Wetlands for remediation of acid-mine drainage Alyssa Shiel

Overview Define acid-mine drainage Define acid-mine drainage Constructed wetlands as passive treatment systems Constructed wetlands as passive treatment systems Acid-tolerant aquatic plants Acid-tolerant aquatic plants Benhar ironstone mine spoil in Central Scotland Benhar ironstone mine spoil in Central Scotland

Acid-mine drainage Drainage flowing from or caused by mining that is typically highly acidic with elevated metal levels Drainage flowing from or caused by mining that is typically highly acidic with elevated metal levels Increased concentrations of cadmium, nickel, lead, zinc, copper and sulfates Increased concentrations of cadmium, nickel, lead, zinc, copper and sulfates The primary source of freshwater metal contamination The primary source of freshwater metal contamination Associated with land contamination and sparse vegetation Associated with land contamination and sparse vegetation May leach into surrounding watercourses May leach into surrounding watercourses

Acid-mine drainage Lowers pH, between 2.0 and 3.0 Lowers pH, between 2.0 and 3.0 Contaminates water with oils, cyanides, acids and alkalies Contaminates water with oils, cyanides, acids and alkalies Reduces buffering capacity Reduces buffering capacity Alters phosphorus availability Alters phosphorus availability Solubilizes some heavy metals Solubilizes some heavy metals

Constructed wetlands as treatment systems Viable treatment system for many mining regions of the world Viable treatment system for many mining regions of the world Passive, low-cost remediation Passive, low-cost remediation Goals Goals Removal of iron from the water column Removal of iron from the water column Removal of other metals Removal of other metals Sulfate reduction Sulfate reduction Alleviation of extreme acidic conditions Alleviation of extreme acidic conditions

Acid tolerant aquatic species Typha sp. (cattails) Typha sp. (cattails) Sphagnum dominates Sphagnum dominates Found to accumulate iron Found to accumulate iron Green algaes Green algaes Chlamydomonas aplanata (<3) Chlamydomonas aplanata (<3) Blue-green algaes Blue-green algaes Spirulina nordstedtii (4.9) Spirulina nordstedtii (4.9) Diatoms Diatoms Navicula nivalis (3.0) Navicula nivalis (3.0) (M. Kelly, 1988)

(Heal and Salt, 1999) Acidic metal-rich drainage from reclaimed ironstone mine spoil 12 month evaluation of a constructed wetland system Benhar ironstone spoil heap in Central Scotland

Benhar before remediation

Ironstone spoil Characterized by pH 2.7 and 247 mg/l total Fe Characterized by pH 2.7 and 247 mg/l total Fe Highly acidic with elevated metal concentrations Highly acidic with elevated metal concentrations Acidity may mobilize iron, manganese, aluminum and other metals Acidity may mobilize iron, manganese, aluminum and other metals Although mining ceased early in the 20th Century, the Bing has remained mostly unvegetated due to the highly acidic and infertile spoil Although mining ceased early in the 20th Century, the Bing has remained mostly unvegetated due to the highly acidic and infertile spoil Mine drainage was polluting a small watercourse which leads into the River Almond Mine drainage was polluting a small watercourse which leads into the River Almond

Ironstone spoil Iron pyrites in ironstone and coal spoil are oxidized to form sulfuric acid when exposed to air and water Iron pyrites in ironstone and coal spoil are oxidized to form sulfuric acid when exposed to air and water At pH above 4, acid production proceeds slowly and is controlled by the rate of oxygen diffusion into the spoil At pH above 4, acid production proceeds slowly and is controlled by the rate of oxygen diffusion into the spoil Below pH 4, an alternative oxidation pathway exists involving the bacterium Thiobacillus ferrooxidans Below pH 4, an alternative oxidation pathway exists involving the bacterium Thiobacillus ferrooxidans

Treatment Creating an aesthetically-pleasing landform Creating an aesthetically-pleasing landform Treatment with dried pelleted sewage sludge, limestone and peat Treatment with dried pelleted sewage sludge, limestone and peat After which trees were planted Betula pubescens and Alnus glutinosa (common alder) After which trees were planted Betula pubescens and Alnus glutinosa (common alder) Construction of settling pond and surface flow wetland to receive spoil drainage Construction of settling pond and surface flow wetland to receive spoil drainage Mushroom compost substrate Mushroom compost substrate Cattails (Typha latifolia). Cattails (Typha latifolia).

Reclamation Acidity, iron, manganese and aluminum concentrations declined Acidity, iron, manganese and aluminum concentrations declined Removed on average 33% of acidity and 20-40% of metal inputs Removed on average 33% of acidity and 20-40% of metal inputs Removal rates decreased in the winter Removal rates decreased in the winter Enabled vegetation establishment Enabled vegetation establishment Effect was spatially variable Effect was spatially variable

Summary Constructed wetlands offer an inexpensive, passive treatment for acid-mine drainage Constructed wetlands offer an inexpensive, passive treatment for acid-mine drainage Several acid-tolerant aquatic species including Sphagnum and Typha sp. Several acid-tolerant aquatic species including Sphagnum and Typha sp. Benhar mine spoil Benhar mine spoil Site history Site history Treatment Treatment Results Results