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The nitrogen-fixing lichen Pettigera aphthosa (L.) Willd. was treated under semi-natural conditions with simulated rain containing different combinations of ammonium, nitrate and sulphuric acid. Nitrogen in neutral solution had no negative effect on the nitrogen fixation rate. Sulphuric acid had a negative effect on nitrogen fixation rate, especially in combination with ammonium. The results could suggest an explanation for the sudden decline of P. aphthosa in southern Sweden. Published in New Phytologist, volume 120, issue 1, on pages 99 - 103, in 1992.
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Conclusions: Elevation, slope and the percentages of bogs and fens in a landscape influence the degree to which mid-boreal lakes are sensitive to acidic deposition orignating from nearby mining operations. Thresholds/Learnings: Synopsis: This study evaluates the acid sensitivity of lakes in Saskatchewan within ~300km of Fort McMurray. The study area is downwind of atmospheric emissions sources from regional oil sands mining operations and there is concern that the lakes may be threatened by acidification. A helicopter sampling program was implemented in late September 2007 and 2008 to measure 16 chemical variables (e.g., Ca, Mg, Na, pH) and 15 environmental variables (e.g., latitude, elevation, slope, percent bog,...
Much of the biogeochemical cycling research in catchments in the past 25 years has been driven by acid deposition research funding. This research has focused on vulnerable base-poor systems; catchments on alkaline lithologies have received little attention. In regions of high acid loadings, however, even well-buffered catchments are susceptible to forest decline and episodes of low alkalinity in streamwater. As part of a collaboration between the Czech and U.S. Geological Surveys, we compared biogeochemical patterns in two well-studied, well-buffered catchments: Pluhuv Bor in the western Czech Republic, which has received high loading of atmospheric acidity, and Sleepers River Research Watershed in Vermont, U.S.A.,...
Although acidifying deposition in western North America is lower than in many parts of the world, many high-elevation ecosystems there are extremely sensitive to acidification. Previous studies determined that the Mount Zirkel Wilderness Area (MZWA) has the most acidic snowpack and aquatic ecosystems that are among the most sensitive in the region. In this study, spatial and temporal variability of ponds and lakes in and near the MZWA were examined to determine their sensitivity to acidification and the effects of acidic deposition during and after snowmelt. Within the areas identified as sensitive to acidification based on bedrock types, there was substantial variability in acid-neutralizing capacity (ANC), which...
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Conclusions: Watershed area and the percentage of a watershed that is covered by forest significantly influence watershed sensitivity to acidic deposition. Based on these landscape pattern indicators, one can identify subregions where acid-sensitive streams are most abundant. Thresholds/Learnings: Synopsis: Hypotheses relating to watershed sensitivity to acidic deposition were tested using a geologic classification scheme and available regional data for the Southern Appalachian Mountains region. Landscape characteristics including lithology, elevation, elevational gradients, landscape position, and forest cover were used in the geologic classification scheme. Acid neutralizing capacity (ANC) was used as the stratifying...


    map background search result map search result map Spatial distribution of acid sensitive and acid-impacted streams in relation to watershed features in the Southern Appalachian Mountains. Chemical characteristics and acid sensitivity of boreal headwater lakes in northwest Saskatchewan. Chemical characteristics and acid sensitivity of boreal headwater lakes in northwest Saskatchewan. Spatial distribution of acid sensitive and acid-impacted streams in relation to watershed features in the Southern Appalachian Mountains.