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  Services » Publications » Technical reports - by year » tr200708

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

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
(1889 kb, 269 seconds to download, 56k modem)

Table of contents

Executive summary i
1 Introduction 1
1.1 Potential sources of the elements 1
1.1.1 Weathering and erosion 1
1.1.2 Past mining 3
1.1.3 Agricultural and horticultural inputs 4
1.1.4 Urban inputs 5
1.2 Previous data 5
2 Study methodology 9
2.1 Sampling objectives 9
2.2 Sampling locations 9
2.2.1 General 9
2.2.2 History of the sample locations 15
2.3 Sample types 16
2.3.1 Manual grab samples 16
2.3.2 Vertical profiles 16
2.3.3 Grab sampling 17
2.4 Analysis and analytical quality assurance 17
2.5 Use of ANZECC sediment quality guidelines 18
3 Results and discussion 19
3.1 Raw results and summary statistics 19
3.2 Comparison with sediment quality guidelines 20
3.2.1 Comparison to the ISQG-Low 20
3.2.2 Comparison to the ISQG-High 21
3.2.3 Key findings 21
3.3 Comparison between the Firth of Thames and other areas 22
3.3.1 Comparison to coastal sediments in Raglan Harbour 22
3.3.2 Comparison of this survey's data with historical data 24
3.3.3 Key findings 25
3.4 Small scale variability 25
3.4.1 Assessment 25
3.4.2 Key finding 26
3.5 Comparisons between sites in the Firth of Thames 26
3.5.1 Statistical analysis and data normalisation 26
3.5.2 Local historical mining sites versus control sites 27
3.5.3 Seaward versus landward 30
3.5.4 Urban areas versus control sites 30
3.5.5 Agriculturally proximate versus control sites 34
3.5.6 Key findings 35
3.6 Correlations and spatial trends 36
3.6.1 Approach and correlation matrix 36
3.6.2 Zinc, cadmium and lead 37
3.6.3 Arsenic and copper 39
3.6.4 Chromium and nickel 41
3.6.5 Mercury 41
3.6.6 Principal components analysis 44
3.6.7 Key findings 45
4 Summary and recommendations 47
4.1 Summary 47
4.1.1 Relative enrichments 47
4.1.2 Comparison to guidelines 47
4.1.3 Local and general sources 47
4.1.4 Probable dominant sources by element 48
4.2 Recommendations 49
References 51
Appendix 1. Further details of each location from which sediment samples were collected by URS as part of this study 53
Appendix 2. Measured concentrations of eight trace elements in 78 sediment samples collected as part of this study 56
Appendix 3. Quality assurance and quality control results 59
Appendix 4. Metal concentrations in sediments normalised against various benchmark variables 61
Appendix 5. Statistical summary of results for eight trace elements in each of the 10 areas sampled 65
Appendix 6. Concentrations of 33 elements, total organic carbon and dry matter in composite shallow (0-2 cm) sediment samples collected in October 2003 from five locations in the Firth of Thames and five locations in Raglan Harbour 70
Appendix 7. Results of Student's t-tests between Thames and Kuranui Bay sites and three mining reference sites (Te Puru, Thornton and Te Mata) 71
Appendix 8. Map showing the full extent of catchments feeding the lower Firth of Thames 72
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