An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada

Electrical conductivity (EC) and geochemical data were interpreted to determine the nature, origin and distribution of salinity in pore waters of sediments in a deltaic environment. The role of diffusion as a mechanism for transporting saline water within lower permeability prodelta and delta slope sediments is specifically investigated. Characteristic vertical salinity profiles at several different regions of the Fraser River Delta, British Columbia (Canada) are identified, including relatively shallow salinity zones in areas currently and historically near main river channels, and deeper salinity zones reaching up to 300 m depth in delta-front and inland areas. Comparison of salinity profiles with the results of a simple salt transport model suggests that diffusion may be a significant mechanism controlling the observed distribution of salinity in current or former estuarine areas of the delta.Density-effects were found not to be significant given the low permeability of the silt through which the salt is diffusing; however, in similar environments with higher permeability sediments, density effects may be significant. In inland and delta front areas, salinity extends to a considerable depth in the silts, beyond what would appear to be possible by diffusion alone, and points to a connate origin.