Ecological training set of freshwater ostracods in Canadian and Siberian periglacial regions

Quantified palaeoenvironmental reconstructions are essential to estimate the impact of future climate changes on ecosystems. Based on faunistic data from regional multireference sites and limnological surveys, ecological training sets can be used to build transfer functions to infer major environmental variables (e.g., temperature, conductivity, DOC, and pH value) in a greater study area. The remote Polar regions are affected by bigger amplitude of climate change than elsewhere on this planet and make ecological training sets in this region so important.Freshwater ostracods from Arctic nvironments have the potential to hindcast glacial/interglacial and stadial/interstadial alaeoclimate variations. Various methods can be applied to fossil assemblages such as indicator species approach, modern analoguetechniques and transfer functions based on ecological training sets.The present training set combines data from the Canadian (Southampton Island at 63-65°N; Bylot Island at 72-73°N) and the Siberian (Central Yakutia at 61°N; Northeast Yakutia at 66°N; Lena Delta at 72°N) high latitudes with reference areas in Central Canada (Whapmagoostui-Kuujjuarapik at 50-55°N; Churchill at 58°N). A total of 75 localities were sampled during field work in 2005-2007. In general, life conditions for aquatic organisms such as freshwater ostracods in the high latitude regions are extremeand limited by short open water periods during the summer and strong variations of water temperatures in the shallow waters. The host waters in periglacial regions are affected by permafrost and thermokarst processes and mostly represented as polygonal ponds or thermokarst lakes in different stages of their development. Generally, the waters in our study area have a mean pH-value of 7.6, ranging from pH 6.0 to pH 9.2. They are characterised by low ionic contents (Condmean = 231μS*cm−1), but the training set includes sites between 4.4 μS*cm−1 (e.g., on Bylot Island) and 1433 μS*cm−1 (e.g., in Central Yakutia). A principal component analysis reveals that 88.5 % of the variability of the environmental data is explained by the first ordination axis corresponding to pH, conductivity and major cations (i.e., Ca, Na). The studied ostracod assemblages are characterised by dominance of single species indifferent regions, e.g., Cyclocypris ovum on Bylot Island, Fabaeformiscandona pedata in the Lena Delta. In general, the species diversity in northern latitudes is relatively low due to the harsh environmental conditions affecting ostracods ontogeny. In total, 16 species were used in the presented data set.Further implementation of the ecological training set into transfer functions for one or more variables are prosperous

Isolation of Lacustrine Basins and Marine Regression in the Kuujjuaq Area, Northern Québec, as Inferred from Diatom Analysis

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.

Control of Biological Exposure to UV Radiation in the Arctic Ocean: Comparison of the Roles of Ozone and Riverine Dissolved Organic Matter

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 highlatitude 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

Lake Water Salinity and Periphytic Diatom Succession in Three Subarctic Lakes, Yukon Territory, Canada

Seasonal changes in water chemistry and periphytic diatom assemblages were monitored for a saline, a subsaline, and 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, similar to changes observed for inland salt lakes in more southern regions. The seasonal changes in water chemistry were less pronounced 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.Key words: lakes, diatoms, seasonal succession, saline, subarctic, YukonOn a observé les variations saisonnières dans la composition chimique de l'eau et les assemblages de diatomées périphytoniques, dans un lac salin, un lac subsalin et un lac d'eau douce dans le centre du Territoire du Yukon. On croit que de tels les lacs salins ne venant pas de la mer, sont très rares dans la région arctique. Les trois lacs étudiés ont tous montré un retrait du rivage dû à la perte d'eau par évaporation au cours de la saison (du 28 mai au 22 août 1992). Au fur et à mesure que la saison avançait, le lac salin montrait une augmentation marquée de conductivité et de salinité semblable à celle observée dans les lacs intérieurs salins de régions plus au sud. Les changements saisonniers dans la composition chimique de l'eau étaient moins prononcés pour les lacs subsalin et d'eau douce. Les populations de diatomées périphytoniques du lac salin variaient directement en fonction des changements de salinité du lac, montrant des changements de succession allant de taxa à faible tolérance au sel (e.g., Nitzschia cf. commutata et N. cf. palea) à des taxa à forte tolérance au sel (e.g., Amphora acutiuscala) pendant la période d'étude. Les diatomées périphytoniques dans les lacs subsalin et d'eau douce ont aussi montré des changements de succession marqués, allant jusqu'à la domination presque complète d'une seule espèce (Cocconeis placentula et Achnanthes minutissima respectivement); ces changements n'étaient cependant pas reliés uniquement à la variation de salinité de l'eau des lacs.Mots clés: lacs, diatomées, succession saisonnière, salin, subarctique, Yuko

Response of Lacustrine Biota to Late Holocene Climate and Environmental Conditions in Northernmost Ungava (Canada)

Sediment cores from three lakes located in the northernmost region of Ungava, Québec (Canada) were examined to define aquatic community and ecosystem variability during the Late Holocene period. A chironomid-based transfer function was used to reconstruct August air temperature trends, and lacustrine primary production was inferred from sedimentary biogenic silica content and siliceous microfossil abundances. Trends in primary production, sediment organic matter content (estimated through loss on ignition), and chironomid-inferred temperature were compared to explore potential effects of environmental change on biotic assemblage composition at centennial to millennial time scales. Although no direct correlation between chironomid-inferred August air temperature and primary production was observed, we found indications that both chironomid and diatom communities were responding to the same overarching regional climatic and environmental processes. Over the last decade, northern Québec has been undergoing notable, rapid warming that contrasts with the relative inertia of the past few millennia. This study provides a baseline against which recent and future environmental changes in this region can be compared. Les archives sédimentaires couvrant la période de l’Holocène tardif ont été examinées dans trois lacs situés dans la région du nord de l’Ungava, au Québec (Canada). Un modèle d’inférence basé sur les assemblages de chironomides a été utilisé pour reconstruire la variabilité des températures de l’air du mois d’août, et la production primaire lacustre a été inférée par le contenu sédimentaire en silice biogénique et les abondances des microfossiles siliceux. Les variations historiques de la production primaire, du contenu organique du sédiment (évalué par la perte au feu) et les températures inférées ont été comparées afin d’explorer les effets potentiels des changements environnementaux sur la composition des assemblages à différentes échelles temporelles (centenaires à millénaires). Malgré le fait qu’aucune corrélation directe n’ait été observée entre les températures inférées en août et la productivité primaire, certaines indications suggèrent que les communautés de chironomides et de diatomées répondaient aux mêmes processus climatiques et environnementaux régionaux. Au cours de la dernière décennie, le nord du Québec a connu un réchauffement rapide et marqué, contrastant avec l’inertie relative des derniers millénaires. Cette étude fournit le scénario de référence par rapport auquel les changements environnementaux actuels et futurs pourront être comparés dans cette région

Étude paléolimnologique de l'histoire trophique du lac Saint-Charles, réservoir d'eau potable de la Communauté Urbaine de Québec

Cette étude utilise une approche paléolimnologique pour reconstituer l'histoire trophique du réservoir d'eau potable de la Communauté Urbaine de Québec (CUQ), le lac Saint-Charles. Ce lac manifeste présentement un manque d'oxygène près du fond à la fin de la stratification estivale et hivernale. L'étude révèle des changements dans la communauté diatomifère fossile depuis environ les 150 dernières années. L'événement ayant entraîné le plus de changements biologiques et physico-chimiques dans le bassin est la transformation hydrologique engendrée par la construction d'un barrage en 1934 qui éleva le niveau du lac d'environ 1,5 à 2 mètres. Par conséquent, il y eut des changements dans la structure des communautés de diatomées avec des effets sur le ratio espèces planctoniques / benthiques, sur la paléoproductivité et les caractéristiques physico-chimiques des sédiments suivant cette période. Les assemblages diatomifères indiquent que les conditions mésotrophes se sont maintenues pendant toute la période étudiée. L'analyse du phosphore total dans les sédiments et la reconstitution à partir des diatomées fossiles du phosphore total dans l'eau montrent une légère diminution de la concentration en phosphore avec le temps. Ces observations démontrent qu'il n'y a pas eu d'accélération du processus d'eutrophisation engendrée par les activités humaines. Par contre, l'analyse géochimique des sédiments révèle un apport plus important de métaux depuis la fin du 19e siècle, qui atteint un plateau vers la fin des années 70.This study adopted a combined paleolimnological-limnological approach towards evaluating the trophic history of Lake Saint-Charles, the drinking water reservoir for a population of 305,000 in the Québec City (Canada) region. Our limnological measurements indicate that the lake is currently in a state of advanced mesotrophy. Water column profiles during late summer stratification (September) showed that the bottom waters were anoxic, enriched in phosphorus (up to 17 µg total P L-1) and had a pH almost 2 units lower than the surface waters. Surface phytoplankton concentrations were high at this time of year with Chlorophyll a concentrations of up to 12 µg·L-1. At the end of winter stratification, oxygen concentrations were below saturation at all depths, ranging from 72% immediately under the ice to 4% at the bottom of the water column. This tendency towards eutrophic conditions was offset, however, by a rapid flushing rate (mean hydraulic residence time=23 days). Because there are concerns that the lake has experienced accelerated nutrient enrichment due to increased human activities in its drainage basin, the objectives of our paleolimnological approach were to document the recent trophic history of this lake, to estimate the extent of recent changes in trophic status, and to identify critical periods of past anthropogenic disturbances from the fossils of siliceous algae (diatoms; class Bacillariophyceae) preserved in its sediments. Quantitative estimates of past total phosphorus (TP) concentrations in the water column of Lake Saint-Charles were obtained by applying a diatom-TP reconstruction model developed for 54 lakes located in south-eastern Ontario to fossil diatom assemblages from a 28 cm long sediment core. The timing of changes in the fossil diatom record was estimated by210 Pb dating. The study reveals changes in fossil diatom assemblage composition during the past ca. 150 years, with the most striking biological and physico-chemical changes occurring immediately after 1934. This date coincides with the construction of a dam, which raised the lake water level by 1.5-2 m. This modification was accompanied by significant shifts in diatom community structure, especially in the planktonic/benthic ratio (with increases in planktonic diatoms Cyclotella stelligera and Aulacoseira distans), and by changes in the physico-chemical characteristics of the sediments. Paleoproductivity increased at the same time, but remained more or less stable following conservation efforts between 1950 and 1970 (e.g., construction of a sewage treatment system). The organic matter content of the sediments showed an increase in the order of 20% between 1850 and 1950, after which it remained constant. Fossil diatom community structure indicates that mesotrophic conditions have prevailed during the recent history of Lake Saint-Charles, and that diatoms typical of eutrophic conditions never became established in the lake. The geochemical analysis of phosphorus in the sediments as well as the diatom-inferred quantitative reconstruction of lake water total phosphorus reveals a slight decrease in total phosphorus over time, from close to 17 µg·L- prior to 1887 to about 13 µg·L- 1 in recent times. These observations suggest that Lake Saint-Charles has not experienced significant recent changes in trophic status due to increased human activities in its drainage basin. However, our geochemical analyses show a sharp rise in metal concentrations (especially Fe, Mn, Cu, Pb and Zn), beginning in the late 19th century, reaching a plateau by the late 1970s, which may be attributed to increased atmospheric pollution since the beginning of intense human colonization in the lake's catchment and surrounding areas. This in combination with the advanced mesotrophic status of the lake indicates the ongoing need for careful management of the watershed to prevent further changes in this important urban water resource

Paleo-environmental gateways in the eastern Canadian arctic – Recent isotope hydrology and diatom oxygen isotopes from Nettilling Lake, Baffin Island, Canada

Nettilling Lake is located on Baffin Island, Nunavut, Canada between the areas of past warming (Canadian High Arctic to the North) and climatic stability (Northern Quebec and Labrador region to the South). Despite being the largest lake in the Nunavut region with a postglacial marine to lacustrine transition history only a few paleo-environmental investigations were completed in this area. The oxygen isotope composition of diatoms (d18O diatom) can provide valuable insights into paleo-environmental conditions. Here, the recent (isotope) hydrology and hydrochemical data from the lake are presented to facilitate the interpretation of a d18O diatom record from an 82 cm sediment core (Ni-2B). The well-mixed lake (d18O water = -17.4‰) is influenced by a heavier (less negative) isotope composition (-18.80‰) from Amadjuak River draining Amadjuak Lake to the South and water of lighter (more negative) isotopic composition (-16.4‰) from the Isurtuq River originating from Penny Ice Cap in the North-East. From the d18O water and d18O diatom of the topmost sample of core Ni-2B a D18O silica-water of 1000 ln alpha(silica-water) = 40.2‰ for sub-recent diatoms of Nettilling Lake was calculated matching the known water-silica fractionation for fossil sediments well and thereby showing the general applicability of this proxy for paleo-reconstructions in this region. Extremely large d18O diatom variations in the core of more than 13‰ are mainly induced by changes in the isotopic composition of the lake water due to a shift from glaciomarine (d18O diatom = +34.6‰) through brackish (+23.4 to +27.2‰) towards lacustrine (+21.5‰) conditions (transition zones glaciomarine to brackish at 69 cm/7300 yr cal. BP and brackish to lacustrine at 35 cm/6000 yr cal. BP) associated with a shift in the degree of salinity. Our study provides the first evidence that paleo-salinity can be reconstructed by d18O diatom. Additionally, for the lacustrine section it could be demonstrated that d18O diatom may serve as a proxy for past air temperature within the same core recording a late Holocene cooling of about 4°C being consistent with other published values for the greater Baffin region

Sedimentary pigments as indicators of cyanobacterial dynamics in a hypereutrophic lake

Abstract Lac Saint-Augustin is an urban lake located on the outskirts of Quebec City, one of North America's oldest cities. Anthropogenic inputs from land clearing, agriculture, highway development and urbanization in the surrounding catchment have resulted in strong impacts on the limnology of the lake throughout the past three centuries. In recent years, this lake has experienced severe eutrophication, including persistent cyanobacterial blooms. In winter 2011, a sediment core was extracted from the deepest area of the lake. A detailed paleopigment analysis was used to assess eutrophication processes in the lake and to determine the timing and appearance of cyanobacterial blooms and their subsequent variability. Extracted chlorophyll a, its degradation products and 11 carotenoid pigments were identified and quantified via reverse-phase high performance liquid chromatography to examine relative changes in the phytoplankton. The results revealed large variations in the phytoplankton community structure of Lac SaintAugustin over the past 356 years. Chlorophyll a concentrations per unit organic matter (OM) increased significantly from the base of the core to present day, rising more than 15-fold from 18.4 lg (g OM) -1 at the base of the core to 287 lg (g OM) in the most recent strata. Biostratigraphical analysis revealed three major periods of enrichment, with episodes of cyanobacterial abundance from the 1890s onwards. The greatest changes occurred in the most recent period (from the 1960s to the present) relative to earlier periods, with pigment increases for all phytoplankton groups. The cyanobacterial pigments canthaxanthin, echinenone and zeaxanthin (also a marker for green algae) showed concentrations in the surface sediments that were significantly above values at the bottom of the core, and these differences were large, even giving consideration to the lesser pigment degradation near the surface. Overall, the results indicate that cyanobacterial blooms are not a recent feature of Lac Saint-Augustin but began to occur soon after catchment modification 150 years ago. The pigment records also imply that cyanobacterial and associated algal populations have risen to unprecedented levels over the last few decades of ongoing development of the Lac Saint-Augustin catchment. This study highlights the utility of multiple pigment analysis of lake sediments for identifying the timing and magnitude of anthropogenic impacts