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Contents

iii

Summary

vii

1

Introduction

1

1.1

Background to project

1

1.2

Sediments in aquatic systems

1

1.3

Acid sulfate soil signals

1

2

Aims and scope

3

2.1

Objective

3

2.2

Study sites

3

2.3

Sampling and analysis

5

2.4

Rationale for analytes measured

5

2.5

Derived parameters

8

2.6

Data analysis

9

3

Results

10

3.1

Spatial distribution

10

3.2

Data relationships

24

3.3

Comparison to guideline values

25

3.4

Nitrogen and phosphorus

26

4

Discussion

29

4.1

Acid sulfate soil indicators

29

4.2

Role of sediment type

32

4.3

Potential effects on aquatic organisms

32

4.4

Comparison with historical data

33

4.5

Results in a global context

35

5

Conclusion and recommendations

38

Appendices

39

Acronyms

46

Glossary

47

References

49

Appendix A — Average values measured in sediment at each site

39

Appendix B — Quality assurance and quality control

44

Figure 1

Conceptual diagram of sediment contamination from acidic drainage

2

Figure 2

Study sites sampled for sediment within the Swan-Canning and Peel-Harvey

estuaries and the Leschenault Inlet

4

Department of Water

iii

Sediment quality in three south-western Australian estuaries

Figure 3

Multidimensional scaling (MDS) plot of replicate samples within the Swan-

Canning and Peel-Harvey estuaries and the Leschenault Inlet (with HCl-

extractable metals, carbon and sulfur measurements as variables)

11

Figure 4

Average particle size distribution for sediment sampled within the Swan-Canning

and Peel-Harvey estuaries and the Leschenault Inlet. The proportion of sand to

mud is shown by the relative shaded areas of colour in each of the circles

13

Figure 5

Average total organic matter (as a percentage of maximum organic matter

observed) within sediment from the Swan-Canning and Peel-Harvey estuaries

and the Leschenault Inlet. The size of the bar that denotes the TOC content is

normalised to the highest measured concentration at any site (i.e. 17 % at S13).14

Figure 6

Average redox potential (Eh range +200 to -200 mV) within sediments from the

Swan-Canning and Peel-Harvey estuaries and the Leschenault Inlet. The scale

of the bar denotes the redox potential of sediments between -200 mV and +200

mV, with the highest Eh recorded at L1 (198 mV at S8), although this is probably

an artefact of sampling (see text)

15

Figure 7

Average chromium reducible sulfur and total sulfur within sediments of the Swan-

Canning and Peel-Harvey estuaries and the Leschenault Inlet as a percentage of

the highest concentration observed (1.7% and 2.6% respectively at site P5)

17

Figure 8

Acid volatile sulfur (AVS) concentration in sediment collected from (A) Peel-

Harvey estuary and (B) Leschenault Inlet (mean ± st. err)

18

Figure 9

Plots of the ratio of AVS to SCr-py for the Peel-Harvey estuary sites (A) and the

Leschenault Inlet (B), and degree of pyritisation (DOP) and degree of sulfidisation

(DOS) for sites in the Peel-Harvey estuary (C) and Leschenault Inlet (D)

19

Figure 10

Average HCl-extractable iron and aluminium, as a percentage of the maximum

HCl-extractable metals observed, within sediment from the Swan-Canning and

Peel-Harvey estuaries and the Leschenault Inlet. The size of the bar that denotes

the metal concentration is normalised to the highest measured concentration of

each at any site (i.e. 25 600 mg kg-1 of iron at S11)

21

Figure 11

Average HCl-extractable chromium and zinc, as a percentage of the maximum

HCl-extractable metals observed, within sediment from the Swan-Canning and

Peel-Harvey estuaries and the Leschenault Inlet. The size of the bar that denotes

the metal concentration is normalised to the highest measured concentration of

each at any site (i.e. 18 mg kg-1 of chromium at S11)

22

Figure 12

Average HCl-extractable copper and lead, as a percentage of the maximum HCl-

extractable metals observed, within sediment from the Swan-Canning and Peel-

Harvey estuaries and the Leschenault Inlet. The size of the bar that denotes the

metal concentration is normalised to the highest measured concentration of each

at any site (i.e. 69 mg kg-1 of copper at S11)

23

Figure 13

Total nitrogen and total phosphorus measured in sediment from the Swan-

Canning estuary and Leschenault Inlet (mean ± standard error)

27

Figure 14

Ratio of nitrogen to phosphorus (N:P) for sediment sampled in the Swan-Canning

estuary and Leschenault Inlet (mean ± standard error)

28

Table 1

Sediment analysis matrix for sampling within the three estuaries

6

Table 2

Correlations between total metal concentrations and HCl-extractable metal

concentrations measured in the Peel-Harvey estuary and Leschenault Inlet

sediments

24

Table 3

Correlation coefficient (R) for HCl-extractable metals exhibiting strong correlation

(R>0.7, p<0.05)

25

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Department of Water

Water science technical series, report no. 18

Table 4

Sites where Interim sediment quality guideline values for metals were exceeded.

In most cases ISQG-low was exceeded. Instances where ISQG-high was

exceeded have been shown in bold type

26

Table 5

Reported chemical qualities of sulfidic materials within sediments of drains

affected by acid sulfate soil drainage waters

30

Table 6

Summary of sediment quality historical data for the Swan-Canning and Peel-

Harvey estuaries and the Leschenault Inlet. Concentrations are reported per dry

weight of sediment

34

Table 7

Sediment quality reported for metal contaminants in estuaries worldwide. n.d. =

not determined

37

Table 8

Average HCl-extractable (b) and total (t) metals (mg kg-1dry weight) for sediments

from sites within the Swan-Canning and Peel-Harvey estuaries and the

Leschenault Inlet. n.d. = not determined, n = 5. Above ISQG-low, above ISQG-

high

39

Table 9

Average values for other analytes in sediments from sites within the Swan-

Canning and Peel-Harvey estuaries and the Leschenault Inlet. n.d. = not

determined, n = 5

42

Table 10

Summary of spike recovery data showing range observed where multiple

samples were analysed

44

Table 11

Summary of lab duplicate data showing the percentage difference between

duplicates for the HCl-extractable metal suite, with data for the total metal suite

shown in parentheses

45

Department of Water

v

Department of Water

vii