�quatic Ecosystem Qnagement Health & Management

Aquatic Ecosystem Health and Management 3 (2000) 65-79 www.elsevier.com/locate/aquech

The large lake ecosystems of northern M.S. Evans*

National Water Research Institute, 11 Innovation Boulevard, Saskatoon, Sask., Canada S7N 3H5

Abstract The Great Lakes of northern Canada are relatively understudied ecosystems in comparison to the better-investigated Laurentian Great Lakes. This chain of lakes extends north from Lake Winnipeg (a shallow prairie lake) to Wollaston Lake and (moderately deep arboreal lakes) to Great Slave Lake (a deep subarctic lake) to Great Bear Lake (a deep lake located in the Arctic Circle). Many of these lakes have experienced minor localized anthropogenic impacts. Impacts include mining and fishingin the north and agricultural and urban impacts in the south. While most of these lakes are located in the relatively undeveloped regions of Canada, the northward migration of natural resource-based industries such as forestry, mining, agriculture and oil and gas operations may potentially affecttheir ecosystem health. Research programs are required to better understand the natural features of these ecosystems to further protect them from anthropogenically driven change. Long­ term monitoring programs are also required to protect fish, water quality and other ecosystem features. An emerging problem is meeting northern community concerns with environmental protection while providing the economic base for an increasingly modern lifestyle. © 2000 Elsevier Science Ltd and AEHMS. All rights reserved.

Keywords: Great Bear Lake; Great Slave Lake; Lake Athabasca; Lake Winnipeg

1. Introduction climate. However, with new technological advances, it is becoming increasingly cost-effective to extract The Great Lakes of northern Canada form a chain and/or harvest these natural resources. One of the of lakes extending from 63°N in the Northwest Terri­ major challenges in developing the north is providing tories to 50°N in Manitoba (Fig. 1). Further south and communities with a sufficienteconomic base to meet to the east lie the Laurentian Great Lakes. In contrast their needs while protecting the environmental integ­ to the Laurentian Great Lakes, the watersheds of the rity of the region. Great Lakes of northern Canada are relatively This paper provides a broad overview of the undeveloped: population levels are low and industrial geography, climate, natural resources and limnology development mostly limited to a few small cities and of the Great Lakes of northern Canada and their towns. Consequently, these lakes are relatively pris­ watersheds. The history of the anthropogenic impacts tine ecosystems in which anthropogenic perturbations in the region is also outlined. are below detection limits and/or localized to small areas. The watersheds of the NorthernGreat Lakes are rich in natural resources and their development has 2. Geography been limited by two factors-their geography and The Great Lakes of northern Canada lie in three * Fax: + 1-306-97 5-5143. watersheds: the Nelson River and Churchill River E-mail address: [email protected] (M.S. Evans). systems which discharge into and the

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LaMa~re

Great Slave

Hudson Bay ~?

Superior

Huron

)ntario

6 s6o lo'oo WESTERN EXTENT OF THE PRECAMBRIAN SHIELD

Fig. 1. Map showing the North Great Lakes and the Laurentian Great Lakes. Redrawn from Patalas (1975).

Mackenzie River system which discharges into the 1975). The central lakes are believed Beaufort Sea. Because these rivers flow north into to have remained ice-covered until some 6500- cold, inhospitable subarctic waters, they have not 7500 years ago. Thus, the Northern Great Lakes are served as important transportation routes linking relatively young ecosystems. inland Canada with the east and west coasts in The Northern Great Lakes lie in large measure on contrast to the St. Lawrence and Fraser River estuaries the Precambrian Shield (Fig. 1). Rocks consist of which had historic importance in shipping and, ulti- highly weathered crystalline, metamorphosed sedi- mately, other industrial development. However, with mentary and volcanic rocks; therefore, soils are thin. new advances in land and air transportation, the devel- To the west are sedimentary Paleozoic deposits. Soils opment of the north is accelerating. in this region originated from glacial drift with areas The Northern Great Lakes were formed during the of alluvial and lacustrine deposits becoming more Pleistocene glaciation (Hutchinson, 1957). The prominent at lower latitudes. Lakes located on the deepest lakes are to the north (i.e. Great Bear and Precambrian Shield have waters with a lower total Great Slave) and the shallowest to the south (i.e. dissolved solids (TDS) content than lakes located in Lakes Winnipeg and Manitoba). Southern Lake sedimentary drainage basins (Patalas, 1975). Rivers Winnipeg and Great Bear Lake are believed to have originating in Paleozoic watersheds can exert a become ice-free some 9000 years ago while Great strong influence on the physical and chemical proper- Slave Lake became ice-free 8200 (East Arm) to ties of the lakes located on the Precambrian Shield. 8500 (West Basin) years ago (Table 1; Patalas, Such influences can include transporting large

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Table 1 Summary features of the Great Lakes of Northern Canada. Data from Patalas (1975) and Herdendorf (1982) except where indicated. Great Slave Lake morphometric data also from Herdendorf (1982) and Rawson (1950). n.a. denotes not available -~

Great Bear Great Slave Athabasca Cree Wollaston Reindeer South Indian Manitoba Winnipeg

West Basin East Arm South Noah

Area (kin 2) 3153 19,400 9168 7900 1152 2062 5569 2253 4625 4900 19,600 ~. Maximum depth (m) 452 60 614 120 60 37 215 37 28 12 17 Mean depth (m) 76 41 185 26 15 21 17 11 n.a. 8 12 Age (years) 9000 8500 8200 7500 7500 6500 6500 6500 n.a. 8000 9000 TDS (mg I 1) 79 160 50 58 27 35 39 63 63 130 150 Secchi disc (m) 20 2.5 9 5.6 7.8 6.8 7.0 2.0 2.0 1.9 1.9 Epilimnion temperature (°C) 4.0 10.0 4.0 13.4 14.9 12.6 14.2 17.5 17.5 18.5 20.2 Total P (Dxg 1 1) 18 ~ 12.5 b 8.8 b 11.5 c n.a. n.a. n.a. 21a n.a. 720 46 d Nitrite-nitrate (ixg 1 1) 143 ~ 144 b 190 b < 1 c n.a. n.a. n.a. n.a. n.a. n.a. Silicon (mg 1 1) 1.9 a 1.3 b 1.0 b n.a. n.a. n.a. n.a. n.a. n.a. n.a. Chlorophyll (Ixg I 1) n.a. 2.7 b 1.7 b 1.1 ~ n.a. n.a. n.a. 5.0 d n.a. 5.10 4.1 d Commercial fish yield No commercial 1358 b No commercial 340 e 119 e 243 ~ 668 e 525 fg 668 e 3333 f (kg year l) ( x 1000) fishery fishery

a From Moore (1980a). b From Fee et al. (1985). c 1985-1988. From Mitchell and Prepas (1990). tm o From Patalas and Salki (1992). I e From Rawson (1960). f From Lake Winnipeg, Churchill and Nelson Rivers Study Board, 1971-1975. 68 M.S. Evans/Aquatic Ecosystem Health and Management 3 (2000) 65-79

volumes of highly turbid water into otherwise clear only on the lakes themselves, but also on their river lakes. Waters originating from Paleozoic watersheds systems and watersheds. also tend to be enriched in TDS and may be rela- tively enriched with nutrients. Thus, lakes located in 4.1. Minerals Paleozoic watersheds tend to be more productive than lakes located in Precambrian Shield watersheds Mineral deposits are an important economic (Rawson, 1960). resource for the Precambrian Shield region. Gold has been mined at Yellowknife on Great Slave Lake since the 1940s: a lead and zinc mine also operated in 3. Climate the region but was decommissioned in recent years. Cobalt, cadmium, copper, lead, nickel, silver and gold The Northern Great Lakes of Canada lie in a conti- deposits lie to the north and east of Lake Winnipeg nental climate region with cool summers, cold (National Geographic Society, 1992). Flin Flon, winters, low annual rainfall and pronounced season- which straddles the Manitoba-Saskatchewan ality in daylength (Environment Canada, 1982a-c). boundary, is the primary mining and smelting center North-south gradients in climate are particularly for the region. Uranium mines have operated on Great pronounced in winter. January air temperatures Bear Lake and Lake Athabasca and are in operation in average -28.9°C at Normal Wells (to the west of central Saskatchewan. More recently, diamond Great Bear Lake), -25.8°C at Hay River (on Great deposits have been discovered to the north of Great Slave Lake) and increase to - 19.0°C at Winnipeg (at Slave Lake. southern Lake Winnipeg). July air temperatures are less variable with latitudes averaging 16.3°C, 15.8°C 4.2. Oil and gas reserves and 20.2°C, respectively, at the same locations. Winter days are short and light intensity low. Significant oil and gas reserves are located in the December solar radiation averages 0.17 MJ m-2 d- Paleozoic watersheds of the Peace and Athabasca at Norman Wells, 0.99 MJm 2 d-1 at Fort Smith rivers. There are many industries extracting and (on the Slave River) and 3.82MJm 2d-1 at processing these reserves in Alberta and, to a lesser Winnipeg. Summer days are long, with near-continuous extent, Saskatchewan (Northern River Basins Study daylight at Great Slave and Great Bear lakes. June solar Board, 1996). Norman Wells, on the Mackenzie radiation averages 23.09 MJ m -2 d -~ at Norman Wells, River, was an important center processing gas and 21.86 MJ m -2 d -~ at Fort Smith and 22.99 MJ m -2 d -t oil extracted from the Delta and at Winnipeg. Precipitation increases with decreas- Beaufort Sea (Lopatka et al., 1990). The refinery at ing latitude, that is, from 328.4 mm year -~ at Norman Wells was recently closed although oil and Norman Wells, 339.9 mm year 1at Hay River to gas continue to be extracted from the region and piped 525.5 mm year 1at Winnipeg. further south from the facility.

4.3. Forestry 4. Natural resources With the exception of the southern, prairie regions There are many valuable natural resources in the of Alberta, Saskatchewan and Manitoba, the majority drainage basins of the Northern Great Lakes including of the watersheds of the Northern Great Lakes are minerals, gas and oil reserves, forestry and soils forested. As a consequence, forestry is a major suitable for agriculture. Utilization of these resources industry, particularly in Alberta where ready access is increasing with improved technology, increased to major rivers (the Peace and Athabasca systems) has market prices and growing community interests in facilitated the development of pulp and paper mills expanding the local economic base. The extraction (Northern River Basins Study Board, 1996). Forestry of these commodities has already affected many of is also important in northern Saskatchewan and in these lakes, and will have increasing impacts not Manitoba and parts of Great Slave Lake.

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4.4. Fishing Hecky et al., 1984). Smaller dams, for example, on the Saskatchewan River, have apparently had beneficial The Northern Great Lakes support abundant fish effects, enhancing the sports fishery and slowing populations. Commercial fisheries are important to nutrient loading to downstream lakes (Orr, 1993). many regional economies (Table 1). The commercial Dams will continue to be built in northern Canada fisheries are greatest in lakes that are sufficiently for hydroelectric power generation for local commu- productive to sustain such fisheries and where there nities and for emerging industries. are ready transportation routes to southern markets. Commercial fisheries have operated on Lake Winnipeg since the 1890s (Franzin et al., 1996), on 5. Limnology of the Northern Great Lakes Lac since the 1920s (Rawson, 1961), on Lake Athabasca since 1926 (Mitchell and Prepas, The Northern Great Lakes generally have not been 1990) and on Great Slave Lake since 1945 (Rawson, well studied for several reasons. First, these lakes are 1947b; Yaremchuk, 1986). The sports fishery is remote from urban centers (including government and growing with lodges located on several Northern academic research organizations), so that research is Great Lakes in addition to the numerous smaller difficult because of the lack of suitable infrastructure. lakes that dot the Precambrian and Paleozoic land- Second, they are located in regions where the climate scape. is severe thus limiting time periods in which research can be readily conducted. Third, because the Great 4.5. Agriculture Lakes of the north are relatively pristine ecosystems, there has been little demand for their environmental Agriculture tends to be limited to the Peace, study. Much of the earlier research on these lakes was Athabasca, Saskatchewan, Red and Assiniboine in response to practical matters related to commercial River watersheds of the Northern Great Lakes region. and sports fisheries, mining tailing pond effluents and The two primary factors limiting agriculture to the sewage effluents in settlements. In more recent years, south are climate (i.e. the length of the growing there have been emerging concerns related to eutro- season) and soils. Spring wheat is the primary crop phication, which stimulated research on Lake grown to the south while canola, oats, peas, barely, Winnipeg; water diversions which stimulated tame hay and forage (alfalfa, timothy and clover) are research on Southern Indian Lake; and long range grown along Peace and Athabasca rivers (National atmospheric and riverine transport of organic Geographic Society, 1992; Northern River Basins contaminants which stimulated research on Great Study, 1996). Most of these crops are subject to appli- Slave Lake and Lake Athabasca. While much of this cations of both nutrients and pesticides that reach the research has been published in the peer-reviewed watersheds of the lakes in the region, especially scientific literature, an even larger volume of informa- during floods which are common in the region. tion exists in the 'gray' literature in various reports.

4.6. Hydroelectric power 5.1. Great Bear Lake

Many of the rivers in the Northern Great Lakes Great Bear is the northern-most of the Northern drainage basins have been dammed for hydroelectric Great Lakes. It has a surface area of 31,320 ktI12, a power generation and, in the southern watersheds, for mean depth of 76 m and a maximum depth of 452 m flood control. Major dams include the W.A.C. Bennett (Table 1). It is irregular in shape with five arms and Dam on the Peace River and the Southern Indian Lake one central area. The Great Bear Lake has a relatively water diversion. Larger dams and diversion projects small watershed (145,870 km 2) for its surface area; have had major environmental impacts including the residence time of water in the lake is 124 years. decreased flooding of delta lakes (Prowse and Great Bear River, the outlet river, flows into the Lalonde, 1996; Prowse et al., 1996) and damage to Mackenzie River (Johnson, 1975a). the commercial fisheries associated with increased The main body of Great Bear is ice-covered from shoreline erosion and flooding (Bodaly et al., 1994; December to May. Freezing begins as early as

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September and the open lake does not become dominated by the calanoid copepod Diaptomus sicilis, completely ice-free until July. Ice reaches a thickness a species well adapted to low temperatures and of 1.5 m in the offshore and 2.6 m in the inshore. seasonally abundant food. Total zooplankton densities Snow cover seldom exceeds 20 cm (Johnson, 1975a). in summer offshore waters ranged from 38,000 to Very little limnological research has been 142,000m 2; densities in inshore waters ranged conducted on Great Bear Lake. Larkin (1948) was from 268,000 to 471,000 m -2 (Johnson, 1975b). The the earliest researcher, investigating the distribution amphipod Pontoporeia and the mysid M. relicta are of the amphipod Pontoporeia and the mysid Mysis probably the most important benthic organisms in the relicta. The next notable limnological research study lake although chironomids, oligochaetes and sphaerid was conducted between 1963 and 1965 by Johnson clams are relatively abundant in shallow waters. (1975a,b) in response to concerns related to the poten- Larkin (1948) reported that Pontoporeia occurred in tial development of commercial fisheries on the lake. an average density of 1593 m -2 down to depths of Johnson (1975a, b) determined that the chemical 15 m but only in an average density of 183 m -2 composition of the lake is extremely uniform, except between 15 and 54 m. Mysis relicta occurred in in regions strongly influenced by inflowing fiver maximum densities of 22 m -2 between 22 and 75 m waters. Total dissolved solids in the main body of (Johnson, 1975b). Cisco (Coregonus artedi), four- the lake range from 78 to 81 ppm. The Dease and horn sculpin (Myoxocephalus quadricornis) and Camsell Rivers have lower TDS (32 and 58 ppm, slimy sculpin (Cottus cognataus) are important forage respectively) while those in the Johnny Hoe and fish for lake trout (Salvelinus namaycush), the domi- Takaatcho Rivers are higher (149 and 212ppm, nant piscivore. (Coregonus clupea- respectively) than the main body of Great Bear formis), primarily a benthic feeder, is abundant but Lake. Water clarity in the lake is in the range of confined to protected bay areas. 12-18 m with Secchi disc depths as great as 29 m Great Bear Lake is pristine. There has been very being recorded (Johnson, 1975a). little development along the lake shoreline. There is Great Bear Lake waters are very cold except during an abandoned uranium mine at Port Radium, a small the very brief subarctic summer. Relatively warm indigenous community at Fort Franklin (Deline) and a waters (up to 15.5°C) are found only in the shallow, few sports fishing lodges. The lake is relatively protected bays. In the more offshore region, waters isolated from the south. Year-round transportation remain cold (ca. 4°C) and weakly stratified throughout occurs by air: there is one commercial airport, and summer. As a consequence of strong vertical mixing, smaller runways are operated by fishing lodges. phytoplankton are mixed below their compensation Great Bear Lake is accessible by road only in winter depth and primary production rates are light-limited. when the tundra, lakes and rivers freeze hard enough The most productive habitats in the lake are in its for overland transport. shallow protected arms. The uranium mine apparently has resulted in only Moore (1980a) reported on the attached and plank- small-scale localized pollution. Metal and radionu- tonic algal communities in the inshore waters of Great clide concentrations in lake trout and whitefish are Bear Lake over the summers of 1976-1978. He also similar to concentrations observed in fish collected reported on nutrient concentrations. Total phos- in lakes which have not been affected by uranium phorous (TP) concentrations averaged 18 ~gP1 1, mine tailings (Swyripa et al., 1995). However, in nitrite-nitrate averaged 143 ~zgN1 -~ and silicon recent years, the people of Deline have become 1.9 mg 1-1. Primary production studies have yet to increasingly concerned about human health impacts be conducted on the Great Bear Lake. associated with radionuclides at the mine site. Plankton and benthos standing stocks are low in The sports fishery has had minimal effects on the Great Bear Lake with the greatest abundance and lake primarily because it is closely regulated. The diversity of invertebrates in the shallow bays fishery, which began operation in the 1960s, initially (Johnson, 1975b). Zooplankton diversity is low fished down the dominant stock of older lake trout and when compared to more southern, productive Great there were local depletions of trophy size fish. In later Lakes (Patalas, 1975). Zooplankton are numerically years, the lake trout population stabilized to the

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current fishing pressures (Yaremchuk, 1986). The he related to mean water column depth. He found lake is closed to commercial fishing. that shallow regions such as the West Basin had greater standing stocks of organisms than deeper 5.2. Great Slave Lake regions such as Christie Bay. However, Rawson also suggested that edaphic factors were important Great Slave Lake has a surface area of 28,568 km 2, because the invertebrate standing stocks were greater a mean depth of 73 m and a maximum depth of 614 m in the higher TDS waters of Christie Bay (ca. (Herdendorf, 1982). It is divided into two regions: the 111 mg 1-1) than the lower TDS waters of McLeod West Basin which is relatively shallow (mean depth Bay (ca. 22 mg 1-1). The highest TDS water was 41 m; maximum depth 163 m) and the East Arm found in the West Basin (ca. 150-175mg1-1), which is substantially deeper. The two main bays of reflecting the strong influence of the Slave River. the East Arm are Christie Bay (mean depth 199 m; Moore also conducted substantial limnological maximum depth 614 m) and McLeod Bay (mean research on Great Slave Lake. Although much of his depth 120 m; maximum ca. 293 m). McLeod Bay is research was applied and focused on concerns related isolated from the main body of Great Slave Lake by to the gold mining industry and sewage effluents from the Talheilei Narrows (Rawson, 1950). The West Yellowknife, Moore also conducted seasonal studies Basin is located on Paleozoic deposits while the of nutrients, plankton and benthos in Yellowknife East Arm is on the Precambrian Shield. Bay. He determined that seasonality in phytoplankton Great Slave Lake has a very large standing crops in Yellowknife Bay was primarily (983,000 km2). The Slave River is the major water related to seasonality in temperature and that nitrate source to the lake contributing some 87% to its concentrations were of secondary importance (Moore, water budget. It also contributes a tremendous sedi- 1980b). Temperature also was the primary factor ment load estimated at 2.64 to 6.72 X 10 l° kg year -~ affecting zooplankton and benthos (Moore, 1977, (Allan, 1979). Thus, water clarity in the West Basin is 1979b). low during summer, with Secchi disc depths typically Patalas and Patalas (1978) investigated zoo- ranging from less than 1-5 m versus 4-13 m in plankton populations in several regions of Great Christie Bay and 11-17 m in McLeod Bay (Rawson, Slave Lake and determined that lake morphometry 1950). Water exits Great Slave Lake via the (region) was the most significant factor affecting the Mackenzie River. Great Slave Lake has a residence distribution of the copepod Limnocatanus macrurus in time of 16 years based on the total lake volume and different regions of the lake. This interpretation is water inflow and 7 years based on the volume of the similar to Rawson's early conclusions. West Basin and the Slave River inflow (calculated Fee et al. (1985) investigated primary production, from Rawson, 1950). nutrients and phytoplankton standing stocks in several Great Slave Lake is the best studied of the regions of Great Slave Lake (and nearby lakes) in Northern Great Lakes. Much of the early research summer 1985. They determined that photosynthetic on Great Slave Lake was conducted by Rawson rates were higher in waters influenced by the Slave who was particularly interested in factors affecting River than waters that received runoff only from the fish yield and the ability of various lakes to support Canadian Shield. Production rates were estimated at commercial fisheries. Rawson conducted baseline 30 g C m 2 year -1 in the inshore waters of the West studies on the Great Slave Lake and described the Basin, the region most influenced by the Slave general features of the lake, made estimates of its River, versus at 15 g C m2year 1 in Christie and potential fish production, outlined the physical McLeod Bays. There was no consistent regional limnology and the ecology of its fish populations pattern in either N or P limitation. The regional and assessed the distribution of its bottom fauna means of TP concentrations ranged from 8.4 to and the distribution and seasonality of the net 15.0 Ixg 1 1 and chlorophyll from 1.2 to 3.9 txg 1-I plankton (Rawson 1947a,b, 1950, 1951, 1953, over the lake. The highest concentrations were 1956). Rawson determined that there were regional found in Yellowknife Bay and lowest in McLeod variations in the standing stocks of organisms, which Bay. Fee et al. (1985) also determined that the West

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Basin had a relatively high fish yield for its estimated that the fishery was adversely affecting the lake trout primary production rate. Similarly, Rawson (1955) population (Yaremchuk, 1986). The East Arm has noted that the West Basin had a relatively high fish supported a sports fishery since 1938 and the industry yield for its mean depth and northern location. This continues to expand. high fish yield may be related to nutrient and particu- The Slave River delta was intensively studied late organic matter inputs from the Slave River. Both during the 1970s. The primary concern was that the P and N inputs are high, especially during the ice-free damming of the Peace River had changed the hydro- period; total dissolved N concentrations reach logic regime of the delta, reducing the amplitude of 1.02mg1-1 and total dissolved P concentrations spring flooding events (Mackenzie River Basin reach 0.35 mg 1 i (Mackenzie River Basin Committee, 1981). This issue has not been fully Committee, 1981). In summer, nutrient levels resolved. Most research efforts related to the damming diminish rapidly as the Slave River plume is diluted of the Peace River have focused on the Peace-Atha- in the lake and as the phytoplankton take up the nutri- basca delta. In recent years, there has been an ents (Evans, 1996). increased interest in organic contaminants in the The West Basin has experienced both localized and Slave River, particularly contaminants being trans- long-range pollution. During the 1970s, tailing pond ported downstream with the Peace and Athabasca effluents from gold mines and sewage effluent from rivers (Northern River Basins Study Board, 1996). Yellowknife had localized effects in Yellowknife and Back bays (Moore, 1978, 1979a; Allan, 1979). Allan 5.3. Lake Athabasca also suggested that some arsenic from the gold mining operations had been transported into the West Basin. Lake Athabasca has a surface area of 7935 km 2, a As the mining companies changed their smelting mean depth of 26 m and a maximum depth of 124 m operations, metal contamination of Yellowknife and (Table 1; Herdendorf 1982). River flow enters the lake Back bays has decreased (Mudroch et al., 1989). The from the east and the west. To the east is the Fond-du Pine Point lead, zinc mine apparently had minor Lac River, which drains Cree and Wollaston lakes on impacts on the lake (Evans et al., 1998). More the Precambrian Shield. To the west is the Athabasca recently, studies have investigated spatial and River, which has an extensive drainage basin in the temporal patterns in polynuclear aromatic hydrocar- prairie regions to the south. Water exits Lake Atha- bons, organochlorine contaminants, dioxins and basca through three channels some 10 km north of the furans in West Basin sediments (Mudroch et al., Athabasca River mouth. These channels in turn empty 1992; Evans et al., 1996). Contaminant concentrations into the Peace River, which then becomes the Slave are low but have shown subtle increases over time. River. During high-water periods (primarily spring Both the Slave River and the atmosphere appear to be ice-breakup) water flow is reversed and the Peace significant sources of these compounds. In addition, River water flows into Lake Athabasca. These peri- organic C and N concentrations in core samples have odic high-water periods also are important in flooding increased since the early 1900s. This increase may be lakes in the Peace-Athabasca delta (Prowse and the result of deforestation and other anthropogenic Lalonde, 1996). activities in the Peace and Athabasca watersheds Rawson (1947c) estimated that Lake Athabasca has and/or to long-range atmospheric transport. Stoermer a drainage area of 271,360 km 2 with 58% of this et al. (1990) reported changes in the phytoplankton region in the Athabasca River watershed. However, communities of McLeod Bay, which they related to because the Athabasca River inflow is close to the long-range atmospheric transport of nutrients. lake outflow, it probably does not contribute as A commercial fishery has been in operation on much as 58% to the total water budget for the main Great Slave Lake since 1945 (Rawson, 1947b). body of Lake Athabasca. There have been no major changes in the fish commu- Very little research has been conducted on Lake nities of the Great Slave Lake associated with this Athabasca. Rawson (1947c) conducted a baseline fishery. However, the East Arm was closed to the study of the physical, chemical and biological char- commercial fisheries in 1974 when it was determined acteristics while Larkin (1948) investigated amphipod

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and mysid populations in the lake. Rawson noted that Athabasca. The system was shut down in the 1980s the central and eastern parts of Lake Athabasca are (Mitchell and Prepas, 1990). clear with Secchi disc depths of 6-7.6 m. Water Human impacts on the lake have been minor. The clarity diminishes to less than 0.2 m at the lake outlet, commercial fisheries apparently have not significantly presumably because of a strong Athabasca River affected fish populations. Similarly, pollution asso- influence, and because the region is shallow (<5 m ciated with the uranium mine has been minor and is deep). In addition, muddy water, associated with the now abating with the closure of the mine (Waite et al., Athabasca River outflow, has extended up to 80 km 1989; Bourbonniere et al., 1995). Polynuclear into the lake on occasion. Nevertheless, the Athabasca aromatic hydrocarbons, dioxins and furans occur in River does not appear to have a dominating effect on low concentrations in lake sediments (Bourbonniere the chemistry of Lake Athabasca. Total dissolved et al., 1995). Oil and tar sands operations are solids concentrations were ca. 58 mgl -l, a value increasing along the Athabasca River, and new studies characteristic of lakes with their primary drainage in are being conducted to investigate impacts. the Precambrian Shield. Rawson (1947c) noted that The major environmental concern for Lake Atha- fish and invertebrate species composition is generally basca, apart from hydrocarbon operations, lies to the similar to that of Great Slave Lake. More recently, west in its delta. The Peace River has had its flow Mitchell and Prepas (1990) summarized the known regulated since 1968 when the W.A.C. Bennett Dam limnological data for the lake. They note that the was constructed. Initially, Peace River flows were main body of the lake is unproductive and that reduced as much as 5600 m 3 sec -1 resulting in water productivity increases in shallow waters including level drops of as much as 3-4 m. This had significant those with a strong Athabasca River influence. This impacts on the delta including a loss of 38% of the is similar to Great Slave Lake, which appears to be area of perched lakes. A meadow and willow commu- most productive in the immediate vicinity of the Slave nity developed on this exposed land. During the late River and to Great Bear Lake, which is most produc- 1960s, the muskrat harvest plummeted from 144,000 tive in its shallow arms. to less than 2000 (Prowse et al., 1996). Remedial A commercial fishery has been in operation in Lake plans were implemented to re-establish spring high- Athabasca since 1926. The fisheries began operation water levels but have not been entirely successful; from the north central shore of the lake where lake minimum water levels are higher and maximum trout dominated the catch. In 1943, the fishery moved flow levels lower than before the dam was to the delta and northern pike and walleye dominated constructed. More recent research indicates that the catch. Catches declined between 1974 and 1985 some aspects of these changes in delta hydrology due to reduced fishing effort, difficulties with woces- are related to long-term climatic variability, that is, sing equipment and licensing (Mitchell and Prepas, there has been a climatically driven reduction in the 1990). Catches continued to decline in later years water budget to these lakes (Prowse and Lalonde, (DFO, 1995). 1996). Lake Athabasca has had little development around its shorelines, especially when compared to Great 5.4. Northern Saskatchewan and Manitoba Lakes Slave Lake. The primary community, Fort Chipeywan, consists of less than 1000 people. Lake The northern region of Saskatchewan is dotted by Athabasca has been bypassed by recent transportation hundreds of lakes (Fig. 2; Table 1). Some lakes are links to the north, that is, by the Mackenzie Highway large (Rawson, 1960), notably Reindeer (surface area, built in the 1950s, which links Edmonton with Great 5569 km2), Wollaston (2062 km2), La Ronge Slave Lake and the lower reaches of the Mackenzie (1178 km 2) and Cree (1152 kin2). Others are smaller River, and by a railroad which was built in 1965, but with areas exceeding 100 km 2, for example, Big which ran north from Edmonton and terminated at Peter Pond (552 km2), Ile a la Crosse (446 km 2) and the now-abandoned Pine Point Mine west of the Churchill (433 km2). These lakes, like Lake Atha- Slave River outflow. A uranium mine operated at basca, are located in relatively remote regions of the Uranium City on the northern shore of Lake province. Many support commercial fisheries.

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Little research has been conducted on these lakes. year (Hecky et al., 1986). Lake Winnipeg is the best The most comprehensive studies were conducted by studied of the three lakes. Rawson. In a synthesis study, Rawson (1960) reported Lake Winnipeg can be divided into northern and that plankton biomass, benthic biomass and fish yield southern basins. The smaller south basin (2780 km 2) were lower in lakes located on the Precambrian Shield receives 80% of its annual water supply from the than in lakes located on glacial drift. He also noted Winnipeg River which drains the Precambrian Shield that physical factors such as vertical mixing appar- and 20% of its water from the Red River located in ently enhanced the productivity of Big Peter Pond glacial till. The Assiniboine River joins the Red River Lake while rapid flushing apparently reduced the at the city of Winnipeg (population ca. 620,000). The productivity of Ile a la Crosse Lake. Researchers Winnipeg River has a drainage basin of some have yet to determine why lakes located on the glacial 126,400 km 2, while the Red River has a drainage till are more productive than lakes located on the basin of 287,500 km 2. However, because much of Precambrian Shield. Such differences probably are the drainage basin of the Red River is located in agri- related to nutrient inputs. cultural lands, it supplies approximately 70% of the The primary environmental stress to these lakes is total P to the south basin (Brunskill et al., 1980; from the sports and commercial fisheries. Some lakes Patalas and Salki, 1992). The larger north basin appear to be responding to overfishing stresses with receives 75% of its water from the Saskatchewan lake trout diminishing in dominance and suckers River, which has a drainage area of 340,400 km2; becoming more prevalent (Gloutney and Chen, much of it located in agricultural lands. Water flows 1992). However, these lakes are poorly studied and out of Lake Winnipeg at the north through the Nelson the current status of most fish populations is not well River. Lake Winnipeg has an estimated water renewal understood. time of 2.9-4.3 years while the south basin has an Some lakes in northern Saskatchewan and Mani- estimated renewal time of only 0.4-0.8 years (Bruns- toba have increased in size following dam construc- kill et al., 1980). tion for hydroelectric power generation. Some such as Relatively little research has been conducted on Tobin Lake (228 km 2) on the Saskatchewan River Lake Winnipeg when compared to Great Slave have become more productive with enhanced fisheries Lake. Much of the research was conducted by provin- (Orr, 1993). Others, such as Southern Indian Lake cial and federal agencies and appears in agency (2391 km 2) experienced severe ecological stresses reports. Detailed zooplankton, phytoplankton and (Newbury et al., 1984) including increased shoreline benthos surveys were conducted in 1969 by members erosion, organic loading and altered flow patterns. of the Freshwater Institute (Department of Fisheries These stresses affected lake productivity, resulting in and Oceans, Winnipeg, MB) in response to eutrophi- the loss of discrete populations of whitefish and cation concerns (Hecky et al., 1986; Patalas and Salki, increased mercury levels in predatory fish (Hecky et 1992; Flannagan et al., 1994). A second survey was al., 1984). conducted in 1994 to further assess the environmental status of Lake Winnipeg. A third survey was 5.5. Lake Winnipeg conducted in 1996 (Cobb, 1996; Kling, 1996; Salki, 1996). More recently, studies have been initiated in Manitoba contains three great lakes (Table 1), Lake response to the spring 1997 Red River flood which Winnipeg, Lake Winnipegosis and Lake Manitoba. transported significant amounts of organic contami- Lakes Manitoba and Winnipegosis and the western nants into the lake from flooded rural and urban half of Lake Winnipeg lie in glacial deposits, but areas further south (Stewart et al., in press). the eastern half of Lake Winnipeg lies in the Precam- There is strong evidence that Lake Winnipeg has brian Shield. All are shallow lakes with a maximum been impacted by anthropogenic activities in its depth of 4 m for Lake Manitoba, 12 m for Lake watershed, especially in the southern basin. Patalas Winnipegosis and 18 m for Lake Winnipeg (Herden- and Salki (1994) reported that plankton biomass dorf, 1982). These lakes are ice-covered from early increased between 1929 and 1969 due to increased November to early June, for about 7 months of the nutrient loading of the southern basin. However,

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I~ _ ._ I Lake Athabasca

\\, I e~ ~"ast°~4 \ ",r I "h cr , '~, ReindeerLake 1

,, FrobisherLake ' ~ ipo.~LakJ Big Pete e li Lake ~i r " ( I Peter~Churchill i Little I Ctl~'~'~ p,wel I POndLake "~ I Lac lie / |I I laCrosse -...Bay i

I WaskesiuLa I MILES I ¢...5,° .~19o ~. I t~ ~ ~o llo Prince Albert

Fig. 2, Map showing the large lakes of northern Saskatchewan. Redrawn from Rawson (1960).

water clarity in the northern basin apparently since the late 1880s (Franzin et al., 1996). The history increased over the same period. Patalas and Salki of the commercial catch was analyzed recently by (1992) related increased water clarity in the north Heuring (1993). In 1993/1994, commercial catches basin to the Cedar Lake-Grand Rapids impoundment. from lakes Winnipeg, Manitoba and Winnipegosis This impoundment may act a sediment and nutrient accounted for approximately 60% of the total provin- trap for the Saskatchewan River. Benthic populations cial catch of 8997 metric tons of fish (DFO, 1995). also changed over the same period; there was a 20% Lake Winnipeg was recently invaded by the exotic reduction in the biomass of the mayfly Hexagenia spp. white bass, Morone chrysops and supports other and the amphipod Diporeia brevicornis was elimi- exotics such as rainbow smelt (Osmerus mordax), nated from the southern basin (Cobb, 1996). common carp (Cyprinus carpio) and black crappie Lake Winnipeg has supported a commercial fishery (Pomixis nigromaculatus) (Franzin et al., 1996;

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Hanke, 1996). Lake Winnipeg is apparently the only development in their watersheds and beyond. Long- Northern Great Lake to have been successfully range atmospheric transport will continue to deliver invaded by an exotic species. Its close proximity to inorganic and organic contaminants and nutrients to the more developed regions of southern Canada (and these lakes, including lakes as remote as Great Bear. northern United States) and its relatively productive Their tributary rivers will also deliver these materials. waters may make it more susceptible to invasions by Of particular concern are lakes fed by the major rivers exotics than the Great Lakes located further to the draining more developed regions and Saskatchewan north. The Red River flood in spring 1997 is a more to the south, especially the Peace and Athabasca recent event (Winnipeg Free Press, 1997) which may rivers. have accelerated the introduction of exotic species Pollution abatement strategies have improved in into the lake including the zebra mussel (Dreissena recent decades with nutrient and contaminant concen- polymorpha), a major nuisance species in the Lauren- trations declining in many southern lakes, including tian Great Lakes. the Laurentian Great Lakes. During these periods, the Northern Great Lakes have remained essentially pris- tine ecosystems. However, because of the slow trans- 6. Factors affecting productivity and standing port of contaminants to the north via atmospheric and stocks riverine routes, the Northern Great Lakes may be experiencing gradual environmental degradation. The two most important factors that have been Additional degradation also may be occurring as shown to affect the productivity and diversity of the economic development of the north continues to Northern Great Lakes are temperature and water accelerate. column depth. Temperature is important, affecting Northern people, particularly those of indigenous physical factors such as ice-cover and biological ancestry, place very strong value on healthy ecosys- factors such as photosynthetic rates and animal tems and in maintaining traditional life styles. As a growth rates. Depth is important because it affects consequence, any detectable form of pollution is of the rate at which the water column is warmed. concern. Nevertheless, as the composition and nature Warming affects vertical mixing which, in turn, of the northern population diversifies and the affects whether or not phytoplankton are mixed economic base broadens, there is a growing pressure below their compensation depth. to develop the North. The challenge will be to develop Rawson (1955) determined that depth was the most the economic resources of the north while protecting important factor affecting the standing crop of the essential integrity of its ecosystems. plankton, benthos and commercial fish production in Global warming may potentially affect the north a broad series of lakes in western Canada. He also through a change in climate (temperature and pre- considered edaphic factors, related to watershed cipitation patterns) and UV-B levels. Increased geology, to be of secondary importance (Rawson temperature will affect a variety of aspects of the 1956, 1960). Patalas (1975) related midsummer crus- Northern Great Lakes including duration of ice tacean zooplankton biomass to mean epilimnion cover, thermal stratification, primary production temperature: temperature, in turn, was related to rates and animal growth rates. Changes in temperature mean lake depth. Patalas and Salki (1992) later devel- and precipitation also will affect runoff patterns oped a regression equation describing the relation including the contribution of the larger rivers to the between P concentrations and zooplankton standing water, sediment, nutrient and other chemical budgets stocks and a third regression which included P and of the large lakes. Rawson (1956) noted significant temperature. differences in net plankton standing stocks between cold and warm springs while more recent research 7. Future concerns suggests that some of the changes in the hydrology of the Peace-Athabasca Delta are climatic in origin The Northern Great Lakes, while largely pristine, (Prowse and Lalonde, 1996). Increased UV-B will continue to be affected by the increased penetration may potentially adversely affect

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shallow-water communities, especially those in clear food web structure and diversity of the Northern waters (Gorham, 1996; Bergeron and Warwick, Great Lakes ecosystems. 1997). Regions such as the East Arm of the Great Slave Lake and the littoral region of the Great Bear Lake may be particularly vulnerable. References Cost-effective monitoring programs must be devel- oped and implemented to protect the Northern Great Allan, R.J., 1979. Heavy metals in bottom sediments of Great Slave Lakes. Basic research must be conducted to under- Lake (Canada): a reconnaissance. Environ. Geol. 3, 49-58. stand these systems better and to select the most Bergeron, M., Warwick, W.F., 1997. Microbial food web responses relevant parameters and strategies for long-term to phosphorus supply and solar UV radiation in a subarctic lake. monitoring. Infrastructure must be developed to Aquat. Microb. Ecol. 12, 239-249. Bodaly, R.A., Hecky, R.E., Fudge, R.J.P., 1994. Increases in support these programs including the training of mercury levels in lakes flooded by the Churchill River diversion, local people who eventually will follow careers in northern Manitoba. Can. J. Fish. Aquat. Sci. 41,682-691. research and monitoring. Short-term and sporadic Bourbonniere, R.A., Telford, S., Kemper, J.B., 1995. Depositional funding opportunities have curtailed research in the history of sediments in Lake Athabasca: geochronology, bulk North. This is in contrast to the long-term and rela- parameters, contaminants and biogeochemical markers, Northern River Basins Study, Project Report 72, Edmonton, tively consistent research effort directed towards the Alta. Laurentian Great Lakes. Brunskill, G.J., Elliot, S.E.M., Campbell, P., 1980. Morphometry, hydrology, and watershed data pertinent to the limnology of Lake Winnipeg. Can. Manuscr. Rep. Fish. Aquat. Sci. 1556 (p. 32). 8. Conclusions Cobb, D.G., 1996. Benthic invertebrates of Lake Winnipeg. In: Todd, B.J., Lewis, C.F., Thorleifson, L.H., Nielsen, E. (Eds.). More research is required to better understand the Lake Winnipeg Project: cruise report and scientific results, structure and functioning of the Northern Great Lake pp. 345-351 Geological Survey of Canada. Open file 3113. ecosystems. Research is also required to better under- Department of Fisheries and Oceans, 1995. Annual summary of fish stand the factors limiting growth, how aquatic organ- harvesting activities, Western Canadian Fisheries, vol. 12, Ministry of Supply and Services, Canada (1993-1994). isms are adapted to the stress characteristics of Environment Canada, 1982a. Solar Radiation (1951-1980), Cana- northern environments and how communities are dian Climate Normals, vol. 1 Atmospheric Environment affected by anthropogenic stress. More effort should Service. be directed toward understanding how river inflow Environment Canada, 1982b. Temperature, Canadian Climate enhances the productivity of many of these lakes. Normals, vol. 2 Atmospheric Environment Service. Environment Canada, 1982c. Precipitation, Canadian Climate Short-term, low-intensity surveys do not provide suffi- Normals, vol. 3 Atmospheric Environment Service. cient information to understand the factors affecting Evans, M.S., 1996. Limnological investigations of the West Basin the productivity and diversity of these lakes. These of Great Slave Lake. March 1994. Northern River Basins Study studies also do not allow for the quantification of Project Report 131, Northern River Basins Study, Edmonton, changes in these lakes due to anthropogenic activities. Alta. Evans, M.S., Bourbonniere, R.A., Muir, D.C.G., Lockhart, W.L., Research studies at Southern Indian Lake, Lake Wilkinson, P., Billeck, B., 1996. Depositional history of sedi- Winnipeg and Great Slave Lake are exceptions ment in Great Slave Lake: spatial and temporal patterns in with a promising beginning. The recent interest in geochronology, bulk parameters, PAHs, and chlorinated long-range contaminant transport to the Northern compounds. Northern River Basins Study Report 99, Edmonton Great Lakes has provided critical information on Northern River Basins Study, Edmonton, Alta. Evans, M.S., Lockhart, L., Klaverkamp, J., 1998. Metal studies of spatial and temporal contaminants trends in Lake water, sediments and fish from the Resolution Bay area of Great Athabasca and Great Slave Lake. Monitoring of the Slave Lake: studies related to the decommissioned Pine Point fisheries is also providing information on changes mine, National Water Research Institute Report 98-87. in commercially caught fish. Nevertheless, these Burlington, Ontario. studies, while invaluable, are not providing all of Fee, E.J., Stainton, M.P., Kling, H.J., 1985. Primary production and related limnological data from some lakes of the Yellowknife, the fundamental information required to address N.W.T. area. Can. Tecb. Rep. Fish. Aquat. Sci., 1409. the many unknowns regarding the productivity, Flannagan, J.F., Cobb, D.G., Flannagan, P.M., 1994. A review of

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the research on benthos of Lake Winnipeg. Can. Manuscr. Rep. subarctic populations of Bosmina longirostris, Holopedium Fish. Aquat. Sci., 2261. gibberum, Codonella crotera, and Ceratium hirundinella. Franzin, W.G., Stewart, K.W., Heuring, L., Hanke, G., 1996. The Hydrobiologia 56, 199-207. fish and fisheries of Lake Winnipeg. In: Todd, B.J., Lewis, C.F., Moore, J.W., 1978. Some factors influencing the density of inver- Thorleifson, L.H., Nielsen, E. (Eds.). Lake Winnipeg Project: tebrates near a sewage outfall. Hydrobiologia 61, 81-93. cruise report and scientific results, pp. 349-354 Geological Moore, J.W., 1979a. Diversity and indicator species as measures of Survey of Canada. Open file 3113. water pollution in a subarctic lake. Hydrobiologia 66, 73-80. Gloutney, B.L., Chen, M.Y., 1992. Status of the Lac La Ronge Moore, J.W., 1979b. Some factors influencing the distribution, fishery 1989 and 1990. Fisheries Technical Report 92-2, seasonal abundance, and feeding of subarctic Chironomidae Saskatchewan Natural Resources, Saskatoon, Saskatchewan. (Diptera). Arch. Hydrobiol. 85, 302-325. Gorham, E., 1996. Lakes under a three-pronged attack. Nature 381, Moore, J.W., 1980a. Attached and planktonic algal communities in 109-110. some inshore areas of Great Bear Lake. Can. J. Bot. 58, 2294- Hanke, G.F., 1996. Biology of young-the-year white bass (Morone 2308. chrysops) in Lake Winnipeg, Manitoba and their interactions Moore, J.W., 1980b. Seasonal distribution of phytoplankton in with native ichthyofauna. MSc thesis, University of Manitoba, Yellowknife Bay, Great Slave Lake. Int. Revue Ges. Hydrobiol. Winnipeg, Manitoba. 65, 283-293. Hecky, R.E., Newberry, R.W., Bodaly, R.A., Patalas, K., Mudroch, A., Joshi, S.R., Sutherland, D., Mudroch, P., Rosenberg, D.M., 1984. Environmental impact prediction and Dickson, K.M., 1989. Geochemistry of sediments in the Back assessment: the Southern Indian Lake experience. Can. J. Fish. Bay and Yellowknife Bay of Great Slave Lake. Environ. Geol. Aquat. Sci. 41,720-732. Water Sci. 14, 35-42. Hecky, R.E., Kling, H.J., Brunskill, G.J., 1986. Seasonality of Mudroch, A., Allan, R.J., Joshi, S.R., 1992. Geochemistry and phytoplankton in relation to silicon cycling and interstitial organic contaminants in the sediments of Great Slave Lake, water circulation in large, shallow lakes of central Canada. Northwest Territories, Canada. Arctic 45, 10-19. Hydrobiologia 138, 117-126. National Geographic Society, 1992. Atlas of the World (Revised) Herdendorf, C.E., 1982. Large lakes of the world. J. Great Lakes 6th ed. National Geographic Society, Washington, DC. Res. 8, 379-412. Newbury, R.W., McCullough, G.K., Hecky, R.E., 1984. The Heuring, L., 1993. A historical assessment of the commercial and Southern Indian Lake impoundment and Churchill River diver- subsistence fish harvests of Lake Winnipeg. MSc thesis, Univer- sion. Can. J. Fish. Aquat. Sci. 41,548-557. sity of Manitoba, Winnipeg, Manitoba. Northern River Basins Study Board, 1996. Northern River Basins Hutchinson, G.E., 1957. Geography, Physics, and Chemistry, A Study Report to the Ministers, Alberta Environmental Protec- Treatise on Limnology, vol. 1, Wiley, New York. tion, Edmonton, Alberta. Johnson, L., 1975. Physical and chemical characteristics of Great Orr, R.A., 1993. Tobin Lake fisheries management. Fisheries Bear Lake, Northwest Territories. J. Fish. Res. Board Can. 32, Management Report 93-3, Fisheries Branch, Saskatchewan 1971-1987. Environment and Resource Management, Regina, Saskatch- Johnson, L., 1975. Distribution of fish species in Great Bear Lake ewan. Northwest Territories, with reference to zooplankton, benthic Patalas, K., 1975. The crustacean plankton communities of fourteen invertebrates, and environmental conditions. J. Fish. Res. North American great lakes. Verh. Internat. Verein. Limnol. 19, Board Canada 32, 1989-2004. 504-511. Kling, H.J., 1996. Fossil and modern phytoplankton on Lake Patalas, J., Patalas, K., 1978. Seasonal variation in size and Winnipeg. In: Todd, B.J., Lewis, C.F., Thorleifson, L.H., reproductive cycles of Limnocalanus macrurus in a deep, Nielsen, E. (Eds.). Lake Winnipeg Project: cruise report and subarctic lake, Great Slave Lake. Verh. Internat. Verein. scientific results, pp. 283-310 Geological Survey of Canada. Limnol. 20, 150-158. Open file 3113. Patalas, K., Salki, A., 1992. Crustacean plankton in Lake Winnipeg: Lake Winnipeg, Churchill, and Nelson Rivers Study Board, 1971- variation in space and time as a function of lake morphology, 1975, 1971-1975. Technical Report Winnipeg, Manitoba. geology, and climate. Can. J. Fish. Aquat. Sci. 49, 1035- Larkin, P.A., 1948. Pontoporeia and Mysis in Athabasca Great 1059. Bear, and Great Slave Lakes. Bull. Fish. Res. Bd. Can. 78, 1-33. Prowse, T.D., Lalonde, V., 1996. Open-water and ice-jam flooding Lopatka, S., Ross, D., Stoesz, R., 1990. Northwest Territories Data of a northern delta. Nordic Hydrol. 27, 85-100. Book, Outcrop Ltd, Yellowknife, NWT. Prowse, T.D., Aitken, B., Demuth, M.N., Peterson, M., 1996. Mackenzie River Basin Commission, 1981. Mackenzie River Basin Strategies for restoring spring flooding to a drying northern study report. A report under the 1978-81 Federal-Provincial delta. Regulated River Res. Manag. 12, 237-250. Study Agreement respecting the water and related resources Rawson, D.S., 1947a. Great Slave Lake. Bull. Fish. Res. Board Can. of the Mackenzie River Basin, Ottawa, Ministry of Supply 72, 45-68. and Services, Canada. Rawson, D.S., 1947b. Estimating the fish production of Great Slave Mitchell, P., Prepas, E. (Eds.), 1990. Atlas of Alberta Lakes Univer- Lake. Trans. Am. Fish. 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