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Regional trends in aquatic recovery from acidification in North America and Europe


Rates of acidic deposition from the atmosphere (‘acid rain’) have decreased throughout the 1980s and 1990s across large portions of North America and Europe1,2. Many recent studies have attributed observed reversals in surface-water acidification at national3 and regional4 scales to the declining deposition. To test whether emissions regulations have led to widespread recovery in surface-water chemistry, we analysed regional trends between 1980 and 1995 in indicators of acidification (sulphate, nitrate and base-cation concentrations, and measured (Gran) alkalinity) for 205 lakes and streams in eight regions of North America and Europe. Dramatic differences in trend direction and strength for the two decades are apparent. In concordance with general temporal trends in acidic deposition, lake and stream sulphate concentrations decreased in all regions with the exception of Great Britain; all but one of these regions exhibited stronger downward trends in the 1990s than in the 1980s. In contrast, regional declines in lake and stream nitrate concentrations were rare and, when detected, were very small. Recovery in alkalinity, expected wherever strong regional declines in sulphate concentrations have occurred, was observed in all regions of Europe, especially in the 1990s, but in only one region (of five) in North America. We attribute the lack of recovery in three regions (south/central Ontario, the Adirondack/Catskill mountains and midwestern North America) to strong regional declines in base-cation concentrations that exceed the decreases in sulphate concentrations.

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Figure 1: Lake and stream monitoring sites.
Figure 2: Regional acidification trend results.


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We thank the LRTAP Working Group on Effects for their support; this Working Group supports the production of international, quality-controlled, comparable data. We also acknowledge the work of the ICP Programme Centre at the Norwegian Institute of Water Research (NIVA), where the data are collated, verified and archived, and thank T. J. Sullivan and M. R. Church for comments and suggestions. This work was supported by the US Environmental Protection Agency.

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Correspondence to J. L. Stoddard.

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Stoddard, J., Jeffries, D., Lükewille, A. et al. Regional trends in aquatic recovery from acidification in North America and Europe. Nature 401, 575–578 (1999).

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