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The Future of Freshwater
The Impacts of Climate Change on
Freshwater in British Columbia’s
Flathead Watershed and Alberta’s
Upper Castle River Sub-basin
Patrick Thompson, MSc (Zoology)
March 2010
CPAWS
Executive Summary
The Flathead Valley in British Columbia and the Castle watershed in Alberta are integral
parts of the Canadian Southern Rocky Mountain Region. Part of the Crown of the
Continent ecoregion, these watersheds occupy a central position in the Rocky
Mountains, providing a link between Banff, Kootenay, and Yoho National Parks in the
north to Waterton and Glacier National Parks in the South. An assessment of the
current abiotic and biotic conditions in these two watersheds was conducted in order to
determine how they might respond to climate changes through the year 2080.
The Flathead watershed contains largely intact and healthy aquatic ecosystems.
Aquatic communities in the Castle watershed are more impacted by human activities
but the watershed remains a valuable and functioning ecosystem biologically. Both
watersheds contain high diversity of native species, including some that are listed as
threatened. The Flathead watershed contains few invasive species while the Castle
valley has populations of non-native trout that pose a threat to the native populations.
Climate change is expected to alter the timing and intensity of water availability in
streams, and the persistence and water level in lakes and ponds. Increased
temperatures are expected to shift species ranges upward in elevation and latitude. This
is anticipated to cause a reshuffling of species within ecosystems so that future
ecosystems will be composed of novel combinations of species, some of which do not
presently overlap in distribution. Many waterbodies and streams that are currently alpine
will convert to montane ecosystems as the tree line moves upwards in elevation.
Climate change is expected to make both watersheds more susceptible to invasion by
new species, some of which may have negative consequences on current ecosystem
processes and species. Warmer temperatures may also increase the occurrence of
hybridization between native and non-native trout species, which threatens the integrity
of native populations.
In general, climate change will disproportionately affect species at higher trophic levels,
because they are more sensitive to changes in temperature, are more dispersal limited,
and may not be able to shift their distributions fast enough to adapt to changing climate.
The lack of glaciers in the watersheds means that changes in water temperature will be
more gradual compared to watersheds fed by disappearing glaciers. The ecological
resilience of the watersheds is increased by their proximity to nearby preservation areas
and by the fact that much of the habitat is intact. Due to its higher degree of
fragmentation, the Castle will likely require restoration efforts to achieve similar
ecosystem resiliency as the Flathead watershed in the face of climate change.
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Table of Contents
Executive Summary ...................................................................................................................... i
1. Current Status of Freshwater Ecosystems ...................................................................... 1
1.1 Abiotic.................................................................................................................................. 1
1.2 Biotic .................................................................................................................................... 2
2. Forecasted Climate Change .................................................................................................. 2
3. Climate Change Effects on Freshwater ............................................................................... 3
3.1 Abiotic.................................................................................................................................. 3
3.11 Streams and Rivers .................................................................................................... 3
3.12 Lakes ............................................................................................................................. 3
3.13 Ponds and Wetlands................................................................................................... 3
3.2 Biotic .................................................................................................................................... 4
4. Adaptation to Climate Change............................................................................................... 6
5. Recommendations................................................................................................................... 7
6. Acknowledgements ................................................................................................................. 7
7. References................................................................................................................................ 8
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1. Current Status of Freshwater Ecosystems
1.1 Abiotic
The Flathead and Castle watersheds are composed of many small streams running off
mountain slopes into larger creeks and finally into the main Flathead and Castle Rivers.
These streams are supplied by rainfall runoff and melt water from high elevation snow
packs. Their velocity is generally high because of the steep terrain over which they flow.
The main Flathead River runs from north to south, flowing into Glacier National Park in
Montana, USA. The Castle River runs northwest, flowing into the Oldman River
reservoir. Both watersheds are part of the larger crown of the continent ecoregion that
spans into the United States (Figure 1).
Figure 1. Map of the Flathead and Castle watersheds in the context of the Crown of the Continent
Ecoregion, Watertown and Glacier National Parks, and the nearby proposed wildlife management area.
Both watersheds contain a few alpine and montane lakes and many smaller ponds and
wetlands. Water quality in the Flathead Valley is very high, with low nutrients and
suspended solids (Hauer, Stanford and Lorang 2007). Water quality in the Castle
watershed is generally good, however, human developments have taken their toll. Road
development, gas exploration, seismic exploration, logging, off-road vehicle access, and
the development of the Castle Mountain Ski Resort have caused increased erosion,
sedimentation, stream bank instability, stream widening, flow alteration, and riparian
degradation in the Castle dating back to the 1950s (Fitch 1997, Fisher 2001). The
construction of the Oldman River Dam and formation of the reservoir inundated the
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lower 12.5 km of the Castle River in 1992. There are no glaciers in the Castle River
watershed and only one small glacier at the head of Starvation Creek in BC’s Flathead
Valley.
1.2 Biotic
The Flathead watershed contains healthy populations of native Bull Trout (Salvelinus
confluentus) and Westslope Cutthroat Trout (Oncorhynchus clarki). There is currently
no hybridization of the Westslope Cutthroat Trout with Rainbow Trout (Oncorhynchus
mykiss). This population of Westslope Cutthroat Trout is currently listed as of Special
Concern by COSEWIC (Committee on the Status of Endangered Wildlife in Canada,
2009). There is also a population of Rocky Mountain Tailed Frogs (Ascaphus
montanus), currently listed as Endangered by COSEWIC. The watershed contains a
high diversity of aquatic invertebrate insects including caddisflies, mayflies, stoneflies,
and chironomids (Hauer et al. 2007).
The Castle watershed contains populations of native Bull Trout and Westslope
Cutthroat Trout. Both species are at risk in the Castle, with low adult populations. There
are established populations of non-native Brook Trout (Salvelinus fortinalis) and
Rainbow Trout (Oncorhynchus mykiss). The watershed contains populations of Longtoed Salamander (Ambystoma macrodactylum), Western Toad (Bufo boreas), and
Columbia Spotted Frog (Rana luteiventris) that are sensitive to habitat disturbance
(Jalkotzy 2005). The Castle watershed likely contains a similar diversity of invertebrate
insects to the Flathead.
2. Forecasted Climate Change
Temperatures in the region are expected to increase in all seasons with the highest
increases occurring in summer (Table 1)(ClimateBC Database,2009). Annual
precipitation is expected to increase marginally if at all. Precipitation is expected
decrease in summer, and more winter precipitation will fall as rain rather than as snow.
In general the region is expected to get hotter with the heat:moisture ratio increasing,
especially in summer, increased evaporation will further reduce water availability. The
Flathead valley is currently ~1.5°C warmer and wetter than the Castle valley because it
is east of the continental divide. Both watersheds are expected to experience similar
changes in climate.
Table 1. Predicted change in climate by 2080 in the Flathead and Castle watersheds based on 3
climate projection models provided by ClimateBC, Department of Forestry, University of British Columbia.
Lowest Predicted Change by
Highest Predicted Change by
Climate Variable
2080
2080
Average Annual Temperature
+ 2.5 °C
+ 4 °C
July Temperature
+ 3 °C
+ 8 °C
January Temperature
+ 2.5 °C
+ 5 °C
Average Annual Precipitation
± 0 °C
+ 120 mm
Average Summer Precipitation
- 30 mm
- 55 mm
Average Snowfall
- 30 mm
- 190 mm
Annual Heat:Moisture Ratio
+ 2.8
+ 3.8
Summer Heat:Moisture Ratio
+ 10
+ 30
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3. Climate Change Effects on Freshwater
3.1 Abiotic
3.11 Streams and Rivers
Warmer temperatures are expected to reduce average stream and river discharge, and
alter the timing of high and low flow periods (Hauer et al. 1997). Streams currently rely
on persistent alpine snow pack as a source of steady melt water throughout the summer
(Poff and Ward 1989). Anticipated reductions in winter snow pack mean that melt water
supply will end sooner in the summer than under current conditions. This will result in
drastic decreases to late summer water flow, some previously persistent streams may
run completely dry. Generally, climate change will likely lead to a concentration of
stream and river discharge in spring and early summer.
Warmer temperatures will cause more precipitation in the fall, winter, and spring to fall
as rain rather than snow. Rainfall runs off immediately, as opposed to snow which melts
slowly. As a result increased rainfall is likely to trigger more high flow and flood events.
High flow events and floods increase erosion, damage streambed and riparian habitats,
and increase the amount of particles suspended in the water, thus reducing water
clarity.
Reduced average flow coupled with warmer temperatures will cause greater fluctuations
in water temperature. Small volumes of water track air temperatures more closely than
large volumes do. Stream and river temperatures should be change dramatically in
extreme hot and cold weather, both of which are expected to increase with climate
change (Magnuson et al. 1997).
3.12 Lakes
Climate change will affect lakes by increasing water temperature and reducing the
number of days per year that ice cover is present (Jensen et al. 2007). Reduced ice
cover will increase surface water temperatures as more sunlight is absorbed by open
water as opposed to ice covered water (Magnuson et al. 1997). Most lakes in the region
are not expected to dry out with climate change because of their large volume.
However, it is expected that they will experience reductions in size as a result of
increased evaporation and reduced inputs from snowpack and precipitation.
3.13 Ponds and Wetlands
Ponds and wetlands are expected to experience the same reductions in water input and
increases in evaporation as lakes and streams. Due to their relatively small volumes
and lack of constant water input, these changes may be more extreme and many of
these waterbodies are likely to dry up completely during the summer(Girdner and
Larson 1995). Ponds and wetlands will also experience larger fluctuations in water
temperatures because smaller volumes of water are less insulated from changes in air
temperature.
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3.2 Biotic
The impacts to abiotic communities resulting from climate change are expected to
cause stress for most organisms living in the aquatic habitats of both regions . Most
species are expected to adapt to climate change by moving to higher elevation and
latitude habitats that are colder; species will migrate to match their specific climactic
requirements (Parmesan and Yohe 2003). Because of the limited size of the Castle and
Flathead watersheds, moving northward is not likely to provide species adequate
respite from warming temperatures. Moving to higher elevations may be possible and
allow species to move relatively short distances to colder habitat. Unfortunately, species
that are only present at high elevations, such as those that inhabit headwater streams
and high alpine habitats, cannot migrate to higher elevations and will most likely
disappear from the region (Hauer et al. 1997).
Ecosystems as a whole are not expected to shift with their component species since
each species has specific habitat, climatic requirements, and dispersal ability (Ackerly
2003, Ibanez, Clark and Dietze 2008). Rather, ecological communities will reassemble
based on which species are tolerant to the local environmental conditions, how they
interact and compete with other species present, and how far they can disperse.
Predicting the distribution of specific biota is difficult, however, because of unanticipated
interactions between species (Davis et al. 1998).
Climate warming is likely to make these watersheds more susceptible to invasive
species as changing environmental conditions cause native species to loose their
competitive advantage (Rahel and Olden 2008). This is of special concern for Bull
Trout, a species that requires cold, clean water. Bull and Westslope Cutthroat Trout
have already been displaced by non-native species such as Brook Trout and Rainbow
Trout in much of their native range. This trend is likely exacerbated by climate change
because these native species have been shown to lose their competitive advantage
over invasive species at higher water temperatures (Destaso and Rahel 1994,
McMahon et al. 2007). While both Brook Trout and Rainbow Trout are already present
in much of the Castle watershed, climate change may increase their distribution and
competitive advantage over native species.
Climate change is expected to disproportionately affect species at higher trophic levels
(Voigt et al. 2003); suggesting that fish populations will be the most impacted of all
types of aquatic biota. Indeed, Keleher and Rahel (1996) estimated that climate
warming this century should result in a 62 % reduction in salmonid habitat range in the
Rocky Mountains. Therefore, we anticipate that many ecosystems in these watersheds
will loose their top predators, thus shortening food webs. This is likely to further disrupt
the food webs as released predation from top predators allows their prey to increase in
abundance, placing increased predation pressure on the species lower down in the food
web, through a trophic cascade (Borer et al. 2005).
Native Westslope Cutthroat Trout hybridize with other species such as the non-native
Rainbow Trout. Warmer temperatures and land use disturbance have been associated
with increased hybridization between these species (Muhlfeld et al. 2009). This is of
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concern because the British Columbia portion of the Flathead contains a population of
Westslope Cutthroat that is currently unhybridized (Boyer, Muhlfeld and Allendorf 2008).
Rocky Mountain Tailed Frogs (Ascaphus montanus) in the Flathead Valley are limited to
streams with water temperatures above 6-8 °C (Dupuis and Friele 2006); climate
change may increase their potential habitat in the Flathead and Castle watersheds.
However, other environmental changes, such as increased suspended particulates in
the water, that result from erosion or anthropogenic alteration of the landscape, will
make streams less habitable for this species (Dupuis and Friele 2006).
There are currently many species of caddisflies present in these watersheds, each with
a very specific thermal requirements (Hauer et al. 2007). As the climate changes, they
will be forced to move higher in the watershed to meet the climate requirements to
which they are adapted. Species that live in the headwaters will be lost and replaced by
species from lower elevations (Parmesan and Yohe 2003). Other invertebrate
organisms such as mayflies, stoneflies, and chironomids are likely to show similar
responses.
Warmer climate is expected to cause the tree line to move upwards in elevation
(Hamann and Wang 2006). This will cause a transition from previously alpine
waterbodies and streams to montane habitats surrounded by trees and vegetation.
Montane waterbodies receive considerably more shading and input of organic matter
compared to alpine water bodies (Hauer et al. 1997). As this transition occurs, specialist
alpine species are expected to be replaced by species better adapted to montane
environments.
Warmer water temperatures and longer growing seasons resulting from longer ice free
periods will likely lead to more algal growth and productivity of aquatic habitats (Jensen
et al. 2007). Fish populations are often positively affected by increased ecosystem
productivity, however, high levels of algal growth can clog waterways and reduce
aquatic habitat quality.
Those species that have the ability to live in habitats that periodically dry up will be
favoured. Some species, such as waterfowl, will be able to move to habitats where
water is still present. Many species of aquatic insects have strategies that allow them to
survive in temporary habitats (Williams 1997). Some form resting stages that can
withstand drying out, some emerge from the water and have aerial adult stages, and
some burrow into the sediment waiting to emerge when water returns. Fish species
present in these watersheds are limited in their ability to survive in temporary habitats,
thus making them more sensitive to climate change.
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4. Adaptation to Climate Change
Glaciers act as a buffer for downstream water (temperature and flow) against warming,
but once they disappear, water temperatures will increase quickly to match the current
climate (Moore et al. 2009). This is likely to be the case in Glacier National Park, directly
south of BC’s Flathead Valley, where estimates suggest that glaciers might be gone as
early as 2030 (Hall and Fagre 2003). Warming increases the rate at which glacial melt
occurs, releasing higher volumes of cold water, which cool waters directly downstream
and increase stream flow. Thus, once the glaciers disappear, temperatures and water
flow actually change over greater magnitudes than they would have from the direct
effect of climate warming. Such rapid change in conditions is extremely hard to deal
with for organisms inhabiting these waters.
The Flathead and Castle watersheds, however, should experience smaller temperature
increases and changes in stream water flow as they are almost entirely fed by
snowpack melt and rainwater, rather than glacial melt. Therefore, aquatic organisms in
these watersheds should experience less overall stress as a result of climate warming
compared to other nearby watersheds containing glaciers.
The relative lack of fragmentation of the Flathead Valley in British Columbia should
make its ecological communities more resilient to climate change (Thrush et al. 2008).
The Castle River watershed has been more altered by human activity and
fragmentation; this has reduced its relative resiliency to climate change. Extensive
restoration efforts will likely have very positive results in terms of increasing ecosystem
resiliency in the Castle because of the high habitat and species diversity still present.
The presence of roads, pipelines, dams, clear cuts, and settlements increases the
potential for intentional and unintentional introduction of invasive species by humans
(With 2002). Furthermore, fragmentation often disrupts the natural movements of
organisms through a landscape, increasing the region’s sensitivity to climate change
(Leibold and Norberg 2004). Organisms can move between habitat patches in a larger
region as a way of dealing with local changes in environmental conditions, such as
temperature and water level. The greater the degree of habitat fragmentation, however,
the more impeded these critical movements become.
Despite the fact that aquatic organisms are limited in their ability to move between
unconnected waterbodies and streams, many have strategies that allow them to
disperse. Amphibians can move over land to find new habitats, and many aquatic
insects have aerial adult life stages that can move to new habitats to reproduce. Smaller
organisms such as zooplankton and algae have resting stages that can be blown
between habitats in the wind or can be transported on the fur or feathers of larger
animals (Havel and Shurin 2004). The relatively intact nature of the Flathead and Castle
watersheds should provide biological communities with higher resilience and resistance
to climate change. The Flathead watershed will likely display a higher degree of
resiliency because it is less fragmented than the Castle.
The Flathead and Castle watersheds are in close proximity to other protected areas and
such as Waterton (Canada) and Glacier (USA) National Parks. This large
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interconnected region of relatively un-impacted habitat should be more resilient to
climate change than a smaller region (Thompson 2009). Larger regions generally
include more species, many of which are functionally similar, but have varying thermal
and other environmental requirements. As climate change alters environmental
conditions, these species may be forced to relocate to new habitats that match their
climactic requirements. High biodiversity in the larger regions of the Flathead and the
Castle increases the potential that functionally important species will be present under
future conditions, although they may be different from those currently present.
Maintaining the ecological integrity of the Flathead and Castle watersheds also
increases the resiliency of surrounding regions to climate change. The Flathead Valley
is upwind (prevailing westerlies) and generally warmer than Waterton National Park and
the Castle wastershed, thus it provides a potential source for organisms that are
adapted to warmer conditions. In the same way, both watersheds could provide
organisms that are adapted to the conditions in colder regions to the north. The
Flathead River allows organisms to easily disperse downstream to Glacier National
Park in the United States and although this region is generally warmer, there could be
some unexpected benefits from this connectivity as conditions change.
5. Recommendations
Human disturbance and further fragmentations in the Flathead and Castle valleys
should be limited in order to preserve the ecological integrity of these watersheds. The
Castle watershed requires restoration efforts including road decommissioning, riparian
health assessment and repair, and measures to improve aquatic connectivity. Healthy,
intact, and interconnected ecosystems should have higher resilience to climate change
and other sources of ecological stress. Relatively unimpacted mountain watersheds in
Southern Canada, such as the Flathead watershed, and to a lesser extent the Castle
watershed, are rare and represent a unique opportunity to protect this type of
ecosystem as the climate changes. The close proximity of these watersheds to other
legally protected areas and their critical location in the Yellowstone to Yukon Corridor,
increases their resilience to climate change, and provides further justification for their
preservation.
6. Acknowledgements
I would like to thank Harvey Locke, Bob Peart, and Sarah Elmeligi for their thoughtful
reviews. I would also like to thank Erin Sexton for invaluable species data and local
perspective from the Flathead Valley. Thanks to Emilia Hurd for producing the map.
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Cover photo credits: main image, Michael Ready ILCP; insets, Justin Black ILCP and Michael Ready ILCP