Lakes In Norway Research Articles

Surprising spectra of root-associated fungi in submerged aquatic plants

Similarly to plants from terrestrial ecosystems, aquatic species harbour wide spectra of root-associated fungi (RAF). However, comparably less is known about fungal diversity in submerged roots. We assessed the incidence and diversity of RAF in submerged aquatic plants using microscopy, culture-dependent and culture-independent techniques. We studied RAF of five submerged isoetid species collected in four oligotrophic freshwater lakes in Norway. Levels of dark septate endophytes (DSE) colonization differed among the lakes and were positively related to the organic matter content and negatively related to pH. In total, we identified 41 fungal OTUs using culture-dependent and culture-independent techniques, belonging to Mucoromycotina, Chytridiomycota, Glomeromycota, Ascomycota as well as Basidiomycota. Sequences corresponding to aquatic hyphomycetes (e.g. Nectria lugdunensis, Tetracladium furcatum and Varicosporium elodeae) were obtained. Eight arbuscular mycorrhizal taxa belonging to the orders Archaeosporales, Diversisporales and Glomerales were also detected. However, the vast majority of the fungal species detected (e.g. Ceratobasidium sp., Cryptosporiopsis rhizophila, Leptodontidium orchidicola, and Tuber sp.) have previously been known only from roots of terrestrial plants. The abundance and phylogenetic distribution of mycorrhizal as well as nonmycorrhizal fungi in the roots of submerged plants have reshaped our views on the fungal diversity in aquatic environment.

Contemporary divergence in early life history in grayling (Thymallus thymallus)

BackgroundFollowing colonization of new habitats and subsequent selection, adaptation to environmental conditions might be expected to be rapid. In a mountain lake in Norway, Lesjaskogsvatnet, more than 20 distinct spawning demes of grayling have been established since the lake was colonized, some 20-25 generations ago. The demes spawn in tributaries consistently exhibiting either colder or warmer temperature conditions during spawning in spring and subsequent early development during early summer. In order to explore the degree of temperature-related divergence in early development, a multi-temperature common-garden experiment was performed on embryos from four different demes experiencing different spring temperatures.ResultsEarly developmental characters were measured to test if individuals from the four demes respond differently to the treatment temperatures. There was clear evidence of among-deme differences (genotype - environment interactions) in larval growth and yolk-to-body-size conversion efficiency. Under the cold treatment regime, larval growth rates were highest for individuals belonging to cold streams. Individuals from warm streams had the highest yolk-consumption rate under cold conditions. As a consequence, yolk-to-body-mass conversion efficiency was highest for cold-deme individuals under cold conditions. As we observed response parallelism between individuals from demes belonging to similar thermal groups for these traits, some of the differentiation seems likely to result from local adaptationConclusionThe observed differences in length at age during early larval development most likely have a genetic component, even though both directional and random processes are likely to have influenced evolutionary change in the demes under study.

The Unexpected Discovery of a Brackish Water Amphipod, Gammarus Zaddachi Sexton, 1912, Found Isolated at 150 M Depth in an Inland Freshwater Lake in Norway

From the deepest layers of the large Lake Eikeren in southern Norway, 48 specimens of an amphipod were collected. Species identification by morphological keys gave as a result Gammarus zaddachi Sexton, 1912. In Europe, this species is only known from shallow brackish water, or from habitats near the sea where brackish sites are reachable. The surface of Lake Eikeren today is 19 m above sea level. Separation from the sea occurred some 5000 years ago. In this 150 m deep lake a long period has then elapsed during which a change from saline to brackish and later to fresh water took place. Today only fresh water prevails in all water layers. The maximum length of G. zaddachi in Lake Eikeren is larger than it is in other European populations. More studies are required to understand how this shallow-living brackish water species has adapted to a life in the deep areas of a freshwater lake.

Physical and chemical consequences of artificially deepened thermocline in a small humic lake – a paired whole-lake climate change experiment

Abstract. Climate change with higher air temperatures and changes in cloud cover, radiation and wind speed alters the heat balance and stratification patterns of lakes. A paired whole-lake thermocline manipulation experiment of a small (0.047 km2) shallow dystrophic lake (Halsjärvi) was carried out in southern Finland. A thermodynamic model (MyLake) was used for both predicting the impacts of climate change scenarios and for determining the manipulation target of the experiment. The model simulations assuming several climate change scenarios indicated large increases in the whole-lake monthly mean temperature (+1.4–4.4 °C in April–October for the A2 scenario), and shortening of the length of the ice covered period by 56–89 days. The thermocline manipulation resulted in large changes in the thermodynamic properties of the lake, and those were rather well consistent with the simulated future increases in the heat content during the summer-autumn season. The manipulation also resulted in changes in the oxygen stratification, and the expansion of the oxic water layer increased the spatial extent of the sediment surface oxic-anoxic interfaces. In addition, the experiment affected several other chemical constituents; concentrations of organic carbon, TotN, and NH4 showed a statistically significant decrease, likely due to both changes in hydrological conditions during the experiment period and increased decomposition and sedimentation. In comparison with the results of a similar whole-lake manipulation experiment in a deep, oligotrophic, clear-watered lake in Norway, it is evident that shallow dystrophic lakes, common in the boreal region, are more sensitive to physical perturbations. This means that projected climate change may modify their physical and chemical conditions in the future.

Possible Implications of Chytrid Parasitism for Population Subdivision in Freshwater Cyanobacteria of the Genus Planktothrix

Populations of the cyanobacterium Planktothrix comprise multiple coexisting oligopeptide chemotypes that can behave differently in nature. We tested whether this population subdivision can, in principle, be driven by parasitic chytrid fungi, which are almost neglected agents of Planktothrix mortality. Two chytrid strains, Chy-Lys2009 and Chy-Kol2008, were isolated from Planktothrix-dominated lakes in Norway. The two strains shared 98.2% and 86.2% of their 28S and internal transcribe spacer rRNA gene sequences, respectively. A phylogenetic analysis placed them in the order Rhizophydiales family Angulomycetaceae. Chy-Lys2009 and Chy-Kol2008 could completely lyse Planktothrix cultures within days, while they failed to infect other filamentous cyanobacteria. The effect on Planktothrix was chemotype dependent, and both chytrid strains showed distinct chemotype preferences. These findings identify chytrid fungi infecting Planktothrix as highly potent and specialized parasites which may exert strong selective pressure on their hosts. According to established hypotheses on host-parasite coevolution, parasitism with the above properties may result in subdivision of Planktothrix populations into coexisting chemotypes and periodic shifts in the relative Planktothrix chemotype composition. These predictions are in agreement with field observations. Moreover, a genetic analysis verified the co-occurrence of Chy-Lys2009 and Chy-Kol2008 or related chytrid strains along with distinct Planktothrix chemotypes in at least one water body. Our findings are consistent with a scenario where chytrid parasitism is one driving force of Planktothrix population subdivision, which in turn leads to polymorphism in parasitic chytrid fungi. Future studies should test the validity of this scenario under field conditions.

The first privately produced map in Norway with a geodetic reference frame

A map of the district surrounding the largest lake in Norway was published in 1796 by the Topographical Society of Norway. Their members contributed private funds for this unique map and for the publication of the Topographical Journal, containing multidisciplinary descriptions, including environmental, of many regions of the country. The map was produced by lieutenant Niels S Darre, a military surveyor and cartographer, as a private undertaking in his own home district. The geodetic reference point of the map is the church at Vang, the position of which had been determined by repeated astronomical observations by its vicar, Abraham Pihl. He had been trained as an astronomical observer by professor Thomas Bugge at the Round Tower Observatory in Copenhagen. A supporting latitude determination in Lillehammer is also noted on the map, obtained by Maximilian Hell in 1769 on his return from Vardo in Northern Norway to Vienna after a successful observation of the transit of Venus. The observed magnetic deviation from astronomically determined north is given. The map also identifies a marker of the great flood of the river Glomma in 1789, causing environmental and social devastation. We have digitized the map and compared it to a 67 km × 82 km section of a modern, digitized topographical map of Norway, by transforming the UTM projection to a meridian through the church at Vang. While most features coregister acceptably by visual inspections of the old and new maps, we note geometrical deviations of up to 1 km in the locations of western shorelines.

Altitudinal and thermal gradients of hepatic Cyp1A gene expression in natural populations of Salmo trutta from high mountain lakes and their correlation with organohalogen loads

The biomarker of xenobiotic exposure cytochrome p450A1 (Cyp1A) was used to analyze the biological response to chemical pollution in Salmo trutta (brown trout) from nine high mountain European lakes in Norway, Tatras, Tyrol, and central Pyrenees. Hepatic Cyp1A mRNA levels correlated both with the reciprocal of absolute annual average air temperatures of the sampled lakes and with muscle concentrations of several hydrophobic organohalogen compounds (OC), including chlorinated polychlorobiphenyls (PCB), DDE, and DDT. The correlation between Cyp1A expression and OC content was observed across the whole temperature range (between −0.7 °C and +6.2 °C), but also in the absence of any thermal gradient. We concluded that airborne pollutants accumulate in high mountain lake fish at concentrations high enough to increase Cyp1A expression, among other possible effects. As geographical distribution of semi-volatile OC is strongly influenced by air temperatures, future climate modifications will potentially enhance their physiological effects in lake ecosystems.

Shifts in Lake N:P Stoichiometry and Nutrient Limitation Driven by Atmospheric Nitrogen Deposition

Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high-N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world's lakes, even in lakes far from direct human disturbance.

Quantitative responses of lake phytoplankton to eutrophication in Northern Europe

Based on the currently largest available dataset of phytoplankton in lakes in northern Europe, we quantified the responses of three major phytoplankton classes to eutrophication. Responses were quantified by modelling the proportional biovolumes of a given group along the eutrophication gradient, using generalized additive models. Chlorophyll-a (Chl-a) was chosen as a proxy for eutrophication because all classes showed more consistent responses to Chl-a than to total phosphorus. Chrysophytes often dominate in (ultra-) oligotrophic lakes, and showed a clear decrease along the eutrophication gradient. Pennate diatoms were found to be most abundant at moderate eutrophication level (spring-samples). Cyanobacteria often dominate under eutrophic conditions, especially in clearwater lakes at Chl-a levels >10 μg l−1 (late summer samples). We compare the relationships among types of lakes, based on the lake typology of the northern geographic intercalibration group, and among countries sharing common lake types. Significant differences were found especially between humic and clearwater lakes, and between low- and moderately alkaline lakes, but we could not identify significant differences between shallow and deep lakes. Country-specific differences in response curves were especially pronounced between lakes in Norway and Finland, while Swedish lakes showed an intermediate pattern, indicating that country-specific differences reflect large-scale geographic and climatic differences in the study area.

Large scale patterns of chemical recovery in lakes in Norway and Sweden: Importance of seasalt episodes and changes in dissolved organic carbon

Trends from 160 lakes in Norway and Sweden for the period 1990–2004 reveal that Scandinavian lakes show clear signs of recovery from acidification. Sulphate has decreased and ANC, alkalinity and pH have increased. During the last 5 a, the decline in SO 4 - has ceased, whereas ANC continues to increase. The results also show decreasing trends for Cl, while Na shows no or very small trends. The increase in the Na/Cl-ratio explains part of the increase in ANC. On average for the period 1990–2004 the decrease in Cl contributes 20–50% of the increase in ANC. The main cause of the trends in Cl in southern Sweden and Norway are probably due to declining seasalt inputs due to a higher frequency of heavy storms in the late 1980s and early 1990s. TOC exhibits increasing trends in regions with median TOC concentrations > 3 mg C/L, however, this does not contribute significantly to the observed increase in ANC.

Fossil midges and palaeosalinity: potential as indicators of hydrological balance and sea-level change

Saline lakes possess midge communities whose composition reflects the range in annual salt concentration fluctuations within the lake basin. Chironomid remains accumulating in such lakes may be used as archives for reconstructing past salinity changes. Quantitative palaeosalinity reconstructions are now available for lakes in parts of Canada and Africa. In arid and semi-arid regions, much potential exists for relating these midge-inferred salinities to past changes in climate. Salinities at these sites may reflect past hydrological changes, especially changes in evaporation/precipitation balance. Recent analyses of coastal lakes in Norway demonstrate that midge fossils are also potentially useful indicators of sea-level changes. Limitations to midge-inferred palaeosalinity reconstructions include non-climate reasons for changes in salinity, such as variation in ionic input and local hydrology, and additional influences on community composition, such as midge habitat preferences, selective predation, and metal toxicity.

Indications of Hormonally Active Substances in Municipal Solid Waste Leachate: Mobilization and Effect Studies from Sweden and Norway

Several species of fish from a freshwater lake downstream a landfill in central Sweden have been found to be exposed to specific endocrine active substances (EAS), possibly able to interact with important functions in the synthesis of steroids and thereby disrupting a normal development of the gonad. A preliminary study of 7 streams and lakes in Norway showed that female perch have a significant reduction in gonad somatic index (GSI) with fish length and weight at one location. This can be an indication of disturbance due to exposure of hormonally active agents over time. Only 2 locations showed significantly difference in GSI and liver somatic index (LSI). Possible explanations can be that the necessary combination between exposure and exposed is exclusive and does not apply in general, or that the effects are masked due to other exposures such as e.g., nutrient, organic or other chemicals, physical or biological loads. The number of sampled locations is, however, too limited to be conclusive. Liver samples are being analyzed for organic pollutants, but these analyses were not ready at the time of publication. A previous study of leachate and sediment samples indicated the presence of several organic pollutants and compounds known to be hormonally active. Investigations of extracts from sediment samples from one of the exposed lake in Sweden showed the presence of both naturally occurring and xenophobic organic compounds. In samples extracted with a base-neutral extraction the compounds 1.1 sulfonyl-bis(4-chlorobenzene) and bis-2-etylhexyl-phtalate were detected. The high lipid affinity of the phtalate correlates with the finding of the compound in the high organic content layer of 20–40 cm in the exposed sediment. Pesticide residues were not found in the samples.

A Late‐glacial chironomid record from Hawes Water, northwest England

AbstractThis paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ18O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ18O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.

Recovery of acidified mountain lakes in Norway as predicted by the MAGIC model

As part of the EU project EMERGE the biogeochemical model MAGIC was used to reconstruct acidification history and predict future recovery for mountain lakes in two regions of Norway. Central Norway (19 lakes) receives low levels of acid deposition, most of the lakes have undergone only minor amounts of acidification, and all are predicted to recover in the future. Central Norway thus represents a reference area for more polluted regions in southern Norway and elsewhere in Europe. Southern Norway (23 lakes), on the other hand, receives higher levels of acid deposition, nearly all the studied lakes were acidified and had lost fish populations, and although some recovery has occurred during the period 1980-2000 and additional recovery is predicted for the next decades, the model simulations indicated that the majority of the lakes will not achieve water quality sufficient to support trout populations. Uncertainties in these predictions include possible future N saturation and the exacerbating effects of climate change. The mountain lakes of southern Norway are among the most sensitive in Europe. For southern Norway additional measures such as stricter controls of emissions of air pollutants will be required to obtain satisfactory water quality in the future.

Coherent responses of sulphate concentration in Norwegian lakes: relationships with sulphur deposition and climate indices

Abstract. The coherence or synchrony in the trends in SO42– concentration in a set of 100 lakes in Norway that have a long-term chemical record was evaluated. Using a statistical technique that compares patterns or trends that are not uni-directional, the lakes were grouped into 18 subsets or clusters, each with between 2 and 11 lakes that had similar trends. These temporal trends were strongly correlated with several climate indices, notably the Arctic Oscillation Index (AOI) measured in the autumn, and the annual North Atlantic Oscillation Index (NAOI). Because these clusters of lakes were spatially dispersed, they could not be compared directly with trends in wet S deposition, because S deposition varied substantially between lakes within each cluster. However, the average trend in SO42– concentration was evaluated in each of 10 regions of Norway that were defined previously on the basis of pollution load, meteorological variables and biogeography. Although these regions did not match the statistically-selected clusters of lakes with equal trends very closely, there were similar, strong correlations between climate indices (the AOI and NAOI) and the 10 average SO42– trends, although there were even stronger relationships with average wet S deposition in the regions. When subsets of lakes with coherent SO42– trends were selected from within each of the 10 regions, both wet S deposition and the climate indices were strongly correlated with those SO42– trends. Hence, lakes in Norway respond to changes in wet S deposition and are influenced by large-scale, i.e. global, climate signals. Future evaluation of recovery of lakes affected by acid deposition must therefore consider the confounding effects of climate and potential climate change. Keywords: recovery, acid deposition, coherence, sulphate, climate change

Long-term changes of the crustacean zooplankton community in Lake Mjøsa, the largest lake in Norway

Lake Mjøsa has been subject to an accelerating eutrophication from the 1950s to the mid 1970s, but comprehensive nutrient reduction efforts caused marked reductions of phytoplankton production and biomass during the 1980s, a process that continued during the 1990s. Zooplankton biomass and species composition was considerably affected during the eutrophication and subsequent oligotrophication. Total crustacean zooplankton biomass decreased along with decreasing algal biomass during the 1980s and 1990s. The seasonal means of zooplankton biomass were positively correlated with seasonal means of phytoplankton biovolume and chlorophyll-a, indicating a primarily bottom up regulation of the zooplankton biomass. Several herbivorous and omnivorous zooplankton species (Daphnia galeata, Bosmina longispina, Limnocalanus macrurus and Cyclops lacustris) were probably negatively affected by reduced algal biomass, whereas other species (Holopedium gibberum and Thermocyclops oithonoides/Mesocyclops leuckarti) seemed to be positively affected. H. gibberum disappeared in the 1960s, but reappeared in the 1980s after the significant reduction in algal biomass and primary production. The temporal trend of T. oithonoides/M. leuckarti indicated a strong competition with cladocerans (mainly B. longispina and D. galeata) in periods with high algal biomass. Early warming of the lake could also have promoted a biomass increase of T. oithonoides/M. leuckarti in later years, although the mean epilimnion temperature did not correlate with seasonal mean biomass of these species. The seasonal mean biomass of Eudiaptomus gracilis, the dominant calanoid, showed substantial fluctuations with 6-7 years between tops, but a decreasing trend during the 1990s. However, there were no significant correlations between this species and any of the environmental variables. The study indicated that dominant cladocerans (D. galeata and B. longispina) are decisive for the success of cisco (Coregonus albula), one of the most important planktivorous fish species, as also described by earlier studies. However it also demonstrated top down control on cladocerans in years with especially large stocks of cisco.

Fish status survey of Nordic lakes: effects of acidification, eutrophication and stocking activity on present fish species composition.

The status of fish populations in 3821 lakes in Norway, Sweden and Finland was assessed in 1995-1997. The survey lakes were chosen by stratified random sampling from all (126 482) Fennoscandian lakes > or = 0.04 km2. The water chemistry of the lakes was analyzed and information on fish status was obtained by a postal inquiry. Fish population losses were most frequent in the most highly acidified region of southern Norway and least common in eastern Fennoscandia. According to the inquiry results, the number of lost stocks of brown trout (Salmo trutta), roach (Rutilus rutilus), Arctic char (Salvelinus alpinus) and perch (Perca fluviatilis) was estimated to exceed 10000. The number of stocks of these species potentially affected by the low alkalinity of lake water was estimated to exceed 11000. About 3300 lakes showed high total phosphorus (> 25 microg L(-1)) and cyprinid dominance in eastern Fennoscandia, notably southwestern Finland. This survey did not reveal any extinction of fish species due to eutrophication. One-third of the lakes had been artificially stocked with at least one new species, most often brown trout, whitefish (Coregonus lavaretus s.l.), Arctic char, rainbow trout (Oncorhynchus mykiss), pike-perch (Stizostedion lucioperca), grayling (Thymallus thymallus), pike (Esox lucius), bream (Abramis brama), tench (Tinca tinca) and European minnow (Phoxinus phoxinus). The number of artificially manipulated stocks of these species in Fennoscandian lakes was estimated to exceed 52000. Hence, the number of fish species occurring in Nordic lakes has recently been changed more by stockings than by losses of fish species through environmental changes such as acidification.

Life‐history variation in perch (Perca fluviatilis L.) in five neighbouring Norwegian lakes

Abstract – We have studied the population dynamics and reproductive biology of perch (Perca fluviatilis L.) from five neighbouring lakes in Norway. The lakes vary in water quality, varying from strongly acidified (pH≤5.0) to not acidified (pH≥6.0). Estimated annual survival rates did not differ among populations. There was no strong relationship between age at maturity in female perch and acidification. However, age at maturity was lower for female perch from the most acidic lake (c. 2 years) compared with perch in the four other lakes (2.5–3.5 years). There was no relationship between acidification level and size‐adjusted egg size, fecundity or reproductive investment (Gonadosomatic index – GSI). Perch in the most acidified lake showed large variation in egg size, the lowest length‐specific fecundity, the highest GSI, and the lowest age at maturity. Environmental stress, such as acidification, induces a number of changes to a lake community. It is therefore difficult to predict how acidification will influence the population dynamics and reproductive biology of a perch population.

Deterioration of atlantic soft water macrophyte communities by acidification, eutrophication and alkalinisation

This review presents an overview of the most important succession patterns and underlying processes associated with the deterioration of soft water macrophyte communities in atlantic and boreo-atlantic regions. As acidification, eutrophication and alkalinisation are the dominant processes, this paper will focus on the successional changes caused by these processes. Observed differences in the succession between soft waters in different areas in Europe are discussed. Most attention has been given to vegetation changes related to acidification, as most research has been carried out on this topic. In acidifying formerly slightly calcareous aquatic systems, a transition takes place from isoetid and other soft water plant communities to vegetation dominated by submerged Sphagnum mosses and Juncus bulbosus forma fluitans. Regional surveys show that this transition is not very common in acidified lakes in Norway, Finland, Canada, and North America. However, the opposite seems to be true for some southern Swedish lakes, some Scottish lakes, lakes in the West European lowlands (The Netherlands and Germany) and also recently for some southern Norwegian lakes. The calcium bicarbonate content of the sediment seems to be an important explanatory variable, as well as the availability and form of inorganic nitrogen. In West European lakes, isoetids disappear during the acidification process. Elsewhere, although Sphagnum mosses and J. bulbosus develop, isoetids continue to coexist. In this paper, it is hypothesized that the succession seen in soft waters outside the West European lowlands has not yet reached the final stage in which isoetids disappear. Thus, the most dramatic deterioration of soft water macrophyte communities has occurred in the West European lowlands, where the number of isoetid sites has decreased dramatically. The West European systems are substantially smaller and shallower than those elsewhere. The morphology of soft water systems is important in determining the way eutrophication becomes manifest. In larger and deeper systems, planktonic algal growth causes a higher turbidity, whilst in smaller and shallower systems lemnids and ricciellids may expand. For a better understanding of the successional differences between soft waters on an interregional scale, further research and cooperation is needed, in which vegetation, physico-chemical and atmospheric deposition data are integrated.

Application of Static Critical Load Models for Acidity to High Mountain Lakes in Europe

Critical load models for acidityprovide a measure of the sensitivity of surfacewaters to acid deposition, and can be used todetermine critical load exceedance and potentiallong-term harmful effects. Three static models,the Steady-State Water Chemistry model, diatommodel and First-order Acidity Balance model, arehere applied to 11 high mountain lakes in Norway,Scotland, the Alps, the Pyrenees and the Tatras.Between five and seven of the lakes show criticalload exceedance, depending on the model used.Nitrogen as well as sulphur deposition isimportant in causing exceedance. Since soil andvegetation cover are generally sparse, geologyand lake retention time appear to be key factorsin the determination of critical load. Retentionof nitrogen is observed, but it is unclearwhether this occurs within the lake or theterrestrial part of the catchment.