Physical Structure of Aquatic Ecosystems

Introduction

Long, narrow deep, fjord-like lakes nestled between high, jagged mountain ranges characterize the landscape of the Columbia Basin. In the Jurassic period, the North American plate moved northwest over the ancestral Pacific basin. As it moved, the leading edge picked up terranes, which folded , thickened and thrust-faulted against the existing continent, forming the dramatic peaks and trenches of the Rocky, Purcell, Selkirk and Monashee Mountain ranges (see Earliest Beginnings). Aquatic ecosystems prior to the most recent Ice Age, 15,000 years ago, are virtually unknown, although fossil remains suggest a flourishing and diverse population of water-based organisms. In BC, no fish survived the Ice Ages. After the ice which covered all of BC retreated 13,000 years ago, fish immigrated from Puget Sound in the west, the southern Columbia River in the south, the Great Plains to the east and from the Yukon refuge to the north. Given the geographic barriers (mountains) to the north, west and east, it is likely that fish from the south populated the Columbia Basin.

Changes to the physical structure of an ecosystem affect the way the plants and animals within the system interact with their physical environment and with each other. In the Columbia River basin, the geological changes which created the long, deep, narrow, steep-sided, fjord-type basins of the Arrow and Kootenay Lakes were dramatic but came gradually, giving ecosystem members time to adapt to their new physical environment. Resident species occupied unique niches and continued to respond to the subtle pressures of competition, predation and minor geographical changes (flooding and landslides for example). Glaciers continue to carve alpine lakes by their movement and melt patterns. Throughout the mountains of the Columbia Basin there are small lakes left by the patterns of glaciation. These small lakes can have unique populations of fish when they have an isolated ecosystem. Many of the lakes are now stocked with trout to support a flourishing tourism fishery. More information on small lakes in the Columbia Basin can be found at: http://www.bcadventure.com

McPhail and Carveth (1992) describe the physical structure of the main drainages in the Columbia Basin thus:

"In their ecology and climate, the upper Columbia and upper Kootenay Rivers are similar. Both rise at high altitude and receive tributaries directly from glaciers in the Rocky and Purcell mountains. Even in summer they are cold, turbulent and silt-loaded environments that resemble the melt-water channels and streams of early postglacial times more than the clear, less turbulent lower reaches of the same rivers. The native fish fauna in the upper reaches of these rivers is limited to a few species that are able to tolerate the harsh environment. Because of the mountainous terrain, there are barriers (falls and rapids) on most upper Columbia tributaries. Usually, only trout or char occur above these barriers, although occasionally there are sculpins. Although both rainbow and cutthroat trout can occur above falls, they rarely co-exist in such situations.

In the lower Columbia and lower Kootenay, the gradient lessens, the silt load settles out and the rivers become clear and, although still strongly flowing, they are less turbulent. As well, both rivers in their lower reaches flow through large, oligotrophic lakes: the Columbia through Arrow Lakes and the Kootenay through Kootenay Lake."

There are numerous mineral hot springs throughout the Columbia Basin. Hot (up to 90 degrees C) alkaline water seeps or flows from the earth after it has been heated by volcanic forces. The hot springs host a variety of blue-green algae or cyanobacteria. Their ability to grow and reproduce in the hot, alkaline, highly mineralized conditions has given rise to the theory that life arose 3.5 billion years ago in similar hot, mineral seas which then covered the earth. Visitors from all over the world are attracted to the developed hot springs resorts such as Nakusp, Halcyon, Fairmont, Radium and Ainsworth Hot Springs, while a map, some off-road driving and a solid pair of hiking boots attracts others to many undeveloped hot springs tucked in amongst the trees in the hills. More information can be found at: http://www.ohwy.com

Human-Induced Changes

Dams and Reservoirs

During the twentieth century, humanity has wrought major physical change on the aquatic ecosystems of the Columbia Basin. The changes we've made have been likened to "an Ice Age in fast forward mode", accelerating the pressure on species hundreds of times, far faster that they can adapt to (MOELP website, 1999). Five dams impede the natural flow of water in the Columbia Basin, their reservoirs flooding a total area of 654.7 square kilometres and holding 15.5 million acre feet more of stream storage than the pre-dam lakes and rivers. It is only now, after over 30 years of altered ecosystems, that the impacts of the dams are being realized.

Columbia River

The Columbia River headwaters are at Columbia Lake, nestled in between the Rocky and Purcell Mountains. As the Columbia River flows north, it collects water from the mountains and flows into Kinbasket Lake. Prior to its damming, the river flowed through the Rockies and then the Columbia Mountains, made a dramatic turn southward at Mica and continued on into Upper Arrow Lake, near Arrowhead (30-40 kilometres south of Revelstoke). The Selkirk (Lardeau and Valhalla Ranges), Purcell (Bugaboo Range) and Monashee (Gold Range) Mountains drain into Arrow Lakes. Arrow Lakes was two lakes, Upper and Lower Arrow, connected by a short riverine section. The Columbia River left Lower Arrow Lakes north of Castlegar, to be joined by Kootenay and Pend d'Oreille Rivers and continue on through Washington and Oregon states.

The Grand Coulee dam was build in 1941 on the Columbia River in Washington state, and later joined by 11 other American dams on the Columbia before it empties into the Pacific Ocean at Astoria, Oregon. Construction of these dams eliminated the migratory salmon and sturgeon from the upper Columbia River valley. As a result of the Columbia River Treaty signed between Canada and the USA in 1964, three hydroelectric dams have been constructed (Keenleyside, Mica and Duncan), their reservoirs now covering a total area of 2023 square kilometres and draining almost 40,000 square kilometres of watersheds. The dams were constructed to store water for hydroelectric power generation in the USA and to help control the periodic and sometimes devastating floods throughout the Columbia River valley. In return for building three dams, BC became entitled to half the additional power generated in the USA that resulted from storage operations in Canada. In 1994, 30 years after the Columbia River Treaty was finalized, a Memorandum of Agreement was signed between BC and the USA which now sees revenue from the downstream benefits flowing back to the valleys the water flowed from.

The Hugh Keenleyside Dam, one of the Treaty dams, was constructed in 1969 at the outflow to lower Arrow Lakes, 8 km north of Castlegar. In order to flood the valley, BC Hydro extirpated people from their lands, often in spite of generations of settlement. The fertile valley bottom was flooded, covering 56.9 square kilometres of streams, marsh, forest and cultivated farm habitat. In the process, 30% of kokanee spawning and rearing habitat in the Arrow Lakes basin was eliminated. The dam increased the size of the existing lakes to a 465 square kilometres reservoir with a volume of 38.6 cubic kilometres and an active storage capacity of 7000 million cubic metres. Arrow Lakes is now a two basin lake with a 287 metre maximum depth in the upper basin, a shallow narrows section and a lower basin with a 194 metre maximum depth.

To satisfy the Columbia River Treaty, Mica Dam was constructed on the upper Columbia River in 1973, forming Kinbasket Lake reservoir. The reservoir is 310 square kilometres, and stretches for 216 km. It can actively store 14,800 million cubic metres of water, assisted by a maximum drawdown of 47 m. Mica is the only Treaty dam with a generating station; it can generate 1736 MW of power. Although no estimate of fish losses was made prior to construction, it was later discovered that some of the trophy rainbow from the Arrow Lakes spawned upstream of the Mica Dam.

Downstream from Mica, Revelstoke Dam and Generating Station were constructed in 1984 to capture the benefits from the water storage in the Mica Reservoir. The dam was not part of the Columbia River Treaty and provides no storage of water. This run-of-the-river dam generates 1843MW of power at Revelstoke. Filling the reservoir created behind the Revelstoke Dam caused the river level to rise; 26.4 square kilometres of land was flooded, including 200 km of tributaries which fed the Columbia River and 150 km of river's mainstream used by spawning Arrow Lakes kokanee, bull trout and rainbow. Some compensation for lost fish and fish habitat has been realized through Hill Creek Hatchery and Spawning Channel (see Research and Management of Aquatic Ecosystems), constructed in 1979.

Kootenay River

The Kootenay River originates in the Rocky Mountains near the source of the Columbia River. While the Columbia flows north around the Big Bend to Mica Dam, the Kootenay River flows south. An option under the terms of the Columbia River Treaty, the Americans built the Libby Dam on the Kootenay River in the USA in 1973, creating the Koocanusa Lake reservoir which spans the Canada-USA border. Koocanusa Lake is 166 km long, covers 186 square kilometres and has a water level which fluctuates 52 metres annually. The huge range in water levels is due, in part, to the need to ensure adequate flow for white sturgeon spawning below the Libby Dam. Kootenay River turns north after the Libby Dam and reenters Canada to flow into Kootenay Lake, contributing 80% of the lake’s inflow.

The Duncan River also feeds Kootenay Lake, comprising 10% of the inflow. Duncan Dam was built on the Duncan River in 1967 to fulfill the obligations of the Columbia River Treaty. The 77.7 square kilometre Duncan Lake reservoir created behind the dam holds runoff from 2396 square kilometres of the Purcell Mountains watersheds. The Lardeau River drains the watersheds around Trout Lake in the Lardeau Range of the Selkirk Mountains and then joins the Duncan River.

The other 10% of the inflow into Kootenay Lake comes from tributaries. A total of 56% of the flow into Kootenay Lake is regulated by dams. When the lake was impounded , the water level increased 2.4 m, and now the annual drawdown is 3 m. Kootenay Lake stretches 107 km from the tip of its North Arm, near Lardeau, to the tip of its South Arm, near Creston and has a 45 km long West Arm jutting from Balfour to Nelson. The total lake covers 390 square kilometres, holds 36.7 cubic kilometres of water and has 24.6 cubic kilometres of water flow out of it each year. On average, its depth is 94 m and its width is 3.8 km. The outflow from the West Arm, near Nelson, is regulated by the 4 power stations of the Kootenay Canal, including the Corra Linn Dam, built in 1931 (for more information on Columbia Basin dams, see their website at http:eww.bchydro.bc.ca/info/generation/generation891.html).

South of Castlegar, the Columbia River is joined by the Kootenay River and then the Pend d’Orielle River. It crosses the Canada-USA border continuing on to the Grand Coulee Dam in Washington and, after passing 11 other American dams, finally meets the Pacific Ocean at Astoria, Oregon.

All of the changes in the structure of the major rivers in the Columbia Basin have had profound effects on the aquatic ecosystems (see Biodiversity of Aquatic Ecosystems). These ecological challenges are currently occupying a major portion of the time and resources of management agencies.

Limnology and Nutrients

A lake's productivity is based on the nutrient molecules contained in its limnetic layer, the layer the sun penetrates into to drive photosynthesis. Nutrients enter the system through erosion of nutrient-bearing rocks and through the decay of organic matter. The portion of nutrients deriving from organic matter comes from two sources: terrestrial and oceanic. Terrestrially-derived nutrients are from the decay of plants that grow around and in the basins and from the animals that eat these plants, or that eat other animals that ate the plants. Oceanic nutrients are from the decay of anadromous (migratory) fish, salmon for example, that consumed phytoplankton in the ocean and returned to the basin to spawn.

The nutrients in a river and lake or reservoir system are affected by dams in two ways that were not fully appreciated before the Columbia Basin dams were built. First, it is now known that a large proportion of the phosphorous in river systems that support large anadromous salmon runs comes from the decaying carcasses of the salmon. In the Canadian portion of Columbia Basin, anadromous salmon runs have been eliminated since construction of the Grand Coulee dam in 1941, depriving the Basin's aquatic ecosystem of this source of nutrients. Second, nutrients in a system tend to be associated with particles, such as clay particles and organic molecules, and these are heavier than water. Consequently, in the still waters behind a dam they tend to sink and become incorporated into the sediments at the bottom, unavailable to nourish the ecosystem. Lakes, as still bodies of water, are often oligotrophic naturally, but the number and size of reservoirs in the Columbia Basin increases the area from which nutrients are sequestered into the sediments, and hence unavailable to support the growth of phytoplankton. A compounding feature is the operation of the reservoirs for hydroelectric development and flood control, imposing an unnatural flow regime (no large spring runoff that otherwise would "flush" some sediments out of the reservoirs). This changes the timing and decreases the residence time of what little nutrient supply there is in the reservoirs, further limiting phytoplankton growth.

Kootenay Lake

Research began on the Kootenay Lake nutrient regime in 1992 in an attempt to understand the dynamics of the aquatic ecosystem. Physical limnological parameters measured include temperature, dissolved oxygen, pH, oxidation-reduction potential (ORP), specific conductance and salinity. These parameters were used to determine the lake’s suitability for fertilization. The North Arm of the lake is colder, with thermal stratification (layers of the lake separated by temperature) beginning in mid July, whereas in the South Arm thermal stratification begins in April and reaches a greater depth. Peak surface temperatures exceed 20 degrees C in the summer while temperatures at 50 metres remained near 4 - 5 degrees C. Deep mixing occurs in October and November. Dissolved oxygen, pH, ORP, specific conductance and salinity continue to be monitored for change as the fertilization experiment proceeds.

Phosphorus (P) and nitrogen (N) are the most common limiting factors in aquatic ecosystems. Phosphorus load, measured as grams P per square metre per year, was low historically, peaking when the Kimberley fertilizer plant was active and then achieving record lows after the Duncan and Libby Dams were constructed. As of 1998, phosphorus load has risen to 13% above historic pre-impoundment levels owing primarily to the fertilization program.

Arrow Lakes

Nutrient loads were examined from April to October of 1997/98 as a first step in understanding lake productivity. Low orthophophate and a high N:P ratio were found, indicating phosphorus-limited oligotrophic conditions. When there is not enough P in an aquatic ecosystem, the phytoplankton, the foundation of the aquatic food chain, doesn't grow.

P enters Arrow Lake from a variety of sources: dissolved organic matter carried in streams, the atmosphere, residential waste, fertilizer applied with the rye seed for dust control in Revelstoke Reach, and, historically (but not since the Grand Coulee Dam was constructed), from the decomposition of anadromous salmon. The total dissolved P in the Arrow Lake reservoir is 197,000 kg P. The P load increases from north to south, enabling higher primary productivity in the Lower Arrow. Although local streams do carry P from dissolved organic matter into the Arrow Lake reservoir, it is found in very low concentration in the water column as it may settle with the cooler stream water.

Although Arrow Lake receives a higher natural total P load than Kootenay Lake, the productivity of the Arrow system is lower than that of Kootenay, possibly due to lower bioavailability, as is being examined.

Nitrogen is another key nutrient for primary production. 90% of nitrogen is in nitrate form; 10% is nitrite. The N:P ratio is 36:1 in the Arrow system, further confirming the P limitation theory. The nitrate concentration decreases from north to south along the reservoir, resulting in a lower N:P ratio in the Lower Arrow, closer to the ratios which are useable by the phytoplankton primary producers. The total dissolved nitrogen in the whole lake is 7,200,000 kg N.

Biodiversity in a lake is a good indicator of nutrient levels. Phytoplankton and zooplankton are tiny plants and animals suspended in the water column where they form the basis for the entire aquatic food chain (see Biodiversity of Aquatic Ecosystems). Phytoplankton and zooplankton population diversity and abundance were assessed in Arrow and Kootenay Lakes. Researchers found phytoplankton abundance and population composition is typical of oligotrophic systems. Zooplankton abundance indicates that Arrow Lakes is less productive than Kootenay Lake which is beginning to show some results from fertilization (see Research and Management of Aquatic Ecosystems. The mysid shrimp numbers found in Arrow Lakes also indicates it to be less productive than Kootenay Lake, and lower Arrow is more productive than upper Arrow. Although the mysid shrimp competition did not cause the collapse of the Arrow Lake ecosystem, it was likely a direct contributor to the decline of the kokanee populations. Kokanee abundance is further evidence that Arrow Lake is less productive than Kootenay Lake and Upper Arrow is less productive than Lower Arrow. Kokanee spawner size and fecundity are depressed compared to historical data available.

Aquatic Ecosystem Topics