Slave River Research Articles

Variability in ice phenology on Great Bear Lake and Great Slave Lake, Northwest Territories, Canada, from SeaWinds/QuikSCAT: 2000–2006

The temporal evolution of the backscatter coefficient, sigma-nought (σ°) from QuikSCAT was evaluated for monitoring ice phenology on Great Bear Lake (66°N, 121°W) and Great Slave Lake (61°40′N, 114°W), Northwest Territories, Canada. Results indicated that σ° from QuikSCAT can be used to detect melt onset, water clear of ice and freeze onset dates on both lakes. An ice phenology algorithm was then developed to assess the spatiotemporal variability on both lakes from QuikSCAT for the period 2000–2006. Results showed that for Great Slave Lake, the average melt onset date occurred on year day (YD) 123, the average water clear of ice date was on YD164, and the average freeze onset date was on YD330. On Great Bear Lake, the average melt onset date occurred on YD139, the average water clear of ice date was YD191, and the average freeze onset date was YD321. Ice cover remained present for at least five weeks longer on Great Bear Lake than on Great Slave Lake and most of the difference can be explained by earlier ice melt on Great Slave Lake. Spatially, on Great Bear Lake, melt onset took place first in the eastern arm, water clear of ice occurred first in southeastern and western arms, and freeze onset appeared first in the northern arm and along the shorelines. On Great Slave Lake, melt onset began first in the central basin and then progressed to the northern and eastern arms later in the season. The central basin of Great Slave Lake cleared earlier than the periphery due to the discharge from the Slave River. Freeze onset on Great Slave Lake occurred first within the east arm, closely followed by the north and west arms, and then finally in the centre of the main basin.

An Investigation of the Thermal and Energy Balance Regimes of Great Slave and Great Bear Lakes

Abstract Great Slave Lake and Great Bear Lake have large surface areas, water volumes, and high latitudinal positions; are cold and deep; and are subject to short daylight periods in winter and long ones in summer. They are dissimilar hydrologically. Great Slave Lake is part of the Mackenzie Basin flowthrough system. Great Bear Lake is hydrologically isolated in its own relatively small drainage basin and all of its inflow and outflow derive from its immediate watershed. Great Slave Lake’s outflow into the Mackenzie River is more than 8 times that from Great Bear Lake. Input from the south via the Slave River provides 82% of this outflow volume. These hydrological differences exert pronounced effects on the thermodynamics, hydrodynamics, and surface climates of each lake. The quantitative results in this study are based on limited datasets from different years that are normalized to allow comparison between the two lakes. They indicate that both lakes have regional annual air temperatures within 2°C of one another, but Great Slave Lake exhibits a much longer open-water period with higher temperatures than Great Bear Lake. During the period when the lakes are warming, each lake exerts a substantial overlake atmospheric cooling, and in the period when the lakes are cooling, each exerts a strong overlake warming. This local cooling and warming cycle is greatest over Great Bear Lake. Temperature and humidity inversions are frequent early in the lake-warming season and very strong lapse gradients occur late in the lake-cooling season. Annually, for both lakes, early ice breakup is matched with late freeze-up. Conversely, late breakup is matched with early freeze-up. The magnitudes of midlake latent heat fluxes (evaporation) and sensible heat fluxes from Great Slave Lake are substantially larger than those from Great Bear Lake during their respective open-water periods. The hypothesis that because they are both large and deep, and are located in high latitudes, Great Slave Lake and Great Bear Lake will exhibit similar surface and near-surface climates that are typical of large lakes in the high latitudes proves invalid because their different hydrological systems impose very different thermodynamic regimes on the two lakes. Additionally, such an extensive north-flowing river system as the Mackenzie is subjected to latitudinally variable meteorological regimes that will differentially influence the hydrology and energy balance of these large lakes. Great Slave Lake is very responsive to climatic variability because of the relation between lake ice and absorbed solar radiation in the high sun season and we expect that Great Bear Lake will be affected in a similar fashion.

Finite volume model for steady-state transverse mixing in streams

Transverse mixing is arguably more important in water quality management than either vertical or longitudinal mixing, especially when dealing with the discharge of pollutants from point sources or the mixing of tributary inflows. A finite volume model with upwind scheme is developed to solve the equation for transverse mixing in steady flow in prismatic channel. The model takes care of variation of transverse mixing coefficient across the channel width. The model has been verified with analytical solutions for constant mixing coefficient and for pollutant injection in the middle and near the bank of streams. The model is inherently mass conservative and captures successfully the discontinuity existing at the upstream boundary. Effect of variable transverse mixing coefficient on the pollutant concentration profiles has been shown for a typical cross-section of the Lesser Slave River. It is found that the computed concentration profiles for variable transverse mixing coefficient are significantly different from those for constant coefficient.

Spatial and temporal perspectives on spring break‐up flooding in the Slave River Delta, NWT

AbstractSpatial and temporal patterns of spring break‐up flooding in the Slave River Delta (SRD), Northwest Territories, are characterized during three years (2003–2005) using water isotope tracers and total inorganic suspended sediment (TSS) concentrations measured from lakewater samples collected shortly after the spring melt. Strongly contrasting spring melt periods led to a moderate flood in 2003, no flooding in 2004 and widespread flooding in 2005. Flooded lakes have isotopically‐depleted δ18O (δ2H) signatures, ranging between − 19·2‰ (−145‰) and − 17·1‰ (−146‰) and most have high TSS concentrations (>10 mg L−1), while non‐flooded lakes have more isotopically‐enriched δ18O (δ2H) signatures, ranging between − 18·2‰ (−149‰) and − 10·6‰ (−118‰) and low TSS concentrations (<10 mg L−1). These results, in conjunction with the isotopic signatures of Slave River water and snowmelt, are used to estimate the proportion of river‐ or snowmelt‐induced dilution in delta lakes during the spring of each study year. Calculations indicate river flooding caused dilution of ∼70–100% in delta lakes, while snowmelt dilution in the absence of river flooding ranged from ∼0–56%. A positive relationship exists between the spatial extent of spring flooding in the SRD and level and discharge on the Slave River and upstream tributaries, suggesting that upstream flow generation plays a key role in determining the magnitude of spring flooding in the SRD. Parallel variations in the 46‐year instrumental Slave River discharge record and flood stratigraphy in the active delta indicate that there is potential for extending the flood history of the SRD, a development that will contribute to a more robust understanding of the drivers of historic, contemporary and future flood frequency in the delta. Copyright © 2008 John Wiley & Sons, Ltd.

Riparian influences on carbon isotopic composition of tree rings in the Slave River Delta, Northwest Territories, Canada

Tree-ring cores from two white spruce ( Picea glauca) trees at each of three sites within the Slave River Delta, Northwest Territories, Canada, were separated, processed for α-cellulose and analyzed for their carbon isotope composition. The three carbon isotope ( δ 13C cellulose) time series, collectively covering the time period from 1689 to 2003, were statistically correlated with average Historical Monthly Climate Grid temperature and precipitation for the period 1901–2000. The results suggest that the trees from all three sites show a distinct trend towards more enriched δ 13C cellulose values with time, implying more stressful environmental conditions possibly related to the overall 20th Century drying of the Slave River Delta. Anthropogenic impacts of heavy logging and the construction of a large upstream dam may also be present in the δ 13C cellulose time series. The main focus of the study relates to the different nature of the three riparian sites. The δ 13C cellulose values of the trees from the two sites ≥ 50 m from the river at higher elevation suggest a relationship with moisture-deficit-stress (MDS) emanating from hydroclimate effects during the non-growing and growing seasons. The δ 13C cellulose values from a site adjacent to the river at lower elevation, however, suggest that these same effects can manifest as moisture-excess-stress (MES) on the trees. The relationships between these two types of moisture stress and the δ 13C cellulose values of the trees from the sites with obvious riparian differences are discussed in detail.

Characterizing the Hydrology of Shallow Floodplain Lakes in the Slave River Delta, NWT, Canada, Using Water Isotope Tracers

ABSTRACTThe relative importance of major hydrological processes on thaw season 2003 lakewater balances in the Slave River Delta, NWT, Canada, is characterized using water isotope tracers and total suspended sediment (TSS) analyses. A suite of 41 lakes from three previously recognized biogeographical zones—outer delta, mid-delta, and apex—were sampled immediately following the spring melt, during summer, and in the fall of 2003. Oxygen and hydrogen isotope compositions were evaluated in the context of an isotopic framework calculated from 2003 hydroclimatic data. Our analysis reveals that flooding from the Slave River and Great Slave Lake dominated early spring lakewater balances in outer and most mid-delta lakes, as also indicated by elevated TSS concentrations (>0.01 g L−1). In contrast, the input of snowmelt was strongest on all apex and some mid-delta lakes. After the spring melt, all delta lakes underwent heavy-isotope enrichment due to evaporation, although lakes flooded by the Slave River and Great Slave Lake during the spring freshet continued to be more depleted isotopically than those dominated by snowmelt input. The isotopic signatures of lakes with direct connections to the Slave River or Great Slave Lake varied throughout the season in response to the nature of the connection. Our findings provide the basis for identifying three groups of lakes based on the major factors that control their water balances: (1) flood-dominated (n = 10), (2) evaporation-dominated (n = 25), and (3) exchange-dominated (n = 6) lakes. Differentiation of the hydrological processes that influence Slave River Delta lakewater balances is essential for ongoing hydroecological and paleohydrological studies, and ultimately, for teasing apart the relative influences of variations in local climate and Slave River hydrology.

Relationships between hydrological and limnological conditions in lakes of the Slave River Delta (NWT, Canada) and quantification of their roles on sedimentary diatom assemblages

Water chemistry and surface sediments were analyzed from 41 shallow lakes representing three previously-defined hydrological categories in the Slave River Delta, Northwest Territories, Canada, in order to identify relationships between hydrological and limnological conditions and their associations with recently deposited diatom assemblages. Evaporation-dominated lakes are physically removed from the influence of the Slave River, and are characterized by high alkalinity and high concentrations of nutrients and ions. In contrast, flood-dominated lakes tend to receive a pulse of floodwater from the Slave River during the spring thaw and have low alkalinity and low concentrations of most nutrients and ions. Exchange-dominated lakes are variably influenced by floodwaters from the Slave River and seiche events from Great Slave Lake throughout the spring thaw and open-water season, and are characterized by a broad array of limnological conditions that are largely dependent on the strength of the connection to these sources of floodwater. Specific diatom ‘indicator’ taxa have been identified that can discriminate these three hydrological lake categories. Evaporation-dominated lakes are associated with high relative abundance of common epiphytic diatom taxa, while diatoms indicative of flood- and exchange-dominated lakes span a wide range of habitat types (epiphytic, benthic) but also include unique planktonic diatoms (Stephanodiscus and Cyclostephanos taxa) that were not found in surface sediments of evaporation-dominated lakes. The planktonic diatom taxa originate from the Slave River, and thus are indicative of river influence. In complex, remote, freshwater ecosystems like the Slave River Delta, integration of results from hydrological and limnological approaches provides a necessary foundation to assess present, past and future hydroecological responses to changes in river discharge and climate.

Wind‐forced seiche events on Great Slave Lake: hydrologic implications for the Slave River Delta, NWT, Canada

AbstractA limited amount of research has focused on northern lacustrine deltas and the impacts of basin processes prevalent at these deltas. Wind‐forced seiche events have received little focus in deltaic studies. The Slave River Delta, located on the south shore of Great Slave Lake (GSL), NWT, is an ideal environment to study the prevalence of wind‐forced seiche events and the impact of seiche events on the hydrodynamics of the delta. This paper presents an historical analysis of seiche activity on GSL and the effect of seiches on water levels of the Slave River Delta. The seasonality, frequency, and magnitude of seiche events on the lake are quantified. A description of the wind characteristics that force these events is included. The radial distributary pattern of the delta suggests that water level response to seiche events within the delta may be particularly complex. Hydrologic data from delta distributaries illustrate the temporal and spatial dynamics of seiche response. During the open‐water season, seiche response in the delta is affected by the seasonal hydrograph of the Slave River and wind conditions. Spatially, the slope of delta distributaries governs seiche response. Responses are most similar among zones in the delta rather than among different distributaries. Copyright © 2006 John Wiley & Sons, Ltd.

Hydroclimatic controls on water balance and water level variability in Great Slave Lake

AbstractOn average, 86% of riverine discharge to Great Slave Lake, Northwest Territories, Canada, was gauged during the period 1964–1998, offering an unprecedented opportunity to study and understand controls on water balance of a large northern lake at the headwaters of the Mackenzie River. A functional daily water balance model, incorporating measurements of riverine inflow, precipitation on the lake surface, evaporation, and riverine outflow was developed, which predicts the amplitude and frequency of annual water level fluctuations, and closes the water balance to within ± 6% for 28 of 35 years and ± 11% for the remaining 7 years, with an overall systematic error of + 2%. Annual water balance estimates for the period 1964–1998 reveal that about 74% of inflow into Great Slave Lake originates from the Peace‐Athabasca catchments that enter the lake via the Slave River, whereas 21% is derived from other catchments bordering Great Slave Lake, and 5% from precipitation on the lake surface. An estimated 94% of water losses occur by riverine outflow to the Mackenzie River and 6% by evaporation from the lake surface. The primary driving force behind water level fluctuations in Great Slave Lake, including the post‐regulation period following development of the W.A.C. Bennett Dam, is shown to be climate‐driven precipitation variability in the Peace‐Athabasca basins. A simple precipitation regression model is developed to simulate water level fluctuations in Great Slave Lake over the past 100 years. Copyright © 2006 John Wiley & Sons, Ltd.

Effects of Prescribed Burning on Herbaceous and Woody Vegetation in Northern Lowland Meadows

Abstract Spring burning of sedge‐grass meadows in the Slave River Lowlands (SRL), Northwest Territories, Canada was applied between 1992 and 1998 to reduce shrub encroachment and enhance Bison bison (bison) habitat, although the impact of fire on preferred bison forage was unknown before management. In the summer of 1998 we conducted a study in the Hook Lake area of the SRL to test the effect of burn frequency (unburned, burned once, or burned three times since 1992) on herbaceous plant community composition and Salix spp. L. (willow) shrub vigor. Plant species abundance, litter biomass, soil pH, and depth of the organic soil horizon were measured in 300 1‐m2 quadrats nested within 30 1,000‐m2 plots in both burned and unburned dry meadows. To test the relationship between frequency and willow vigor, all willow shrubs within the plots were assigned a vigor score from I (dead) to IV (flourishing). The spring burns appear to have reduced willow vigor; however, shrub survival remained high (76%) on the most frequently burned meadows. Ordination plots resulting from canonical correspondence analysis suggest that multiple spring burns influenced plant community composition in dry meadow areas and that less palatable bison forage species (e.g., Carex aenea Fern. and Juncus balticus L.) were correlated with a regime of three spring burns. Our results suggest that frequent spring fires in the Hook Lake area have only a small negative effect on willow cover but may reduce the abundance of primary bison forage plants compared with less frequently burned meadows.

A review of hydroecological results of the Northern River Basins Study, Canada. Part 1. Peace and Slave rivers

AbstractDuring the early 1990s a multi‐component research programme was initiated by the Northern River Basins Study (NRBS) in Canada to answer the question: How does and how could flow regulation affect the aquatic ecosystem? Research focused on the major headwaters of the Mackenzie River, the Peace and Slave rivers, which became regulated in 1968 by the W.A.C. Bennett Dam in the Rocky Mountains. The lack of knowledge about the hydroecology of large northern rivers as well as a paucity of data for this relatively isolated basin required that studies be undertaken to assess how flow regulation had modified the physical template of this system. Research focused on quantifying the regulation effects on the flow regime, ice conditions, fluvial geomorphology and riparian vegetation of the Peace and Slave rivers and the Slave River Delta.Results of the NRBS studies indicate that regulation of the Peace River has shifted the pattern of seasonal flows and damped flow extremes creating a less variable annual regime. Increased winter releases from the reservoir have virtually eliminated the formation of a complete winter ice cover for a significant distance below the dam and delayed ice‐cover formation farther downstream. Higher ice levels that accompany increased winter flows are thought to affect the frequency and magnitude of ecologically important ice‐induced floods that occur during the spring. Although more difficult to link solely to the effects of flow regulation, pronounced morphologic and vegetation changes have been observed along the Peace River, including channel narrowing via the abandonment of secondary/backwater channels and in‐channel shoaling along the lower reaches. Vegetation succession has been especially evident on abandoned bar surfaces. Morphological changes were also observed in the Slave River Delta, particularly along the ecologically sensitive outer margin of the delta. Copyright © 2002 Environment Canada. Published by John Wiley & Sons, Ltd.

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Cumulative environmental impacts driven by anthropogenic stressors lead to disproportionate effects on indigenous communities that are reliant on land and water resources. Understanding and counteracting these effects requires knowledge from multiple sources. Yet the combined use of Traditional Knowledge (TK) and Scientific Knowledge (SK) has both technical and philosophical hurdles to overcome, and suffers from inherently imbalanced power dynamics that can disfavour the very communities it intends to benefit. In this article, we present a ‘two-eyed seeing’ approach for co-producing and blending knowledge about ecosystem health by using an adapted Bayesian Belief Network for the Slave River and Delta region in Canada's Northwest Territories. We highlight how bridging TK and SK with a combination of field data, interview transcripts, existing models, and expert judgement can address key questions about ecosystem health when considerable uncertainty exists. SK indicators (e.g., bird counts, mercury in fish, water depth) were graded as moderate, whereas TK indicators (e.g., bird usage, fish aesthetics, changes to water flow) were graded as being poor in comparison to the past. SK indicators were predominantly spatial (i.e., comparing to other locations) while the TK indicators were predominantly temporal (i.e., comparing across time). After being populated by 16 experts (local harvesters, Elders, governmental representatives, and scientists) using both TK and SK, the model output reported low probabilities that the social-ecological system is healthy as it used to be. We argue that it is novel and important to bridge TK and SK to address the challenges of environmental change such as the cumulative impacts of multiple stressors on ecosystems and the services they provide. This study presents a critical social-ecological tool for widening the evidence-base to a more holistic understanding of the system dynamics of multiple environmental stressors in ecosystems and for developing more effective knowledge-inclusive partnerships between indigenous communities, researchers and policy decision-makers. This represents new transformational empirical insights into how wider knowledge discourses can contribute to more effective adaptive co-management governance practices and solutions for the resilience and sustainability of ecosystems in Northern Canada and other parts of the world with strong indigenous land tenure.

The global control of silicate weathering rates and the coupling with physical erosion: new insights from rivers of the Canadian Shield

The chemical evolution of the surface of the Earth is controlled by the interaction of rainwaters, the atmosphere and the continental crust. That is the main reason why the knowledge of the parameters that control chemical denudation on Earth is of crucial importance. We report chemical and isotopic analyses for river waters from the Canadian Shield in order to estimate chemical weathering fluxes. We present a comparison of the chemical composition and Sr isotopic composition of a set of rivers sampled in the Slave Province (Northwest Territories, Canada) and in the Grenville Province (Québec, Canada). The surface waters of these high latitude catchments are very dilute, with the Slave rivers about three times more concentrated than the Grenville rivers. A detailed analysis of the Sr isotopic composition and chemical signature of these rivers shows that silicate weathering reactions are not the only mechanisms that control solute concentrations. An atmospheric component, constituted by the dissolution of evaporite and carbonate aerosols, is necessary to explain the dispersion of chemical ratios such as Ca/Na, Mg/Na, Sr/Na and Cl/Na. These aerosols probably have a local origin. Chemical denudation rates for the Slave Province are four times lower than those found in the Grenville Province (0.35 and 1.55 tons/km 2/yr respectively). Compared to a panel of surface waters from other shield areas of the world, the Slave Province appears to have the lowest chemical denudation rate in the world. In a chemical weathering rate vs. temperature plot, shield rivers define a triangular relationship, hot climate being able to produce the most variable denudation rates. But no simple relationship between chemical weathering rates and temperature or runoff is observed, in contrast to rivers draining basaltic areas. We show that a global power law (0.66 exponent) exists between chemical denudation rates and physical denudation rates, indicating that the shield areas with low mechanical denudation (such as the Slave Province or Cameroon) have also low chemical denudation rates. These results give importance to physical denudation in determining the chemical weathering rates of silicates. We think that any further modeling on Earth’s long term climate will have to take into account this fundamental coupling between mechanical and chemical weathering fluxes.

Identification of Freshwater and Anadromous Inconnu in the Mackenzie River System by Analysis of Otolith Strontium

Abstract Because trace elements from the environment are incorporated into the otoliths of fish as they grow, otolith microchemistry can be used to reconstruct key aspects of their environmental history, such as migratory patterns. We used scanning proton microprobe analysis on otoliths of inconnu Stenodus leucichthys from the Mackenzie River system (Northwest Territories, Canada) to determine whether patterns of strontium (Sr) distribution supported the hypothesis that some populations are anadromous while others remain in a low-Sr freshwater environment. The otoliths of inconnu from the Slave River had low, flat Sr profiles, indicating that these fish spent their entire lives within a freshwater environment. In contrast, while the otoliths of inconnu from the Arctic Red River varied substantially, they generally had low, flat profiles near the core followed by oscillating patterns of high and low Sr through to the outer edge of the otolith. These latter profiles indicate that these fish spent their firs...

Flow modelling to estimate suspended sediment travel times for two Canadian Deltas

Abstract. The approximate travel times for suspended sediment transport through two multi-channel networks are estimated using flow modelling. The focus is on the movement of high sediment concentrations that travel rapidly downstream. Since suspended sediment transport through river confluences and bifurcation movement is poorly understood, it is assumed that the sediment moves at approximately the average channel velocity during periods of high sediment load movement. Calibration of the flow model is discussed, with an emphasis on the incorporation of cross-section data, that are not referenced to a datum, using a continuous water surface profile. Various flow regimes are examined for the Mackenzie and the Slave River Deltas in the Northwest Territories, Canada, and a significant variation in travel times is illustrated. One set of continuous daily sediment measurements throughout the Mackenzie Delta is used to demonstrate that the travel time estimates are reasonable. Keywords: suspended sediment; multi-channel river systems; flow modelling; sediment transport

Migration Patterns of Freshwater and Anadromous Inconnu in the Mackenzie River System

Radiotelemetry, long-term seasonal gillnetting, and a synthesis of existing historical data revealed that both freshwater and anadromous inconnu Stenodus leucichthys in the Mackenzie River system are migratory, but their feeding/overwintering habitats and the timing and distance of their spawning migrations differ substantially. An anadromous population (Arctic Red River) began upstream migration 2–2.5 months earlier and spawned approximately 3 weeks earlier than did a freshwater population (Slave River), likely because of latitudinal differences in temperature regimes and the additional distance required by anadromous inconnu to reach spawning grounds. Little mixing occurred between anadromous inconnu in the lower Mackenzie River and freshwater inconnu in the Great Slave Lake area, and based on tagging data, a third fluvial form may exist in the upper Mackenzie River. Inconnu in the lower Mackenzie migrate more extensively and use both coastal areas and the outer Mackenzie Delta for feeding and overwintering, whereas inconnu in the Great Slave Lake area feed and overwinter in the lake and migrate shorter distances to spawn. Given these differences and the importance of inconnu for both domestic and commercial use, future research should focus on both the genetic and life history differences of the two migratory forms.

Cumulative effects assessment for the Northern River Basins Study

The primary objective of the Northern Rivers Basins Study (NRBS)was to advance the understanding of how anthropogenic developments haveimpacted the ecology of the Peace, Athabasca and Slave rivers, Canada.To investigate these multiple stressor impacts, the NRBS used acumulative effects assessment (CEA) based upon a weight of evidenceapproach. This CEA determined the exposure and effects of multiplestressors on these systems and included experimental verification ofcausality and linkage of this understanding to field data. Fish studiesconfirmed that dioxins and furans occur in the food web at low levelsacross the basins; detection frequencies for all2,3,7,8-substituted dioxin/furan congeners (2,3,7,8 TCDD/TCDF)were highest near bleached kraft pulp mills. PCDD/Fs, rather thanPCBs or organochlorine pesticides, were the chemicals of concern forhuman exposure. In addition, the recent decline in concentrations ofdioxins and furans in fish was commensurate with improvements in pulpmill treatment technologies. Throughout the basins, enrichment occurredbelow pulp mill and municipal discharges. Multiple stressor effects ofpulp mill effluent were separated from one another by using experimentsthat demonstrated that the primary impact of the mill effluent wasnutrient enrichment. River state was also greatly influenced byhydrologic impacts. In particularly, the Bennett Dam changed the ecologyof the Peace-Slave river-delta systems more than 1500~km downstream,while climate variability was an important contributing factor for thesedelta impacts. Notable contributions of the NRBS model were thecooperation among governments, aboriginal peoples, non-governmentorganizations, industry and other stakeholders, and the two-waycommunications flow among the scientific community and these groups.NRBS science was also deemed relevant because 16 questions forwarded bystakeholders focused the Study's CEA on specific issues of importancewithin the basin. In summary, the NRBS model of CEA included four keycomponents: (1) communication of stakeholder priorities to producerelevant science questions; (2) pursuit of the best availablescientific understanding of ecosystem impacts by engaginginterdisciplinary science teams; (3) assessment of futureenvironmental condition through monitoring and follow-upinvestigation; and (4) communication of results to managers toproduce appropriate regulatory change. This CEA model combines theseelements with scientific rigor to generate meaningful information tostakeholders while also improving regional assessments of riverbasins.

Integrated assessment of ecosystem integrity of large northern rivers: the Northern Rivers Basins Study example

The Northern River Basins Study (NRBS) assessed the ecologicalstate of three complex northern river basins for which we had a limitedunderstanding of the physical, chemical and biological environment. Amajor challenge of this study was the choice of ecosystem components tomonitor. This process was guided by determining the indicators thatwould best assess environmental state relative to ecosystem objectivesarticulated by people living within the basin. This charge lead the NRBSto use a cumulative effects assessment framework that measured stressorexposure and their effects along with the development of plausiblecause-effect mechanisms. Thus, the NRBS developed and applied anintegrated assessment framework that included public stakeholders,various levels of government and scientists. A key feature of thisframework was the ability to allow feedback among these groups toproduce the syntheses of science results, and the resultant managementresponses that ultimately modified environmental regulations. Papers inthis series present the results of the NRBS and emphasize theinterdisciplinary nature of this project. Investigations evaluated theroles of flow regulation, nutrients, contaminants, and their interactiveeffects, on the integrity of the Athabasca, Peace and Slave rivers,Canada. Novel contributions of the NRBS model included the cooperationamong governments, aboriginal peoples, non-government organizations,industry and other stakeholders, and the two-way communications flowamong the scientific community and these groups.

Contaminant sources, distribution and fate in the Athabasca, Peace and Slave River Basins, Canada

Northern river ecosystems worldwide are under increasing environmental stress from degrading developments that influence water quality and associated ecological integrity. In particular, contaminant-related threats to these systems are rising from enhanced industrial and municipal effluent discharges along with elevated non-point source inputs related to land-use activities such as forestry, agriculture, mining and long-range atmospheric transport. In this regard, the contaminants program of the Northern River Basins Study (NRBS) in western Canada identified key contaminant sources to the Athabasca, Slave and Peace river basins (particularly related to pulp-mill developments) and assessed their environmental fate and distribution in water and sediments. The study also developed and employed new analytical approaches and generated improved models to predict contaminant transport and fate in the aquatic environment and related food webs. Consequently the study focused on those contaminant families identified in characterization studies as arising from key point- and non-point sources within the basins or as being of greatest toxicological significance. These included resin acids, polychlorinated dioxins and furans, polychlorinated biphenyls, chlorinated phenolics, polyaromatic hydrocarbons and selected heavy metals such as mercury. Low or non-detectable concentrations of a number of contaminant groups were found in the ambient water phase including chlorinated phenolics, some chlorinated dioxins and furans and some resin acids. For both suspended and depositional sediments, significant declines were observed over the study period for the major chlorinated contaminant groups tested, correlating directly with the implementation of improved effluent treatment in many of the pulp mills located in the basins. In general, the environmental levels of chlorinated organic and metal contaminants in water or sediments were low and within Canadian health or environmental guidelines. It is hoped that the approaches used and lessons learned from the NRBS will be of use to others assessing contaminant and multiple stressor issues in other large river ecosystems.

Fish health in the Peace, Athabasca and Slave river systems

The response of large river systems to human development isoften hard to predict. The spatial scale of these systems makes themdifficult to study and their ecology (particularly in the case of largenorthern rivers) is often poorly understood. To provide an ecologicalassessment of three large river basins in northern Canada, the NorthernRiver Basins Study (NRBS) undertook a multi-disciplinary approach toassess environmental and socio-economic impacts of development. Resultspresented here focus on key findings relating to studies of fish healthwithin the basins. It was known at the outset of the NRBS that dioxins,furans and other organic contaminants would be present in the system.However, NRBS research indicated low levels of environmentalcontamination, particularly compared to other systems in Canada andelsewhere in the world. In addition, contaminant loads in fish generallyconform to Canadian guidelines for both aquatic and human health;although, levels of dioxins, furans, PCBs and mercury in biota didexceed guidelines at certain times and in certain locations. The weightof evidence indicates that many of the fish in these basins exhibitsigns of physiological stress. Of particular concern was the findingthat sex hormone levels in burbot and longnose sucker collected fromnear-field pulp-mill locations were significantly depressed, and thatnumbers of immature fish in these same locations were unexpectedly highand more likely to show external abnormalities. In addition, there is aperception that fish in the lower reaches of the Peace-Athabasca basinsand in the deltas are of lower quality. Studies of fish health have beenintegrated with other technical studies in a cumulative effectassessment and will provide a basis for future research and managementdecisions within these basins.