Characterisation of suspended particulate matter in the Rhone River: insights into analogue selection

Selection of realistic suspended particulate matter (SPM) analogues remains vital for realising representative experimental and modelling approaches in predicting the environmental fate of pollutants. Here, we present the characterisation of dissolved-ion and SPM compositions for nine sampling sites over the length of the Rhone River. Dissolved-ion concentrations remained stable, but SPM concentrations varied among sampling sites. Size fractionation and mineralogical characterisation of the SPM revealed that the same minerals (e.g. quartz, calcite, muscovite) constituted every size class from 0.5 to >50 mu m, as is usually found with allochthonous and large-scale systems. To gain insight into SPM analogue selection, aggregation kinetics of silica, calcite, muscovite, feldspars and clays were monitored in the native filtrate and related to the respective zeta potentials (z). An SPM mixture of calcite (49 %), muscovite (14 %), feldspar (23 %) and chlorite (14 %) proved the best match for the Rhone SPM, demonstrating that mineral surface chemistry, structure and size are all important in selecting a realistic SPM analogue for a riverine system.