Northern River Basins Study and the Athabasca River: The Value of Experimental Approaches in a Weight-of-Evidence Assessment

This chapter illustrates how field, laboratory, and mesocosm studies were used to clarify the relative roles of nutrients and toxicants in altering biota downstream from municipal sewage and pulp mill discharges. The Northern River Basins Study (NRBS) produced more than 150 technical and synthesis reports. The NRBS is particularly relevant today because the Athabasca River and its tributaries drain Canada’s largest economic development project, the Canadian oil sands. Although the NRBS had a broad scope encompassing bioaccumulative chemical and human health concerns, the chapter describes the studies used to explain the observed patterns in benthic communities. In field surveys, the abundance of benthic invertebrates was consistently greater downstream from sewage and pulp-mill inputs. Evidence was developed using a tiered (i.e., stepwise) approach that included field observations, laboratory tests, and mesocosm (artificial stream) studies.