Dynamics of Particulate Trace Metals in the Tidal Reaches of the Ouse and Trent, UK

Abstract

Samples of suspended particulate matter (SPM) have been collected in the tidal reaches of the Ouse and Trent over seven surveys covering the annual cycle of riverine conditions. Settling experiments were carried out on water samples to differentiate permanently suspended particulate material (PSPM) from temporarily suspended particulate material (TSPM). The results indicated that PSPM, additional to the riverine component, was created within the turbidity maximum zone (TMZ) during tidal resuspension. The PSPM varied between 10% and 50% of the total SPM and could be transported quasi-conservatively down-estuary. The concentrations of particulate Cd, Fe, and Zn (available to 1M HCl) were determined in PSPM and TSPM, as well as samples of the bulk SPM. The trace metal concentrations in PSPM were seasonally variable and generally higher than in TSPM, which had relatively constant concentrations. The trace metal concentrations in PSPM and TSPM were used to develop a two-component, particle mixing model, which was applied to the interpretation of the bulk SPM concentrations of Cd and Zn. It is postulated that as the PSPM encounters the salinity gradient labile Cd and Zn desorb from the particles. On the basis of these results an additional mechanism for generating estuarine maxima in dissolved trace metals has been proposed.