Trace elements in sediments of the lower eastern coast of the Firth of Thames

TR 2007/08
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Report: TR 2007/08

Author: N Kim

Abstract

In 2004, Waikato Regional Council tested for trace elements in shallow sediments from five sites spread across the lower Firth of Thames. Results indicated the presence of moderately elevated mercury in sediments at three of the sampling locations and suggested a need for further investigation.

Waikato Regional Council then commissioned URS New Zealand Ltd (URS) to undertake more extensive sediment sampling of the eastern coast of the lower Firth of Thames and to produce a report on this. During June 2005, URS collected 78 sediment samples from the following 11 locations:

  • Kuranui Bay
  • Piako River mouth
  • Tararu
  • Tapu
  • Te Mata
  • Te Puru
  • Thames mudflats
  • Thames urban area
  • Thornton Bay
  • Waihou River mouth
  • Waiomu.

All sediment samples were analysed for arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc. Samples collected from selected sites also underwent analysis for grain size, lithium, iron and aluminium, to aid in interpreting the results. Statistical tests were applied to ascertain if there were significant differences between sites. URS submitted their final report and assessment to Waikato Regional Council in 2006.

This review has been adapted from the URS report and incorporates additional data and information which has come to light since sampling was carried out.

Trace elements in sediments of the lower eastern coast of the Firth of Thames [PDF, 1.8 MB]