Hudson Plains Ecozone+ Evidence for key findings summary
- Lakes and rivers
- Ice across biomes
Key finding 1
National key finding
At a national level, the extent of forests has changed little since 1990; at a regional level, loss of forest extent is significant in some places. The structure of some Canadian forests, including species composition, age classes, and size of intact patches of forest, has changed over longer time frames.
The boreal forests of the Hudson Plains Ecozone+ form an important part of the largest intact tract of forest in Canada, which is also considered one of the largest intact forests remaining in the world.Reference 17 However, the Hudson Plains Ecozone+ has a lower proportion and density of forest than many other forested ecozones+ in Canada.Reference9, Reference18 Owing to widespread wet edaphic conditions, forests there are primarily open and often poorly delineated from the many small bodies of water and non-forested wetlands on the landscape. Truly closed forest stands more typically associated with boreal forests are generally confined to better-drained embankments, slopes, flats, and riverbank levees.Reference 19, Reference20 As such, forest productivity in this ecozone+, as reflected in volume per hectare, is low (42 mReference3 /ha) compared to that of the adjacent Boreal Shield and Taiga Shield ecozones+. Reference 21 Overall, forest density decreases from south to north (Figure 2).Reference9, Reference22 On an area basis, coniferous forest types (conifers ≥75% of total) dominate (54.9%) over mixedwood (34.6%), broadleaved (1.1%), and unclassified (9.5%) ones.Reference21 Spruce is the leading genus in 88% of all forest stands.
Inventory and monitoring information is very limited for forests in this ecozone+, inhibiting the ability to track changes and report on trends.Reference 4 A coarse-scale satellite remote sensing analysis of land cover classes from 1985 to 2005, however, suggests no significant changes are occurring in the extent of forest cover.Reference 9 Overall reductions in forest cover from 1985 to 2005 were small (0.25%) and primarily due to fire, i.e., burned areas that have not yet revegetatedReference9 (see also Natural disturbances on page 63). Given the coarse scale of the analysis, the errors in mapping may, however, be greater than the small amount of change detected. There is also currently little evidence to suggest that the treeline may be moving (see Tundra biome on page 24).
Data are also insufficient to assess trends in forest structure, including: species composition; age class or time-since-fire; and relative intactness. The ecozone+’s forests are, however, also assumed stable in these respects, given an effectively natural and apparently unchanged disturbance regime (see Natural disturbances on page 63) with only minimal anthropogenic disturbance (see Intact landscapes and waterscapes on page 51), including forest harvest. Although commercial forestry is an important industry elsewhere in Canada’s boreal forest (see for example Anielski and Wilson, 2009Reference23 ), it has not been important in this ecozone+, presumably because of the low productivity of its forests, limited existing access to them, and insufficient markets. Currently, only a very small portion at the southern end of the ecozone+ forms part of a forest management unit in Ontario where commercial harvesting may be permitted,Reference24 and planning for potential commercial forestry has been undertaken in the Moose Factory area by the Moose Cree First Nation.Reference25, Reference26 Anthropogenic fragmentation is also very minor, rendering the ecozone+’s forests particularly important for species such as woodland caribou and wolverine that tend to thrive in large tracts of intact and/or unroaded landscape (see Intact landscapes and waterscapes on page 51).
Key finding 3
National key finding
High loss of wetlands has occurred in southern Canada; loss and degradation continue due to a wide range of stressors. Some wetlands have been or are being restored.
The Hudson Plains Ecozone+ is considered Canada’s largest wetland complex, and the third largest in the world.Reference27 These extensive wetlands provide critical habitat for many breeding bird populations.Reference 28 Two sites, Southern James Bay Migratory Bird Sanctuaries (comprised of Moose River Bird Sanctuary and Hannah Bay Bird Sanctuary) and Polar Bear Provincial Park (see also Protected areas on page 30), have been designated Wetlands of International ImportanceReference29 because of the staging and breeding habitat these ecosystems respectively provide for geese, dabbling ducks, and tundra swans.Reference 28 Several species of national conservation concern (such as short-eared owl and yellow rail) also use the ecozone+’s inland (freshwater) wetlands.Reference 14, Reference30 Also notable is that a large proportion of wetlands in the Hudson Plains Ecozone+ are peat-forming wetlands (bogs and fens), making this ecozone+ Canada’s largest peatland complex and the second largest at northern latitudes (>40-50º ).Reference 31 As such, the ecozone+’s peatlands contribute significantly to global carbon-cycling and climate regulation (see Climate regulation, a regulating ecosystem service on page 49).
Although there has been high loss of wetlands in southern Canada, there are few documented changes or trends in the distribution, extent (expansions or contractions), or condition of wetlands in the Hudson Plains Ecozone+, albeit these wetlands are for the most part not being monitored. The ecozone+’s wetlands are assumed healthy with extensive peatlands largely intact, with a few notable exceptions where changes have occurred.
The most important documented change in the ecozone+’s wetlands is in the coastal biome, where about one-third of the coastal salt marsh vegetation from Manitoba to James Bay has been destroyed, and additional areas damaged, as a result of overuse by overabundant lesser snow geese (see Coastalbiome on page 20). However, the phenomenon is also occurring to some extent in the freshwater marshes and fens of the adjacent tundra biome, as a decrease of preferred salt marsh forage forces the geese to move inland to nest and feed (see Tundrabiome on page 24).
Other known stressors of wetlands in the ecozone+ include hydroelectric and mining developments, both of which may cause loss of wetlands or alter wetland classes. Where river flows in the ecozone+ have been reduced by hydroelectric development (for example, Eastmain and Opinaca rivers, see Lakes and rivers on page 16), some desiccation has occurred downstream with, for example, shrubby species expanding at the expense of pioneer wetland species.Reference 32 Conversely, some wetlands in the ecozone+ were affected by flooding in 1980Reference32 when waters diverted from the Eastmain and Opinaca rivers flooded 740 km² of land at the northeast edge of the ecozone+ to create the 1,040 km² Opinaca reservoir that is part of the La Grande hydroelectric complex that continues to the north (see Taiga Shield Evidence for Key Findings SummaryReference33 for further discussion).Reference34 Diversion in 2009 of 72% of the mean annual flow of the Rupert River north to the La Grande complex is further changing wetland hydrology in the Quebec portion of the ecozone+.Reference35
The ecozone+’s only active mine, the Victor open-pit diamond mine (90 km west of the mouth of the Attawapiskat River) was constructed beginning in 2006, opened in 2008,Reference36 and is expected to operate for at least 12 years.Reference37 Although the mine occupies a relatively small area of the ecozone+ (~28.8 km² in direct project-related developmentsReference37), the potential area affected by it, like other mining operations, is considerably larger than the mine itself. As well, although a reclamation plan is in place for the mine,Reference38 some activities associated with the mine can adversely affect the ecozone+’s wetlands to the extent that areas will not be restorable.Reference 37 Wetlands are being impacted by dewatering (potentially affecting an area up to ~500 km² Reference39), as well as infilling during development of mine infrastructure; replacement with mineral stockpiles; and drainage interruption around stockpiles.Reference 37 Some wetlands have also been altered through construction of winter roads and transmission lines from Attawapiskat.
Additional resource developments (see Intact landscapes and waterscapes on page 51) and especially climate change (see Climate change on page 42) are notable future concerns for the ecozone+’s wetlands. Although climate-related changes in the extent of inland (freshwater) wetlands are generally not apparent in this ecozone+, a long-term change or trend involving partial degradation and conversion of frozen peat plateau bogs to fens is suggested in an area from the Nelson River north to Churchill.Reference40
Key finding 4
Lakes and rivers
National key finding
Trends over the past 40 years influencing biodiversity in lakes and rivers include seasonal changes in magnitude of stream flows, increases in river and lake temperatures, decreases in lake levels, and habitat loss and fragmentation.
No clear trends in overall river-flow and lake-level regimes (for example, magnitude, frequency, timing, duration, and flashiness of low and high flow events) are evident for undeveloped waters in the Hudson Plains Ecozone+, albeit this result is based on data from only two reference hydrometric stations with data judged useful for this analysis.Reference10 Indeed, the Hudson Bay basin has one of the most deficient streamflow networks in Canada.Reference41 Reduced total annual volume of freshwater naturally discharged from several of the ecozone+’s rivers is, however, indicated in studies of the broader Hudson Bay region.Reference42-Reference44 These trends for reduced total volume of freshwater discharged (1964 to 2000 or 2003), disregarding rivers with hydroelectric development or correcting for them, are correlated with large-scale climate oscillationsReference42 and associated with a four day advance in annual peak discharge rate and a decline in peak intensity.Reference43
Lakes and rivers in the ecozone+ are relatively undisturbed and generally assumed to be in good condition overall. However, hydroelectric developments have affected flow rates and other physical parameters of some rivers and created a large reservoir (Opinaca) in the ecozone+, along with associated impacts on biota (see below). Monitoring is mostly limited to these hydroelectric developments, while the remoteness of most of the area’s hundreds of rivers/streams and tens of thousands of small lakes and ponds precludes a comprehensive survey of their component fish communities.Reference14, Reference45 Portions of the Hudson Plains Ecozone+ are, however, recognized as supporting among the highest diversity of freshwater fish species in Canada.Reference 46, Reference47
Rivers in the Hudson Plains Ecozone+ are typically shallow, slow moving, and have cut deeply into the clay and alluvial sediments.Reference 48 The ecozone+ is drained by twelve major rivers: the Churchill, Nelson, and Hayes rivers in Manitoba; the Moose, Albany, Attawapiskat, Winisk, and Severn rivers in Ontario; and the Harricana, Rupert, Eastmain, and Nottaway rivers in Quebec. The large quantities of nutrients and organic material carried by these rivers make the coastal zone (see Coastalbiome on page 20), and especially the river deltas, very productive for fish and wildlife.Reference47 As well, the large volume of freshwater they discharge dilutes the saltwater in Hudson and James bays to a salinity one-third that of normal oceanic water,Reference49 which in turn allows this inland sea to freeze over completely each year (see Sea ice on page 26).
Hydroelectric developments are currently the principal direct human influence on rivers in this ecozone+ (but mining near Attawapiskat is having smaller-scale effectsReference37). The few hydroelectric developments located within the ecozone+ are near the southern boundaries, concentrating downstream effects within the lowlands (Figure 3). Two hydroelectric generating complexes (Long Spruce, established 1976-77; and Limestone Rapids, established 1989) are located along the Nelson River and one generating station (Otter Rapids, established 1961) is located on the Abitibi River (a tributary of the Moose River). Development in the eastern portion of the ecozone+ includes a complex of eight sites associated with the Eastmain River and Opinaca reservoir (established 1979-80), as part of the La Grande hydroelectric complex. After waters from the Eastmain River and its tributary, the Opinaca River, were diverted to the more northerly La Grande River, flows of the Eastmain River (at its mouth into James Bay) and the confluencing Opinaca River were reduced by 90% and 87%, respectively.Reference32, Reference 34
In addition to altering river flow rates, hydroelectric developments have altered the magnitude and timing of fluctuations in river flows. For example, post-development studies ~50 km downstream of the Otter Rapids generating station (Abitibi River) reported diurnal water level fluctuations of 0.7-0.9 m in summer and dewatering of one-third to one-half of the river channel during low flows.Reference51 The effects of water level fluctuations at this station are still apparent at least 75 km downstream.Reference52
Rivers in the Hudson Plains Ecozone+ are also influenced by hydroelectric developments upstream, within adjacent ecozones+. Diversion of water from the Churchill River to the Nelson River is noteworthy, as it reduced the flow of the Churchill River into Hudson Bay by about 40%.Reference53 The recent (2009) diversion of 72% of the mean annual flow of the Rupert River north to the La Grande hydroelectric complexReference35 is likewise noteworthy (though lateral flow from tributaries increases the flow at the river mouth to ~48%). Overall, river channel fragmentation and/or flow regulation have strongly affected the Churchill and Nelson river systems in Manitoba, the Moose River system in Ontario, and the Eastmain and Rupert river systems in Quebec.Reference 35, Reference54 The Albany River in Ontario and Nottaway River in Quebec are systems that are considered moderately affected.Reference54
The hydroelectric developments in and around the ecozone+ (described above) are associated with changes in river biota. Lake sturgeon in the northwestern part of the ecozone+ is assigned an elevated “at risk” status category by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) due in part to hydroelectric development (see Lake sturgeon on page 61). Changes in fish habitat and community composition, including a loss in dominance of lake sturgeon, have also occurred in the reduced flow portions of the Eastmain and Opinaca riversReference 34 (see also the estuary and near-shore impacts in the Coastalbiome on page 20). Fish species composition also did not fully recover following impoundment of the Opinaca reservoir in 1980, even though total fishing yield stabilized by 1996 to levels near baseline.Reference34 An additional concern with this reservoir has been the mobilization of mercury and its subsequent bioaccumulation and contamination of fish (see Contaminants on page 38). Impacts on benthic macroinvertebrate communities are also evident, as in the Abitibi River downstream of the Otter Rapids generating station.Reference52
Although construction of hydroelectric facilities appears to have peaked in the ecozone+ in the late 1970s to early 1980s,Reference10 a high potential exists for more. At least one additional development is proposed for the Nelson River.Reference55, Reference56 In Ontario, seven of the 15 new hydroelectric developments included in the Ontario Power Authority’s supply mix plan for development by 2025 are in the ecozone+, along Abitibi (4), Albany (2), and Moose (1) rivers.Reference57 Additional hydroelectric developments are also either in progress or being considered in Quebec.Reference35, Reference58 Cumulative impacts from multiple hydroelectric developments in the Hudson Bay watershed is an ongoing concern.Reference59,Reference60.Reference61,Reference62,Reference63
The Hudson Plains Ecozone+ contains a multitude of mostly shallow bog lakes and ponds that freeze to the bottom in winter, but some larger lakes are deep enough that they do not freeze to the bottom and can, therefore, support fish communities.Reference40, Reference64Reference65Reference66 Owing to remoteness and limited harvest, fish populations in these lakes are assumed to be generally healthy overall, despite insufficient monitoring.Reference45
Information on trends in water levels, water temperature, and water quality is not available for most natural lakes in this ecozone+. However, observations from thermal monitoring of Hawley Lake are notable from the perspective of unusual warming and fish kills (Hawley Lake is one of four lake trout lakes located near the Sutton Ridges). During the unusually warm summer of 2001, Hawley Lake showed strong and unusual thermal stratification, with temperatures exceeding 20°C in the surface layerReference67, Reference68 (Figure 4). Lake trout in the lake were not affected because ample coldwater habitat remained below the epilimnion.Reference67 Warm air temperatures (daily maximums >30°C) combined with the unusual thermal stratification in this headwater lake, however, contributed to a major die-off of anadromous brook trout, as well as white sucker, downstream in the lower reaches of the Sutton River (which drains Hawley Lake) close to its intersection with the Hudson Bay coast.Reference68 Anadromous brook trout summer in the cold ocean but return to spawn and overwinter in cool freshwater rivers and lakes.
Such die-offs of fish during warming events have rarely been recorded within arctic or subarctic watersheds (but see also Hori (2010)Reference69 regarding Aboriginal knowledge of lake whitefish and sucker die-offs in the lower Albany River during a heat wave and period of reduced precipitation in 2005) and it was suggested that this may be among the first of an increasing number of die-offs of vulnerable anadromous stocks that will occur as climate change proceedsReference68 (Climate changeis discussed on page 42). The seasonal sea ice cover in Hudson and James bays moderates the continental climate, but the sea ice season has been shortening (see Sea ice on page 26) and rivers may consequently be warming. Reduced river flows in the region (see earlier) may also contribute to warming.
Key finding 5
National key finding
Coastal ecosystems, such as estuaries, salt marshes, and mud flats, are believed to be healthy in less-developed coastal areas, although there are exceptions. In developed areas, extent and quality of coastal ecosystems are declining as a result of habitat modification, erosion, and sea-level rise.
New land emerges and vegetation develops continuously along the coastline of Hudson and James bays, as a result of one of the highest rates of isostatic rebound in North America.Reference70 The coastal biome of the Hudson Plains Ecozone+ is dominated by extensive tidal flats, salt marshes, and shallow waters,Reference 5 including some of the largest and best-developed polar salt marshes in the world (i.e., those characterized by the presence of permafrost).Reference71 These salt marsh ecosystems provide important breeding grounds and staging areas for a large number of migratory waterfowl and shorebirds.Reference 72-Reference76 Subtidal eelgrass beds are also an important component of the coastal ecosystem along the Quebec coast in eastern James Bay and in isolated portions of the Ontario James Bay coast.Reference77-Reference79 Eelgrass beds provide feeding grounds and nurseries for coastal fish species and invertebrates, and forage for brant, Canada geese, and ducks.
The Hudson Plains Ecozone+ is an exception to the national key finding that coastal ecosystems tend to be healthy in areas with little development. The coastal-intertidal zone, and in particular its extensive salt marshes, has been under considerable stress over the past four decades, predominantly due to a continuous increase in foraging (grazing and grubbing) by lesser snow goose, but also by increasing Canada goose breeding and moulting populations in this area.
The Mid-Continent population of lesser snow goose, to which individuals migrating through and nesting in both Manitoba and Ontario belong, has greatly increased over the past four decades, by as much as 7% per year,Reference 80 with the adult portion of the population reaching as many as 7 millionReference81 or moreFootnote ‡. The goose population increase is thought to be principally a result of human influences outside the Hudson Plains Ecozone+, including increased supply of agricultural food on wintering grounds (mostly in the southern United States) and along migration routes, declining harvest rate, and the development of refugia.Reference80, Reference83 In many years, especially those with late snow melt and thaw, millions of geese are held up in the Hudson Plains Ecozone+ on their northward journey, exacerbating the impact of their foraging.
Within these grass- and sedge-dominated coastal salt marshes, intensive foraging by the geese has led to vegetation loss, shifts in plant community composition, and exposure and sometimes erosion of sediment. Reference81, Reference 83, Reference84 As snow geese forage with increasing intensity, an apparent trophic cascade occurs wherein swards of their preferred forage species (Puccinellia phryganodes and Carex subspathacea) are replaced by mudflats often devoid of vegetation.Reference 85, Reference86 The trophic cascade is sustained by positive feedbacks. One such feedback involves grubbing in spring, whereby geese uproot large areas of P. phryganodes and C. subspathacea and other species in the salt marshes, fragmenting swards and exposing the edges to secondary effects such as erosion, drying, and hypersalinity. The combined effect of the grubbing and the secondary processes is a reduction in the amount of above-ground vegetative matter. The second feedback involves grazing during the nesting season and following hatch. The remaining sward area, both intact and fragmented, is grazed more intensively by ever larger numbers of geese, allowing for less compensatory growth, and eventual exhaustion of the plants. The end result is an alternate stable state, wherein large areas of exposed sediments are resistant to re-colonization (Figure 5) because few plants can germinate or establish in the saline sediments. The effects are long-lasting when foraging pressure continues and recovery can take decades.Reference81 In some cases, the geese have been forced to move inland to freshwater marshes and fens in the adjacent tundra biome to nest and feed due to the scarcity of preferred salt marsh forage (see Tundrabiome on page 24).Reference 83, Reference87
Trends showing increasing area damaged over time are evident from remote-sensing analyses, whereby successive waves of plant community destruction are seen to transform the entire intertidal ecosystem (Figure 6). Similar processes, feeding pressure, and damage to coastal vegetation have been described from Manitoba to James Bay, including Akimiski Island, Nunavut. Approximately one third of the coastal salt marsh vegetation in the ecozone+ has been destroyed by geese since the 1970s and a far greater area will be severely damaged if this intense foraging pressure continues.Reference 88 Not only does the destruction of salt marshes remove important food resources for species that feed directly on the vegetation, it also reduces suitability of the zone for other bird species dependent on these habitats for nesting and foodReference 89, Reference90 (see also Food webs on page 66).
Changes in overland river flow and associated nutrient and sediment loads that result from hydroelectric developments in and around the Hudson Plains Ecozone+ (see Lakes and rivers on page 16) have impacted salinity and other aspects of habitat quality in the interfacing estuarine and marine environments of Hudson and James bays. For example, the 90% reduction in flow at the mouth of the Eastmain River associated with its diversion north to the La Grande River has led to a greater intrusion of saltwater into the Eastmain River estuary with associated impacts on the fish community.Reference34 Marine species (sculpin, Greenland cod, sand lance) now inhabit the saltwater portion of the estuary; although anadromous lake whitefish and cisco still migrate up the estuary in fall to spawn, their overwintering area is smaller due to the saltwater intrusion; and feeding grounds for walleye are now 5 to 10 km further upstream.
In the near-shore environment, hydroelectric development in the broader James Bay region, and particularly the increased flow output from the La Grande River (to which flows from the Eastmain and Opinaca rivers were diverted), has been implicatedReference91 in a steep decline in subtidal eelgrass beds along the eastern James Bay coast.Reference 92, Reference93 Reduced salinity during the major growing period (June and July) and increased duration of ice cover related to reduced salinity were suggested as the major causes of a sudden and precipitous decline in eelgrass health near the La Grande River, while wasting disease, climate change, and isostatic rebound were rejected as major causes.Reference 93
Climate change is an important future threat to the ecozone+’s coastal biome (see Climate change on page 42) but sea-level rise is less of a concern for this ecozone+ than for some other coastal areas (for example, Tsuji et al., 2009Reference 94) due to an especially high rate of isostatic rebound.Reference70 Still, the combined effect of isostatic rebound and sea-level rise could reduce the rate of successional development of coastal systems.
Ecozone+ - specific key finding
The tundra in the Hudson Plains Ecozone+ represents the southernmost zone of continuous tundra vegetation and continuous permafrost in North America.Reference14, Reference 76, Reference95, Reference96 It occurs as a series of beach ridges and inter-ridge areas (extensive sedge meadows and fens and shrub-dominated fens), in a band of land contiguous with the inland side of the coastal-intertidal zone, from Churchill, Manitoba to near the Lakitusaki River, Ontario, in the area of continuous permafrostReference97, Reference98 (see Figure 9 in Ice across biomes). The most inland tundra sites comprise a forest-tundra landscape. The defining tree “line” itself has been described as erratic, extending farthest north on river levees and beach ridges where drainage is better and the active layer deeper.Reference 99
Information is insufficient for analysis of trends in extent or condition of the tundra in the Hudson Plains Ecozone+ as a whole. However, a portion of the ecozone+’s tundra, and in particular its freshwater marshes, is being damaged from excessive feeding by a greatly expanded lesser snow goose population (see the Coastalbiome on page 20 for further discussion of snow goose damage). That is, in some cases the geese have so drastically depleted their preferred food sources (P. phyganodes and C. subspathacea) in the coastal salt marshes that they have moved to forage in less desirable areas within tundra freshwater marshes with similarly devastating effects.Reference100, Reference 101 In response to development of hypersaline soils in grubbed areas, Salix sp. shrubs have been reduced as much as 65%,Reference102, Reference 103 resulting, in turn, in declines of tundra-nesting bird populations located close to snow goose colonies.Reference 83, Reference89 Sammler et al., 2008Reference 101 have shown that localized nesting populations of semipalmated sandpipers, dunlins, savannah sparrows, Lapland longspurs, and other tundra-nesting passerines were more frequent in intact sedge meadow habitats than those altered by goose activity. Although no area-wide population effects were reported, it is likely that as degraded areas expand with continued goose foraging, area-wide effects will occur.Reference 101
Damage to plant communities on both the drier beach ridges and wetter inter-ridge areas of the tundra is also being caused by the operation of wheeled vehicles (tundra buggies/ATVs) in ManitobaReference97 and in OntarioReference 104 (Figure 7).
The tundra, which reaches its most southerly Canadian extent in the Hudson Plains Ecozone+, is especially vulnerable to climate change and associated permafrost thaw (see Climate change on page 42). Currently, there is no strong evidence that the ecozone+’s treeline is moving north (for example, Scott et al., 1987Reference 105), as is occurring in some other northerly locations in Canada and the world (for example, Harsch et al., 2009Reference 106). The treeline in this ecozone+ has, however, received relatively little direct study. Ballantyne (2009)Reference107 recently documented increases of 12.6% and 6.9% of shrub and tree cover, respectively, in a 2.55 km² study area just north of the functional treeline at Churchill. Climate-driven change to the ecozone+’s tundra may also be suggested by a long-term (non-successional) change or trend involving partial degradation and conversion of frozen peat plateau bogs to fens in an area from the Nelson River north to Churchill.Reference40
Key finding 7
Ice across biomes
National key finding
Declining extent and thickness of sea ice, warming and thawing of permafrost, accelerating loss of glacier mass, and shortening of lake-ice seasons are detected across Canada’s biomes. Impacts, apparent now in some areas and likely to spread, include effects on species and food webs.
The sea ice in Hudson and James bays is significantly changing. Loss of sea ice is correlated with deteriorations in the polar bear subpopulations that use sea ice as habitat in winter and the terrestrial environment of the Hudson Plains Ecozone+ in summer. On the terrestrial landscape, permafrost degradation is suspected, but cannot currently be confirmed due to insufficient monitoring data. Data are also insufficient for analysis of trends in lake and river ice.
Hudson Bay, along with James Bay to the south and Foxe Basin to the north, is the largest inland sea in the world and the only sea at this latitude that goes through a complete cryogenic (ice) cycle each year.Reference108, Reference 109 This factor has been primary in shaping the ecosystem around it by creating much cooler temperatures than what is typical of this latitude.Reference110 These cooler temperatures provide the conditions necessary to maintain the southernmost continuous permafrost in North AmericaReference95, Reference 96 and support species of arctic affinity, such as polar bear, arctic fox, and some plants, at their southernmost occurrence (see also Polar bear on page 54).Reference99, Reference111, Reference 112
The winter maximum extent of sea ice has not changed, and Hudson and James bays continue to completely freeze over each year. However, sea ice extent in the broader Hudson Bay marine ecosystem declined significantly over the period 1979 to 2006, on the order of -5.3 ±1.1% per decade, with decreases evident in all seasons except winter.Reference 108 As well, significant trends for longer ice-free periods each year have been detected in areas of Hudson and James bays adjacent to the Hudson Plains Ecozone+, associated with later freeze-up dates, earlier break-up dates, or both, depending on location (see inset).Reference109, Reference 113-Reference115 On average, the annual ice-free period in western Hudson Bay, southern Hudson Bay, and James Bay has increased by ~3 weeks since the mid-1970s.Reference 109 These trends in sea ice are correlated with significant negative impacts on polar bear, which is dependent on sea ice as habitat and a platform for hunting and feeding on seals (see Polar bear on page 54for further discussion). These trends in sea ice are projected to continue, such that James Bay and the southern portion of Hudson Bay (i.e., marine areas adjacent to the ecozone+) may become substantially to completely ice-free by 2100 (see Climate change on page 42).
Sea Ice is Changing
Analysis of historical sea ice data for Hudson and James bays reveals that this inland sea is becoming increasingly ice-free. Gough et al., (2004)Reference 115 found significant trends for earlier dates of sea ice break-up in southwestern Hudson Bay over the period 1971 to 2003. Although they did not find a trend in later freeze-up dates, the trend for earlier break-up alone resulted in an approximate increase in ice-free conditions by approximately 0.49 days per year (Figure 8). Subsequent work that expanded the study area to include the entire Hudson Bay region found a significant trend for earlier break-up in James Bay, southern Hudson Bay, and western Hudson Bay with magnitudes ranging from 0.49 to 1.25 days earlier per year, coincident with temperature trends in these areas.Reference109
Source: redrawn from Gough et al., 2004 Reference115 (p 303, fig 2) with permission from Arctic Institute of North America. D ata from t he Canadian Ice Service archives
Long description for Figure 8
The Hudson Plains Ecozone+ supports the most southern continuous permafrost in North AmericaReference95, Reference 96 and includes a full range of permafrost types across its geography (Figure 9). At the northern extent of the ecozone+, continuous permafrost can be found beneath the coastal ridges and wetlands. As little as 20 km inland from the coast in some areas (as near York Factory), the terrain changes to palsas, localized geomorphic mounds indicative of a transition from continuous to discontinuous permafrost. Sporadic discontinuous and isolated patches of permafrost are found further south, while permafrost is absent at the most southerly extent of the ecozone+ in areas away from the coast. The presence of permafrost, and its effective retention of surface water, contributes greatly to the unique nature of this ecozone+ as Canada’s largest wetland complex.
Sufficient data are not currently available with which to evaluate trends in the extent and condition of permafrost, or associated shifts in permafrost boundaries, in the Hudson Plains Ecozone+. Until relatively recently, no permafrost thermal monitoring sites were located and maintained there to help track changes as is being done elsewhere in Canada’s north.Reference117, Reference 118 Ten year data are now available for a permafrost site at Churchill, Manitoba,Reference119 a new permafrost monitoring site was established in 2007 at York Factory, Manitoba,Reference 120 and two more sites have recently been added in northern and southern areas of Wapusk National Park, Manitoba.Reference 121 In Ontario, annual summer monitoring of permafrost began in 2007 and a permanent monitoring site (Brant River) is now in place.Reference122
Changes in permafrost, however, are suspected in the Hudson Plains Ecozone+. Both collapse and erosion features and aggrading features are visible in the ecozone+’s permafrost tension zone and collapse features appear to have become more widespread over time, as in the Ekwan to Lake River areas of the northern James Bay coast.Reference 99 In recent decades, casual observations have also been made of slumping and collapse of river banks along the Hayes and Nelson rivers in the vicinity of York Factory, Manitoba, close to the boundary between discontinuous and continuous permafrost. Partial degradation and conversion of frozen peat plateaus to fens, as well as the enlargement of some associated lakes from eroding shorelines, is also suggested in the area from the Nelson River north to Churchill.Reference40 Moreover, although the relatively short 10 year permafrost record from Churchill shows no significant trend to date, comparison of this data with the much longer climate record at Churchill suggests that the air temperature warming there might have resulted in permafrost warming of ~0.5°C since the mid-1970s.Reference119 Permafrost loss is known to be occurring just outside both western and eastern ecozone+ boundaries in areas where permafrost is discontinuous and in isolated patches respectively.Reference123, Reference 124
Modeling for the Hudson Bay region forecasts a loss of ~50% or more of the continuous permafrost and a virtual elimination of a climate that supports permafrost by 2100,Reference95, Reference125 which would have significant impacts on ecozone+ integrity (see Climate change on page 42).
Lake and river ice
Data are insufficient for analysis of long-term trends in river and lake ice in the Hudson Plains Ecozone+.Reference7 For example, trends in break-up dates for the lower Attawapiskat, Albany, and Moose rivers (near the James Bay coast) were inconclusive when examined from disparate community-based data sources.Reference126 It is, therefore, not known from monitoring if trends being observed elsewhere in northern Canada for earlier break-up and in some cases also later freeze-up of freshwater iceReference127-Reference129 are occurring in this ecozone+. Changes in freshwater ice are, however, suspected. Aboriginal peoples in western James Bay have noted changes in the break-up and/or freeze-up of rivers,Reference 126 as well as a reduction in ice thickness both in naturally flowing rivers and rivers with flows modified by hydroelectric developments and longer ice-free periods for some inland lakes.Reference61
- Footnote ‡
This population estimate is higher than estimates derived from mid-winter population surveys reported in other references (for example Canadian Wildlife Service Waterfowl Committee 2009,Reference82 referenced in Canadian Biodiversity, Ecosystem Status and Trends 2010). Mid-winter survey estimates are known to largely underestimate total population levelsReference83 and are most useful for examining trends in relative population size over time.
- Reference 3
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