Spatial Variation of Sediment Oxygen Demand in Athabasca River: Influence of Water Column Pollutants

Sediment samples were collected from fifteen different locations along Athabasca River in an attempt to quantify the sediment contribution to oxygen demand. SOD rates along Athabasca River ranged from 0.09 g/m²⋅d to 0.71 g/m²⋅d near ambient temperature (<4°C). SOD rates generally increased downstream, however, inter-site differences were also influenced by the physical and chemical properties of the sediment. SOD rates were also higher below wastewater discharges and tributary confluences. Variation in SOD rates along the river system were positively correlated with water column concentration of TOC, TDP, Cholorphyll-α. Sediment characteristics such as grain size was a fundamental factor in determining SOD rates. Fine grained sediment in depositional areas tended to have higher SOD. The result also highlighted the importance of inclusion of sediment diagenesis and biochemical reactions inside sediment in water quality models that seek to represent water chemistry and particularly carbon, nitrogen, phosphorus and dissolved oxygen. Results from the Athabasca River suggest that SOD rates are a primary forcing function in large high order rivers that should be determined from the complex physical and chemical factors that control it rather than from water column nutrients.