Quantitative Interpretation of Halogen Porewater Concentration Profiles in Lake Sediments

Halogen ion migration through clay-rich sediments is particularly well documented in cores from Loch Lomond, Scotland, where distinctive patterns for CI, Br and I have been observed. The sediments are a sequence of marine and limnic silts and clays which cover glacial deposits. The marine band, resulting from a transgression 6900 y B.P. to 5400 y B.P., acts as a source for the halogens. p]A 1-D conceptual model and code has been developed taking into account variations in the concentration boundary conditions and the accumulation of sediments. The model has been calibrated against the CI concentration distributions for which boundary conditions can be estimated readily. p]The model has been applied to Br and I profiles. Deviations between the Cl-calibrated model and the measured profiles were attributed to reactive processes. Release rates from the marine band for Br and I are deduced. Their sensitivity with respect to system properties, assumptions over boundary and initial conditions and reaction mechanisms is discussed.