STEEP DECLINES IN ATMOSPHERIC BASE CATIONS IN REGIONS OF EUROPE AND NORTH-AMERICA

HUMAN activities have caused marked changes in atmospheric chemistry o ver large regions of Europe and North America. Although considerable a ttention has been paid to the effects of changes in the deposition of acid anions (such as sulphate and nitrate) on terrestrial and aquatic ecosystems1-7, little is known about whether the concentrations of bas ic components of the atmosphere have changed over time8,9 and what the biogeochemical consequences of such potential changes might be. In pa rticular, there has been some controversy8-12 as to whether declines i n base-cation deposition have countered effects of recent reductions i n SO2 emission. Here we report evidence for steep declines in the atmo spheric concentrations of base cations (sum of non-sea-salt Ca2+, Mg2, K+ and Na+) over the past 10 to 26 years from high-quality precipita tion chemistry records in Europe and North America. To varying but gen erally significant degrees, these base-cation trends have offset recen t reductions in sulphate deposition in the regions examined. The obser ved trends seem to be ecologically important on decadal timescales, an d support earlier contentions8-10 that declines in the deposition of b ase cations may have contributed to increased sensitivity of poorly bu ffered ecosystems.