Acid Rain and Effects on Plant Life

1. Acid Rain and Effects on Plant Life A presentation by: Catharine Merli

2. Brief Overview • Introduction: What is acid rain, and general background • Formation of Sulfuric and Nitric Acids • The main culprits of acid rain damage • Effects to plants • harm to leaf tissues • Decreased minerals • Harmful effects to microbes and effects on nutrient availability • Conclusions / Summary

3. Introduction: • Acid rain = Increased acidity in precipitation, which may include rain, fog or snow • First discovered in 1800’s by Angus Smith • Natural rain is naturally acidic at pH of 5.0-5.6 CO2 (g) + H2O (aq) H2CO3 (aq)

4. IntroductionContinued: • Two main culprits of acid rain • SO2 • NOx - Caused mainly by burning of fossil fuels - COAL • These two main culprits react within the atmosphere to form sulfuric and nitric acids. • 1990 Clean Air Act Amendments • More enforcement of emissions of culprits of acid rain

5. Sources of Acid Rain Culprits For More Information Please Visit Environmental Protection Agency Website

6. Formation of H2SO4 • Radical Oxidation of SO2 to H2SO4, • Gas Phase SO2 (g) + .OH (g) --> HO-.S-O­2 (g) HO-.S-O­2 (g) + O2 (g) --> HOO. (g) + SO3 (g) SO3 (g) + H2O (g) --> H2SO4­ (g) Courtesy of Dr. Kelly, ESU Chemistry Department

7. Formation of H2SO4 (continued) • Liquid Phase SO2 (g) <=> SO2 (aq) SO2 (aq) + 2 H2O <=> H3O+ (aq) + HSO3-1 (aq) HSO3-1 (aq) + H2O2 (aq) or O3 <=> HSO4-1 + H2O Courtesy of Dr. Kelly, ESU Chemistry Department

8. Formation of HNO3 • Another atmospheric oxidation reaction Gas Phase NO2 (g) + .OH (g) --> HNO3 (g) Liquid Phase NO2 (g) <=> NO2 (aq) NO2 (aq) + O3 (aq) --> NO3-1 (aq) + O2 (aq) Courtesy of Dr. Kelly, ESU Chemistry Department

9. Sulfuric Acid: 3D Model

10. Nitric Acid: 3D Model

11. What Does This Mean for plants? • Increased acidity in soil and in water on plant surfaces can adversely effect plants • Direct harm to leaf tissues: cuticle and wax layers • Decreased minerals in soil / decreased nutrient uptake • Harmful effects to microbes in soil and lichens, effecting nutrient availability All of these factors add to the stress of plants and prolonged exposure may lead to plant death

12. Direct effects to Plant Surfaces • Acid precipitation can directly effect tissues on plant surfaces • Study on white clover exposed to acid mist treatments of pH4 or lower • Disabled stomata function, leading to increases in drying rate, and therefore increase in drought suseptibility

13. Direct effects to Plant Surfaces (cont.) • Decreases in production of flowers in Acomastylis rossii (Apple blossoms) exposed to artificial acid precipitation • Many plants also showed decreases in leaf production • Probable cause: oxidative damage to leaves especially pores, reducing CO2 intake • Serious detriment to cuticle wax formation

14. Direct effects to Plant Surfaces (cont.) • -Sitka Spruce outer wax on cuticle: effects after acid rain exposure • shown to greatly reduce freezing tolerance leaving trees vunerable • Wax damage may be followed by cuticle damage which would allow entrance of acidic pollutants and may cause chlorotic damage leading to decreased photosynthetic ability -

15. Leachingof Nutrients/ Minerals • Displacement of nutrients, especially, Ca2+, Mg2+, and other inorganic ions due to mostly ion exchange with H+ from acids • Cations migrate through cuticle by interacting with negative charges • Anions in through pores with in the cuticle

16. Leachingof Nutrients/ Minerals (continued) • Leaching of minerals due to acid rain also takes place in the soil • Cation exchange • Reduces the amount of available nutrients for plants to utilize for normal functioning • Mg2+ leaching in soils with lichens due to elevated H+ can effect cation ratios within the lichen • May be useful biomarker for acid deposition

17. Calcium Depletion in Plasma Membranes • Displacement of Ca2+ by H+ • Calcium plays important role in plasma membrane stability especially in conifers • Removal destabilizes membrane • Leads to decrease in freeze tolerance

18. Microbial effects on Nutrients • Bacteria play important role in nutrient cycling, especially nitrogen • Through Break down of organic matter • Some can fix atmospheric N • 12 year study on soil bacteria in northern Europe • Significant decreases in respiration rates • Some findings indicated possible adaptibility, but these effects still may leave ecosystems vunerable

19. Microbial effects on Nutrients (continued) • Physiological effects noted in cyanobacteria found in some lichen species in tundra ecosystems • Nitrogenase activity, when treated with sulfuric and nitric acid solutions decreased up to 53% and 96% respectively • Delicate balance of tundra ecosystem may be jeopardized by loss of this nutrient flow

20. One Extra Point • In contrast to nutrient leaching caused by acid rain, continual deposition of acid precipitation can also cause nutrient loading. • Areas with large occult deposition have seen increase in nutrient load, in the form of nitrate, ammonium, and sulphate • Ion concentrations in fog were recorded up to 60-85% higher in air masses coming from the east vs. from the west (in Europe study)

21. Summary • Acid Rain caused by influxes of • SO2 • NOx • In turn are oxidized in atmosphere to sulfuric and nitric acid • Overly acidic precipitation has a variety of effects on plant life

22. Conclusion • The effects on plants due to acid rain range in severity • Depends on species • Can depend on existing environmental conditions • 1990 CAAA have lead to reductions in SO2 output, but NOx levels have remained steady • Overall concern • Stress on stability and increased vulnerability to primary producers of the planets ecosystems