entire paper: medium quality (927K); (scanned from paper original: notes about this process)

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