Sediment Bound Contaminants in a Remote Northern Delta

Deltas of major rivers are among the most productive and environmentally sensitive components of riverine systems in cold regions, and are of great hydrological and ecological importance. Much of their productivity stems from the supply of nutrient-rich sediments that rejuvenate in-channel, perched and riparian habitats. Such sediments, however, can also be a source of organic contaminants, and deltas, because of their natural tendency to accumulate sediments, may become retention zones or sinks of these. The objective of this research was to determine the nature of sediment-related organic contaminant deposition in the Slave River Delta, Canada - a remote area that is now experiencing the effects of rapid upstream development. A special focus was placed on the protracted low-flow period that characterizes the winter period during which there should be a significant deposition of fine-grained sediment - size fractions with an affinity to adsorb organic contaminants. Results of an exploratory field program conducted during the 1997 pre-breakup and pre-freeze-up periods support the concept that the under-ice period is a time of significant fine-grained sediment deposition. Moreover, the contaminant load was found to be higher at the end of the winter flow recession rather than in late autumn following the major summer flow events. Comparisons of the observed contaminant levels measured in the delta are also made with those recorded by others in the upstream river that feeds the Slave Delta and in Great Slave Lake downstream of the delta.