Sediment Focussing – Implications for Contaminant Fate

Neil Graham

This section of the ProDoc Leman 21 research effort investigates contaminant fate in the lake sediments of Vidy Bay, Lausanne. The objectives include investigation of sediment focussing through the measurement of vertical and lateral fluxes of sediments, and the assessment of the colloidal fraction of particulate matter suspended in the nepheloid layer above the sediment-water interface. Natural radionuclides are being analysed in this research effort as they can be used as surrogates for many contaminants which are introduced into water systems.

Vertical flux is being assessed via sediment traps. These traps collect allochthonous and autochthonous material as it travels through the water column to the lake bed. These sediment traps are located at two of three sampling sites stretching SSW from the outlet pipe of the WWTP in Vidy Bay. Horizontal flux is being assessed through the analysis of sediment cores taken at all three sites along the sampling transect. Differences in monthly radionuclide activities in the sediments give insight into sediment focussing processes occurring in Vidy Bay. In addition to these sampling techniques, two mult-parameter data collection units have been placed at two of the sites in Vidy Bay. These probes will be used to assess current velocity and direction, in addition to turbidity and temperature, in hopes of correlating sedimentation data with Vidy’s hydrodynamics

The sediment-water interface contains much suspended colloidal and particulate matter. This matter has been shown to readily adsorb contaminants and is able to transport them to other parts of the lake. Characterization of the colloidal fraction will help infer relationships between colloidal composition and contaminant adsorption which in turn lends to the investigation of pollutant fate.


Neil Graham is from Canada and has completed a B.Sc.(2005, cum laude) and M.Sc.(2008) in chemistry at Laurentian University in Sudbury, ON, Canada. His background includes work as an analytical chemist in environmental research with MIRARCO in Sudbury, Canada. It also includes work as an analytical chemist/Quality Control Manager at the Elliot Lake Research Field Station in Sudbury. Neil holds the status of Chartered Chemist in the province of Ontario, Canada.