The nature of sediments in our watersheds, and how to track them
The input of sediment into river systems is a natural process that is important for maintaining aquatic health and function. However, inputs of sediment have changed worldwide due to a range of land uses such as agriculture, road building, forestry, urbanization to name a few. In many cases this has led to a dramatic change in the quantity and quality of sediments entering river systems (Figure 1) such that in some instances the input of sediment represents a significant ecological and human health concern due to the impact of sediment on aquatic habitats (e.g., sedimentation and its impact on fish spawning areas) and water quality (e.g., as a carrier of contaminants). Fine-grained sediment (less than 63 microns) has been identified as one of the main concerns within the Nechako River Basin. In response to these concerns we are employing established sediment fingerprinting techniques to determine the relative contribution of sediments from different sources (such as agricultural fields and channel banks) within the Nechako River Basin
Figure 1. Excessive sediment transport during freshet near Vanderhoof, BC
Fingerprinting involves selecting and measuring a suite of physical and/or biogeochemical properties (i.e., “fingerprints”) that can be used to distinguish between two or more potential sediment sources (Figure 2)
In our study we have collected suspended sediments using time-integrated samplers (Figure 3) that were placed in creeks throughout the Nechako watershed as well as within the mainstem of the Nechako River.
Figure 3. A time integrated sediment sampler on the bank and being deployed in a creek
Figure 4. Dr. David Gateuille sampling large clay channel banks on the upper Nechako River
We are then comparing the sediment we have retrieved from the creeks and river with materials collected from potential sources such as soils from intact, burned and logged woodlands, crop and hay fields, pastures, road sides, urban and industrial areas, and channel banks (Figure 4).
In addition to collecting fine river sediments using time-integrated samplers, we have also collected a number of sediment cores from a variety of locations on the flood plain of the Nechako (Figure 5). By analyzing the sediment contained in these cores – which have been deposited on the floodplain over the last few decades during flood events - this will help us to understand the changes in the sediment sources and dynamics of sediment deposition in the vicinity of Vanderhoof.
By determining where the main sources of fine sediment are, and how these have changed over time, we hope that this information can be used to help mitigate some of the problems associated with fine sediments in the Nechako River Basin. Results from the First Phase of our Research can be found here and the goals and objectives of Phase 2 of our research can be found here .
This research has been supported by funds from the BC Real Estate Foundation Partnering Fund, Laboratoire des Sciences du Climat et de l'Environnement, and The French Académie des Sciences
Figure 5. Dr. Phil Owens and friends taking core samples near Vanderhoof, BC