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Considerations for remediation of acid mine lakes in South-West Australia Lessons from old lakes

Considerations for remediation of acid mine lakes in South-West Australia Lessons from old lakes Clint McCullough & Mark Lund. smart mine lakes. ~1.5 km. ~3 km. Fill Time ~50 yrs Final Volume >200 GL. 180 m. Lake Kepwari. Muja. What models already exist?.

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Considerations for remediation of acid mine lakes in South-West Australia Lessons from old lakes

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  1. Considerations for remediation of acid mine lakes in South-West Australia Lessons from old lakes Clint McCullough & Mark Lund smart mine lakes

  2. ~1.5 km ~3 km Fill Time ~50 yrs Final Volume >200 GL 180 m Lake Kepwari Muja

  3. 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. Poorer environmental quality

  5. 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)

  6. Trends of historical lakes

  7. Influences on lake chemistry • Abiotic • Catchment surface water inflow • Groundwater through-flow • Biotic • Sulfate reduction • Primary production Abiotic processes probably more important

  8. Surface water contributions Blue Waters Overburden in catchment, unstable banks with little vegetation Black Diamond Less spoil, better vegetated and more stable

  9. Surface water inflow 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. Stratification

  11. pH change in Blue Waters

  12. Lake water chemistry changes during stratification Although a slow process, groundwater thru-flow perhaps more important than previously thought *Total N assumed to be conservative in anoxic hypolimnion (no 1o production), limited denitrification

  13. Sulfate Reduction Mulch Mulch + P P 20 µg L-1

  14. pH change in mesocosms

  15. Trends of historical lakes

  16. 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. Light limitation of photosynthesis Euphotic depth

  18. 20µg/L phosphorus, 20µg/L & mulch Mulch only Primary production Phosphorus, nitrogen, carbon and light may all limit phytoplankton production.

  19. Conceptual models of lakes Surface waters Stockton Black Diamond Blue Waters Ewington Primary production Sulfate reduction Winter groundwater Summer groundwater

  20. 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.

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