Modeling Past and Future Acidification of Swedish Lakes
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Modeling Past and Future Acidification of Swedish Lakes Filip Moldan, Bernard J. Cosby, Richard F. Wright
Received: 15 May 2012 / Revised: 17 September 2012 / Accepted: 8 November 2012 / Published online: 4 January 2013
Abstract Decades of acid deposition have caused acidification of lakes in Sweden. Here we use data for 3000 lakes to run the acidification model MAGIC and estimate historical and future acidification. The results indicate that beginning in about 1920 a progressively larger number of lakes in Sweden fell into the category of ‘‘not naturally acidified’’ (DpH[0.4). The peak in acidification was reached about 1985; since then many lakes have recovered in response to lower levels of acid deposition. Further recovery from acidification will occur by the year 2030 given implementation of agreed legislation for emissions of sulphur (S) and nitrogen (N) in Europe. But the number of catchments with soils being depleted in base cations will increase slightly. MAGIC-reconstructed history of acidification of lakes in Sweden agrees well with information on fish populations. Future acidification of Swedish lakes can be influenced by climate change as well as changes in forest harvest practices. Keywords
Sweden Lake Acidification Model
INTRODUCTION Decades of acid deposition have caused acidification of lakes and streams in large areas of Sweden (Almer et al. 1974). Ecological effects include impairment and loss of thousands of fish populations (Tammi et al. 2003). Since the mid-1980s international agreements conducted as part of the United Nations Economic Commission for Europe (UN-ECE) Convention on Long-Range Transboundary Air Pollution (CLRTAP) have achieved substantial reductions in the emissions of sulphur (S) and nitrogen (N) compounds to the atmosphere (UNECE 2012). In response, lakes in Sweden (Wilander and Fo¨lster 2007) and
elsewhere in Fennoscandia have begun to recover from acidification (Skjelkva˚le et al. 2001). The most recent protocol to the Convention, the Gothenburg protocol, entailed nearly 80 % reduction in S emissions from peak years in the late-1970s, and has been largely implemented by the target year 2010. Currently negotiations are underway in the CLRTAP to achieve yet greater reductions in emissions to be implemented by the year 2020. In 1999, Sweden adopted 15 Environmental Quality Goals as part of an environmental policy for a sustainable Sweden (http://www.sweden.gov.se/sb/d/5775). These are to be achieved by the year 2020. One of these is ‘‘Natural Acidification Only’’. Determination of natural acidification of lakes necessitates assessment of the chemical status in pre-industrial times. The official Swedish criterion of anthropogenic acidification is that the decrease in lake pH relative to pre-industrial status be less than 0.4 pH units (Fo¨lster et al. 2007). This criterion is based primarily on analyses of lake water chemistry and biological status of two organism groups; fish, and littoral invertebrate fauna (Fo¨lster et al. 2007). During the past 20 years, Swede
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