Regionalisation of chemical variability in European mountain lakes

18 páginas, 6 tablas, 7 figuras.1. We carried out a coordinated survey of mountain lakes covering the main ranges across Europe (including Greenland), sampling 379 lakes above the local tree line in 2000. The objectives were to identify the main sources of chemical variability in mountain lakes, define a chemical classification of lakes, and develop tools to extrapolate our results to regional lake populations through an empirical regionalisation or upscaling of chemical properties. 2. We investigated the main causes of chemical variability using factor analysis (FA) and empirical relationships between chemistry and several environmental variables. Weathering, sea salt inputs, atmospheric deposition of N and S, and biological activity in soils of the catchment were identified as the major drivers of lake chemistry. 3. We tested discriminant analysis (DA) to predict the lake chemistry. It was possible to use the lithology of the catchments to predict the range of Ca 2+ and SO4 2) into which a lake of unknown chemistry will decrease. Lakes with lower SO4 2) concentrations have little geologically derived S, and better reflect the variations in atmospheric S loading. The influence of marine aerosols on lakewater chemistry could also be predicted from the minimum distance to the sea and altitude of the lakes. 4. The most remarkable result of FA was to reveal a factor correlated to DOC (positively) and NO3 ) (negatively). This inverse relationship might be the result either of independent processes active in the catchment soils and acting in an opposite sense, or a direct interaction, e.g. limitation of denitrification by DOC availability. Such a relationship has been reported in the recent literature in many sites and at all scales, appearing to be a global pattern that could reflect the link between the C and N cycles. 5. The concentration of NO3 ) is determined by both atmospheric N deposition and the processing capacity of the catchments (i.e. N uptake by plants and soil microbes). The fraction of the variability in NO3 ) because of atmospheric deposition is captured by an independent factor in the FA. This is the only factor showing a clear pattern when mapped over Europe, indicating lower N deposition in the northernmost areas. 6. A classification has been derived which takes into account all the major chemical features of the mountain lakes in Europe. FA provided the criteria to establish the most important factors influencing lake water chemistry, define classes within them, and classify the surveyed lakes into each class. DA can be used as a tool to scale up the classification to unsurveyed lakes, regarding sensitivity to acidification, marine influence and sources of S.Funding was provided by the European Union (EMERGE project EVK1-CT-1999-00032), Spanish Ministry of Science and Technology (CICYT grant REN2000-0889 ⁄GLO), and the Austrian Ministry for Education, Science and Culture.Peer reviewe

High mountain lakes and atmospherically transported pollutants

Mountain regions occupy about a quarter of the global terrestrial land surface and provide goods and services to more than half the humanity. Global environmental change threatens the integrity of these systems and their ability to provide the goods and services upon which humanity has come to depend. This book gives an overview of the state of research in fields pertaining to the detection, understanding and prediction of global change impacts in mountain regions. More than 60 contributions from paleoclimatology, cryospheric research, hydrology, ecology, and development studies are compiled in this volume, each with an outlook on future research directions.Peer reviewe

Regional influence of acid deposition and climate change in European mountain lakes assessed using diatom transfer functions.

18 páginas, 5 tablas, 6 figuras.1. Mountain lake sediments are valuable archives of environmental change. However, the presence of multiple drivers of change over similar or overlapping timescales may obscure palaeolimnological signals obtained using traditional statistical analyses. 2. As part of the European Union-funded EMERGE programme, sediment cores were obtained from 209 mountain lakes across 11 lake districts spanning gradients of altitude, latitude, geochemistry and atmospheric deposition. Surface sediments (0–0.5 cm) were subsampled to represent modern conditions corresponding with chemical and environmental measurements, while core bottom (15–17 cm) sediments were subsampled to represent the pre-industrial period. 3. We used a novel approach to explore the relative importance of environmental drivers of change in diatom communities. First, we used canonical correspondence analysis (CCA) to identify the most significant variables explaining diatom community distributions in lake surface sediments. Lake water pH, nitrate concentration/dissolved organic carbon (DOC) and ice-free period were identified as uniquely significant explanatory variables along three primary axes of variation. The modern data set was then used to construct transfer functions linking diatom communities to these key variables. We applied these transfer functions to core bottom samples to reconstruct change since the pre-industrial period. 4. Drivers of diatom community change differed among regions. Diatom-inferred pH declined in five acid-sensitive lake districts (Central & Southern Norway, Piedmont Ticino, Retezat Mountains, Scotland and Tatra Mountains), consistent with acidification caused by sulphur and nitrogen deposition. Diatom-inferred pH increased in two lake districts [Julian Alps (JA), Pyrenees (PY)], probably due to eutrophication and climate warming-induced increases in weathering rates respectively. 5. Diatom inference models for nitrate and DOC were not independent. However, diatom-inferred nitrate increased in all lake districts with detectable changes, except for the Retezat Mountains. These changes are consistent with increased nitrogen deposition and leaching in the industrial period and are independent of acidification effects, presumably reflecting a nitrogen fertilization effect. Diatom-inferred DOC increased in the Central Alps and Scotland but decreased in Central Norway and Northern Finland, in contrast to increasing trends reported for Northern Europe and North America over the last 10–20 years. Conflicting drivers of change in DOC such as recovery from acidification and climate change further confound the interpretation of diatom-inferred changes. 6. Changes in the diatom-inferred ice-free period varied across regions. Warming is indicated in Central Norway, Scotland, Piedmont Ticino and the Pyrenees, while cooling is suggested in the more southern and eastern Julian Alps and Rila Mountains. Where detectable changes in diatom-inferred pH and ice-free period coincide there is generally an association between acidification and climate warming. Since warming is associated with increased weathering and alkalinity generation it is therefore possible that climate warming has reduced the impacts of acidification in acid-sensitive lake districts.This study was originally funded under the EU EMERGE Programme (EVK1-CT-1999-00032) and subsequently under the EU 6th Framework Euro-limpacs Programme (Contract No. GOCE-CT-2003-505540).Peer reviewe