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Benthic microbial biofilms attached to rocks (epilithic) are major sites of carbon cycling and can dominate ecosystem primary production in oligotrophic lakes. We studied the bacterial community composition of littoral epilithic biofilms in five connected oligotrophic high mountain lakes located at different altitudes by genetic fingerprinting and clone libraries of the 16S rRNA gene. Different intra-lake samples were analyzed, and consistent changes in community structure (chlorophyll a and organic matter contents, and bacterial community composition) were observed along the altitudinal gradient, particularly related with the location of the lake above or below the treeline. Epilithic biofilm genetic fingerprints were both more diverse among lakes than within lakes and significantly different between montane (below the tree line) and alpine lakes (above the tree line). The genetic richness in the epilithic biofilm was much higher than in the plankton of the same lacustrine area studied in previous works, with significantly idiosyncratic phylogenetic composition (specifically distinct from lake plankton or mountain soils). Data suggest the coexistence of aerobic, anaerobic, phototrophic, and chemotrophic microorganisms in the biofilm, Bacteroidetes and Cyanobacteria being the most important bacterial taxa, followed by Alpha-, Beta-, Gamma-, and Deltaproteobacteria, Chlorobi, Planctomycetes, and Verrucomicrobia. The degree of novelty was especially high for epilithic Bacteroidetes, and up to 50 % of the sequences formed monophyletic clusters distantly related to any previously reported sequence. More than 35 % of the total sequences matched at <95 % identity to any previously reported 16S rRNA gene, indicating that alpine epilithic biofilms are unexplored habitats that contain a substantial degree of novelty within a short geographical distance. Further research is needed to determine whether these communities are involved in more biogeochemical pathways than previously thought. [ABSTRACT FROM AUTHOR]

1. A survey of c. 350 remote high altitude and high latitude lakes from 11 different mountain regions was undertaken to explore species distribution across Europe at a scale not previously attempted. 2. Lakes were sampled for planktonic crustaceans, rotifers, littoral invertebrates and sub-fossil chironomids, diatoms and cladocerans. Each lake was characterised in terms of water chemistry, morphology, catchment attributes and geographical location. 3. Separatetwinspan analyses were undertaken on diatom, chironomid, planktonic crustacean, littoral invertebrate and cladoceran (chydorids only) data to classify sites according to taxonomic composition. For most datasets there was a spatial component to the classification with distinct geographical groups emerging – Norway and Scotland, Finland and Central/Eastern Europe. 4. Constrained ordination methods were employed to examine how species responded to a range of environmental factors, which were aggregated into a series of component groups – proximal environment (the chemical, trophic and physical attributes of the lake), catchment characteristics and geographical location. Several key environmental gradients were identified, which explained significant levels of the variance across several of the biological groups including dissolved organic carbon (chironomids, planktonic crustaceans), temperature (chironomids and littoral invertebrates), chloride/sea-salt (littoral invertebrates, diatoms and rotifers), lake morphology (all groups), calcium/pH (diatoms), nitrate (chydorids, littoral invertebrates, rotifers and planktonic crustaceans) and fish (littoral invertebrates). In some cases these statistical relationships are likely to represent direct ecological constraints and, in others, it is probable that the environmental variable is acting as a surrogate for some other attribute or process. 5. Variance partitioning was undertaken to quantify how much of the variation in each biological group could be uniquely attributed to variables representing the proximal environment, catchment characteristics and geographical location. For most groups the location of the lake tends to explain the greatest variation in species composition across the Lake Districts. The proximal environment was also important but, with the exception of diatoms, secondary to location. Therefore, a strong geographical signal emerged from the analyses. Three distinct limno-regions were identified; Nordic (Scotland and Norway), Sub-Arctic (Northern Finland) and Alpine (Pyrenees, the Alps and Eastern Europe ranges). 6. Our results have implications for the development of regionalisation schemes based on biological responses to environmental gradients; (i) lake ‘types’ based on environmental factors cannot be extrapolated throughout Europe, even within the relatively narrow gradients found in remote mountain lakes, (ii) biotic response to large-scale variations in environmental conditions, such as those that could be expected with climate change, is likely to vary according to regions because of the biogeographical differences among them. [ABSTRACT FROM AUTHOR]

The integrated assessment models that drive atmospheric pollutant emission reduction policies within Europe, under the Convention on Long-range Trans-boundary Air Pollution, work at the scale of the EMEP grid (50 × 50 km). Critical loads are used to link anthropogenic deposition to adverse effects for individual ecosystems within each grid cell. The critical loads have two aspects, ecosystem area and the ecosystem specific critical load. The presence of highly acid-sensitive ecosystems within these grid cells can lead to very low critical loads of acidity which provide emission targets that are difficult to achieve: these cells are known as "binding grid squares". Since mountain lakes are highly sensitive to environmental change, their inclusion in critical loads assessments might be expected to result in lower EMEP scale critical loads. The combination of mountain lakes data with those from other ecosystems already included in the integrated modelling shows unexpected results. The average accumulated exceedance of critical loads of acidity may increase with either the presence of significant mountain lake catchment areas within grid cells or the presence of highly acidified clusters of sites. These circumstances occur in only a small number of grid cells. Furthermore, the relatively low sensitivity of mountain lakes to acidification in some regions means that their inclusion in EMEP scale models would lead to a relaxation of emission abatement requirements because of an increase in the area of ecosystems not exceeding critical loads and a decrease in AAE. Hence the potential effects of the inclusion of mountain lake critical loads of acidity in EMEP scale models vary greatly on a regional basis. The assumption that mountain lakes data could increase the incidence of "binding grid squares" is found to be unlikely. [ABSTRACT FROM AUTHOR]