1. 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

2. Centre of Excellence for Sustainable Mine Lakes Muja 180 m ~3 km ~1.5 km Fill Time ~50 yrs Final Volume >200 GL Lake Kepwari

3. 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

4. Centre of Excellence for Sustainable Mine Lakes Black Diamond EwingtonStocktonBlue Waters Area (Ha)61.11612 Depth (m)8114724 Conductivity (µS cm -1 )42110734681368 pH5.44.45.54 Sulphate (mg L -1 )46303190 Ammonia (µg L -1 )52222319 NOx (µg L -1 )1633183 FRP (µg L -1 )2222 Chlorophyll a (µg L -1 )0.30.60.40.5 Aluminium (mg L -1 )0.0060.60.0062 Calcium (mg L -1 )4.41.92.25.9 Magnesium (mg L -1 )10.510.97.514.3 Iron (mg L -1 )0.010.30.020.3 Poorer environmental quality

5. 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 (KFe 3 [SO 4 ] 2 [OH] 6 ), Jurbanite (Al[SO 4 ][OH]5H 2 O) & Ferrihydrite (Fe[OH] 3 ), –This often releases further H + ions –No evidence of metal sulfides Despite this acidity has reduced from >150 mg CaCO 3 L - 1 (Chicken Creek) to <20 mg CaCO 3 L -1 (old lakes)

6. Centre of Excellence for Sustainable Mine Lakes Trends of historical lakes

7. Centre of Excellence for Sustainable Mine Lakes Influences on lake chemistry Abiotic 1)Catchment surface water inflow 2)Groundwater through-flow Biotic 3)Sulfate reduction 4)Primary production Abiotic processes probably more important

8. Centre of Excellence for Sustainable Mine Lakes Surface water contributions Blue Waters Overburden in catchment, unstable banks with little vegetation Black Diamond Less spoil, better vegetated and more stable

9. Centre of Excellence for Sustainable Mine Lakes Surface water inflow Mean pHMean acidityMean alkalinity Ewington (n=6) 5.55.65.8 Blue Waters (n=10) 4.719.02.7 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.

10. Centre of Excellence for Sustainable Mine Lakes Stratification

11. Centre of Excellence for Sustainable Mine Lakes pH change in Blue Waters

12. Centre of Excellence for Sustainable Mine Lakes Lake water chemistry changes during stratification Black Diamond EwingtonBlue Waters Max diff. surface – bottom Temperature 0.8 o C1.4 o C3.6 o C Δtemperature vs ΔSulfate (r 2 ) -34% Groundwater sulfate, sediment release? 57% Sulfate reduction? 84% Sulfate reduction? Δtemperature vs bottom Total N* (r 2 ) -25% Chara uptake? 4% Benthic algae? 55% Ammonia - sediment *Total N assumed to be conservative in anoxic hypolimnion (no 1 o production), limited denitrification Although a slow process, groundwater thru-flow perhaps more important than previously thought

13. Centre of Excellence for Sustainable Mine Lakes P Mulch + P Mulch 20 µg L -1 Sulfate Reduction

14. Centre of Excellence for Sustainable Mine Lakes pH change in mesocosms

15. Centre of Excellence for Sustainable Mine Lakes Trends of historical lakes

16. Centre of Excellence for Sustainable Mine Lakes Sulfate Reducing Bacteria activity Sulfate reduction is limited by availability of labile carbon. Sulfate reduction is likely to be a relatively weak alkalinity process.

17. Centre of Excellence for Sustainable Mine Lakes Light limitation of photosynthesis Euphotic depth

18. Centre of Excellence for Sustainable Mine Lakes Primary production 20µg/L phosphorus, 20µg/L & mulch Mulch only PChlor a Black Diamond 2.00.31 Blue Waters 1.80.50 Ewington1.80.60 Stockton2.00.37 Phosphorus, nitrogen, carbon and light may all limit phytoplankton production.

19. Centre of Excellence for Sustainable Mine Lakes Blue Waters Conceptual models of lakes Surface waters Summer groundwater Winter groundwater Primary production Sulfate reduction Black DiamondStockton Ewington

20. 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.