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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]