Acid Lakes from Lignite Mines Dan Henderson

Lignite  Brown/soft coal.  Used for steam electric power generation.  Mined in open pits.  Production declining in most countries.

____ ____ ____ ____Where  Germany (Lusatia)  Russia  United States (SE)  Australia  Greece

___ _____ ____ ___ _____ ____ ___ _____ ____ ___ _____ ____ Acid Mining Lakes (AML)  Artificial Lakes form in open pits when mining ceases. Groundwater recharge Groundwater recharge Stream inputs Stream inputs  Natural Lakes receive Acid Mine Drainage (AMD) from nearby mines.  pH as low as 2 recorded in some lakes.

___ ___ _______ ___ ___ _______ ___ ___ _______ ___ ___ _______ Acid Mine Drainage  Outflow of acidic water from mines.  High Concentrations of sulfate and iron  Result from pyrite (iron sulfide) and other sulfides from mine tailings oxidizing in water.  Bacteria found in rock may promote acidification (acidophiles).  Vary depending on local geology.

Effects on Lake Chemistry  Metals are more soluble at lower pHs.  High concentrations of dissolved Fe. Light Attenuation Light Attenuation  High concentrations of Al. May limit P May limit P  May also increase levels of Mn, Zn, As, and Pb.  Depend on acid neutralizing capacity.

Effects on Vegetation  Low pH Limits species diversity and richness.  Many plants cannot tolerate high metal concentrations.  Tolerant species may thrive.  Vegetation may increase surface concentrations of metals by evapotranspiration.

Phytoplankton  Development not directly related with pH decrease.  Decrease related to limitations of inorganic carbon, phosphorus, and underwater light.

Effects on other Biota  Limits lake food for birds and wildlife that find food in lake.  Low pH decreases fish diversity and richness.  Insect larvae and crustaceans not likely to be found below pH of 4.  Usually enough silica still present for diatom development.

Why treat AMLs  Ecosystem Health  Wildlife  Recreation  Aesthetics

Main Treatment Methods  Preventative measures best approach.  Altering mine site hydrology.  Sulfate reducing bacteria.  Application of organic wastes.  Application of alkaline materials (Limestone).  Wetlands.

Sulfate reducing bacteria  Good method for treatment.  Require anaerobic conditions which may be limited in well mixed lakes.  Increase alkalinity and help eliminate Fe and sulfate.  Most are heterotrophs which require and may be limited by organic carbon.

Biobags (Organic Wastes)  Bags of organic material placed into lakes.  Form anoxic microbial reaction compartments.  Increase organic carbon and P concentrations which promote sulfate reducing bacteria.  Increase primary production by increasing nutrients. (Eutrophication)  Use local organic material.

Application of Limestone and/or Phosphorus  Limestone increases pH levels needed for biological growth.  Reduces metal concentrations by making them less soluble.  Phosphorus is frequently limited in AMLs.  Phosphorus promotes phytoplankton development and biological growth.

Wetlands  Used extensively in last two decades to remove metals from AMD.  Precipitation of sulfides.  Roots of wetland plants release oxygen and form Fe plaque taking other metals with it.  Biological Uptake.

More treatment methods  Inundation  Bacteriacides for acidophiles  Coating pyrite to prevent oxidation  More needed

Progression  Some lakes may take decades to recover.  Allochthonous alkalinity of river water will promote progress.  Bottom of food chain must be established first to support the rest.  Ultimate goal is to establish fish populations.

Results  All methods have been shown to work.  Best methods are very site specific.  A combination is usually the best approach.  Certain species found to recover much faster than others.  Neutralized AMLs have much greater species richness.

Importance  Treatment of AMLs may produce circum- neutral lakes much faster than if left alone.  May prevent the loss of diversity.  Treated lakes may be used for recreation and promote ecosystem health.

Research Needed  A low percentage of AMLs have been studied.  Recovery methods can be expensive and time consuming.  AMLs continue to grow in number even though mining is in decline.  Many effects of AMD may yet to be identified and understood.

Conclusion  Raising pH to near circum-neutral level is how most AMLs are treated, but this is not sufficient to meet all ecological demands.  Effects on ecosystems, treatment processes, and recovery times all vary greatly.  Lake acidification is a worldwide problem and limnologists are needed to continue to refine, identify, and implement new strategies for remediation.

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