Liming placed in a long-term perspective: a paleolimnological study of 12 lakes in the Swedish liming program |
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Authors: | Matilda Guhrén Christian Bigler Ingemar Renberg |
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Affiliation: | 1.Department of Ecology and Environmental Science,Ume? University,Ume?,Sweden |
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Abstract: | Since the 1970s liming has been practised on a large scale in Sweden to mitigate acidification and several thousand lakes
and streams are limed repeatedly. The Swedish monitoring program ISELAW (Integrated Studies of the Effects of Liming Acidified
Waters) studies the long-term effects of liming. This paper summarizes the paleolimnological part of the program. Sediment
cores from 12 lakes were analysed to study the development of the lakes from pre-industrial time until the present, and address
questions about natural conditions and the effects of early human impact, acidification, and liming. Diatoms were used to
reconstruct the pH history and to study shifts in species composition due to acidification and liming. Analyses of lead and
spheroidal carbonaceous particles were applied for indirect dating and as indicators of the atmospheric deposition of pollutants
associated with acid rain. Pollen analysis was performed in eight of the lakes to study the vegetation and agricultural history.
The natural pH (prior to human disturbance) was between 5.3 and 6.5 in the eight lakes where the complete post-glacial sediment
sequence was recovered. Pollen from anthropochores and apophytes indicated early agricultural land use in the vicinity of
the lakes from 1000 to 2000 years ago, and pH increased with land use in six of these lakes. Five of the lakes have been acidified
during recent decades, and in all 12 lakes some effects of liming were recorded in the diatom assemblage. The lakes show different
responses to liming, including a return to a pre-acidification diatom composition or a shift to a state previously not recorded
in the lake’s histories. This study accentuates the complexity of biological response to acidification and liming, and highlights
the importance of historical perspectives to assess the current state of a lake’s ecosystem and to establish adequate restoration
goals. |
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Keywords: | Acidification Liming Diatoms Water quality Paleolimnology Lake sediments |
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