European Mountain Lakes Research Articles

Identifying factors that affect mountain lake sensitivity to atmospheric nitrogen deposition across multiple scales

Increased nitrogen (N) deposition rates over the past century have affected both North American and European mountain lake ecosystems. Ecological sensitivity of mountain lakes to N deposition varies, however, because chemical and biological responses are modulated by local watershed and lake properties. We evaluated predictors of mountain lake sensitivity to atmospheric N deposition across North American and European mountain ranges and included as response variables dissolved inorganic N (DIN = NNH4+ + NNO3–) concentrations and phytoplankton biomass. Predictors of these responses were evaluated at three different spatial scales (hemispheric, regional, subregional) using regression tree, random forest, and generalized additive model (GAM) analysis. Analyses agreed that Northern Hemisphere mountain lake DIN was related to N deposition rates and smaller scale spatial variability (e.g., regional variability between North American and European lakes, and subregional variability between mountain ranges). Analyses suggested that DIN, N deposition, and subregional variability were important for Northern Hemisphere mountain lake phytoplankton biomass. Together, these findings highlight the need for finer-scale, subregional analyses (by mountain range) of lake sensitivity to N deposition. Subregional analyses revealed differences in predictor variables of lake sensitivity. In addition to N deposition rates, lake and watershed features such as land cover, bedrock geology, maximum lake depth (Zmax), and elevation were common modulators of lake DIN. Subregional phytoplankton biomass was consistently positively related with total phosphorus (TP) in Europe, while North American locations showed variable relationships with N or P. This study reveals scale-dependent watershed and lake characteristics modulate mountain lake ecological responses to atmospheric N deposition and provides important context to inform empirically based management strategies.

Composition of highly diverse diatom community shifts as response to climate change: A down-core study of 23 central European mountain lakes

Alpine mountain lake biota are adapted to harsh conditions making them particularly vulnerable to global change. However, as each mountain lake has a different limnology, there are supposed to be differential responses and degrees of resilience to climate change. In this study, 23 lakes in the Bavarian-Tyrolian Alps differing in altitude, size and geology were examined for their diatom community response to climate warming. Subfossil data were related to 210Pb and 137Cs-dated sediment cores. Correspondence and regression analyses revealed five different assemblage developments depending on lake depth, altitude and origin. Planktic species, especially Cyclotella, dominated deeper and lower-altitude mountain lakes earlier and stronger. This depends on the stability and temperature of the epilimnion which in turn determines the tipping point. Instead, shallow lakes exhibit higher species reorganizations of diatom assemblages. Mountain lakes of lower altitudes or affected by water level fluctuations (WLF) establish complex substrata and Achnanthidium accompanied by epiphytic species or Denticula tenuis in WLF-lakes replace dominating Staurosira. Conversely, alpine shallow lakes lack directional shifts and Staurosira dominate, but approach the tipping point of macrophyte establishment. In a deep doline lake, Diploneis species replace Nitzschia denticula with negligible planktic proportions. In mountain lakes with direct anthropogenic influence, enhanced nutrient supply disguises diatom response to global warming. These findings revealed deep mountain lakes with low nutrient levels to be more resilient to climate change than shallow lakes with a higher trophic status as the onset of the response to rising temperatures is earlier and thus smoother. In conclusion, subfossil diatom analyses can provide a powerful tool for climate change assessment and other anthropogenic impacts on mountain lakes.

Postglacial succession of caddisfly (Trichoptera) assemblages in a central European montane lake

The Bohemian Forest lakes, situated along the Czech-German-Austrian border, were strongly affected by atmospheric acidification between the 1950s and the late 1980s. The subsequent chemical recovery of the lake water should precede and enable a biological recovery, including changes in caddisfly (Insecta: Trichoptera) assemblages. Nevertheless, local pre-acidification data and detailed knowledge of the lake district history are missing, making evaluation of lake recovery difficult. We performed high-resolution analysis of caddisfly remains in a 2.2 m long sediment profile from Prasilske Lake covering the complete history of the lake-catchment evolution. Caddisfly larvae are good indicators of environmental conditions and their subfossil remains are well preserved in unconsolidated waterlaid sediments. A total of 10 caddisfly morpho-taxa were found providing a record from 11,400 cal. yr. BP to the present. With the exception of Athripsodes aterrimus, all identified species are currently present in the Bohemian Forest glacial lakes or their inflow streams but not all of them are documented in Prasilske Lake. The caddisfly fauna consisted of acid-resistant, acid-tolerant and eurytopic species since the Early Holocene. Based on our results, the acid, dystrophic state of Prasilske Lake has been occurring since the lake formation. We conclude that the first signs of natural acidification appeared not later than during the Holocene onset in the Bohemian Forest region. Furthermore, we did not detect any abrupt changes in the species composition connected to the period of anthropogenic acidification during the twentieth century. This study provides for the first time a record of postglacial succession of caddisfly assemblages in a central European mountain lake.

Zooplankton community composition of high mountain lakes in the Tatra Mts., the Alps in North Tyrol, and Scotland: relationship to pH, depth, organic carbon, and chlorophyll-a concentration

Abstract The European EMERGE (European Mountain lake Ecosystems: Regionalisation, diaGnostic & socio-economic Evaluation) project was a survey of high mountain lakes (above treeline) across Europe using unified methods of sampling and analysis. The sampling was carried out in summer or autumn 2000, and comprised biological samples, and samples for chemical analysis. Data from three lake districts are used in this paper: the Tatra Mts. in Slovakia and Poland (45 lakes), the Alps in Tyrol in Austria (22 lakes), and Scotland (30 lakes). As it is shown by multiple regression analysis, DTOC (dissolved or total organic carbon) is the key variable for most groups of zooplankton. With increasing DTOC and mostly with chlorophyll-a decreasing, pH increasing and depth decreasing, macrofitrators with coarse filter meshes are replaced by microfiltrators with fine filter meshes. Higher DTOC may increase bacterioplankton production and advantage species able to consume bacteria (microfiltrators). Other zooplankton species also differ in their preference for DTOC, chlorophyll-a, pH and depth, but DTOC being positively correlated with chlorophyll-a and pH positively correlated with depth. It may be caused by their different preference for food quality in terms of C:P ratio.

Background fish feminization effects in European remote sites.

Human activity has spread trace amounts of chemically stable endocrine-disrupting pollutants throughout the biosphere. These compounds have generated a background level of estrogenic activity that needs to be assessed. Fish are adequate sentinels for feminization effects as male specimens are more sensitive than humans to exogenous estrogenic compounds. High mountain lakes, the most distant environments of continental areas, only receive semi-volatile compounds from atmospheric deposition. We analyzed the expression levels of estrogen-regulated genes in male fish from these mountain lakes in Europe. Incipient feminization involving expression of estrogen receptor and zona radiata genes revealed a widespread diffuse estrogenic impact. This effect was correlated with the concentrations of some organochlorine compounds in fish and was consistent with the persistent occurrence of these tropospheric pollutants in the most remote planet regions. These results should be of general concern given the increasing endocrine disruption effects in human populations.

Brown and brook trout populations in the Tatra Mountain lakes (Slovakia, Poland) and contamination by long-range transported pollutants

AbstractFish living in the extreme conditions of the Tatra Mountain lakes were evaluated from a biological point of view as well as an important biomarker of long-range transported pollutants. In Veľke Hincovo pleso and in Morskie Oko, specimens of brown trout (Salmo trutta) of extraordinarily advanced age were found (ages of 18+ and 17+ years, respectively). The capture of a 17+ year-old brown trout in Morskie Oko (2400 g, 540 mm) indicated the presence of the so-called ferox life strategy. The growth of brook trout (Salvelinus fontinalis) was faster than the growth of brown trout in the younger year classes, and while the growth of brook trout stopped after the age of 5+, the growth of brown trout continued. Concentrations of long-range transported pollutants (HCHs, HCB, DDTs, PCBs, PBDEs, and trace metals) in the Tatra Mountain fish were mostly associated with fish age, body weight and length, type of fish tissue, and lake altitude. Persistent organic pollutants (POPs) in fish muscle were dominated by PCBs 138, 153, 180, and p,p’-DDE. Conversely, PBDEs concentrations ranged at substantially lower levels compared to other POPs. Altitude correlated significantly with concentrations of a-HCH, HCB, p,p’-DDT, p,p’-DDE, and with PCBs 28 and 52. The highest contents of trace metals were found in kidney and liver samples, with higher concentrations in Veľke Hincovo pleso than in Morskie Oko. The overall highest trace metal concentration levels were found for Fe, Cu, and Zn. In comparison with other European mountain lakes, the Tatra Mountain lakes are among the more contaminated.

Chinese Arctic Yellow River Station Research Monitoring Program. 1. Polycyclic Aromatic Hydrocarbons in Sediment from Svalbard

Surface sediments of the west coast of Svalbard near Ny-Ålesund Spitsbergen were collected. PAHs of lake sediments (mean: 260, range: 11 - 1100 ng/g dry wt) were higher than previously report of surface lake sediment in Svalbard 1995, suggesting significant PAH contamination is occurring due to long-term atmospheric transport and local coal mining and fossil fuel sources, pointing to the role of Arctic lakes as potential reservoirs of semi-volatile organic compounds, including PAHs. Compound-specific analysis revealed different PAH patterns between Svalbard lakes and European high mountain lakes, showing higher proportions of low molecular weight compounds and lower levels of high molecular weight PAHs in Svalbard lakes. PAH indicator ratios suggest that the majority of PAHs in lake sediments have pyrogenic origins (coal mining, fossil fuel and biomass combustion), while coastal marine sediments were mainly contaminated by petroleum-derived PAHs (shipping activities in coastal areas, and perhaps as a result of an oil spill in 1986). Sediment fluxes of PAHs were estimated to be 0.2 - 22 ng cm-2yr-1. The current PAH levels exceeded Canadian sediment quality guidelines, suggesting the presence of possible risks for aquatic organisms and the need for further studies.

Felicitations for the Aquatic Ecosystem Health and Management Society

I first became involved in the activities of the Aquatic Ecosystem Health and Management Society (AEHMS) (Canada) when I was invited to participate in the Tropical Ecosystems Congress in Dehradun, Uttarakhand State, India. This meeting was co-organised by the International Society for Tropical Ecology and H. N. B. Garhwal University. Within the congress, AEHMS co-sponsored an international symposium on Climate Change: Impact, Assessment and Management. This brought together scientists from Europe, North America and India highlighting research on aquatic, terrestrial and alpine ecosystems. The symposium enabled researchers from very different environments to share results, experience and approaches to tacking problems associated with changing climate globally. The meeting provided a platform for me to present some of the methods and approaches being used in Europe to deal with the effects of interactions between climate change and other key drivers of change on freshwater ecosystems (under the auspices of the EU Project Euro-limpacs) as well as highlighting two decades of work on European Mountain Lakes. In turn I was able to learn more about some of the presssing issues facing environmental scientists in a very vulnerable and stressed part of the world. By co-organising this session within the Tropical Ecosystem Congress, AEHMS provided a forum whereby scientists and managers from India were able to exchange ideas and explore approaches with researchers in Europe and North America, across a range of ecosystem types. This typifies the key role played by AEHMS in promoting an integrated, holistic approach to aquatic resource management at the global scale. Since the society was established, similar meetings have been held in Mexico, Brazil, Malaysia, the Gulf States, Tanzania, China, and Nepal, as well as in Europe and North America. Conferences and symposia are generally accompanied by special issues of the journal Aquatic Ecosystem Health and Management providing a legacy of the discussions held in the meetings and a vehicle for the publication of interdisciplinary, and cross-­sectoral research at a truly international level.Globally problems arising from agricultural intensification, urbanisation, land use change, industry and globalisation and climate change present a range of increasingly complex management challenges. Those responsible for the protection, conservation, and sustainable management of global aquatic resources are required to tackle a wide variety of stressors resulting from these pressures such as organic and inorganic pollution, flow and morphology alteration, surface and groundwater abstraction, land use change, climate variability and change, invasive species, pathogens. This multitude of interacting stressors adversely affects physical, chemical and ecological water status. It is no longer possible to examine stresses, nor indeed ecosystems, in isolation. Management solutions require integrated, multidisciplinary approaches. Many of these stresses occur at a global scale. A key role is played by organisations such as AEHMS in promoting “international, interdisciplinary, and cross-­sectoral communication and collaboration among scientists, universities, governments, industry, and public sectors for the development of practices and measures for aquatic ecosystem health.” The AEHMS in particular has a significant impact through its practical approaches to increasing the understanding, communication and integrated thinking required to sustainably manage aquatic resources. A key mission is to “disseminate information and provide training on the concept of aquatic ecosystem health.” The objectives of the Society are thus achieved tangibly through publications, newsletters, conferences, symposia and workshops. In addition to the bienniel AEHMS conferences organised across the world, the Society has also organised symposia focusing on specific key issues such as, the ecology and fisheries of Lake Huron, assessments of sediment quality, ecosystem modelling, and Great Lakes of the World. At these meetings key scientists and others with vested interests are brought together to tackle some of the critical aquatic management issues we are facing. Further, AEHMS has taken concrete steps to advance integrated and holistic approaches by (i) initiating working groups within the context of specific topics such as Sediment Quality Assessment, Great Lakes of the World (GLOW) and ecotechnology bioassays, remediation and restoration and (ii) establishing chapters across the world promoting ecosystem health, restoration, and conservation.More recently, the AEHMS has recognised the importance of adopting an integrated ecosystem-based approach in aquatic sciences. The Society has focused considerable effort on promoting the ecosystem approach and management not only in developed regions but also globally particularly in developing regions of Africa, the Middle East, South America, India, China and Malaysia.With aquatic ecosystems and resources facing truly global problems, problems caused by multiple interacting stresses operating across ecosystem types, all inextricably linked to human/socio-economic systems, the role of the AEHMS in promoting and supporting holistic, integrated management approaches at the global scale will be crucial.

A 274-lake calibration data-set and inference model for chironomid-based summer air temperature reconstruction in Europe

A 274-lake calibration data-set for chironomid-based temperature reconstruction is presented which is based on the taxonomic amalgamation of a 117-lake data-set from Switzerland and a 157-lake data-set from Norway and Svalbard. Taxonomic consistency of the two data-sets was ensured by joint microscope sessions by the two involved analysts, re-identifying chironomid assemblages in the Swiss data-set to reach an identical taxonomic resolution as in the Norwegian data, and by double-checking selected samples of the Norwegian calibration data-set. The combined Swiss-Norwegian calibration data-set contains information on the distribution of 154 chironomid taxa over a July air temperature range of 3.5–18.4 °C, a pH range of 4.7–8.8, and an altitudinal range of 5–2815 m asl from lakes in temperate, subarctic, arctic, and alpine environments. Inference models developed based on this data-set using weighted averaging-partial least squares (WA-PLS) regression outperformed inference models based on maximum likelihood regression. After outlier deletion WA-PLS regression predicted July air temperature with a bootstrapped (cross-validated) root mean squared error of prediction (RMSEP) of 1.40 °C. Inference models developed from the separate regional data-sets have an RMSEP of 1.16 and 1.43 °C for the Norwegian and the Swiss calibration data-set, respectively. The WA-PLS inference model based on the Norwegian data-set adequately predicted July air temperature based on chironomid assemblages in the Swiss data-set (RMSEP 2.05 °C; r 2 0.74). In contrast, the WA-PLS model based on the Swiss chironomid assemblages performed poorly in inferring July air temperatures based on the Norwegian chironomid assemblages (RMSEP 2.70 °C; r 2 0.39). We attribute this discrepancy to the large proportion of chironomid taxa in Norwegian samples not represented in the Swiss data-set, the larger range of both pH and lake types included in the Norwegian calibration data-set, and the lack of some chironomid taxa with an arctic and boreal distribution in the Swiss data-set. The WA-PLS inference model based on the combined Swiss-Norwegian calibration data-set is the largest taxonomically consistent chironomid-based inference model available to date and outperforms other existing models if the r 2 and RMSEP relative to the overall temperature gradient are examined. We demonstrate that the combined model can reconstruct a larger range of temperatures when applied to fossil assemblages than models based on the Norwegian or Swiss calibration data-sets only. The combined data-set includes the majority of chironomid taxa expected in late Pleistocene and Holocene sediments of lakes from Northern, Eastern, and Central Europe as well as from southern European mountain lakes. The newly developed WA-PLS inference model is therefore well suited for developing continental-scale reconstructions of late Quaternary temperature change based on chironomid records from different parts of Europe.

Characteristics of sedimentary polycyclic aromatic hydrocarbons (PAHs) in the subtropical Feitsui Reservoir, Taiwan

Polycyclic aromatic hydrocarbons (PAHs) are usually loaded through atmospheric deposition into a water body and eventually into sediments. We study the PAHs from a 22-cm sediment core collected from the subtropical Feitsui Reservoir in Taiwan, and find the PAHs deposition characteristics in the reservoir, the man-made water body, is different from those in natural water bodies. The surficial sedimentary PAH fluxes are significantly higher than those in the European high altitude mountain lakes and those in the northeastern USA urban/industrial lakes. However, the catchment-corrected PAH fluxes normalized by the ratios of the catchment area to the water surface area are comparable to those of remote lakes in Europe and USA, suggesting the sedimentary PAHs in the reservoir is fluvial dominated, i.e., the reservoir system concentrated the atmospheric PAHs from the catchment area into the sediments. PAHs distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. We also find the vehicular transport upstream of the reservoir is likely one of the PAHs sources to this reservoir.

Sediment accumulation rates in European lakes since AD 1850: trends, reference conditions and exceedence

Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions. Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from 210Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates, 11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity (3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm−2 yr−1) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm−2 yr−1). SARs for other lake-types ranged between 0.012 and 0.024 g cm−2 yr−1. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future.

Structure of pelagic microbial assemblages in European mountain lakes during ice-free season

Structure of pelagic microbial assemblages in European mountain lakes during ice-free season

A spectral approach to satellite land cover classification of remote European mountain lake districts

A spectral approach to satellite land cover classification of remote European mountain lake districts

Input of organochlorine compounds by snow to European high mountain lakes

Summary1. Persistent organic pollutants (POPs) can be trapped by and accumulate in cold regions. To understand POP accumulation in temperate high mountain lakes, we collected samples of snow from the catchments of several high mountain lakes in Europe.2. Organochlorine compounds (OCs) are regularly found in snow collected in European high mountain sites. Polychlorobiphenyls (PCBs) were found in all samples examined. Hexachlorocyclohexanes (HCHs) are also common whereas DDTs and hexachlorobenzene were found less frequently.3. Comparison of the concentrations of these pollutants in snow with OC levels in the waters of these lakes or atmospheric deposition during cold periods shows that the snowpack constitutes a significant seasonal PCB reservoir in all catchments and that snow trapping is a major mechanism for the incorporation of HCHs in the lakes situated in the coldest sites, e.g. Gossenköllesee in the Alps.4. Correlation of the concentrations of the PCB congeners in snow versus mean annual winter temperature shows higher accumulation at lower temperatures. The less volatile PCBs exhibit higher temperature dependences than the more volatile congeners. This trend differs from altitudinal dependences observed in other sites such as Canada and may be related to the specific range of winter temperature in each area of study.

Regionalisation of chemical variability in European mountain lakes

Summary1. 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 Ca2+ and SO42− into which a lake of unknown chemistry will decrease. Lakes with lower SO42− 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.

Remote European mountain lake ecosystems: regionalisation and ecological status

Summary1. A survey of c. 350 remote high altitude and high latitude lakes from 12 different mountain regions across Europe was undertaken to explore ecosystem variability, climate forcing, environmental conditions and pollution threats at a scale not previously attempted.2. Lakes were sampled for a range of contemporary and sub‐fossil organisms including planktonic crustaceans, rotifers, littoral invertebrates, chironomids, diatoms and cladocerans. Survey and cartographic data were used to determine environmental characteristics at each site. Organic pollutants and trace metal concentrations were measured in the lake sediment.3. A number of separate studies were undertaken which examined the environmental characteristics of the surveyed lakes (climate forcing and chemical composition), distribution of biota relative to local, regional and biogeographical factors and pollution threats (acidification, heavy metals and persistent organic pollutants) to these sensitive ecosystems.4. There is a strong regional element to the way that environmental factors combine (including climate and pollution threats) and the biota responds in mountain lakes across Europe. From a management perspective it is clear that lake classification and the development of useful typologies and assessments of reference conditions should be undertaken at regional rather than pan‐European scales.5. There are some common features across lake districts related to the timing of industrialisation, but the studies carried out on metals, organic pollutants and nitrate deposition indicate that each lake district has distinct pollution threats. Climate warming already affects most of the lake districts and there are considerable uncertainties as to how this will modify conditions in remote European mountain systems.6. The lake district concept goes beyond a geographical construct and merits further theoretical and experimental development as an ecological concept.

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

Summary1. 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.

Regionalisation of remote European mountain lake ecosystems according to their biota: environmental versus geographical patterns

Summary1. 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. Separate twinspan 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.

Viability and potential for immigration of airborne bacteria from Africa that reach high mountain lakes in Europe

We have analysed the diversity of the bacteria, which grow after addition of concentrated airborne particles and desert dust in different microcosms combinations with water samples from oligotrophic alpine lakes. We used, on the one hand, airborne bacteria transported by an African dust plume and collected in a high mountain area in the central Pyrenees (Spain). On the other hand, we collected desert dust in Mauritania (c. 3000 km distance, and a few days estimated airborne journey), a known source region for dust storms in West Africa, which originates many of the dust plumes landing on Europe. In all the dust-amended treatments we consistently observed bacterial growth of common phyla usually found in freshwater ecosystems, i.e. Alpha-, Beta- and Gammaproteobacteria, Actinobacteria, and a few Bacteroidetes, but with different composition based on lake water pretreatment and dust type. Overall, we tentatively split the bacterial community in (i) typical freshwater non-airborne bacteria, (ii) cosmopolitan long-distance airborne bacteria, (iii) non-freshwater low-distance airborne bacteria, (iv) non-freshwater long-distance airborne soil bacteria and (v) freshwater non-soil airborne bacteria. We identified viable long-distance airborne bacteria as immigrants in alpine lakes (e.g. Sphingomonas-like) but also viable putative airborne pathogens with the potential to grow in remote alpine areas (Acinetobacter-like and Arthrobacter-like). Generation of atmospheric aerosols and remote dust deposition is a global process, largely enhanced by perturbations linked to the global change, and high mountain lakes are very convenient worldwide model systems for monitoring global-scale bacterial dispersion and pathogens entries in remote pristine environments.

Persistent toxic substances in remote lake and coastal sediments from Svalbard, Norwegian Arctic: Levels, sources and fluxes

Surface sediments from remote lakes and coastal areas from Ny-Ålesund, Svalbard, Norwegian Arctic were analyzed for polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). Relatively high levels of PAHs were encountered from several lakes from Ny-Ålesund, which were within the range of levels reported for European high mountain lakes and some urban/industrialized areas in the world, pointing to the role of remote Arctic lakes as potential reservoir of semi-volatile organic compounds. Specific patterns of PBDEs were observed, showing higher concentrations of lower brominated compounds such as BDE-7, 17 and 28. Estimated surface sediment fluxes of PAHs in Ny-Ålesund remote lakes were similar to those observed for some European high mountain lakes. The current PAH levels in sediments from three lakes exceeded Canadian sediment quality guidelines, suggesting the presence of possible risks for aquatic organisms and the need for further studies.