Acid Rain Causes Regional Effects Treatment

Acid Formation and Deposition Release of SO2 and NOX by anthropogenic activities can result in acid formation, deposition SO2 reacts in the atmosphere to form H2SO4 (sulfuric acid) NOX react in the atmosphere to form HNO3 (nitric acid) oxidation SO2 oxidation NO, NO2, N2O H2SO4 HNO3

Acid Rain: Source Fossil Fuel Burning Sulfur: Coal When burned, coal sulfur oxidizes to SO2(g) Release of SO2 Atmospheric H2SO4 Dry acid particulates (sulfate aerosols) Nitrogen: Combustion (any) Any combustion process involving air will form NOX Automotive exhaust Power plant emissions Forest fires

What is acidity of Natural Rain? Carbonic acid Dissolution of atmospheric CO2 into cloud droplets forms dissolved carbonic acid (H2CO3), giving some weak acidity (clean rainwater pH ~ 5.6) CO2 + H2O = H2CO3 H2CO3 = HCO3- + H+ (H+ gives acidity) Weak acids = Carbonic acid, most organic acids

pH Scale pH = -log[H+]

Acid Rain distribution in the US (1955 - 1999) pH of clean rainfall ~5.6

Sources of Sulfur Pollution in the US Data from 1998 Most emissions are from electric utilities Coal burning Fuel Combustion (Heating) (3%) Other (8%) Transportation (7%) Industrial Sources (15%) Electric Utilities (67%)

Sources of Sulfur Pollution in the US Transportation (5%) Data from 2002 Total emissions down 34% since 1990 Most emissions are from electric utilities Coal burning Other (3%) Industrial Sources (8%) Fuel Combustion (84%) - 70% of this is electrical utilities

Sulfate Deposition Animation National Atmospheric Deposition Program

Sources of NOX Pollution in the US Data from 1998 Most emissions are from transportation Nitrogen oxide emissions from automobiles Electric Utilities (25%) Other (5%) Fuel Combustion (Heating) (5%) Transportation (53%) Industrial Sources (12%)

Sources of NOX Pollution in the US Other (2%) Fossil Fuel Combustion* (34%) Data from 2002 Total: 16% decrease since 1990 Most emissions are from transportation Nitrogen oxide emissions from automobiles Transportation (59%) Industrial Sources (5%) *22% electrical; 12% heating fuels

NO3 and NH4 Atmospheric Deposition Animations

Results of Acid Rain Direct damage to surface materials Stone monuments (especially limestone, marble) Paint Plastics Ecological damage Acidification of watersheds Lakes Rivers Groundwater Damage to soil nutrient capacity Decline of forest growth, health

Geology and Acid Rain Effects Natural buffering Aquifer rock and surface exposed rock can naturally buffer acidity, depending on rock composition Carbonate rock: strongly buffers pH, neutralizes acidity from rain CaCO3 + H+ = Ca2+ + HCO3- (a tiny bit of limestone dissolves) Limestone rock Will neutralize acid rain, ameliorating the effects of acid deposition Silicate rock Does not react with acids as quickly, will not provide much buffering capacity, does not neutralize acid deposition

Areas Sensitive to Acid Rain in the US Sensitive areas Exposed silicate bedrock No significant carbonates Other areas Carbonates (mostly limestone) exposed at surface

Effects of Acid Deposition: Soils Nutrient Leaching Acids mixing into soil solutions will be neutralized, at first… Nutrient cations (Mg2+, Ca2+, K+, Na+,…..) will leach from soil organic matter and minerals Cations are released into solution H+ (acidity) is taken up by soil particles, organic acids in soil Leached nutrients will be washed away in water as it drains down through soil layers into groundwater, or into surface water channels Long term effects: Leaching of mineral cations = starvation of soil, plants Exhaustion of soil buffering capacity (ability to neutralize acid deposition)

Caused by soil exhaustion through acid leaching of nutrients “Forest decline” Caused by soil exhaustion through acid leaching of nutrients Slow onset Encroaches over decades Will require decades to centuries to recover Smoky Mtns in Eastern USA Black Forest, Germany China

Acidification of Lakes Like soils, lakes can buffer pH Depends on bedrock beneath lake Limestone bedrock has greater buffering capacity Sustained acidification can exhaust buffering capacity of lake water, surface sediments… Lake pH drops once buffering capacity is used up Dramatic declines in aquatic life (insects, molluscs, fish) Requires decades to centuries to recover Remediation Expensive, only partially effective, must be repeated Addition of lime (CaO) to lakes is a common method

Acidification of Lakes Geochemical / Ecological Effects Aluminum toxicity Al is very insoluble at neutral pH In low-pH lake water (<5), thouh, Al solubility increases Toxic: dissolved Al interferes with gill function, O2 uptake Shelled animals At lower pH, more difficult to build chitinous shells, calcite tests Crayfish shells soften below pH ~5.1

Acidification Effects on Lakes (Norway species)

Acid Mine Drainage (AMD) Mining for base metal sulfide minerals Cd, Cu, Pb, Zn, Ag, Au, Pt, others…. Economic ore minerals of these metals are often hosted in pyritic rock Excavation and dumping of mine waste (spoil) at the surface Produces large volumes of pyritic rock at surface Opens passages into subsurface rock, allowing air, water flow Long term effects: Oxidation of sulfide minerals by bacteria Flux of acidic drainage from discontinued mine sites http://www.npr.org/templates/story/story.php?storyId=7812258

Yellow Dog Plains Sulfide Mine (Upper Peninsula, MI) High grade nickel and copper deposits, hosted in sulfide 2006: Kennecott Minerals applies for air discharge, groundwater discharge, mining, land use lease and exploration lease permits from MDEQ Permits granted in 2008, but US EPA must still approve underground injection control permit & National Wildlife Foundation is challenging the permitting

Thiobacillus ferrooxidans Acidophilic bacterium (lives at pH < 2) Fixes C by oxidizing Fe(II) and S(-II) in pyrite Produces acidity Very common

Biological Sulfur Transformations Weathering of Pyrite (FeS2) Environmental Effects… The net reaction 4FeS2(pyrite) + 15CO2 + 23H2O => 8SO42- + 2Fe2O3(hematite) + 15”CH2O” + 16H+ Produces four moles of acid per mole of weathered pyrite. In natural weathering, low-pyrite rocks are slowly weathered and thus do not yield significant acidification of soils, rivers But mining for high-concentration pyrite rocks produces large amounts of exposed pyrite in one place Pyrite weathering in air Wholesale acid production (Acid Mine Drainage)

AMD Effects Red or orange color is due to particulates of oxidized Fe compounds (rust) in the water

AMD Effects

Iron Mountain Mine, CA Presently a Superfund site, former site of base metal mining… now a massive AMD problem ca.water.usgs.gov/water_quality/acid/ Nordstrom and Alpers (1999)

Iron Mountain Mine, CA Declared a Superfund site in 1983, former site of base metal mining… now a massive AMD problem Runoff from mine Inside the mine

Iron Mountain Mine, CA Waters draining from mine area are pH < 1 Lowest recorded pH values on Earth (-3.5) Highest dissolved metal contents ever recorded (1000s ppm) Mine drainage Keswick Reservoir

Iron Mountain Mine, CA Highly contaminated mine runoff, sediment Mine sediment (1% Cu by weight) Keswick Reservoir

Photo from EPA Superfund 25th Anniversary Water treatment plant was built in 1994 *>1.3 billion gallons of acid mine drainage have been treated so far