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Regional assessment of the current extent of acidification of surface waters in Europe and North America

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Kari Austnes, Julian Aherne, Jens Arle, Marina Čičendajeva, Suzanne Couture, Jens Fölster, Øyvind Aaberg Garmo, Jakub Hruska, Don Monteith, Max Posch, Michaela Rogora, James Edward Sample, Brit Lisa Skjelkvåle, Sandra Steingruber, John L. Stoddard, Rafał Ulańczyk, Herman Van Dam, Manuel Toro Velasco, Jussi Vuorenmaa, Richard Frederic Wright, Heleen de Wit


The current status of surface water acidification related to air pollution in Europe and North America has been assessed using country reports, monitoring data, critical loads and exceedance data, acid sensitivity and deposition maps, and data reported under the European Commission’s Water Framework Directive (WFD). Acidification is still observed in many countries, but the extent and severity vary. Maps of acid sensitivity and deposition suggest that surface water acidification is present in regions and countries for which no data or reports were delivered for the current assessment. Existing national monitoring varies in the ability to assess the spatial extent of acidification and the recovery responses of acidified sites. The monitoring requirements under the European Union’s National Emission Ceilings Directive are expected to reverse the recent decline in the number of monitoring sites observed in some countries. The information reported under the WFD is currently of limited value in assessing the extent of acidification of surface waters in Europe. Chemical recovery in response to reductions in acid deposition can be slow, and biological recovery can lag severely behind. Despite large and effective efforts across Europe and North America to reduce surface water acidification, air pollution still constitutes a threat to freshwater ecosystems.