A palaeolimnological test of the influence of Norway spruce (Picea abies) immigration on lake-water acidity

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Abstract
The effect of recent land use and subsequent vegetation changes per se on surface-water acidity is difficult to ascertain because of the complicating factor of enhanced levels of anthropogenic acid deposition that occurs at the same time as land-use changes. Expansion of conifers is a major contemporary vegetation change in Sweden and other countries. The immigration of Norway spruce (Picea abies (L.) Karst.) into Sweden about 3000 years ago provides, however, a suitable means of assessing the acidification ability of spruce per se on surface waters. Pollen analysis was used to identify the arrival of spruce in the catchments of eight acid-sensitive Swedish boreal-forest lakes. pH and dissolved organic carbon (DOC) were inferred from diatom assemblages for time periods covering some hundred years before and after the establishment of spruce. Redundancy analysis (RDA) was used to assess whether catchment vegetation had significant effects on the diatom assemblages. At four sites there were significant changes in the diatom assemblages associated with the arrival of spruce, but none of the lakes acidified. At three sites, however, diatom- inferred DOC increased with the arrival of spruce, probably as a result of the accumulation of raw humus.