PARENT SESSION
Organized Oral Session 5: Mercury cycles: Sources, mass balances, bioaccumulation, and options to manage affected systems
Organizer(s): EPH Best, JG Wiener, and D Planas
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 511 C, Level 5, Palais des congrès de Montréal

Mercury species in the Scheldt estuary (Belgium and The Netherlands): Dynamics, budgets and biomagnification.

Baeyens, Willy¹, Leermakers, Martine¹, ¹ Vrije Universiteit Brussel, Brussels, Belgium

ABSTRACT- Seasonally, dissolved and particulate total mercury, methylmercury (MeHg) and metallic mercury (Hg^o) concentrations in the Scheldt estuary (Belgium and the Netherlands) were assessed in the period 1991 to 1999. In the same period fish samples were analysed too. In winter, total dissolved Hg concentrations are elevated in the upper estuary, decrease exponentially in the low salinity range followed by a very slow decrease towards the mouth. In summer, they are low upstream, increase in the low salinity range or in the mid-estuary and sometimes show an increase in the lower estuary. Total dissolved MeHg concentrations are much lower in winter than in summer. In summer, the MeHg concentrations are low at low salinity, they show a first increase in the salinity range from 3 to 12, a decrease in the mid-estuary and a second increase in the lower estuary. Hg^o concentrations are higher in summer than in winter and Hg^o formation rates vary from 0.2 to 3% d^-1, comparable to those found in other aquatic environments. Evasion fluxes of Hg^o were calculated using a shear turbulence model resulting in fluxes of 226-284 pmolm^-2d^-1 in winter and 500-701 pmolm^-2d^-1 in summer. Particulate Hg and MeHg concentrations show a decreasing trend from upper to lower estuary. In the fluvial part of the Scheldt, dissolved Hg increases in the most upstream stations, while particulate Hg shows no particular pattern. Dissolved MeHg ranges from 0.1 to 0.39 pmolL^-1 and particulate MeHg from 3.1 to 43.5 pmolg^-1. The MeHg concentrations are comparable to those found in the estuary and no seasonal variations could be observed. TOC/TN versus 13C profiles in suspended matter (SPM) allow us to distinguish SPM sources and to understand SPM mixing and sedimentation in the estuary. Using this information together with the river flow, seasonal budgets of the various Hg species could be calculated. Although the Scheldt estuary is much more polluted than the North Sea, Hg levels, as well as the % of MeHg, in Scheldt fish were lower than in North Sea fish. For the same species, biomagnification is always higher in the North Sea than in the Scheldt.

Key words: mercury, speciation, budgets, Scheldt estuary