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Significance of Arsenic in Sediments of Lake Rotoroa (Hamilton Lake)

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Report: TR 2011/18
Author: Pattle Delamore Partners Ltd


Pattle Delamore Partners Limited (PDP) were commissioned to assist with the evaluation of the significance of arsenic in the sediment of Lake Rotoroa (Hamilton Lake), in Hamilton city. 

Although this report focuses mainly on the significance of arsenic within the sediments of the lake, the concentrations of a number of other elements (Cd, Cr, Cu, Fe, Hg, Ni, P, Pb and Zn) were also measured in the sediment and overlaying waters.  The results of all of these elements are presented in this report together with an assessment of the environmental significance of the elements, the method of deposition of the elements and the relationship of the lake chemistry to the chemistry of other lakes in the Waikato region. 

Significance of Arsenic in Sediments of Lake Rotoroa (Hamilton Lake) (3 mb)

Table of contents

  Executive summary vii
  Note on terms xi
  Glossary xv
1 Introduction 1
1.1 Aims of this report 1
1.2 History of Lake Rotoroa 2
1.3 Water quality of Lake Rotoroa 4
1.4 Flora and fauna of Hamilton Lake 4
1.5 Previous sediment quality investigations of Hamilton Lake 5
1.6 Chemistry of arsenic in sediments and natural waters 6
1.7 Arsenic in New Zealand 7
1.8 Trace elements in urban stormwater 9
1.9 Pollution incidents and discharges into Hamilton Lake 10
2 Study methodology 11
2.1 Sample collection methodology 11
2.2 Use of ANZECC sediment quality guidelines 16
3 Results 17
3.1 Raw results and summary statistics 17
3.2 Core samples 18
3.3 Surface water samples 18
3.4 Comparison with sediment quality guidelines 19
3.5 Key findings 25
4 Comparison with other data 26
4.1 Comparsion with historical data for Hamilton Lake 26
4.2 Comparison with sediment quality in other Waikato lakes 32
4.3 Key findings 36
5 Correlations and spatial trends 37
5.1 Approach and correlation matrix 37
5.2 Spatial data 42
5.3 Spatial distribution of elements within the sediment cores 45
5.4 Key findings 46
6 Human health risk assessment 48
6.1 Introduction 48
6.2 Exposure scenarios 49
6.3 Risk assessment 50
6.4 Key findings 53
7 Discussion 53
 7.1 Are the sediments "contaminated land"? 53
7.2 Sources of enrichment of elements in Hamilton Lake sediments 55
7.3 Changes in sediment quality over time 57
7.4 Long term management of the sediments 59
8 Conclusions and recommendations 59
 9 References 61
  Table of figures  
  Table of tables