Sediment sources and Dynamics:Results from Phase 1

Given that the Nechako River watershed is so large, we decided to focus our efforts on a smaller sampling area. We chose to include the mainstem of the Nechako upstream of Vanderhoof and also included most of the sub-basins along the mainstem up to the Kenny Dam due, in part, to the distribution of Nechako River white sturgeon. We sampled suspended sediments at six sites on the mainstem of the Nechako as well as nine tributaries (Figure 1).  

Our sediment fingerprinting research has been able to demonstrate that the main sediment sources for the samples collected at Vanderhoof vary over the field season and that the times of contributions from the erosion of channel bank material matches well the hydrograph (Figure 2). To see full details of our research relating to the sediment fingerprinting in Phase 1 of our research, please click here.

Sediment quality

While there has been much interest and focus on sediment sources to the mainstem Nechako River, we have received queries from stakeholders regarding whether sediments in the basin are potentially contaminated with legacy and emerging chemical pollutants including current-use herbicides and pesticides. The concerns raised have included the potential adverse impacts of pollutants on human health as well has the potential affects on regional freshwater ecosystems that support anadromous salmon and the endangered Nechako white sturgeon population.

Sampling PAHs
Todd French collecting bottom sediments near Fort Fraser, BC

The objective of this part of the study was to assess the chemical quality of suspended and channel bottom sediments within the context of polychlorinated biphenyls (PCBs), polybrominated diphenyl ether (PBDEs) flame retardants, legacy organochlorine (OC) pesticides, polycyclic aromatic hydrocarbons (PAHs), organophosphorus and phenoxy acid herbicides, and labile (exchangeable) metals/metalloids that are associated with toxicity. We also synthesized historical (1980s to 1998) datasets for organic and inorganic pollutants in Nechako River watershed sediments (Figure 1).

Most all of the compounds we detected in bottom sediments were always well below provincial and federal guidelines for the protection of aquatic life. However, concentrations of some total labile metals in suspended and/or bottom sediments often exceeded provincial threshold effect levels and, in some cases, approached or exceeded probable effect levels (Figure 3). This work raises some concerns regarding organopollutants, metals and perhaps excessive nutrients in the sediments of the Nechako River and its major tributaries and their potential impacts on the reproductive physiology, condition and growth of white sturgeon. This work has also been valuable in helping to interpret our sediment fingerprinting results in terms of the sources of fine sediment.

The full details of this research project can be found by clicking here