The role of individual terrain units in the water balance of wetland tundra

Abstract

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.

Radiation balance of wetland tundra at northern treeline estimated from remotely sensed data

“…2, summer 1991 was atypical of the 'normal' conditions that have been observed in the area over the last 50 yr with respect to both temperature and precipitation (Boudreau & Rouse 1995). Average temperatures for the months of June, July, and August 1991 were more than 3°C above normal.…”

“…8). Field studies suggest that, because of local advective effects, these small water bodies may play a larger role in the regional water balance than their areal coverage suggests (Bello & Smith 1990, Boudreau & Rouse 1995. For these reasons TM imagery should be compared with AVHRR to investigate the potential for improving the temporal coverage.…”

“…When looking at the June data alone (Table 3a), the ground-based measurements are much lower than those estimated with Landsat TM (difference of 31 to 47 W m -2 when the lake site is excluded). Differences of this magnitude are expected as the frost table is typically located 15 to 40 cm (depending on terrain type) below the surface in late June (Boudreau & Rouse 1995).…”

Capturing temporal and spatial variability in the chemistry of shallow permafrost ponds

“…The HBL are the largest contiguous wetland complex in North America, with thousands of lakes and ponds in the landscape (Keller et al, 2014;Dyke and Sladen, 2010) from impeded drainage due very low topographic gradients (Boudreau and Rouse, 1995) and the presence of permafrost. Ponds have been demonstrated to be stably stratified in the eastern HBL , while the very shallow (< 1 m) ponds in the western HBL are assumed to be well mixed by wind action (Bello and Smith, 1990).…”

“…Ponds have been demonstrated to be stably stratified in the eastern HBL , while the very shallow (< 1 m) ponds in the western HBL are assumed to be well mixed by wind action (Bello and Smith, 1990). Ponds in the western HBL have been shown to be nutrient-limited (Eichel et al, 2014;Symons et al, 2012), restricted in surface and groundwater connection (Boudreau and Rouse, 1995), with steep banks and thick, organic sediments with dense mats of benthic blue-green, green, and diatomaceous algae (Macrae et al, 2004;Gray, 1987), with the dominant diatom genus being Denticula (Macrae et al, 2004). Symons et al (2012) showed the most abundant phytoplankton communities to be Chlamydomonas spp., Sphaerocystis spp., Diatoma spp., and Crugienella spp.…”