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Submitted to: Mcgraw-Hill Encyclopedia for Science
Publication Type: Other Publication Acceptance Date: 5/20/2001 Publication Date: 7/9/2001 Citation: Schnabel, R.R. 2001. Acid rain. Mcgraw-Hill Encyclopedia for Science. p. 61-63. Interpretive Summary: Technical Abstract: Acid rain is a process in which sulfur and nitrogen gases produced by industry and automobiles are transformed into acids in the atmosphere, transported from their source and deposited on terrestrial and aquatic ecosystems. The effect of acid deposition on a particular ecosystem depends largely on its acid sensitivity, its acid neutralization capability, and the amount of acid added to the system. Predictable changes in water chemistry, as the pH of surface waters decreases, include decreased alkalinity, decreased buffering capacity, and increased concentrations of aluminum, magnesium, and iron. Such changes in water chemistry generally result in decreased diversity of aquatic species and reduced productivity. In forest ecosystems, lower pH inhibits root growth making trees more susceptible to drought. Excess nitrogen in leaves and sap attracts insects. Less calcium uptake reduces a trees ability to wall off injuries, making it more susceptible to insects and disease. Acid deposition also makes trees less cold tolerant. However, forest trees are also continuously stressed by competition for light, water, and nutrients, by disease organisms, by extremes in climate, and by atmospheric pollutants making cause and effect relationships difficult to establish. The impact of acid deposition on terrestrial and aquatic ecosystems is not uniform. While increases in acid deposition may stress some ecosystems and reduce their stability and productivity, others may be unaffected. With current levels of acid deposition, the impact on both aquatic and terrestrial ecosystems is strongly influenced by the acid sensitivity of forest soil and soils surrounding aquatic ecosystems. |
