Centre of Excellence for Sustainable Mine Lakes
Considerations for remediation of acid
mine lakes in South-West Australia
Lessons from old lakes
Clint McCullough & Mark Lund
smart mine lakes
Centre of Excellence for Sustainable Mine Lakes
Muja
180 m
~3 km ~1.5 km
Fill Time ~50 yrsFinal Volume >200 GL
Lake Kepwari
Centre of Excellence for Sustainable Mine Lakes
What models already exist?
Collie has a four old mine lakes (abandoned in early 1960s).
They feature a range of;– morphologies,– catchment features,– water chemistries,– ecologies
Fertile ground for understanding what influences mine lake development
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Black Diamond
Ewington Stockton Blue Waters
Area (Ha) 6 1.1 16 12
Depth (m) 8 11 47 24
Conductivity (µS cm-1) 421 1073 468 1368
pH 5.4 4.4 5.5 4
Sulphate (mg L-1) 46 30 31 90
Ammonia (µg L-1) 52 22 23 19
NOx (µg L-1) 163 3 18 3
FRP (µg L-1) 2 2 2 2
Chlorophyll a (µg L-1) 0.3 0.6 0.4 0.5
Aluminium (mg L-1) 0.006 0.6 0.006 2
Calcium (mg L-1) 4.4 1.9 2.2 5.9
Magnesium (mg L-1) 10.5 10.9 7.5 14.3
Iron (mg L-1) 0.01 0.3 0.02 0.3
Poorer environmental quality
Centre of Excellence for Sustainable Mine Lakes
What happened over 45 years?
• Metals/sulphate have precipitated out to form– Goethite (FeO.OH), Gibbsite (AL[OH]3), with possibly small
amounts of Jarosite (KFe3[SO4]2[OH]6), Jurbanite (Al[SO4][OH]5H2O) & Ferrihydrite (Fe[OH]3),
– This often releases further H+ ions– No evidence of metal sulfides
• Despite this acidity has reduced from >150 mg CaCO3 L-
1 (Chicken Creek) to <20 mg CaCO3 L-1 (old lakes)
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Trends of historical lakes
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Influences on lake chemistry
• Abiotic1) Catchment surface water inflow
2) Groundwater through-flow
• Biotic3) Sulfate reduction
4) Primary production
Abiotic processes probablymore important
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Surface water contributionsBlue Waters
Overburden in catchment, unstable banks with little
vegetation
Black DiamondLess spoil, better vegetated and more stable
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Surface water inflow
Mean pH Mean acidity Mean alkalinity
Ewington (n=6)
5.5 5.6 5.8
Blue Waters (n=10)
4.7 19.0 2.7
Unstable catchments may have buried iron-bound phosphorus and secondary minerals effectively
removing them from these systems.
Ongoing catchment contributions of acidity may hinder lake water quality remediation.
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Stratification
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pH change in Blue Waters
2.5
3
3.5
4
4.5
5
5.5
605
/97
07/9
7
09/9
7
11/9
701
/98
03/9
8
05/9
807
/98
09/9
8
11/9
8
01/9
903
/99
05/9
9
07/9
9
09/9
9 Dates
pH Top
Bottom
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Lake water chemistry changes during stratification
Black Diamond
Ewington Blue Waters
Max diff. surface – bottom Temperature
0.8oC 1.4oC 3.6oC
Δtemperature vs
ΔSulfate (r2)
-34%Groundwater sulfate,
sediment release?
57%Sulfate
reduction?
84%Sulfate
reduction?
Δtemperature vs bottom Total N* (r2)
-25%Chara uptake?
4%Benthic algae?
55%Ammonia -sediment
*Total N assumed to be conservative in anoxic hypolimnion (no 1o production), limited denitrification
Although a slow process, groundwater thru-flow perhaps more important than previously thought
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P
Mulch + P
Mulch
20 µg L-1
Sulfate Reduction
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pH change in mesocosms
3
3.5
4
4.5
5
5.5
6
Jun-
2003
Jul-2
003
Aug
-200
3
Sep
-200
3
Oct
-200
3
Nov
-200
3
Dec
-200
3
Jan-
2004
Feb
-200
4
Mar
-200
4
Apr
-200
4
May
-200
4
Jun-
2004
Dates
pH
Control
Mulch + P
Mulch
P
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Trends of historical lakes
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Sulfate Reducing Bacteria activity
Sulfate reduction is limited by availability of labile carbon.
Sulfate reduction is likely to be a relatively weak alkalinity process.
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Light limitation of photosynthesis
Euphotic depth
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Primary production
20µg/L phosphorus,
20µg/L & mulchMulch only
P Chlor a
Black Diamond
2.0 0.31
Blue Waters
1.8 0.50
Ewington 1.8 0.60
Stockton 2.0 0.37
Phosphorus, nitrogen, carbon and light may all limit phytoplankton production.
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Blue Waters
Conceptual models of lakes
Surface waters
Summer groundwater
Winter groundwater
Primary production
Sulfate reduction
Black DiamondStocktonEwington
Centre of Excellence for Sustainable Mine Lakes
Conclusions
• Water quality is largely stable as abiotic processes are the major determinator of water chemistry in acid mine lakes
• Alkalinity-generating biotic processes can be made to dominate through additions of macro-nutrients
• However, biotic remediation processes are weaker than current abiotic processes e.g., acid inputs
For passive biological remediation strategies to be successful, they need assistance, and not
hindrance, from simultaneous abiotic factors.