Elemental mercury concentrations and formation rates in the Scheldt estuary and the North Sea

Concentrations of Hg0 in surface waters and atmosphere of the Scheldt estuary and the North Sea are presented and their relationship with biological processes is discussed. Hg0 concentrations in the Scheldt estuary range from 0.1 to 0.38 pmol•l−1 in the winter and from 0.24 to 0.65 pmol•l−1 in the summer and show a positive relationship with phytoplankton pigments. In the North Sea Hg0 concentrations range from 0.06 to 0.8 pmol•l−1 and are higher in coastal stations. Transfer velocities across the air–sea interface were calculated using a classical shear turbulence model. Volatilization fluxes of Hg0 were calculated for the Scheldt estuary and the North Sea. For the Scheldt estuary the fluxes range from 226–284 pmol•m−2•d−1 in winter and 500–701 pmol•m−2•d−1 in summer and for the North Sea the fluxes range from 59–1110 pmol•m−2•d−1 for an average windspeed of 8.1 m•s−1. These fluxes are comparable to the wet and dry depositional fluxes to the North Sea. Hg0 formation rates necessary to balance the volatilization fluxes vary from 0.2 to 4% d−1.