Hydrology, carbon dynamics and hydrochemical properties of ponds in an extensive low gradient High Arctic wetland, Polar Bear Pass, Bathurst Island, Nunavut, Canada

Ponds form the dominant feature of Polar Bear Pass (PBP), one of the largest wetlands in the Canadian High Arctic, and in order to understand the ramifications of climatic changes on PBP we must first understand the ponds' responses to seasonal changes in climatic, physical, chemical, and carbon components. Fieldwork (2007-2010) at PBP aimed (i) to determine water budgets of ponds with various hydrologic settings, (ii) to identify the processes controlling the changes in pond carbon and geochemistry on seasonal and inter-annual bases with a special focus on the snowmelt period, and (iii) to establish the baseline hydrochemistry and hydrology of ponds within the PBP wetland complex. Pond systems at PBP have two hydrologic settings: (i) ones which are hydrologically connected to additional sources of water from their catchments beyond seasonal inputs of snowmelt and rainfall, or (ii) ponds which fail to form a link or only have a limited connection with their surrounding catchments. Intensive seasonal monitoring of water and carbon mass balance showed that elevated loads of dissolved organic carbon (DOC) in ponds were mostly of terrestrial origin and occurred in ponds receiving meltwater from snowbeds and/or discharge from hillslope creeks. The seasonal strength in the connectivity of a pond to its catchment from snowmelt to the postsnowmelt period was critical in controlling DOC loads and concentrations. This study provided the first estimates of DOC yields at Polar Bear Pass, and reported elevated DOC loadings from wet meadow catchments into ponds. This highlights their importance as a source of carbon to pond ecosystems during snowmelt and heavy rainfall events. The water chemistry and environmental data showed that waters at PBP were dominated by calcium and bicarbonate ions that fell on a common dilution line, however, they had distinct proportional major ionic variability due to the location, lithology, and level of water-bedrock interaction, and these dynamics were controlled by differences in climatic conditions and hydrologic connectivity. Results relating to pond-landscape linkages and their role in solute transport to ponds showed (i) elevated surface and subsurface water contribution to ponds in hydrologically connected catchments. The primary mechanism for solute and carbon transport was overland flow during snowmelt and surface/subsurface inflow during the post-snowmelt season. There was (ii) a potential for higher solute inflow during seasons with frequent or large precipitation events. Lastly, (iii) isolated ponds were subject to evapo-concentration resulting in solute enrichment in pond waters during warm, dry periods. An analysis of carbon dioxide (C02) concentrations in surface waters during snowmelt was conducted to provide the first estimates of this greenhouse gas in ponds at PBP and to further support the interpretation of hydro logic and carbon dynamics in ponds during the snowmelt and early post-snowmelt season. Surface waters at PBP were strong sources of C02 to the atmosphere, with C02 emissions dramatically increasing at the beginning of snowmelt and then declining during peak snowmelt. The required inputs of carbon to support the estimated C02 emissions could be explained by surface or subsurface inflows of dissolved organic carbon and dissolved inorganic carbon, and possibly from mineralization of terrestrial organic carbon in the water column and sediments of ponds. The findings of this study will aid in the future management of the PBP wetland, and may be applied to other arctic ponds situated in High Arctic wetland environments or in any area in the circumpolar Arctic that has similar geomorphologic features and climatic setting

Water Body Distributions Across Scales: A Remote Sensing Based Comparison of Three Arctic Tundra Wetlands

Water bodies are ubiquitous features in Arctic wetlands. Ponds, i.e., waters with a surface area smaller than 104 m2, have been recognized as hotspots of biological activity and greenhouse gas emissions but are not well inventoried. This study aimed to identify common characteristics of three Arctic wetlands including water body size and abundance for different spatial resolutions, and the potential of Landsat-5 TM satellite data to show the subpixel fraction of water cover (SWC) via the surface albedo. Water bodies were mapped using optical and radar satellite data with resolutions of 4mor better, Landsat-5 TM at 30mand the MODIS water mask (MOD44W) at 250m resolution. Study sites showed similar properties regarding water body distributions and scaling issues. Abundance-size distributions showed a curved pattern on a log-log scale with a flattened lower tail and an upper tail that appeared Paretian. Ponds represented 95% of the total water body number. Total number of water bodies decreased with coarser spatial resolutions. However, clusters of small water bodies were merged into single larger water bodies leading to local overestimation of water surface area. To assess the uncertainty of coarse-scale products, both surface water fraction and the water body size distribution should therefore be considered. Using Landsat surface albedo to estimate SWC across different terrain types including polygonal terrain and drained thermokarst basins proved to be a robust approach. However, the albedo–SWC relationship is site specific and needs to be tested in other Arctic regions. These findings present a baseline to better represent small water bodies of Arctic wet tundra environments in regional as well as global ecosystem and climate models

Sustainability of High Arctic Ponds in a Polar Desert Environment

Arctic wetland environments are sensitive to ongoing climate change as seen by the recent loss of lakes and ponds in southern Alaska, Siberia, and northern Ellesmere Island, Canada. A clearer picture of the mechanisms accounting for these losses or the persistence of ponds is presently required. To better understand and quantify the hydrologic processes that are leading to the sustainability or demise of High Arctic ponds, a detailed study was conducted during the summer seasons of 2005 and 2006 at Somerset Island, Nunavut (72˚43' N, 94˚15' W). A water balance framework that quantifies water inputs, losses, and storage was employed on four ponds situated in three broad geomorphic areas (coastal, bedrock, and glacial terrain, which includes plateau and moraine). The initial snow cover amount influenced the water level pattern for the summer season. Large end-of-winter snow accumulations in the deep Bedrock pond ensured large initial water storage and seasonal sustainability despite variable climatic conditions and a coarse substrate, which encouraged subsurface outflow. Connectivity to a stream draining an upland area and a melting late-lying snowbed nearby allowed the small Moraine pond to maintain stable water levels throughout both years. Sandy soils typical of the Coastal and Plateau ponds favored seepage and subsurface water losses, leading to desiccation of these ponds during dry periods. Lateral water losses from the Coastal pond were enhanced by the presence of a downslope frost crack that formed a steep hydraulic gradient with the pond. High initial snowfall and substantial rain maintain pond water levels, but in years with low snowfall and dry conditions, ponds are vulnerable to disappearance unless a range of dependable hydrological linkages exists.Les milieux humides de l’Arctique sont sensibles aux changements climatiques continus, tel que l’atteste la perte récente de lacs et d’étangs du sud de l’Alaska, de la Sibérie et du nord de l’île d’Ellesmere, au Canada. À l’heure actuelle, il faut obtenir une meilleure idée des mécanismes à la source de ces pertes ou à la source de la persistance des étangs. Afin de mieux comprendre et de quantifier les processus hydrologiques qui entraînent la durabilité ou la disparition des étangs de l’Extrême arctique, une étude détaillée a été réalisée au cours des étés 2005 et 2006 à l’île Somerset, au Nunavut (72˚43' N, 94˚15' O). À quatre étangs situés dans trois grandes zones géomorphologiques (côtière, roche de fond et terrain glaciaire, ce qui comprend plateaux et moraines), on a utilisé un cadre de référence de bilan hydrique quantifiant les gains, les pertes et le stockage d’eau. La quantité de couverture de neige initiale exerçait une influence sur le modèle de niveau d’eau pendant la saison d’été. Les fortes accumulations de neige en fin d’hiver dans la profonde roche de fond des étangs donnaient lieu à un important stockage initial de l’eau et à la durabilité saisonnière malgré des conditions climatiques variables et un substrat grossier, ce qui favorisait l’écoulement en-dessous de la surface. La connectivité à un cours d’eau drainant une zone plus élevée et un lit de neige tardif et fondant situé tout près a permis au petit étang de la moraine de maintenir des niveaux d’eau stables au cours des deux années. Les sols sableux typiques des étangs de la côte et du plateau favorisaient le suintement et la perte d’eau en-dessous de la surface, ce qui a mené à la dessiccation de ces étangs pendant les périodes sèches. Les pertes latérales d’eau de l’étang côtier étaient rehaussées par la présence d’une gélivure de pente descendante qui formait un gradient hydraulique prononcé dans l’étang. D’importantes chutes de neige initiales et une pluie considérable ont pour effet de maintenir les niveaux d’eau des étangs, mais pendant les années où les chutes de neige sont faibles et où les conditions sont sèches, les étangs sont susceptibles de disparaître à moins qu’il n’existe une gamme de liaisons hydrologiques fiables

Water body distributions across scales: a comparison of three Arctic wetlands

Water bodies are ubiquitous features in Arctic wetlands, ranging from very small polygonal ponds to very large thermokarst lakes. Ponds, i.e. waters with a surface area smaller than 1 ha, have been recognized as hotspots of biological activity and greenhouse gas emissions. Regional and global models, however, cannot resolve ponds due to the coarse resolution. The aims of this study were to identify common characteristics of Arctic wetlands regarding (1) water body size and abundance, and (2) Landsat subpixel fraction of water cover. We mapped water bodies in three Arctic wetlands, i.e. Polar Bear Pass on Bathurst Island in the Canadian High Arctic, Samoylov Island in the Lena River Delta in Siberia, Russia, and Barrow Peninsula on the Alaska Coastal Plain. High-resolution (0.3 to 4 m) water body maps were overlain on to Landsat albedo maps to extract the proportion of open water within a Landsat mixed pixel. At all three sites ponds occupied 95% of the total number of surface waters. Surface waters smaller than 0.1 ha, which cannot be detected with Landsat data, still contributed 60% and higher to the total number. All study areas showed similar rates of decline in water body abundance with increasing water surface area (Fig. 1). Previous studies have fitted abundance-size distributions of water bodies to the Pareto distribution, which appears linear on a log-log plot. Our data, however, shows paretian behavior only in the upper tail of the distribution so that the Pareto distribution strongly overestimates small water bodies. Landsat albedo increased with decreasing proportion of open water cover per Landsat pixel. Linear regressions for albedo values with a subpixel water cover between 100% and less than 5% showed r-square values larger than 0.8, which constitutes a better performance than other more complex unmixing methods. In conclusion, all three wetlands showed similar properties regarding size-abundance data of water bodies, scaling errors, and retrieval of subpixel water cover via Landsat albedo. Common scaling procedures regarding surface waters can therefore be applied to similar wetland regions across the Arctic for implementation in regional and global ecosystem and climate models

Sustainability of High Arctic Ponds in a Polar Desert Environment

Arctic wetland environments are sensitive to ongoing climate change as seen by the recent loss of lakes and ponds in southern Alaska, Siberia, and northern Ellesmere Island, Canada. A clearer picture of the mechanisms accounting for these losses or the persistence of ponds is presently required. To better understand and quantify the hydrologic processes that are leading to the sustainability or demise of High Arctic ponds, a detailed study was conducted during the summer seasons of 2005 and 2006 at Somerset Island, Nunavut (72˚43' N, 94˚15' W). A water balance framework that quantifies water inputs, losses, and storage was employed on four ponds situated in three broad geomorphic areas (coastal, bedrock, and glacial terrain, which includes plateau and moraine). The initial snow cover amount influenced the water level pattern for the summer season. Large end-of-winter snow accumulations in the deep Bedrock pond ensured large initial water storage and seasonal sustainability despite variable climatic conditions and a coarse substrate, which encouraged subsurface outflow. Connectivity to a stream draining an upland area and a melting late-lying snowbed nearby allowed the small Moraine pond to maintain stable water levels throughout both years. Sandy soils typical of the Coastal and Plateau ponds favored seepage and subsurface water losses, leading to desiccation of these ponds during dry periods. Lateral water losses from the Coastal pond were enhanced by the presence of a downslope frost crack that formed a steep hydraulic gradient with the pond. High initial snowfall and substantial rain maintain pond water levels, but in years with low snowfall and dry conditions, ponds are vulnerable to disappearance unless a range of dependable hydrological linkages exists.Les milieux humides de l’Arctique sont sensibles aux changements climatiques continus, tel que l’atteste la perte récente de lacs et d’étangs du sud de l’Alaska, de la Sibérie et du nord de l’île d’Ellesmere, au Canada. À l’heure actuelle, il faut obtenir une meilleure idée des mécanismes à la source de ces pertes ou à la source de la persistance des étangs. Afin de mieux comprendre et de quantifier les processus hydrologiques qui entraînent la durabilité ou la disparition des étangs de l’Extrême arctique, une étude détaillée a été réalisée au cours des étés 2005 et 2006 à l’île Somerset, au Nunavut (72˚43' N, 94˚15' O). À quatre étangs situés dans trois grandes zones géomorphologiques (côtière, roche de fond et terrain glaciaire, ce qui comprend plateaux et moraines), on a utilisé un cadre de référence de bilan hydrique quantifiant les gains, les pertes et le stockage d’eau. La quantité de couverture de neige initiale exerçait une influence sur le modèle de niveau d’eau pendant la saison d’été. Les fortes accumulations de neige en fin d’hiver dans la profonde roche de fond des étangs donnaient lieu à un important stockage initial de l’eau et à la durabilité saisonnière malgré des conditions climatiques variables et un substrat grossier, ce qui favorisait l’écoulement en-dessous de la surface. La connectivité à un cours d’eau drainant une zone plus élevée et un lit de neige tardif et fondant situé tout près a permis au petit étang de la moraine de maintenir des niveaux d’eau stables au cours des deux années. Les sols sableux typiques des étangs de la côte et du plateau favorisaient le suintement et la perte d’eau en-dessous de la surface, ce qui a mené à la dessiccation de ces étangs pendant les périodes sèches. Les pertes latérales d’eau de l’étang côtier étaient rehaussées par la présence d’une gélivure de pente descendante qui formait un gradient hydraulique prononcé dans l’étang. D’importantes chutes de neige initiales et une pluie considérable ont pour effet de maintenir les niveaux d’eau des étangs, mais pendant les années où les chutes de neige sont faibles et où les conditions sont sèches, les étangs sont susceptibles de disparaître à moins qu’il n’existe une gamme de liaisons hydrologiques fiables

Snowmelt hydrology and carbon dynamics in wetland ponds at Polar Bear Pass, Bathurst Island, Nunavut, Canada

Wetlands are important ecological niches in High Arctic environments, providing habitats for northern fauna and flora. Generally, these wetland complexes are composed of a series of ponds, wet meadows, and areas of wet and dry ground (Woo and Young 2006) and possess linkages to surrounding terrain (e.g. hillslope streams, late-lying snowbeds). These connections have the ability to transfer water and nutrients into wetlands, but as yet, little is known about the importance of these contributions or the mechanisms which control them. A large number of ponds exist at Polar Bear Pass, Bathurst Island and are connected to their surrounding watersheds through various linkages and thus receive different hydrological and nutrient inputs. Since, ponds are numerous in this wetland and form the dominant land-use of this wetland-complex, the objective of this study was to understand the snowmelt hydrology, carbon dynamics (DOC, DIC, CO2, CH4) and carbon balance in a series of shallow tundra ponds comprising an extensive wetland system

Hydrochemistry, water level, and discharge of water from Samoylov Island, Lena Delta, northeastern Siberia, in 2008

Although ponds make up roughly half of the total area of surface water in permafrost landscapes, their relevance to carbon dioxide emissions on a landscape scale has, to date, remained largely unknown. We have therefore investigated the inflows and outflows of dissolved organic and inorganic carbon from lakes, ponds, and outlets on Samoylov Island, in the Lena Delta of northeastern Siberia in September 2008, together with their carbon dioxide emissions. Outgassing of carbon dioxide (CO2) from these ponds and lakes, which cover 25% of Samoylov Island, was found to account for between 74 and 81% of the calculated net landscape-scale CO2 emissions of 0.2-1.1 g C/m**2/d during September 2008, of which 28-43% was from ponds and 27-46% from lakes. The lateral export of dissolved carbon was negligible compared to the gaseous emissions due to the small volumes of runoff. The concentrations of dissolved inorganic carbon in the ponds were found to triple during freezeback, highlighting their importance for temporary carbon storage between the time of carbon production and its emission as CO2. If ponds are ignored the total summer emissions of CO2-C from water bodies of the islands within the entire Lena Delta (0.7-1.3 Tg) are underestimated by between 35 and 62%