This file is part of the following reference:

Briffa, Tony Edward (2004) The partitioning of trace metals in the sediments of Lake Moondarra. PhD

thesis, James Cook University

Access to this file is available from:

http://eprints.jcu.edu.au/11914

The Partitioning of Trace Metals in the Sediments of Lake Moondarra

A thesis presented for the degree of

Doctor of Philosophy

at

James Cook University

by

Tony Edward Briffa

August 2004

Acknowledgements

I would like to thank Mount Isa Mines Limited (MIM) for funding the research that is

reported in this thesis. In particular I would like to acknowledge the help given to me

by Mr. Oscar Kadletz (MIM) , Ian Brown (MIM) and the MIM dive team. Mr.

Michael Ridgeway who allowed me to use the chemical laboratory facilities at MIM.

Mr John Knights (MIM) for his assistance in identifying the mineral components of

the sediment.

I am also grateful for the advice and encouragement given to me by my supervisor Dr.

Michael Ridd.

Finally, I would like to thank my family, Susan, Maree-Louise and Luke for their

patience, understanding and encouragement during the years that I have studied,

culminating in the completion of this thesis.

ii

Statement of sources

I declare that this thesis is my own work and has not been submitted in any form for

another degree or diploma at any university or other institution of tertiary education.

Information derived from published or unpublished work of others has been

acknowledged in the text and a list of references provided.

iv

Statement of access

I, Tony Edward Briffa, the author of this thesis, understand that James Cook

University will not make this thesis available within the University Library without

first obtaining written permission from me prior to allowing access in accordance with

the agreement between James Cook University and myself. This agreement was put in

place at the request of Mount Isa Mines who sponsored the study. All users who have

got written permission to consult this thesis must sign the following statement.

In consulting this thesis I agree not to copy or closely paraphrase it in whole or in part

without the consent of the author, and to make proper written acknowledgment for

any assistance which I have obtained form it.

, / -...... (!.. if P. .f/. ~ P. ~~ ....... .

iii

Table of Contents

ABSTRACT ..................................................................................................................................................................... X

1 INTRODUCTION ...................................................................................................................................................... 1

1.1 STUDY AIMs .............................................................................................................................................................. 2

2 GENERAL DESCRIPTION OF LAKE MOONDARRA ....................................................................................... 4

2.1 MINERAL PROCESSING ACTIVITIES ............................................................................................ , .............................. 4

2.2 GEOGRAPHICAL INFORMATION .................................................................................................................................. 6 2.2.1 Local geography / geology ............................................................................................................................... 6 2.2.2 Description of the Local Climate ..................................................................................................................... 6

2.2.3 Lake Moondarra location .............................................. .................................................................................... 8 2.3 LAKE MOONDARRA WATER QUALITY ........................................................................................................... 10

2.3.1 Lake Moondarra Water Nutrient and Metal Concentrations ......................................................................... 14 2.4 DISCUSSION OF LAKE TURN-OVER ........................................................................................................................... 16

3 LITERATURE REVIEW ......................................................................................................................................... 20

3.1 SEDIMENT EXTRACTION SCHEMES ......................................................................................................................... 21 3.1.1 The exchangablefraction .................................... ........................................................................................... 23 3.1.2 The organic fraction ........................................ ............................................................................................... 23 3.1.3 Metal carbonate minerals .............................................................................................................................. 24 3.1.4 Iron and manganese complexes ............................................. ......................................................................... 24 3.1.5 The residual phase ......................................................................................................................................... 24 3.1.6 Bioavailable metals ........................................................................................................................................ 24

3.2 TRACE METAL PARTITIONING ................................................................................................................................ 25 3.2.1 Coeur d'Alene Lake .................................................. ...................................................................................... 25 3.2.2 Trace Metal Transformations in Sediments ........... ......................................................................................... 26

3.3 SEDIMENT QUALITY ................................................................................................................................................ 34 3.3.1 ANZECC Sediment Quality Guidelines .......................................................................................................... 34 3.3.2 Sediment Toxicity ........................................................................................................................................... 36

4 METHODOLOGy .................................................................................................................................................... 38

4.1 SAMPLING METHODS .............................................................................................................................................. 38 4.1.1 Suiface Sediment Samples ............................................... .............................................................................. 38 4.1.2 Sediment Trap Samples ............................................................................................................ ..................... 40 4.1.3 Sediment Core Samples ............................................... ...................................................... ............................. 40 4.1.4 Atmospheric Deposition Samples ................................................................................................................... 41

4.2 METAL SPECIATION EXTRACTION SCHEMES .......................................................................................................... 41 4.2.1 Interstitial Water ........................................................................................................................................... 42 4.2.2 Sequential Extraction Scheme ....................................................................................................................... 42

4.3 ANALYTICAL TECHNIQUES ..................................................................................................................................... 46 4.3.1 Trace Metal Determinations (atomic absorption spectrophotometry) .......................................................... 46 4.3.2 Trace Metal Determinations (ICP-MS) ........................................................................................................ 48 4.3.3 Organic Matter Determination ......................................... ............................................................................. 48 4.3.4 Total Sulfur Determinations . ......................................................................................................................... 49 4.3.5 Eh and pH Determinations ......................................... ................................................................................... 49

4.4 METHOD VALIDATION ............................................................................................................................................ 50 4.4.1 Determination of importance of a nitrogen atmosphere ............................................................................... 50 4.4.2 Efficacy of the Sequential Extraction Scheme ................................................................................................. 55 4.4.3 Matrix Effect checks ...................................................................................................................................... 57 4.4.4 Standard Reference Material Checks ............................................................................................................ 57

5 COMPARISON OF SURFACE SEDIMENTS ...................................................................................................... 59

5.1 VALIDITY OF COMPARING DIFFERENT LOCATIONS WITHIN LAKE MOONDARRA ...................................................... 59 5.2 SPATIAL VARIATION IN TRACE METAL CONCENTRATIONS WITH RESPECT TO LOCATION ........................................ 62 5.3 EFFECT OF WATER DEPTH ON TRACE METALPARTITIONING ..................................................................................... 76 5.4 CHAPTER SUMMARY ............................................................................................................................................... 80

v

6 HYDROUS SEDIMENTS IN LAKE MOONDARRA ........................................................................................... 84

6.1 SEDIMENTATION RATES AND EFFECTOFRAINFALL. ................................................................................................ 85 6.2 TRACE METAL PARTITIONING OF SEDIMENT TRAP SAMPLES .................................................................................... 87 6.3 TRACE METAL PARTITIONING OF WITH RESPECT TO SEDIMENT DEPTH (CORE SAMPLES) ....................................... 10 1 6.4 CHAPTER SUMMARy ............................................................................................................................................. 1 08

7 DETERMINATION OF TRACE METAL SOURCES ....................................................................................... 111

7 .1 SURFACE SEDIMENTS ................................................................................................................. , .......................... 115 7.2 SEDIMENT TRAP SAMPLES ..................................................................................................................................... 117 7.3 SEDIMENT CORES .................................................................................................................................................. 125 7.4 CHAPTER SUMMARY ............................................................................................................................................. 129

8 SEDIMENT TOXICITY ........................................................................................................................................ 131

8 .1 COMPARISON OF TRACE METAL CONCENTRATIONS WITH ANZECC GUIDELINES ................................................. 131 8.2 PORE WATER PARTITIONING AND CONTROLLING FACTORS .................................................................................. 138 8.3 CHAPTER SUMMARy ............................................................................................................................................. 142

9 SEDIMENT STABILITY MODELING ............................................................................................................... 144

9.1 LABORATORY BENCH TOP OXIDATION STUDy ....................................................................................................... 144 9.1.1 Experimental procedure ............................................. ................................................................................. 145 9.1.2 Experimental Data ...................................................................................................................................... 147

9.2 INVESTIGATIONS OF TRACE METAL UPTAKE BY SEDIMENTS .................................................................................. 150 9.2.1 Experimental Procedure ............................................. ...................................................... ........................... 150 9.2.2 Analysis of Results ............................................. .......................................................................................... 151

9.3 ROLE OF ORGANIC MATERIAL ON TRACE METAL TRANSFORMATIONS IN THE SEDIMENTS .................................... 157 9.4 CHAPTER SUMMARY ............................................................................................................................................. 163

10 ISOTOPIC LABELING EXPERIMENTS ......................................................................................................... 164

10.1 EXPERIMENTALPROCEDURE ............................................................................................................................... 165 10.2 EXPERIMENTAL RESULTS .................................................................................................................................... 168

10.2.1 Partitioning of Copper .............................................................................................................................. 168 10.2.2 Partitioning of Lead ................................................................................................................................... 178

10.3 CHAPTER SUMMARY ........................................................................................................................................... 184

11 CONCLUSIONS AND RECOMMENDATIONS .............................................................................................. 185

11.1 CONCLUSIONS ..................................................................................................................................................... 18 5 11.2 RECOMMENDATIONS .......................................................................................................................................... 187

REFERENCES ............................................................................................................................................................. 189

APENDICES ................................................................................................................................................................. 208

APPENDIX 1: RAINFALL DATA .................................................................................................................................. 208 APPENDIX 2: MIM HYDROLAB DATA ....................................................................................................................... 210 APPENDIX 3: MIM LAKE MOONDARRA CHEMICAL MONITORING ............................................................................. 216 APPENDIX 4: LOCATION OF LAKE MOONDARRA SURFACE SEDIMENT SAMPLING SITES 225 APPENDIX 5: SURFACE SEDIMENT DATA ................................................................................................................... 226 APPENDIX 6: WATER DEPTH AT SAMPLING SITES ..................................................................................................... 243 APPENDIX 7: SURFACE SEDIMENT TRACE METAL SOURCES ..................................................................................... 244 APPENDIX 8: SEDIMENT TRAP DATA ......................................................................................................................... 246

Vl

List of Tables

Table 2.1.1 Copper Ore Mineralogical Components 5

Table 2.1.2 Lead Zinc Ore Mineralogical Components 5

Table 2.3.1.1 Analysis results (mg/L) of Lake Moondarra at the Pump Station sampling site 15

Table 2.3.1.2 Mean concentrations of key heavy metals in water samples taken at the Dam 15

Wall

Table 3.3.1.1 Selected ANZECC Threshold Limits 35

Table 4.2.1 Wet and dry weights of sediment samples 42

Table 4.3.1.1 AAS instrument parameters used in analysis 46

Table 4.3.1.2 Detection Limits for the various extractants 47

Table 4.4.1.1 Statistical summary of organic phase extractions in air and under nitrogen 51

Table 4.4.1.2 Statistical summary of amorphous inorganic phase extractions in air and under 52

nitrogen

Table 4.4.1.3 Statistical summary of crystalline inorganic phase extractions in air and under 53

nitrogen

Table 4.4.1.4 Statistical summary of sulfidic phase extractions in air and under nitrogen 54

Table 4.4.2.1 Comparison of 4 step sequential and total extractions 55

Table 4.4.2.2 Results of modified extraction schemes 56

Table 4.4.3.1 Recoveries from spiked extracts 57

Table 4.4.4.1 Analyses of the standard lake sediment sample (LKSD-1) 58

Table 5.1.1 Mineralogical composition of selected surface sediments 61

Table 5.2.1 Percentage of trace metal associated with each phase 73

Table 5.2.2 Percentage Fe associated with each phase 75

Table 5.3.1 Trace metals associated with the crystalline inorganic phase 78

Table 5.3.2 Trace metals associated with the sulfidic phase 79

Table 6.2.1 Partitioning of metals in sediment trap samples 88

Table 6.2.2 Phase associations in surface and suspended sediments at Pump Station 90

Table 6.2.3 Phase associations in surface and suspended sediments at Dam Wall 92

Vll

Table 6.2.4

Table 6.2.5

Table 6.2.6

Table 6.2.7

Table 7.1

Table 7.2.1

Table 7.2.2

Table 7.2.3

Table 7.2.4

Table 7.2.5

Table 7.2.6

Table 7.2.7

Table 7.3.1

Table 7.3.2

Table 7.3.3

Table 8.1.1

Table 8.2.1

Table 8.2.2

Table 9.1.1.1

Table 9.2.2.1

Table 9.2.2.2

Table 9.2.2.3

Table 10.1.1

Table 10.1.2

Table 10.1.3

Phase associations in surface and suspended sediments at Spring Creek

Phase associations at Pump Station during the wet and dry seasons

Phase associations at Dam Wall during the wet and dry seasons

Phase associations at Spring Creek during the wet and dry seasons

Trace metal concentrations in potential sources (%)

Relative contribution of trace metal sources in suspended sediment samples

Surface and suspended sediment trace metal source comparisons at Pump

Station

Surface and suspended sediment trace metal source comparisons at Dam Wall

Surface and suspended sediment trace metal source comparisons at Spring

Creek

Comparison of relative source contributions at Pump Station in wet and dry

seasons

Comparison of relative source contributions at Dam Wall in wet and dry

seasons

Comparison of relative source contributions at Spring Creek in wet and dry

seasons

Relative trace metal source contributors with sediment depth at Pump Station

Relative trace metal source contributors with sediment depth at Dam Wall

Relative trace metal source contributors with sediment depth at Spring Creek

Total trace metal concentration in Rifle Creek Dam surface sediments /lg/g

Pore Water trace metal concentrtaion with respect to location

Pore water trace metal concentration with respect to water4 column depth

Selected surface sediment samples used in oxidation study

Trace metal associated with organic phase compared to total concentrations

Trace metal uptake by sediment

Trace metal removal by sediment with the organic phase removed

Samples used in Isotopic Experiments

Elemental Composition (Ilg/g)

Experimental Chemical Conditions

94

96

98

100

112

117

121

122

122

124

124

125

126

127

128

132

141

142

145

152

154

155

166

166

167

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List of Figures

FIGURE 2.2.2.1 :MOUNT ISA AVERAGE MONTHLY RAINFALL ............................................................................................... 7

FIGURE 2.2.2.2:ANNuALRAINFALL IN MOUNT ISA 1926 TO 1997 ...................................................................................... 7

FIGURE 2.2.3.1 :MAP SHOWING THE LOCATION OF LAKE MOONDARRA .............................................................................. 9

FIGURE 2.3.1:A VERAGE DISSOLVED OXYGEN CONTENT 23/8/95 TO 27/5/98 ..................................................................... 10

FIGURE 2.3.2:WATER TEMPERATURE 23/8/95 - 27/5/98 ..................................................................................................... 11

FIGURE 2.3.3:DISSOLVED OXYGEN CONTENT 23/8/95 - 27 /5/98 ........................................................................................ 11

FIGURE 2.3.4:TuRBITY 23/8/95 - 27/5/98 .......................................................................................................................... 12

FIGURE2.3.5:pH AT THE DAM WALL 23/8/95 - 27/5/98 .................................................................................................... 13

FIGURE 2.3.6:pH AT THE PUMP STATION 23/8/95 - 27/5/ 98 .............................................................................................. 13

FIGURE 2.3.7: VARIATION OF AVERAGE pH WITH DISSOLVED OXYGEN AT THE DAM WALL ............................................. 13

FIGURE 3.2.2.1: ANAEROBIC ORGANIC DECOMPOSITION .................................................................................................. 28

FIGURE3.2.2.2:IRON AND ARSENIC CYCLING AT THE REDOX BOUNDARY ....................................................................... 30

FIGURE 3.2.2.3 :POURBAIX DIAGRAM FOR FE .................................................................................................................... 31

FIGURE 4.1.1.1 : SAMPLING SITES IN LAKE MOONDARRA ................................................................................................... 39

FIGURE 5.2.1: SPATIAL DISTRIBUTION OF PB IN LAKE MOONDARRA ................................................................................ 63

FIGURE 5.2.2: SPATIAL DISTRIBUTION OF Cu IN LAKE MOONDARRA ............................................................................... 65

FIGURE 5.2.3: SPATIAL DISTRIBUTION OF CD IN LAKE MOONDARRA ................................................................................ 67

FIGURE 5.2.4: SPATIAL DISTRIBUTION OF ZN IN LAKE MOONDARRA ............................................................................... 69

FIGURE 5.2.5: SPATIAL DISTRIBUTION OF As IN LAKE MOONDARRA ............................................................................... 71

FIGURE 6.1 : AVERAGE TURBIDITY WITH WATER COLUMN DEPTH AT PUMP STATION ........................................................ 84

FIGURE 6.1.1: PUMP STATION SEDIMENTATION RATES ..................................................................................................... 86

FIGURE 6.1.2: DAM WALL SEDIMENTATION RATES .......................................................................................................... 86

FIGURE 6.1.3: SPRING CREEK SEDIMENTATION RATES ..................................................................................................... 87

FIGURE 6.3.1:PB PARTITIONING WITH SEDIMENT DEPTH AT PUMP STATION .................................................................... 102

FIGURE 6.3.2:Cu PARTITIONING WITH SEDIMENT DEPTH AT PUMP STATION ................................................................... 102

FIGURE 6.3.3:ZN PARTITIONING WITH SEDIMENT DEPTH AT PUMP STATION ................................................................... 102

FIGURE 6.3.4:PB PARTITIONING WITH SEDIMENT DEPTH AT DAM WALL.. ....................................................................... 104

FIGURE 6.3.5:Cu PARTITIONING WITH SEDIMENT DEPTH AT DAM WALL ........................................................................ 105

FIGURE 6.3.6:ZN PARTITIONING WITH SEDIMENT DEPTH AT DAM WALL.. ....................................................................... 105

ix

FIGURE 6.3.7:PB PARTITIONING WITH SEDIMENT DEPTH AT SPRING CREEK .................................................................... 107

FIGURE 6.3.8:Cu PARTITIONING WITH SEDIMENT DEPTH AT SPRING CREEK ................................................................... 107

FIGURE 6.3.9:ZN PARTITIONING WITH SEDIMENT DEPTH AT SPRING CREEK .................................................................... 108

FIGURE 7.1.1 : SOURCE CONTRIBUTIONS TO SURFACE SEDIMENT TRACE METAL CONCENTRATIONS ................................. 115

FIGURE 7.2.1: SOURCE CONTRIBUTIONS TO PUMP STATION SUSPENDED SEDIMENT TRACE METAL

CONCENTRATIONS ................................................................................................................................................... 119

FIGURE 7 .2.2:S0URCE CONTRIBUTIONS TO DAM WALL SUSPENDED SEDIMENT TRACE METAL

CONCENTRATIONS ................................................................................................................................................... 120

FIGURE 7.2.3: SOURCE CONTRIBUTIONS TO SPRING CREEK SUSPENDED SEDIMENT TRACE METAL

CONCENTRATIONS ................................................................................................................................................... 120

FIGURE 8.1.1 :ANZECC SEDIMENT QUALITY RISK-BASED DECISION TREE ..................................................................... 133

FIGURE 8.1.2: DISTRIBUTION OF LEAD BETWEEN OPERATIONALLY DEFINED FRACTIONS IN THE

SEDIMENTS OF THE FLOODED LEICHHARDT RIVER BED OF LAKE MOONDARRA ...................................................... 134

FIGURE 8.1.3: DISTRIBUTION OF LEAD BETWEEN OPERATIONALLY DEFINED FRACTIONS IN THE

SEDIMENTS OF THE REST OF LAKE MOONDARRA ..................................................................................................... 135

FIGURE 8.1.4: DISTRIBUTION OF COPPER BETWEEN OPERATIONALLY DEFINED FRACTIONS IN THE

SEDIMENTS OF THE FLOODED LEICHHARDT RIVER BED OF LAKE MOONDARRA ...................................................... 135

FIGURE 8.1.5: DISTRIBUTION OF COPPER BETWEEN OPERATIONALLY DEFINED FRACTIONS IN THE

SEDIMENTS OF THE REST OF LAKE MOONDARRA ..................................................................................................... 136

FIGURE 8.1.6: DISTRIBUTION OF ZINC BETWEEN OPERATIONALLY DEFINED FRACTIONS IN THE SEDIMENTS

OF THE FLOODED LEICHHARDT RIVER BED OF LAKE MOONDARRA ......................................................................... 136

FIGURE 8.1.7: DISTRIBUTION OF ZINC BETWEEN OPERATIONALLY DEFINED FRACTIONS IN THE SEDIMENTS

OF THE REST OF LAKE MOONDARRA ....................................................................................................................... 137

FIGURE 8.2.1: DISTRIBUTION PLOT FOR PB ..................................................................................................................... 139

FIGURE 9.1.2.1: PB, Cu, ZN, CD AND As RELEASE AS CONDITIONS CHANGE ANOXIC TO OXIC ........................................ 147

FIGURE 9.1.2.2: FE AND MN RELEASE AS CONDITIONS CHANGE ANOXIC TO OXIC ........................................................ '" 147

FIGURE 9.1.2.3: PB, Cu, ZN, CD AND As RELEASE AS CONDITIONS CHANGE OXIC TO ANOXIC ........................................ 148

FIGURE 9.1.2.4: FE AND MN RELEASE AS CONDITIONS CHANGE OXIC TO ANOXIC ........................................................... 149

FIGURE 9.2.2.1: SEDIMENT BLANK PB RELEASE WITH MECHANICAL AGITATION OF SEDIMENT ....................................... 153

FIGURE 9.2.2.2: SEDIMENT BLANK Cu RELEASE WITH MECHANICAL AGITATION OF SEDIMENT ....................................... 153

x

FIGURE 9.2.2.3: SEDIMENT BLANK ZN RELEASE WITH MECHANICAL AGITATION OF SEDIMENT ....................................... 154

FIGURE 9.3.1: SURFACE SEDIMENT pKA INFLECTION POINT ............................................................................................ 158

FIGURE 9.3.2: PB EXTRACTED FROM SEDIMENT BY ORGANIC ACIDS ................................................................................ 160

FIGURE 9.3.3: CU EXTRACTED FROM SEDIMENT BY ORGANIC ACIDS ............................................................................... 160

FIGURE 9.3 A: ZN EXTRACTED FROM SEDIMENT BY ORGANIC ACIDS ............................................................................... 161

FIGURE 9.3.5: FE EXTRACTED FROM SEDIMENT BY ORGANIC ACIDS ................................................................................ 161

FIGURE 9.3.6: TRACE METALS EXTRACTED FROM SEDIMENT BY MIXED ORGANIC ACIDS ................................................ 162

FIGURE 10.2.1.1: VARIATION IN CU CONCENTRATION IN FILTERED, UNFILTERED AND PORE WATER IN

COLUMN 1 ............................................................................................................................................................... 169

FIGURE 10.2.1.2: VARIATION IN Cu CONCENTRATION IN FILTERED, UNFILTERED AND PORE WATER IN

COLUMN 2 ............................................................................................................................................................... 171

FIGURE 10.2.1.3: VARIATION IN CU CONCENTRATION IN FILTERED, UNFILTERED AND PORE WATER IN

COLUMN3 ............................................................................................................................................................... 171

FIGURE 1 0.2.104: VARIATION IN FE CONCENTRATION IN COLUMN 3 ............................................................................... 173

FIGURE 10.2.1.5: Cu KD (MODIFIED) WITH SEDIMENT RE-SUSPENSION ........................................................................... 174

FIGURE 10.2 .. 1.6: VARIATION IN CU ISOTOPIC RATIOS IN COLUMN 1 ............................................................................. 176

FIGURE 10.2.1.7: VARIATION IN Cu ISOTOPIC RATIOS IN COLUMN 2 .............................................................................. 176

FIGURE 10.2.1.8: VARIATION IN Cu ISOTOPIC RATIOS IN COLUMN 3 (UNSPIKED) .......................................................... 177

FIGURE 10.2.2.1: VARIATION INPB CONCENTRATION IN FILTERED, UNFILTERED AND PORE WATER IN

COLUMN 1 ............................................................................................................................................................... 179

FIGURE 10.2.2.2: VARIATION IN PB CONCENTRATION IN FILTERED, UNFILTERED AND PORE WATER IN

COLUMN 2 ............................................................................................................................................................... 180

FIGURE 10.2.2.3: VARIATION IN PB CONCENTRATION IN FILTERED, UNFILTERED AND PORE WATER IN

COLUMN 3 ............................................................................................................................................................... 180

FIGURE 10.2.204: PB KD (MODIFIED) WITH SEDIMENT RE-SUSPENSION ............................................................................ 181

FIGURE 10.2.2.5: VARIATION INPB ISOTOPIC RATIOS IN COLUMN 1 .............................................................................. 182

FIGURE 10.2.2.6: VARIATION IN PB ISOTOPIC RATIOS IN COLUMN 2 .............................................................................. 182

FIGURE 10.2.2.7: VARIATION IN PB ISOTOPIC RATIOS IN COLUMN 3(UNSPIKED) ............................................................ 183

xi

Abstract

This study examines the spatial distribution and phase associations of trace metals

within Lake Moondarra sediments for the period from 1998 - 2000. Factors effecting

phase partitioning in the sediments are evaluated, with particular reference to

elements As, Cd, Cu, Pb and Zn. The other aims of this study were to identify the

sources of the trace metals within the sediments of Lake Moondarra and determine the

stability of these sediments with respect to oxidation events.

Because no standard method is used by all researchers for determining the partitioning

of trace metals within the sediments, the first part of this study was devoted to

validating methods. Method testing showed that for sediments collected in Lake

Moondarra sequential extractions of anoxic sediments can be done in air with minimal

impact on the partitioning of the trace metals with the sediment, providing the sample

is stored frozen and thawed in a nitrogen atmosphere.

The flooded Leichhardt River bed contains elevated levels of Pb, Cu, Zn, As, and Cd

compared to the rest of Lake Moondarra. A non linear optimisation technique applied

to the sediment data indicated that the most likely source of the trace metals is

atmospheric fallout and Pb/Zn tailings left in the Leichardt River by now discontinued

waste disposal practices. The fallout and tailings constituted typically less than 5% of

the sediment mass. There is little change in the relative contributions of these with

sediment depth. This suggests that none of the remediation work done by MIM to

remove Pbl Zn tails from the Leichhardt River bed has had an effect on sediment

quality to date as there is no major change in trace metal concentration with sediment

xii

depth. Application of the ANZECC (2000) sediment quality guidelines indicated that

toxicity testing should be done on the sediments of Lake Moondarra, particularly the

flooded Leichhardt River bed.

The sequential extraction results indicate that most trace metals in the sediments of

Lake Moondarra are not present as sulfides. The partitioning data show that the trace

metals have undergone significant transformation either prior to entering Lake

Moondarra or in situ in the benthic sediments. The prevailing belief that the trace

metals in the sediments of Lake Moondarra are present as stable sulfides with low

solubility products and hence have limited impact on the environment is flawed. The

trace metals in the sediment are dynamic with trace metals being released to the water

column under anoxic conditions and re-sorption of trace metals under oxic conditions.

Laboratory testwork on the sediments of Lake Moondarra indicates that iron redox

chemistry and associated adsorption and desorption of trace metals in the suspended

sediment layer is the dominant mechanism in controlling the release or removal of

trace metals from the water column. Laboratory testwork also indicates that anaerobic

decomposition of organic material may play a significant role in phase

transformations within the sediments of Lake Moondarra.

xiii