Trace Elements in Sediments of the Lower Eastern Coast of the Firth of Thames
Report: TR 2007/08
Author: Nick Kim
Abstract
In 2004, Environment Waikato 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.
Environment Waikato 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 Environment Waikato 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
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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 |