The water balance of a High Subarctic wetland was measured in a newly established research basin near Churchill, Manitoba, Canada. Measurements spanned the growing season from early June through to the end of August 1991. The watershed was instrumented such that the water budget could be monitored over each of the dominant terrain unlts. The study basin has 5 major terrain types consisting of sedge-dominated wetland, upland lichen-heath, tundra lakes and ponds, willowbirch wetland, and open spruce forest, in decreasing order of coverage. These terrain units, and the ecosystem as a whole, are representative of coastal wetlands underlain by permafrost in the Hudson Bay Lowland. Runoff and thus streamflow were closely tied to the moisture status of the peatlands and to the depth of the active layer. During 2 unusually dry periods, the peatlands remained wet, which indicates a lack of water mobility when the water table drops below the surface of the wetland. Streamflow response to rainfall during these periods was small in comparison to early summer when the frost table was near the surface, or to wet periods when the water table rose above the surface. Energy balance measurements showed the lakes and ponds to have about 15 % higher net radiation than wetlands and 29% greater than upland lichen-heath. From 9 to 18% of net radiation was used in thawing and heating the ground whereas the latent heat flux for the various terrain types utilized from 49 to 83 % of net radiation. Even with unusually large rainfalls that occurred in July, evaporation exceeded precipitation over the course of the summer. Despite this, runoff was high and required a large negative change in groundwater storage to account for it. The lichen-heath and ponds exhibited the greatest change in water storage. The drainage of water from the uplands to the lowlands maintained the soil moisture of the peatlands and contributed to streamflow. Each terraln type had a characteristic water balance due to differences in one or more of the hydrologic variables (evapotranspiration, runoff and storage). This has important lrnplications concerning the impact on the water balance of a change in surface cover brought about by a change in climate.

Traditional methods of measuring surface net radiation involve point measurements that represent only a small area surrounding the instrumented sites. Remotely sensed spaceborne data offer the means by which to obtain estimates of the outgoing fluxes at the regional scale. The objective of this study was to estimate surface albedo, surface thermal exitance, and net radiation using Landsat Thematic Mapper (TM) data over wetland tundra at northern treeline near Churchill, Manitoba, Canada. Ground-based measurements of each component of the radiation balance were acquired at 5 locations coincident with 2 TM overpasses during summer 1991. Each location was representative of 1 of the major terrain types found in the Hudson Bay Lowlands (i.e. sedge-dominated wetland, upland lichenheath, tundra lakes and ponds, willow/birch wetland, and open spruce-tamarack forest). The mean absolute differences between remote sensing estimates and field measurements (all sites combined) are 0.01 for albedo, 25.7 W m -2 for thermal exitance, and 14.1 W m -2 for net radiation. The 2 summer 1991 TM images (June and August) were then used to examine within and between terrain type variations in surface net radiation during the growing season. TM imagery from August 1984 and August 1991 were also utilised to investigate differences in surface fluxes between a dry year (1984) and a wet year (1991). Results indicate that surface wetness and, to a lesser extent, phenology are the 2 main factors controlling the radiation balance during the summer period in this subarctic tundra-forest landscape.