Technical Thematic Report No. 11. - Western Interior Basin Ecozone+ Evidence for key findings summary
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.
Forests cover 73% of the ecozone+. Footnote 12 Forests of the WIBE are classified into eight biogeoclimatic zones. Footnote 13 The Interior Douglas-fir, Montane Spruce, and Engelmann Spruce-–Subalpine Fir zones –in that order of extent–comprised 84% of the total forested area in 2005 (Figure 5). The Ponderosa Pine zone covers 5% of the WIBE. This zone, along with the Bunchgrass zone, occupies lower elevations where land use is most intense and where habitat occurs for many species at risk. The WIBE includes three of the four zones identified in 2008 as areas of greatest conservation concern in BC (Bunchgrass, Ponderosa Pine, and the xeric site series of the Interior Douglas-fir zones). Footnote 14
An analysis of forest density using remote sensing showed that in 2005 almost half of 1 km2 cells within the WIBE were more than 80% forested. Footnote 12. Twenty-two percent of the WIBE area is covered by intact forest landscape fragments larger than 100 km2 (Figure 6). A landscape fragment is defined as a contiguous mosaic, naturally occurring and essentially undisturbed by significant human influence. It is a mosaic of various natural ecosystems including forest, bog, water, tundra, and rock outcrops. These intact fragments are primarily located in the mountainous western part of the ecozone+.
The WIBE contains about 860 million m3 of wood in commercially harvested species. Footnote 13 The 2008 annual allowable harvest in the WIBE was approximately 7.3 million m3 (3.3 million m3 in the Okanagan-Shuswap Forest District and 4 million m3 in the Kamloops Forest District). Footnote 17
Commercial harvest and planting have changed the tree composition of forests. The BC Ministry of Forests analyzed the change in forest composition in monocultures or mixed stands of conifers and deciduous trees. The report provides a comparison of the proportion of one tree species dominated stands (monocultures) and mixed tree species stands by addressing their species composition before and after harvest. There was no analysis of the variety of tree species present. The analysis distinguished, for example, whether a ponderosa pine-dominant stand had changed to a Douglas-fir-dominant stand, but it did not show a change in status for a spruce–pine stand that was converted to a nearly pure pine stand. Footnote 18
The report also separated stands before and after harvest under pre-1987, 1987–1995, and 1995–2004 policy regimes. Prior to 1987, primary silvicultural obligation belonged to the provincial government. From 1987 to 1995, obligations fell to licensees. The years 1995 to 2004 coincide with the implementation of the Forest Practices Code and the Forest and Range Practices Act. Reforestation obligations commence at the time of harvest and end when the reforested stand of trees is declared "free growing." Free growing obligations can be met either naturally (natural regeneration) or artificially (planting). Footnote 18
Overall, forest stands with a single tree species (monoculture) declined in areas without timber harvest but increased in harvested areas. Approximately 39% of the non-harvested forest land base was monoculture prior to 1987. From 1987 to 2004, monocultures declined by 9%. However, the amount of monoculture at free growing has increased by about 9% post-1987, since licensees and BC Timber Sales had the primary silvicultural obligation (Figure 8). For deciduous stands at the free growing stage, the amount of mixed stands increased from 12 km2before harvest to 373 km2 after harvest.
The extent of lower elevation forests declined from 1800 to 2005. An analysis of aerial photographs of the Okanagan and Lower Similkameen valleys from 1800, 1938, and 2005 illustrated losses of 27% for Douglas-fir–pinegrass gentle slope forest ecosystems (Figure 9) and 53% for ponderosa pine–bluebunch wheatgrass gentle slope forest ecosystems (Figure 10). Footnote 20
Additional information about changes in forested ecosystems is in the Ecosystem conversion section on page 40 and in the Natural disturbance section on page 79.
Key finding 2
National key finding
Native grasslands have been reduced to a fraction of their original extent. Although at a slower pace, declines continue in some areas. The health of many existing grasslands has also been compromised by a variety of stressors.
Native grasslands comprised 2% of the WIBE in 2005. These grasslands are the northernmost extension of the Pacific Northwest Bunchgrass type, Footnote 21 also described as the Great Basin Sagebrush Desert Biome. Footnote 22These grasslands are unique in Canada because they are dominated by bluebunch wheatgrass (Pseudoreogneria spicata), a species that rarely occurs east of the Rocky Mountains, and because they are differentiated from grasslands in Washington and Oregon due to a higher proportion of boreal species in their plant and animal communities. Footnote 23 Footnote 24
BC's grasslands are one of Canada's most endangered ecosystems. Footnote 23, Footnote 25, Footnote 26, Footnote 27, Footnote 28. Low-elevation grassland communities are the rarest land cover type in BC and are concentrated in three of BC's four biogeoclimatic zones of conservation concern (Interior Douglas-fir, Ponderosa Pine, and Bunchgrass). Footnote 14 Grasslands provide habitat for species at risk and contribute disproportionately to biodiversity. Footnote 25, Footnote 26 For example, over 30% of BC's species at risk including American badgers (Taxidea taxus jeffersonii), burrowing owls (Athene cunicularia), pallid bats (Antrozous pallidus), western rattlesnakes (Crotalus oreganus), and long-billed curlews (Numenius americanus) live in the grasslands of the WIBE. Footnote 29 Over 40% of BC's vascular plant flora are found in grasslands Footnote 27 even though grasslands cover less than 1% of BC. Footnote 27
Since 1850, 1,188 km2 (16%) of the WIBE's grasslands have been converted to agriculture, high-density urban development, and low-density development (Figure 11). Footnote 27, Footnote 30 Although grasslands continue to be lost in some areas, most of the loss (15%, or 1,114 km2) occurred before 1990 (Figure 12). The greatest losses prior to 1990 occurred in the Northern Okanagan Basin Ecosection, with 48% of its grasslands lost, and in the Southern Okanagan Highland Ecosection, with 39% lost (Figure 12). Footnote 31
.Source: updated from the Grasslands Conservation Council of British Columbia, 2004. Footnote 31
Long Description for Figure 11
The main map shows the extent of grasslands concentrated along the main river systems in the WIBE. Historically there were more grasslands around Salmon Arm, Vernon, Kelowna and Penticton. An inset map shows the grassland regions for all of BC. The largest concentration is in the WIBE and north of the WIBE. There are also grasslands in the northeast and furthest east in the province.
Source: BC Ministry of Environment, 2007a Footnote 30; modified from data produced by the Grasslands Conservation Council of British Columbia, 2004, 2007. Footnote 29, Footnote 31 This information is provided by the Province of BC under the Open Government License for Government of BC Information v.BC1.0.
Long Description for Figure 12
This horizontal stacked bar chart shows the following information:
lost mid 1800s
- 1990 (km2)
lost 1990 -
|Southern Thompson Upland||143.5||0||1323|
|Southern Okanagan Highland||77.9||0||125|
|Northern Okanagan Basin||329.2||17||380.6|
|Southern Okanagan Basin||69.1||13.7||320.5|
From 1800 to 2005 in the Okanagan and Lower Similkameen valleys, the antelope-brush–needle-and-thread grass shrub-steppe ecosystem declined by 68% (Figure 13), the big sagebrush shrub-steppe ecosystem declined by 33% (Figure 14), and the Idaho fescue–bluebunch wheatgrass grassland ecosystem declined by 77% (Figure 15). Footnote 20 Footnote 32 The loss of these ecosystems was mainly due to development at lower elevations. Footnote 20 These three ecosystems are presently in early seral stages and invaded by non-native species due to decades of intensive livestock grazing. Footnote 20 Further, many of the richest soils have been cultivated, Footnote 33 Footnote 34 leaving remaining grasslands on less productive soils.
Grasslands in the WIBE are at risk in and outside of protected areas. Grasslands outside of protected areas could be converted to agricultural, commercial, and residential uses. In 2004, 40% of grasslands were in private holdings whereas only 8% of grasslands were in protected areas. Footnote 30 The extent of grasslands, whether protected or not, can also be reduced by the alteration of natural disturbance regimes. For example, the suppression of wildfires in the Ponderosa Pine biogeoclimatic zone allowed forests to encroach into grasslands. Footnote 35 Footnote 36 Footnote 37 Footnote 38 About 90% of all BC's grasslands are grazed by domestic livestock, degrading the ecosystems and facilitating the spread of invasive plants. Footnote 31 In a study of 17 grazed grassland sites in the Southern Interior, non-native plants covered 35% of the sites with some sites having 85% coverage of non-native species. Footnote 39 Increasing pressure from recreational activities, such as disturbances from off-road vehicles and conversion to golf courses, also threaten grasslands. Footnote 31Additional information can be found in the Invasive non-native species section on page 44 and the Natural disturbance section on page 79.
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.
Wetlands occupy a small portion (<1%) of the WIBE due to the region's climate, soil, and topographic features. Footnote 40 Footnote 41 Nevertheless, they play a crucial ecological role particularly because wetlands in arid areas support more species than other ecosystems. Footnote 40 Footnote 42 Wetlands of the WIBE support many species at risk such as Wallis' dark saltflat tiger beetles (Cicindela parowana wallisi), Great Basin spadefoots (Spea intermontana), short-rayed alkali asters (Symphyotrichum frondosum), and small-flowered lipocarphas (Lipocarpha micrantha). Footnote 43
Most wetlands in this area are located in valley bottoms where development is also concentrated and 85% of wetlands have been lost since European settlement--mainly due to conversion to agriculture and more recently for urban development. Footnote 44 Footnote 20 In 1800, the South Okanagan and Lower Similkameen valleys had 178 km2 of wetlands, by 1938 the area had decreased to 69 km2, and by 2005 there were fewer than 30 km2 remaining. Footnote 20
The loss among different wetland communities in the South Okanagan and Lower Similkameen valleys has varied. For example, from 1800 to 2005, shrubby water birch–red-osier dogwood riparian wetlands declined by 92% (Figure 16), black cottonwood–red-osier dogwood riparian floodplain by 63% (Figure 17), and cattail marshes by 41%. Footnote 20 Wetlands continue to be lost and degraded by urbanization, intensive agriculture, and, in some areas, heavy recreational use. Footnote 20 Footnote 45 Footnote 46 In addition, invasive species and climate change pose serious threats. Footnote 47
Additional information can be found in the Ecosystem conversion section on page 40 and the Invasive non-native species section on page 44.
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.
Approximately 2% of the WIBE area is covered by lakes, rivers, and streams. Footnote 13 These support diverse aquatic communities including species at risk such as chiselmouth fish (Acrocheilus alutaceus) and Rocky Mountain ridged mussels (Gonidea angulata). Anadromous salmon migrate to parts of the Okanagan Basin and the Thompson Basin; the Adams River is also an important breeding area for sockeye salmon (Oncorhynchus nerka).
The Thompson Basin contains Kamloops and Nicola lakes as well as portions of Shuswap and Adams lakes. The Thompson River forms at the confluence of the North and South Thompson rivers and flows to the Fraser River. West of Lillooet and draining to the Fraser River are the Downton Lake and Carpenter Lake reservoirs and the Anderson Lake and Seton Lake reservoirs. A portion of the Fraser River mainstem is captured in the WIBE.
The WIBE also contains a chain of lakes along the Okanagan Valley floor that flow via the Okanagan/Okanogan River (Canadian and U.S. spellings, respectively) into the Columbia River in Washington State. Wood and Kalamalka lakes drain into Okanagan Lake, the largest in the series, and then Skaha, Vaseux, and Osoyoos lakes. Osoyoos Lake straddles the Canada–U.S. border.
Annual net inflow to Okanagan Lake is variable (Figure 18) and influences water levels (Figure 19), which affect the annual availability of spawning habitat for the shore-spawning variant of kokanee (Oncorhynchus nerka kennerlyi Footnote 48 The loss of tributary streams and the establishment of mysis shrimp (Mysis diluviana, formerly M. relicta), an invasive non-native species, also reduced populations of kokanee. More information about mysis shrimp can be found in the Invasive non-native species section on page 44 and the Food webs section on page 85.
Source: BC River Forecast Centre, 2011 Footnote 49
Long Description for Figure 18
This bar chart shows the following information:
Inflow volume (millions m3)
This bar chart shows the following information:
Note: The average volume from 1981 to 2010 is marked on the figure (535 million m3).
Source: Environment Canada, 2009 Footnote 50
Long Description for Figure 19
This line graph illustrates the following:
From the mid-1970s to 2001, nutrient levels in Skaha and Osoyoos lakes (measured as total phosphorus concentration in spring) declined by 52% and 40% respectively. Footnote 51These reductions are attributed to the implementation of sewage treatment plants and reduced nutrient inputs from agricultural sources. Nutrient reductions reduced the amount of phytoplankton and increased the concentration of oxygen in the lower (hypolimnetic) layer of these lakes, which benefits salmonids. Since 2001, the concentrations of phosphorus have remained relatively stable (see Figure 38 in the Nutrient loading and algal blooms section on page 52).
Saline lakes and ponds in Kamloops and the southern Okanagan contain unique chemistry, non-vascular plants, and invertebrates. Footnote 52 Footnote 53 In addition, microbialites--large coral-like structures produced by cyanobacteria--occur in two lakes near Lillooet. Footnote 14
Most of the watersheds in the WIBE are snowmelt-driven systems with high spring freshets. The spring freshet, from April to June, can account for as much as 90% of annual stream flow. Footnote 54 After the freshet, water flow generally remains low for the summer, fall, and winter. Changes in streamflow associated with climate change have been recorded in the Similkameen and Kettle rivers and are discussed in the Climate change section on page 55.
The BC Ministry of Environment sets water quality objectives for streams (and other waterbodies) that are or may be affected by human activities. Footnote 55All of the major rivers and many of the smaller streams in the WIBE are monitored regularly for physical, chemical, and biological characteristics to ensure that they meet the water quality objectives. For select sites, a Water Quality Index Footnote 56was calculated in 2002–2004 to assess the overall quality for the end uses of the water, such as drinking water, recreation, irrigation, or habitat for aquatic life. Footnote 57Water quality varied from marginal to good at eight sites from 2002 to 2004 (Table 3). For example, the water quality of the Fraser River at Hope improved through reductions of adsorbable organohalogens (AOX) and chloride from 1979–2004, due to abatement of pulp mill waste entering the river. The water quality of the Okanagan River at Oliver declined from 1980–2002 due to agricultural runoff (Table 3). Footnote 57
|Site (Years of Records)||WQI Table Footnote a Score||Rank Table Footnote a||Trend||Concerns monitored||Cause of Trend|
|Fraser River at Hope|
|84.2||Good||Improving||Adsorbable organohalogens (AOX), chloride||Pulp mill waste abatement|
|Kettle River at Carson|
|71.0||Fair||Stable||-||No past trend|
|Kettle River at Midway|
|76.7||Fair||Stable||-||No past trend|
|Okanagan River at|
|Salmon River at Salmon Arm (1985–2004)||45.8||Marginal||Stable||Fecal coliforms||Agricultural non-point source abatement|
|Similkameen River at Princeton (1989–1997)||83.2||Good||Stable||-||No past trend|
near US Border
|Thompson River at Spences Bridge|
|65.2||Fair||Stable||Chloride, dioxins, and furans in fish||Pulp mill waste abatement|
Benthic invertebrates were collected from urban streams in the Okanagan for use as indicators of stream health. The benthic index of biological integrity (B-IBI) is a measure of the ability of streams to support biological communities including algae, invertebrates, fish, and aquatic mammals and birds. The B-IBI is a composite index based on a series of metrics characterizing the stream invertebrate community, including total taxa, number of plecoptera taxa, number of ephemeroptera taxa, number of intolerant taxa, and number of clinger taxa. These metrics responded predictably to cumulative watershed disturbance and ly distinguished urban and highly altered sites from low impact sites. Footnote 58Of 31 stream sites assessed, 68% were in fair, poor, or very poor condition, 16% were in good condition, and 16% were in excellent condition (Figure 20). Footnote 58 Low B-IBI scores suggest that these streams are subject to stressors such as the loss of riparian vegetation, channelization, stormwater inputs, and degraded water and sediment quality.
The categories in parentheses indicate the estimated stream condition based on index score.
Source: Jensen, 2006 Footnote 58
Long Description for Figure 20
This bar chart shows the following information:
|B-IBI score||Number of streams|
|5-8 (very poor)||3|
Habitat alteration and loss
Increasing human population, urbanization, and a history of changes to lake and stream systems will continue to alter the hydrology and availability of water in the WIBE. The Okanagan Basin has experienced the most substantial modifications to its hydrologic regime as a result of the construction of storage dams, withdrawals of water for residential, agricultural, and industrial uses, and channelization of the Okanagan River. These impacts include changes in the annual rate of flow and alteration or removal of floodplains and riparian areas of the Okanagan River. Footnote 20
Most Okanagan streams and headwater lakes have been dammed; outlets of five of the six large Okanagan valley floor lakes are regulated, and there are reservoirs on many of the upstream tributaries. Footnote 59From 1913 to 1998, the number of dams on inflows to the Okanagan Lake increased from 11 to 147. Footnote 60
Portions of the land in the Thompson and Fraser basins within the WIBE are upstream of a dam (Figure 21). In addition, all the land area of the Okanagan, Similkameen, and Kettle watersheds is upstream of a dam. Okanagan, Skaha, Vaseux, and Osoyoos lakes all have outlet dams (Penticton, Skaha, McIntyre, and Zosel dams, respectively), and two of them are managed to allow the passage of fish upstream (Zosel Dam downstream of Osoyoos Lake and McIntyre Dam downstream of Vaseux Lake; the latter was modified in 2009). Footnote 61The passage of fish upstream is barred on the Similkameen River by the Enloe Dam (in Washington State), which was built at the site of a natural barrier to the passage of fish. There are no dams on the mainstems of the Fraser, North and South Thompson, and Kettle rivers.
Water allocation and diversion
Water allocations and diversions from lakes and streams in the WIBE are primarily for residential, agricultural, commercial, industrial, water storage, and habitat conservation uses. Water may also be allocated to power production and mining. Many parts of the WIBE, especially in the Okanagan and Thompson basins, have high rates of water diversion (Figure 22). The majority of water use restrictions on streams in BC are located in the WIBE. Footnote 62
Water availability and use is well studied in the Okanagan Basin because of the Okanagan's growing population and arid conditions. The volume of surface water licensed for withdrawal per year is 443,000 megalitres (or 443 million m3, equivalent to 177,200 Olympic-sized swimming pools). Footnote 63An additional 351,000 megalitres per year are licensed for conservation and other non-consumptive uses. Footnote 63In the Okanagan watershed, 235 streams are considered "fully recorded," meaning that there was no additional water available to allocate more water licences. Footnote 64
Actual water use is not necessarily equivalent to water allocation in that water may be licensed for use but the licensee does not use the total volume allowed by the license. From 1996 to 2006, the average annual water use in the Okanagan Basin was 219,000 megalitres with 67% of this volume coming from surface water sources. Footnote 63During that time period, water use was 187,000 megalitres in 1997 (a wet year) and 247,000 megalitres in 2003 (a dry year). Footnote 63The increased use in 2003 was mainly due to agricultural and outdoor residential uses. Water use also varies throughout the year with the rate increasing in spring when irrigation begins and peaking in late July to mid-August. The largest annual users of water in the Okanagan Basin are the agricultural sector (55%) and residential users (31%). Footnote 63
The Okanagan–Similkameen Basin has the lowest amount of water (measured as area, m2) per capita in Canada. Footnote 65Demand for water in this water-scarce region is rising with ongoing population, urban, and agricultural growth. Footnote 66The consequence of a limited initial water supply in conjunction with human demands for water, increased evaporation, and climate change impacts on the seasonal rate of flow is a scarcity of water for aquatic and riparian ecosystems, especially during drought years. Footnote 67
Channelization of Okanagan River
Sections of the Okanagan River were channelized for flood control and irrigation from 1949 to the mid-1950s (Figure 23). Footnote 68, Footnote 69 Before channelization, the Okanagan River regularly flooded communities within its floodplain; particularly large floods occurred in 1928, 1942, and 1948. Footnote 68The channelization shortened the river from 61 km to 41 km and decreased the areal extent of its floodplain from 2.12 km2 in 1800 to 0.15 km2 in 2005. Footnote 20 A few sections of the river remain in a natural or semi-natural state, Footnote 70but 93% of the natural river has been lost. Footnote 20
The Okanagan River Restoration Initiative, sponsored by the Canadian Okanagan Basin Technical Working Group, is restoring part of the river to its original configuration. The 1-km section, just north of Oliver, will provide important habitat for salmon and trout, reduce the risk of flooding of lands adjacent to the floodplain, and allow riparian vegetation to re-establish. Footnote 71
Additional information about habitat loss and fragmentation in lakes and rivers can be found in the Ecosystem conversion section on page 40.
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.
Over time, the loss of glaciers can reduce the amount of water in glacial streams in summer and lead to increased water temperatures. Footnote 73Both streamflow and temperature are important factors for aquatic organisms, particularly cold-adapted species like salmonids. Footnote 73 Footnote 74 Footnote 75Since the mid-1970s, the loss of ice in southwestern Canada's glaciers has accelerated. Footnote 76
The World Glacier Monitoring Service recorded a 37 m reduction of ice thickness for Place Glacier, southwest of Lillooet near the western boundary of the WIBE, from 1964 to 2008 (Figure 24). Footnote 74The Bridge Glacier, northwest of Lillooet, declined from 92 km2 to 84 km2 (7%) between 1995 and 2005 (Figure 25). Footnote 75
Additional information related to glacier melt can be found in the Climate change section on page 55.
Source: Demuth et al., 2009. Footnote 74Data provided by World Glacier Monitoring Service.
Long Description for Figure 24
This line graph shows the following information:
|Year||Metres of water equivalent|
Note the westward recession of the main tongue of the glacier.
Source: Stahl et al., 2008 Footnote 75 This material is reproduced with permission of John Wiley & Sons, Inc.
Long Description for Figure 25
This figure contains two maps: in 2005, non-forest has grown as the main tongue of the glacier receded compared to 1995.
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Jensen, E.V. 2006. Cumulative effects monitoring of Okanagan streams using benthic invertebrates, 1999 to 2004. Ministry of Environment. Penticton, BC. 60 p.
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Merritt, W.S., Alila, Y., Barton, M., Taylor, B., Cohen, S. and Neilsen, D. 2006. Hydrologic response to scenarios of climate change in sub watersheds of the Okanagan Basin, British Columbia. Journal of Hydrology 326:79-108.
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Hall, K., Stockner, J., Schreier, H. and Bestbier, R. 2001. Nutrient sources and ecological impacts on Okanagan Lake. Institute for Resources and Environment, University of British Columbia. Vancouver, BC.
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Alex, K. 2010. Providing fish passage at McIntyre Dam. Bilateral Okanagan Basin Technical Working Group Meeting. 24 February, 2010. Penticton, BC. Meeting presentation.
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Shepherd, P., Neale, T. and Cohen, S. 2004. Water Management. In Expanding the dialogue on climate change and water management in the Okanagan Basin, British Columbia. Edited by Cohen, S., Neilsen, D. and Welbourn, R. Environment Canada, Agriculture and Agri-Food Canada and the University of British Columbia. Chapter 3. pp. 11-24.
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Symonds, B.J. 2000. Background and history of water management of Okanagan Lake and River. BC Ministry of Environment, Lands and Parks. Penticton, BC. 8 p.
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Milner, A.M., Brown, L.E. and Hannah, D.M. 2009. Hydroecological response of river systems to shrinking glaciers. Hydrological Processes 23:62-77.
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Demuth, M.N., Sekerka, J., Bertollo, S. and Shea, J. 2009. Glacier mass balance observations for Place Glacier, British Columbia, Canada (updated to 2007). Spatially referenced data set contribution to the National Glacier-Climate Observing System, state and evolution of Canada's glaciers [online]. Geological Survey of Canada. (accessed 3 March, 2011).
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