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La presente etude a permis de determiner la flore diatomifere de quatre sources thermales situees au Canada (Iles de la Reine-Charlotte en Colombie Britannique et Takhini au Yukon), au sud-ouest de l'Islande et au Japon (mont Hakone). La composition en especes des assemblages de chaque echantillon est decrite et appuyee par des illustrations originales. Certains assemblages sont constitues d'especes dominantes, telles que Diadesmis gallica W. Smith pour l'echantillon de Takhini, Brachysira microcephala (Grunow) Compere et Achnanthes minutissima Kutzing pour l'Islande et Pinnularia sp. [aff. anglica (Cleve) Krammer] pour le Japon. La majorite des taxons repertories sont des formes alcaliphiles et circumneutrales selon leur affinite pour le pH, et de formes oligohalobes, mesohalobes et euryhalobes selon la salinite. La comparaison de la microflore entre les quatre sources echantillonnees nous amene a la conclusion qu'on ne peut ici etablir de flore diatomifere specifique aux sources thermales. L'eloignement...

Chrysophyte stomatocysts from the surface sediments of 49 lakes located on a north–south transect in the Yukon and Northwest Territories, Canada, were investigated for their potential use as indicators of environmental change in northern latitudes. Photographic plates and descriptions, following International Statospore Working Group guidelines, illustrate 19 new stomatocyst morphotypes. The main patterns of floristic variation in the data set were explored using canonical correspondence analysis, which indicated that gradients of chloride (r2 = 0.73), dissolved inorganic carbon (r2 = 0.63), and surface-water temperature (r2 = 0.55) were important in influencing species assemblages. Compared with the diatom-temperature inference model developed from the same set of lakes, the stomatocysts provided a slightly less robust model. These results suggest that stomatocysts are weakly, though significantly, related to some of the gradients in lake water chemistry in this data set and can provide a complement to other paleoecological markers. Key words: chrysophyte stomatocysts, inference models, northwestern Canada.

Des donnees sur les caracteristiques limnologiques et chimiques obtenues pour 59 lacs dans le Yukon et la partie adjacente des Territoires du Nord-Ouest (Canada) ont ete interpretees a l'aide de l'analyse de regression lineaire et de l'analyse des composantes principales. Les sites d'etude sont des lacs qui representent une grande variete de regions ecoclimatiques, echelonnees sur de longs gradients de latitude (60°37'-69°35'N) et d'altitude (15 a 1387 m au-dessus du niveau de la mer). Les echantillons d'eau preleves dans chacun des lacs ont ete analyses pour determiner la concentration des ions traces, des metaux traces, des elements nutritifs et de la chlorophylle a. La plupart des lacs etaient pauvres en solutes (conductivite moyenne de 160 μS.cm -1 ) et leur pH variait de legerement acide a alcalin (etendue de pH = 5,9 a 9,3). La composition ionique a varie de Ca-Cl-Na pres de l'ocean Arctique a Ca-HCO 3 vers l'interieur des terres, ce qui reflete des differences dans les bassins hydrographiques locaux et la proximite de la mer. De maniere generale, les sites arctiques et alpins ont presente de nombreuses similitudes, mais des differences considerables en ce qui a trait a la chimie de l'eau ont ete observees entre les sites situes a l'interieur du Territoire du Yukon. Ces differences peuvent etre liees aux differences touchant les caracteristiques du substrat rocheux et de la vegetation du bassin versant.

Data on the water chemistry and limnology of 24 lakes located between Yellowknife (62 8279N, 1148219W) and Contwoyto Lake (658309N, 1108009W) in the central Northwest Territories were examined using principal components analysis and other statistical techniques. The study sites were mostly shallow ( Zmax = 2.5-25 m; mean = 8.2 m), nutrient-poor (3.4- 12.7 mg total phosphorus/L; mean = 6.6 mg · L -1 ), low-alkalinity lakes. Water was typically low in solutes (specific conductance near 0-100 mS · cm -1 ), with slightly acidic to alkaline pH (6.2-8.9). Levels of all nutrients and major ions showed identical trends of decreasing concentrations with increasing latitude, with the highest concentrations generally in lakes with conifer-forested catchments in the south. Resume : Les donnees sur les caracteristiques chimiques et limnologiques de 24 lacs situes entre Yellowknife (62 8279N, 1148219W) et le lac Contwoyto (658309N, 1108009W) dans le centre des Territoires du Nord-Ouest (T.N.-O.) ont ete examinees a l'aide de l'analyse des composantes principales. Les sites d'etude etaient pour la plupart des lacs peu profonds ( Zmax = 2,5 a 25 m; moyenne = 8,2 m), pauvres en elements nutritifs (3,4 a 12,7 mg · L -1 en phosphore totale, moyenne = 6,6 mg · L -1 ) et de faible alcalinite. De maniere typique, l'eau etait pauvre en solutes (conductivite electrique pres de 0 a 100 mS · cm -1 ), et son pH variait de legerement acide a alcalin (6,2 a 8,9). Les concentrations de tous les elements nutritifs et des ions majeurs ont montre des tendances identiques, c.-a-d. qu'ils diminuaient avec l'augmentation de la latitude, les concentrations les plus elevees se trouvant generalement dans les lacs meridionaux avec forets de coniferes dans le bassin versant. (Traduit par la Redaction)

Diatoms, chrysophyte scales and cysts, and the siliceous plates of thecoamoebae were studied from the surface sediments of 20 freshwater habitats in Fennoscandia. The study sites are distributed along a latitudinal transect extending from southern Finland to northern Norway, spanning boreal forest through arctic tundra vegetational zones. Diatom assemblages were usually dominated by acidophilic, periphytic members of the genera Achnanthes, Fragilaria and Navicula. Marked shifts in diatom assemblage composition were recorded along the latitudinal transect, whereas scaled chrysophytes were rare in all study sites. Meanwhile, siliceous protozoa were common, but did not exhibit any noticeable trends in assemblage composition with changing latitude. A comparison of the Fennoscandian diatom assemblages with those recorded from freshwater sites near Yellowknife (central Northwest Territories, Canada) revealed similar trends in diatom assemblage composition with changing ecoclimatic zones in both regions. Moreover, canonical correspondence analysis showed that diatom assemblages in cold, dilute tundra sites were effectively separated from sites with forested catchments from both the Fennoscandian and Canadian transects. The general similarity between the two regions suggests that autecological data and the resulting environmental transfer functions based on diatom assemblages may eventually be joined from North American and European regions.

We identified, enumerated, and interpreted the diatom assemblages preserved in the surface sediments of 59 lakes located between Whitehorse in the Yukon and Tuktoyaktuk in the Northwest Territories (Canada). The lakes are distributed along a latitudinal gradient that includes several ecoclimatic zones. It also spans large gradients in limnological variables. Thus, the study lakes are ideal for environmental calibration of modern diatom assemblages. Canonical correspondence analysis, with forward selection and Monte Carlo permutation tests, showed that maximum lake depth and summer surface-water temperature were the two environmental variables that accounted for most of the variance in the diatom data. The concentrations of sodium and calcium were also important explanatory variables. Using weighted-averaging regression and calibration techniques, we developed a predictive statistical model to infer lake surface-water temperature, and we evaluated the feasibility of using diatoms as paleoclimate proxies. This model may be used to derive paleotemperature inferences from fossil diatom assemblages at appropriate sites in the western Canadian Arctic.

Pingualuk Lake fills a deep crater in the Parc National des Pingualuit on the Ungava Peninsula (Nunavik, Canada) and is isolated from nearby surface waters. The main objectives of this study were to determine and compare the concentrations of two atmospherically derived contaminants, mercury and perfluorinated chemicals (PFCs), in the lake water column and fish of Pingualuk Lake and to assess the physical and biological factors influencing contaminant concentrations. Mercury concentrations in arctic char muscle tissue were comparable to those of char in other Arctic lakes, while the total amount of PFCs was below reported levels for remote lakes in the Arctic and elsewhere. Stable isotope and stomach content analyses were made to investigate the feeding ecology of the Pingualuk Lake arctic char population and indicated the possibility of multiple feeding groups. Genetics characteristics (MH and mtDNA) of fish from Pingualuk Lake revealed that this population is likely distinct from that of nearby Laflamme Lake. However, both arctic char populations exhibit differential variation of their allele families. Physical characteristics determined for Lake Pingualuk revealed that the water column was inversely stratified beneath the ice and extremely transparent to visible and ultraviolet radiation. The highest mercury concentrations (3 – 6 pg mL-1 TH g) occurred just beneath the ice surface in each lake. Pingualuk Lake, given its near pristine state and exceptional limnological features, may serve as a most valuable reference ecosystem for monitoring environmental stressors, such as contaminants, in the Arctic.

[1] Thermokarst (thaw) ponds and lakes are distributed throughout arctic and subarctic regions; however their natural variability and temporal evolution recorded in the bottom sediments are poorly understood. This paper presents a multiproxy study conducted in a subarctic site with many thermokarst ponds near Kuujjuarapik-Whapmagoostui, on the eastern shore of Hudson Bay. Sedimentological, geochemical and chronological analyses have been performed on short sediment cores (10–20 cm) retrieved from limnologically contrasted ponds. Analyses revealed two distinct sedimentary facies, from bottom to top: 1) massive marine silts and clays deposited during postglacial Tyrrell Sea transgression (ca. 8000 to 6000 cal yr BP), subsequently emerged by glacio-isostatic rebound and more recently (ca. 1500 to 400 cal yr BP) affected by permafrost inception and growth; 2) laminated organic-rich lacustrine muds deposited since permafrost thawing and subsidence, i.e., since thermokarst pond inception (the last centuries). Despite displaying strikingly different water colors, the study ponds showed similar long-term developmental patterns regarding their physico-chemical properties (as recorded in the sediments), such as decreasing mineral grain size (from silts to clays), decreasing major chemical element concentrations, increasing organic matter content, and decreasing bottom water oxygen concentrations (from well-oxygenated to anoxic/hypoxic conditions).

Fourier transform infrared spectroscopy (FTIRS) can provide detailed information on organic and minerogenic constituents of sediment records. Based on a large number of sediment samples of varying age (0-340 000 yrs) and from very diverse lake settings in Antarctica, Argentina, Canada, Macedonia/Albania, Siberia, and Sweden, we have developed universally applicable calibration models for the quantitative determination of biogenic silica (BSi; n = 816), total inorganic carbon (TIC; n = 879), and total organic carbon (TOC; n = 3164) using FTIRS. These models are based on the differential absorbance of infrared radiation at specific wavelengths with varying concentrations of individual parameters, due to molecular vibrations associated with each parameter. The calibration models have low prediction errors and the predicted values are highly correlated with conventionally measured values (R = 0.94-0.99). Robustness tests indicate the accuracy of the newly developed FTIRS calibration models is similar to that of conventional geochemical analyses. Consequently FTIRS offers a useful and rapid alternative to conventional analyses for the quantitative determination of BSi, TIC, and TOC. The rapidity, cost-effectiveness, and small sample size required enables FTIRS determination of geochemical properties to be undertaken at higher resolutions than would otherwise be possible with the same resource allocation, thus providing crucial sedimentological information for climatic and environmental reconstructions.

[1] Permafrost thaw ponds result from the irregular melting and erosion of frozen soils, and they are active sites of greenhouse gas emissions to the atmosphere throughout the circumpolar North. In the discontinuous permafrost region of Nunavik, Canada, thaw ponds show pronounced differences in color even among nearby ponds, ranging from white to green, brown and black. To quantify this optical variation and to determine its underlying controlling mechanisms, we studied the apparent and inherent optical properties and limnological characteristics of the ponds. The pond colors were well separated on a color coordinate diagram, with axis values determined from above‐water spectral reflectance measurements. Our analyses of optical properties and their empirical relationships with optically active substances showed that the differences in color could entirely be attributed to variations in the concentration of two optically active substances: dissolved organic carbon, which was a major contributor to spectral absorption, and nonalgal suspended particulate matter, which contributed to spectral scattering as well as absorption. The latter component was dominated by small sized particles that had unusually high mass‐specific absorption and scattering properties. Analysis of high spatial resolution, multispectral satellite imagery of these ponds showed that these two optically important constituents could be estimated by multivariate modeling. The results indicate that remote sensing surveys will provide valuable synoptic observations of permafrost thaw ponds across the vast subarctic region, and may allow scaling up of local greenhouse gas flux measurements to regional and circumpolar scales.

FUTURE greenhouse warming is expected to be particularly pronounced in boreal regions1, and consequent changes in vegetation in these regions may in turn affect global climate2–4. It is therefore important to establish how boreal ecosystems might respond to rapid changes in climate. Here we present palaeoecological evidence for changes in terrestrial vegetation and lake characteristics during an episode of climate warming that occurred between 5,000 and 4,000 years ago at the boreal treeline in central Canada. The initial transformation — from tundra to forest-tundra on land, which coincided with increases in lake productivity, pH and ratio of inflow to evaporation — took only 150 years, which is roughly equivalent to the time period often used in modelling the response of boreal forests to climate warming5,6. The timing of the treeline advance did not coincide with the maximum in high-latitude summer insolation predicted by Milankovitch theory7, suggesting that northern Canada experienced regionally asynchronous middle-to-late Holocene shifts in the summer position of the Arctic front. Such Holocene climate events may provide a better analogue for the impact of future global change on northern ecosystems than the transition from glacial to nonglacial conditions.

[1] We welcome the opportunity to respond to Gajewski's [2008] comments on our study [Antoniades et al., 2007, hereinafter referred to as A07]. We demonstrate here that his assertions are not supported by the evidence and that the conclusions in A07 are based on a sound interpretation of the data.

Our understanding of long-term environmental change in arctic and antarctic lakes has advanced markedly over the last two decades. This research has been driven primarily by the growing realization that circumpolar regions are critical research areas for the study of global climatic and environmental change. Logistical improvements (e.g., increased availability of aircraft, research bases, enhanced communication technology, etc.) have also made polar research safer and more feasible. Nonetheless, high costs often preclude many research initiatives, and declines in government funding programs have resulted in the closure of some key monitoring stations that are essential for understanding many of the basic environmental, limnological, and hydrological

[1] An analysis of diatoms and fossil pigments in a sediment core from perennially ice-covered Ward Hunt Lake at latitude 83°N in Nunavut, Canada revealed striking changes in diatom communities and sedimentary pigment concentrations during the last two centuries. Diatoms were found only in the upper 2.5 cm of the sedimentary record, and where present, diatom assemblages were composed almost entirely of Staurosirella pinnata. Photosynthetic pigments were present in low concentrations throughout the sedimentary profile, consistent with the ultra-oligotrophic nutrient status of the lake. Pigment concentrations varied slightly in the lower sections of the core, and began to increase gradually at the 4 cm horizon followed by an increase of two orders of magnitude in the uppermost 2.5 cm. The changes observed in the sedimentary record of Ward Hunt Lake had similar trajectories to those observed post-1850 elsewhere in the circumpolar Arctic, and imply that aquatic communities even in the most extreme northern lakes have been strongly impacted by recent climate warming.

Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared.

1. Paleolimnological research in polar regions: An introduction. Reinhard Pienitz, Marianne S.V. Douglas and John P. Smol 2. Geochronology of high latitude lake sediments. Alexander P. Wolfe, Gifford H. Miller, Carrie A. Olsen, Steven L. Forman, Peter T. Doran and Sofia U. Holmgren 3. Physical and chemical properties and proxies of high latitude lake sediments. Scott F. Lamoureux and Robert Gilbert 4. Palynology of North American arctic lakes. Konrad Gajewski and Glen M. MacDonald 5. Algal indicators of environmental change in arctic and antarctic lakes and ponds. Marianne S.V. Douglas, Paul B. Hamilton, Reinhard Pienitz and John P. Smol 6. Aquatic invertebrates and high latitude paleolimnology. Ole Bennike, Klaus P. Brodersen, Erik Jeppesen and Ian R. Walker 7. Use of water isotope tracers in high latitude hydrology and paleohydrology. Thomas W.D. Edwards, Brent B. Wolfe, John J. Gibson and Dan Hammarlund 8. Lake sediments as records of arctic and antarctic pollution. Derek C.G. Muir and Neil L. Rose 9. Paleolimnology of the middle and high Canadian Arctic. Alexander P. Wolfe and I. Rod Smith 10. Paleolimnology of the North American Subarctic. Bruce P. Finney, Kathleen Ruhland, John P. Smol and Marie-Andree Fallu 11. Holocene paleolimnology of Greenland and the North Atlantic islands (north of 60 N). N. John Anderson, David B. Ryves, Marianne Grauert and Suzanne McGowan 12. Paleolimnological research from northern Russian Eurasia. Glen M. MacDonald, Thomas W.D. Edwards, Bruce Gervais, Tamsin E. Laing, Michael F.J. Pisaric, David F. Porinchu, Jeffrey A. Snyder, Nadia Solovieva, Pavel Tarasov and Brent B. Wolfe 13. Paleolimnological studies in arctic Fennoscandia and the Kola Peninsula (Russia).Atte Korhola and Jan Weckstrom 14. Paleolimnological studies from the Antarctic and subantarctic islands. Dominic A. Hodgson, Peter T. Doran, Donna Roberts and Andrew McMinn 15. Paleolimnology of extreme cold terrestrial and extraterrestrial environments. Peter T. Doran, John C. Priscu, W. Berry Lyons, Ross D. Powell, Dale T. Andersen and Robert J. Poreda 16. Epilogue: Paleolimnological research from arctic and antarctic regions. Reinhard Pienitz, Marianne S.V. Douglas and John P. Smol

Evaluation and assessment of fresh and inland water quality at the regional and global scales is not a simple task. UNEPs GEMS/Water has operated a comprehensive freshwater quality monitoring and assessment programme for over 20 years and is the only such global programme. GEMS/Water operates by inviting national governments to provide water quality data from their water quality monitoring programmes. The data is then compiled into a global database, GLOWDAT, which is a value-added process. GEMS/Water, United Nations agencies and other international organizations use the data to undertake global and regional scale water quality assessments. More than 100 countries participate in the programme that has a database of>1.6 million data entries. Participating countries control, for example, the type of data collected, the location of sampling sites, the frequency of monitoring, the analytical and field methods used and the frequency at which data is transferred to GEMS/Water. In order to make effective water quality assessments, identify emerging water quality issues and environmental ‘hotspots’, the data available must be of good quality, comparable between countries for a specific parameter, be geographically representative for a given region and be up-to-date. The only way for GEMS/Water to ensure that all these characteristics are satisfied in GLOWDAT would be for GEMS/Water to operate its own global water quality-monitoring programme. This is economically unfeasible. However, GEMS/Water has an operational manual, a modular training course and operates a QA/QC programme to help countries with data quality. Some countries have modernized their water quality programme, a complex and comprehensive activity that includes legal and institutional considerations, technical issues, and a strategic program of capacity building. Implementation of such comprehensive programmes in more countries will lead to better quality data for GEMS/Water.

We aimed to determine whether the copepod assemblages in lakes and ponds of northern Quebec, Canada, were closer in composition to those found in southern Quebec, or to those reported from the subarctic and arctic. Six calanoid and five cyclopoid species were identified from 37 ponds and lakes located in the region between 55° N and 59° N. Species diversity was generally low, ranging from 0 to 4 species per lake. Dominant species were Leptodiaptomus minutus and Acanthocyclops vernalis. The species assemblages showed high affinity with those found in forested regions of southern Quebec. Exceptions were Leptodiaptomus tyrrelli, previously only recorded west of Hudson Bay, and Hesperodiaptomus arcticus, hitherto recorded north of 58° N. Relationships between the lakes, species, and environmental variables were explored using multivariate analysis. Lakes situated along the coast and on two offshore islands clustered together and were characterised by higher conductivity and pH than those lakes located further inland. Leptodiaptomus tyrrelli was common in these coastal lakes. Canonical correspondence analysis revealed statistically significant relationships between copepod distributions and conductivity, dissolved organic carbon and pH. These three variables accounted for 70% of the variation in the species' distribution.

The effect of stratospheric ozone depletion on increases in ambient levels of solar ultraviolet (UV) radiation in high-latitude regions' has raised concerns about the response of northern ecosystems to environmental change. The concentration of coloured dissolved organic material, which is derived from terrestrial vegetation and acts as a screen for ultraviolet radiation, is low in high-latitude lakes. The underwater light environment in these lakes is therefore likely to be sensitive to small variations in the supply of this material, in addition to the effects of ozone depletion. Here we use fossil diatom assemblages in combination with bio-optical models to estimate the magnitude of past variations in the underwater light regime of a lake at the boreal tree line. We find large shifts in underwater UV-B, UV-A and photosynthetically available radiation associated with changes in the input of coloured dissolved organic material into subarctic lakes during the Holocene. The inferred changes in biological exposure to UV radiation were at least two orders of magnitude greater than those associated with moderate (30%) ozone depletion. Our findings indicate that freshwater ecosystems at present located across vegetation gradients will experience significant shifts in underwater spectral irradiance through the effects of climate change on catchment vegetation and the export of coloured dissolved organic material.

Reports of severe stratospheric ozone depletion over the Arctic have heightened concern about the potential impact of rising ultraviolet-B (UV-B) radiation on north polar aquatic ecosystems. Our optical measurements and modelling results indicate that the ozone-related UV-B influence on food web processes in the Arctic Ocean is likely to be small relative to the effects caused by variation in the concentrations of natural UV-absorbing compounds, known as chromophoric dissolved organic matter (CDOM), that enter the Arctic basin via its large river inflows. The aim of our present study was to develop and apply a simple bio-optical index that takes into account the combined effects of attenuation by atmospheric ozone and water column CDOM, and photobiological weighting for high-latitude environments such as the Arctic Ocean. To this end, we computed values for a biologically effective UV dose rate parameter ("weighted transparency" or T*) based on underwater UV measurements in high-latitude lakes and rivers that discharge into the Arctic Ocean; measured incident UV radiation at Barrow, Alaska; and published biological weighting curves for UV-induced DNA damage and UV photoinhibition of photosynthesis. The results underscore how strongly the Arctic Ocean is influenced by riverine inputs: shifts in CDOM loading (e.g., through climate change, land-use practices, or changes in ocean circulation) can cause variations in biological UV exposure of much greater magnitude than ozone-related effects.

PAGES news • Vol 17 • No 3 • October 2009 Sc ie nc e H ig hl ig ht s: P al eo lim no lo gy of the subtropical region of South America (i.e., the transition between the tropics and the extra tropics) in deciphering the forcing factors of past changes in atmospheric circulation. Both Argentinean and Uruguayan Holocene paleolimnological records indicate similar paleoclimatic trends, i.e. dominant dry conditions were observed during cold phases, whereas wet conditions prevailed during warm climatic phases. To our knowledge, this is the first attempt to integrate paleoclimatic data for the whole Pampean region. In addition, our results underscore the need to reinforce paleoclimate research at mid-latitudes in South America, in an attempt to fully appreciate natural climate variability beyond the instrumental record, as well as to design new strategies for the sustainable development of ecosystems and natural resources.

Seasonal changes in water chemistry and periphytic diatom assemblages were monitored for a saline, a subsaline, and a freshwater lake in the central Yukon Territory. Athalassic saline lakes, such as these, are believed to be extremely rare in arctic regions. All three study lakes exhibited a gradual shoreline retreat over the season (28 May to 22 August 1992) due to evaporative water loss. As the season progressed, the saline lake exhibited a marked increase in conductivity and salinity, sim ilar to changes observed for inland salt lakes in more southern regions. The seasonal changes in water chemistry were less pronounce d in the subsaline and freshwater lakes. The periphytic diatom populations of the saline lake closely tracked changes in the lake 's salinity, exhibiting a successional shift from taxa with low salt tolerances (e.g., Nitzschia cf. commutata and N. cf. palea) to those with high salt tolerances (e.g., Amphora acutiuscula) over the study period. Periphytic diatoms in the subsaline and freshwater lakes also exhibited marked successional changes, shifting to almost complete dominance by a single species ( Cocconeis placentula and Achnanthes minutissima respectively), but these shifts were not related to lake water salinity alone.

Mercury (Hg) profiles were compared to profiles of climate indicators including microfossil remains and algal-derived or S2 carbon (C) in dated sediment cores from 14 lakes spanning latitudinal and longitudinal gradients across the Canadian high and subarctic. Hg fluxes increased postindustrialization (post-∼1850) in 11 of these lakes (postindustrialization Hg fluxes (ΔHgF(F)) = 2-24 μg m(-2) y(-1)). Correction of HgF(F) for catchment contributions demonstrated that Hg deposition originating from catchment-independent factors, such as atmospheric deposition, increased since industrialization in all 14 lakes. Several of these lakes also showed postindustrial shifts in algal assemblages consistent with climate-induced changes. Eleven lakes showed post-1850s increases in S2F(F), suggesting that lake primary productivity has recently increased in the majority of our sites (ΔS2F(F) = 0.1-4 g m(-2) y(-1)). Other studies have interpreted significant relationships between Hg:S2 concentrations in Arctic sediment as support for the algal scavenging hypothesis, which postulates that Hg fluxes to Arctic sediments are largely driven by S2. However, in six of our lakes we observed no Hg:S2 relationship, and in one lake a significant negative Hg:S2 relationship was observed due to increased Hg and decreased S2 C deposition during the postindustrialization period. In six of the seven lakes where a significant positive Hg:S2 relationship was observed, algal assemblages either did not change through time or the timing of the shifts did not correspond to changes in Hg deposition. Our results demonstrate that, although Arctic lakes are experiencing a myriad of changes, including increased Hg and S2 deposition or changing algal assemblages, increased lake primary productivity does not appear to be driving changes in Hg fluxes to sediments.

The phototrophic communities in meromictic, perennially ice-covered Lake A, on Ellesmere Island in the Canadian High Arctic, were characterized by pigment analysis using high performance liquid chromatography. Samples were taken to determine the vertical changes down the water column as well as a variation between years. These analyses showed that Lake A had distinct phototrophic communities in its oxic and anoxic layers. The pigment analyses indicated that phototrophic biomass in the upper, oxic waters was dominated by picocyanobacteria, while in the lower, anoxic layer photosynthetic green sulphur bacteria were dominant. Interannual variation in pigment concentrations was related to the penetration of photosynthetically active radiation in the water column, suggesting that light availability may be limiting the net accumulation of photosynthetic bacterial biomass in Lake A. Pigment analysis of the surface sediments indicated that deposition was dominated by the photosynthetic sulphur bacterial contribution. The sedimentary record of bacterial pigments in polar meromictic lakes offers a promising tool for the reconstruction of past changes in ice cover and therefore in climate. 2009 Elsevier B.V. and NIPR. All rights reserved.

Several recent studies have successfully applied diatom-based paleolimnological techniques to infer past hydrological changes in arctic and subarctic regions. For example, we summarize arctic studies that attempt to determine changes in peat water content, flood frequency, river discharge, effective moisture and ice cover in northern regions. Some of the investigations are still in preliminary stages, but represent innovative approaches to study arctic and subarctic paleohydrology. New data demonstrate that lake depth, which may be related to changing hydrological conditions, is a significant variable influencing the distributions of diatom taxa in lake surface sediment calibration sets from Wood Buffalo National Park (WBNP), on the border of Alberta and the Northwest Territories, Canada, and from Fennoscandia (mainly northwest Finland). Weighted averaging regression and calibration methods were used to develop quantitative inference models for lake depth using diatom assemblages preserved in surface sediments. The predictive abilities of the transfer functions were relatively high (for WBNP r2 = 0.70 and RMSE = 2.6 m, and for Fennoscandia r2 = 0.88 and RMSE = 1.8 m). However, evaluating the transfer functions using jack-knifing procedures indicated lower predictive abilities, possibly reflecting the relatively small sample size and/or short gradients used in these calibration sets. Such transfer functions can be used to track overall trends in lake levels, and provide an objective assessment as to directions of changing lake levels. Any interpretations of inferred lake levels, especially those related to climate change, must be made cautiously and must include some understanding of the local, present-day hydrological system.

Lakes are a major feature of Arctic and Antarctic landscapes and are likely to be sensitive indicators ofclimate change. New bio-optical technologies for in situ measurements (e.g. UV-profiling) and remote sensing (e.g. light detection and ranging) now offer a suite of options for long-term monitoring at these sites. Certain properties of high-latitude lakes are highly responsive to changes in climate forcing and could be targeted within a monitoring strategy based on optical properties; these include lake levels, lake-ice dynamics, phytoplankton biomass and chromophoric dissolved organic matter (CDOM). High-latitude lakes are optically sensitive to changes in CDOM export from their surrounding catchments that could result from climate effects on hydrology and vegetation. Using a new model based on biologically weighted transparency, we show that a 20% change in GDOM concentration (as measured by dissolved organic carbon) can have a much greater effect on UV inhibition of phytoplankton than a similar percentage change in stratospheric ozone. Much of this effect is due to UV-A, because the reduced photodamaging effect per unit energy (i.e. low biological weighting) in this waveband is offset by its higher incident flux at the lake surface relative to UV-B and its deeper penetration into the water column. These transparency calculations also show that small changes in CDOM in polar lakes will have a large effect on underwater light availability for photosynthesis. The spectral absorption and fluorescence properties of CDOM lend themselves to a variety of optical monitoring approaches. Future research on the paleo-optics of GDOM will allow the interpretation of current optical trends in high-latitude lakes relative to the scales of natural variability in the past.

Les lacs de villégiature du Québec méridional sont soumis à des pressions anthropiques croissantes. Conséquemment, on observe une intensification de l’eutrophisation avec les effets indésirables que cela comporte, tels une diminution de la biodiversité et un accroissement des espèces tolérantes comme les cyanobactéries. Le premier objectif de l’étude consiste à documenter les interactions qui s’opèrent entre les variables limnologiques et géologiques à l’étude et le processus d’eutrophisation. Le second objectif vise à déterminer a posteriori l’état trophique des lacs étudiés. Pour ce faire, des analyses de corrélations, de groupement et de covariances ont été menées grâce à l’utilisation d’une série de données comptant 57 variables environnementales. Les analyses de corrélations ont montré, tel que normalement observé, qu’il y a un lien étroit entre la concentration de phosphore total, l’abondance des algues et la diminution de la transparence de l’eau. De plus, l’accroissement de la biomasse primaire dans les lacs eutrophes et hypereutrophes était corrélé avec l’augmentation des concentrations d’aluminium dissous. Par ailleurs, les résultats montrent que la géologie des bassins versants joue un rôle prépondérant sur les propriétés alcalines des lacs et conséquemment, le niveau de production primaire semble s’en trouver accrue. Enfin, l’ensemble des lacs à l’étude représente un gradient trophique complet, soit des conditions trophiques classées ultra-oligotrophes à hypereutrophes, ce qui permettra d’effectuer une étude comparative entre le gradient trophique et la structure des communautés de diatomées lors des travaux futurs., Recreational lakes in southern Quebec are under increasing anthropogenic pressure. As a consequence, an increasing state of eutrophication has been observed, associated with some negative side effects, such as loss of biodiversity and a rise in tolerant cyanobacteria. The first objective of our study was to document the relationships that exist between the geological setting and the limnological characteristics of the study lakes and the process of eutrophication. To this end, correlation, cluster and covariance analyses were conducted using a data set including 57 environmental variables. The correlation analysis usually showed a close link among the total phosphorus concentration, algal abundance and decreasing water transparency in all study lakes. In addition, an increase in primary biomass in eutrophic and hypertrophic lakes was correlated with increasing concentrations of dissolved aluminium. Our results also show that the geological composition of a lake’s watershed strongly controls its alkaline properties and, consequently, its level of primary production. Finally, our set of lakes represented a complete trophic gradient, with trophic conditions ranging from ultra-oligotrophic to hypertrophic. This data set provides a starting point for future studies into the relation between the trophic gradient and the structure of diatom communities in temperate lakes.

The Holocene sediment records of two lakes, located 50 km south of the Ungava Bay coast near Kuujjuaq have been examined using diatom analysis in order to trace basin isolation from marine influence. The succession of diatom zones clearly documents paleoenvironmental changes induced by glacio-isostatic uplift and regression of postglacial D'lberville Sea through consecutive periods of marine occupation, isolation from the sea and subsequent lacustrine conditions. Diatom analysis proved to be an effective tool in identifying the position of the isolation contact in the sediment columns and in defining the related changes in paleosalinity and isolation dynamics. Based on the Sedated isolation contacts and the threshold elevations of both lakes, a tentative emergence curve has been reconstructed which is in agreement with curves from adjacent areas. This allowed, for the first time, to infer trends in glacio-isostatic rebound and duration of marine submergence for an area from which paleogeographical data are almost entirely lacking. The curve shows that, following déglaciation about 7000 years ago, the Kuujjuaq area experienced continuous and rapid emergence in the order of 5.7-5.8 m/century until 4800-4300 years BP. Thereafter, emergence slowed to a rate of approximately 0.9 m/century. This study provides further evidence for the usefulness of diatom analysis in reconstructing sea-level changes and land uplift of formerly glaciated regions., Le contenu diatomifère de carottes provenant du fond de deux lacs situés près de Kuujjuaq à 50 km au sud du rivage de la baie d'Ungava, a été examiné en vue de retracer les phases d'isolement de ces lacs de la mer postglaciaire d'lberville. La succession stratigraphique des zones de diatomées démontre clairement les changements paléoenvironnementaux provoqués par le relèvement isostatique postglaciaire et la régression marine; on reconnaît en effet dans les séquences diatomologiques une phase d'occupation marine, une phase d'isolement de la mer et une phase lacustre subséquente. L'analyse des diatomées s'est révélée un outil utile pour identifier la phase et les modalités d'isolement des bassins devenus lacustres et pour retracer les changements de paléosalinités associés. En tenant compte des dates au 14C sur les unités d'isolement, de l'altitude du seuil de ces lacs et de la forme des courbes d'émersion des régions adjacentes, une courbe d'émersion préliminaire de la région de Kuujjuaq a pu être construite. Cette courbe montre qu'après la déglaciation, datée à 7000 BP, !'emersion fut rapide et continue à un taux moyen de l'ordre de 5,7-5,8 m/siècle jusqu'à environ 4800-4300 BP. Par après, !'emersion fut plus lente, à un taux d'environ 0,9 m/siècle. Cette étude s'ajoute à d'autres pour mettre en évidence le grand potentiel de l'analyse des diatomées pour la reconstruction précise de courbes de variation du niveau marin et de relèvement isostatique des régions englaciées., Um die Abtrennung (Isolation) zweier kùstennaher Seen von marinem Einflup rekonstruieren zu konnen, wurden deren holozane Sedimente auf ihren Gehalt an fossilen Diatomeen untersucht. Die beiden Seen befinden sich etwa 50 km sùdlich der Ungava Bay in der Nâhe Kuujjuaqs. Die Abfolge der Diatomeenassoziationen dokumentiert eindeutig durch isostatische Landhebung bewirkte palàogeographische Verânderungen, wie z.B. das Zurùckweichen des post-glazialen d'lberville Meeres mit aufeinander folgenden Phasen mariner Ùberschwemmung, Isolation vom Meer und Ùbergang zu Sùpwasserbedingungen. Die Diatomeenanalyse erlaubte die Festlegung der exakten Lage des Isolationshorizontes, der Sedimente marinen Ursprungs von SGp-wassersedimenten trennt. Darùber hinaus erlaubte sie die Rekonstruktion der im Verlaufe der Heraushebung erfolgten Isolations-prozesse und Salzgehaltsschwankungen. Durch radiometrische Altersbestimmung (14C) der Isolationshorizonte und Ermittlung der Hôhenlage der randlichen Strandterrasse beider Seen konnte eine Landhebungskurve erstellt werden, die generell mit denen benachbarter Regionen im Gebiet der Ungava Bay ùbereinstimmt. Anhand dieser Landhebungskurve kann festgehalten werden, dap das Gebiet um Kuujjuaq in der Zeitspanne von letztem Eisrùckzug vor etwa 7000 Jahren bis 4800-4300 BP kontinuierliche und schnelle Heraushebung in der Grôpenordnung von 5,7-5,8 m/Jahrhundert erfuhr. Danach hat sich die Heraushebungsgeschwindigkeit bis auf etwa 0,9 m/Jahrhundert verlangsamt. ­

Diatom analyses of sediments from a high elevation lake situated in an Engelmann Spruce - Subalpine Fir (ESSF) forest of south-central British Columbia, Canada, reveal long-term climate and water chemistry change. During the transition from the late-glacial / Pleistocene to the xerothermic early Holocene, small, benthic Fragilaria diatoms species that grew under low light conditions in Sicamous Creek Lake gave way to planktonic Cyclotella species that require open-water conditions. Warm temperatures in the mesothermic Holocene are indicated by smaller Cyclotella species and large, benthic pennate diatoms. Diatom communities reflected Neoglacial cooling in the late Holocene, with abundant Nitzschia fonticola and Achnanthes minutissima. Small, benthic Fragilaria regained abundance, suggesting cooling and conditions similar to the late-glacial interval. Diatom community composition responded to the deposition of the Mt. Mazama and Mt. St. Helens tephras, though the Mazama eruption caused greater change in relative abundance of various taxa within the assemblage. Correspondence analysis shows distinct communities have occurred since the initiation of sedimentation, likely due to climate controlled landscape and vegetation changes; diatom-inferred pH values using various models and training sets show limited acidification change occurred through the lake’s history., Les analyses de diatomées fossiles préservées dans les sédiments du lac Sicamous Creek en haute altitude, situé dans la partie centrale-sud de la Colombie-Britannique, Canada, révèlent des changements du climat et de la chimie de l'eau dans une forêt composée principalement d’épinette d’Engelmann et de sapin subalpin. Au passage du Tardiglaciaire / Pléistocène à l’Holocène supérieur xérothermique, les petites espèces benthiques du genre Fragilaria qui dominaient dans le lac Sicamous Creek sous des conditions de faible lumière ont été remplacées par des espèces planctoniques du genre Cyclotella qui sont favorisées par des conditions d'eau ouverte. Les températures élevées durant l’Holocène mésothermique sont caractérisées par des espèces de Cyclotella de petite taille et par des diatomées pennées benthiques de grande dimension. Le refroidissement dû à la néoglaciation durant l’Holocène inférieur est reflété par l’abondance de Nitzschia fonticola et Achnanthes minutissima dans les communautés de diatomées. Les petites diatomées benthiques du genre Fragilaria regagnaient en abondance, suggérant des conditions froides semblables à celles observées durant le Tardiglaciaire. La composition de la communauté des diatomées a changé en réponse aux retombées aériennes de téphra en provenance des monts Mazama et St. Helens, bien que l'éruption du mont Mazama ait provoqué un plus grand changement dans l’assemblage. L'analyse de correspondances démontre l’apparition des communautés distinctes depuis le début de la sédimentation probablement en raison des changements du paysage et de la végétation qui étaient contrôlés par le climat. Des valeurs de pH déduites des diatomées, utilisées dans différents modèles statistiques et avec diverses séries de calibration, indiquent une acidification limitée au cours de l'histoire du lac.