Abstract:Carbon dioxide fluxes and water balance were examined in 43 tundra ponds in the northern portion of the Hudson Bay Lowland near Churchill, Manitoba. Most of the ponds were hydrologically disconnected from their catchments during dry periods throughout the post-melt season. However, episodic reconnection occurred following large precipitation events where depression storage was exceeded. Significant shifts in pond chemistry were observed following precipitation events, with the degree of CO 2 saturation increasing during these periods. Pond CO 2 concentrations rapidly fell to pre-event levels following events, suggesting that hydrological connectivity can affect the magnitude and direction of CO 2 gas fluxes in tundra ponds. Atmospheric CO 2 invaded ponds with highly organic sediments for most of the summer, suggesting that terrestrially derived inorganic carbon was insufficient to meet the demands of algal net production. In contrast, ponds with highly mineral sediments continued to evade CO 2 during the summer. In a subset of 11 ponds, long-term rates of carbon accumulation in sediment ranged from 0Ð6 to 2Ð2 mol C m 2 year 1 . Very strong correlations existed between average sediment accumulation rates and pond perimeters and basin areas suggesting that peat may be a major source of sediment carbon. Aeolian transport is also a potentially large source of sediment carbon.

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Three sites were instrumented to measure all components of the energy balance. The sites were located in the Churchill, Manitoba region and comprised a Sea Site on a sand spit 1 km seaward from the mainland, a Nearcoast Site 2 km inland from the coast and an Inland Site 65 km inland. Measurements were made continuously over a 90-day period from 19 May to 16 August 1984. This period encompassed the bulk of the growing season.The measurements were stratified into onshore and offshore wind directions and were compared for 10-day periods. The comparisons show very significant differences attributable to the cold summer conditions promoted by the sea ice in Hudson Bay. The ground heat flux and latent heat flux were much greater during offshore winds but the sensible heat flux was greatest for onshore winds. Air temperatures averaged 7°C warmer for offshore than for onshore winds. The reasons for these differences are detailed and the climatic modifications that would probably result from earlier sea-ice melt are discussed. Some implications of climatic modification are also noted. RÉSUMÉOn a équipé d'instruments trois sites pour la mesure de toutes les composantes du bilan énergétique. Les sites se trouvent à Churchill au Manitoba et étaient formés d'un site marin, situé sur une languette de sable à 1 km de la rive, un site quasi-côtier, situé à l'intérieur et à 2 km de la rive et un site intérieur situé à 65 km de la rive. Les mesures, s'étendant sur une période de 90 jours, ont été effectuées d'une façon continue à partir du 19 mai jusqu'au 16 août 1984. Cette durée a inclus la majorité de la saison de croissance. On a subdivisé les mesures en deux catégories: une catégorie associée aux vents de mer et une autre associée aux vents de terre; les mesures ont été comparées par périodes de 10 jours. Les comparaisons révèlent la présence de différences considérables qui seraient attribuées aux conditions d'un été froid résultant des glaces de mer de la baie a"Hudson. ATMOSPHERE-OCEAN 23 (4) 1985, 375-392 0705-5900/85/0000-0375S01.25/0 © Canadian Meteorological and Océanographie Society Downloaded by [94.242.222.23] at 13:30 01 June 2016 376 / Wayne R. Rouse and Richard L. Bello Le flux de chaleur terrestre et le flux de la chaleur latente étaient bien plus élevés durant les conditions de vent de terre, par contraste, le flux de la chaleur sensible était le plus élevé au cours de vents de mer. Au cours des conditions de vent de terre, les températures de l'air étaient en moyenne TC plus chaudes que celles des conditions associées aux vents de mer. On discute des raisons expliquant ces différences ainsi que des modifications climatiques qui résulteraient probablement d'une fonte précoce de la glace de mer. On note aussi les conséquences qu'une modification de climat pourrait avoir. IntroductionAs indicated by Bello and Rouse (1985) there is a strong correlation between the summer concentration of sea ice along the southwest coast of Hudson Bay and cold summer temperatures, decreased positive degree-days and increased wind ...

Abstract:Assessing moisture contents of lichens and mosses using ground-based high-spectral resolution spectrometers offers immense opportunities for a comprehensive monitoring of peatland moisture status by satellite/airborne imagery. This study investigates the impact of various moisture conditions of the lichens Cladina stellaris and Cladina rangiferina, and the mosses Dicranum elongatum and Tomenthypnum nitens on the spectral signatures obtained. Reflectance and moisture content measurements of these species were made in a laboratory setting, while maintaining the natural moisture conditions of the samples; once the moisture and spectral measurements were complete, the samples were returned to the field and placed in their natural setting, continuously receiving moisture from precipitation and groundwater and losing water through evaporation and drainage. Previously, we correlated the present spectral indices with the moisture contents of the above species, whereas the current study developed new species-specific indices to improve the detection of the plants' moisture contents. The relationship between the plants' moisture content and the water table position was examined as well. It was found that the lichens are not responsive to variations in the water table position, whereas the mosses, specifically D. elongatum, are quite sensitive to changes in the water table position. Thus, the use of the mosses spectral indices may contribute to an indirect evaluation of the water table position. Overall, the results suggest that the unique spectral signatures of the above species can be detected by satellite and airborne imagery, whereas the mosses, can be used as indicators of peatlands moisture status.

Abstract:Assessing moisture contents of lichens and mosses using ground-based high-spectral resolution spectrometers offers immense opportunities for a comprehensive monitoring of peatland moisture status by satellite/airborne imagery. This study investigates the impact of various moisture conditions of common subarctic lichen and moss species upon the spectral signatures obtained. The lichens are Cladina stellaris and Cladina rangiferina, and the mosses are Dicranum elongatum and Tomenthypnum nitens. Reflectance and moisture content measurements of these species were made in a laboratory setting, while maintaining the natural moisture conditions of the samples; once the moisture and spectral measurements were complete, the samples were returned to the field and placed in their natural setting, continuously receiving moisture from precipitation and groundwater and losing water through evaporation and drainage. Changes in reflectance of the visible to shortwave infrared (SWIR) range (400-2500 nm) at various moisture contents were examined, as well as the potential of current spectral reflectance indices to evaluate the plants' moisture contents was examined. Results indicate that the SWIR region is useful in identifying variations in plants moisture conditions, while the unique spectral signatures of the lichens and mosses in the visible and near-infrared range suggest that these species may be detected by satellite and airborne imagery. Of current spectral indices, the normalized difference infrared index (NDII) was most successful in identifying the above plants' moisture content (details are discussed in the paper). Future study should focus on the development of improved moisture content spectral indices, as well as upscaling reflectance data and spectral indices.