Effects of acidity in precipitation on terrestrial vegetation

Abstract

Over the last several decades rain in the Northeastern United States has become more acidic presumably as a result of anthropogenic inputs of SOX and NOX to the atmosphere and their conversion to H2SO, and HNO3. Present experimental results suggest that acidic precipitation would initially affect organisms on leaf surfaces and epidermal cells of leaves of higher plants. More internal cell layers would be affected with increasing duration or frequency of exposure. Differences in responses of plant foliage among plant species to acidic precipitation appear to be due to the degree of leafwetting and differences in responses of leaf cells to low pH rain. Moreover, within the same plant, particular structures or cell types may be more sensitive than others. If the United States is to utilize coal reserves for electric power generation that might increase rainfall acidity in the future, an assessment of the impact that acidic rain might have on terrestrial vegetation is necessary. In one experiment, field-grown soybeans were exposed to short duration rainfalls of either pH 4.0, 3.1, 2.7, or 2.3 to provide inputs of 50, 397, 998, or 2506 μeq•of H+, respectively, above ambient levels throughout the growing season. Control plots received only ambient rainfalls. These additional H + decreased seed yield, 2.6, 6.5, 11.4, and 9.5%, respectively. A treatment response function determined between H + treatments and seed yield was y = 21.06 − 1.01 log x had a correlation coefficient of − 0.90. Researchers must design additional experiments with adequate experimental controls to assess the impact that acidic rain, at the present pH levels of 3.0 to 4.0 or at anticipated worst-case levels, that could occur if the acidity of rain should increase. Only a holistic view of the impacts that acid precipitation may have on vegetation will enable optimal energy and environmental policy decisions to be made.