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.