Influence of Acid Rain on Weathering Rates

Abstract

Acid rain has resulted in the acidification of lakes and streams over large areas of Europe and North America, and has been implicated in the recent widespread forest dieback in Europe. Chemical weathering releases base cations to the soil cation-exchange complex and thus represents the ultimate defense against acid rain. Determination of weathering rate for whole catchments is required to predict future acidification of soils and surface waters. Weathering rate can be estimated by several independent methods which range from laboratory experiments with pure minerals to input-output budgets at whole catchments. Inasmuch as congruent dissolution of many rock-forming minerals involves the consumption of hydrogen ions, acidification of soils by acid rain can be expected to result in an increase in weathering rate. Evidence from field and laboratory experiments, however, is so far insufficient to judge whether the rate of chemical weathering does indeed change due to the deposition of acid from the atmosphere. Recent models of soil and water acidification suggest that acid deposition causes only small changes in the pH of soil solution, and thus changes in weathering rate due to changes in soil chemistry may be minor. Research on the influence of acid rain on weathering rates has been given high priority in both Europe and North America.