Trends in surface water acidification in Europe and North America (1989-1998)

During the last 20 years, emission reductions in Europe and North America h ave resulted in decreased atmospheric S-deposition of up to 50%, while N-de position has stayed almost constant. Data from 98 ICP Waters sites were tes ted for trends in concentrations of major chemical components for the 10-ye ar period 1989-1998 using the nonparametric seasonal Kendall test. The site s were grouped into regions and types for meta-analysis. All of the regions had highly significant downward trends in SO42-* concentrations. Nitrate c oncentrations, on the other hand: show no regional patterns of change. Conc entrations of base cations declined in most regions. All regions showed ten dencies of increasing DOC. The low ANC sites showed the largest rates of re covery. Neither the high NO3- or low NO3- groups of sites exhibited signifi cant trends in NO3- concentrations. Alpine (non-forested) sites show clear and consistent signals of recovery in ANC and pH, and appropriate (relative to SO42-* trends) rates of base cation decline.