Intra- and inter-estuarine variability of particle microstructure

A systematic study has been made of the particle microstructure and chemical composition of suspended solids from large U.K. estuaries (Humber, Mersey, Tamar) and a German estuary (Elbe). The mean specific surface areas of the suspended solids were in the sequence Elbe (25.6 m² g^-1) = Humber (24.0 m² g^-1) > Tamar (14.9 m² g^-1) > Mersey (9.6 m² g^-1). In addition, the Elbe, Humber and Tamar estuaries had higher specific surface areas in the very low salinity, turbidity maximum zone. There was no evidence of similar effects in the Mersey Estuary. These differences in specific surface areas (and hence the heterogeneous chemical reactivity of the particles) are interpreted in terms of the relative proportions of carbon to iron and manganese in the samples. Thus, the high specific surface area in the Humber is associated with a C/Fe + Mn ratio of 4, whereas that for the Mersey is about 11. The implication of these results is that the surface chemical composition determines the particle reactivity and where adsorbed ions are ultimately located on the particle (i.e. either on the surface or in the internal pore structure). This finding is discussed in the context of the uptake of dissolved constituents and the potential for irreversible adsorption.