COMBINING MODELING AND MONITORING TO DETERMINE FLUXES OF WATER, DISSOLVED AND PARTICULATE METALS THROUGH THE DOVER-STRAIT

Contaminant fluxes in a shelf sea system are determined from a series of interrelated studies involving monitoring, modelling and theoretica l development. Year-long measurements of currents through the Dover St rait were made in 1990-1991 using both shore-based high frequency (HF) radar and a bottom-mounted acoustic Doppler current profiler (ADCP). These measurements were combined to determine both the residual compon ent of tidal flow and the wind-forced residual flow resulting in an es timate of the net long term flow into the North Sea of 94,000 m(3) s(- 1)-a value in close agreement with the most recent high resolution mod elling of Salomon et al. (1993). The temporal variability in these rad ar and ADCP observations are compared with synoptic wind, tide gauge a nd numerical model data. The fluxes of the dissolved metals Cd, Cu, Ni , Pb and Zn through the Straits are then calculated using concentratio ns in the Strait derived from a study by McManus and Prandle (1994). T he latter involved multiple regression of model simulations of dispers ion (with the model flow through the Dover Strait corresponding to the above monitored value) against data from four surveys in the southern North Sea carried out in 1988-1989 as part of the North Sea Project. The mean concentrations determined from this inverse modelling techniq ue depend directly on the net water flux through the Strait. Thus, sin ce it is shown here that the results for the more conservative metals Cd, Cu, Ni and Zn agree closely with direct measurements by Statham et al. (1993), this lends further confidence to this new estimate of net flow derived from monitoring. The flux of suspended sediments is calc ulated using time and cross-sectionally averaged suspended sediment co ncentrations obtained during a cruise in June 1990 (Jones et al., 1993 ). The particulate metal fluxes are calculated by combining these susp ended sediment concentrations with the dissolved metal concentrations and published Kd (partitioning coefficient) values. These dissolved an d particulate metal fluxes are also shown to be in reasonable agreemen t with the values derived by Statham ct al. (1993). The net, particula te plus dissolved, flux of these metals through the Strait represents between one-sixth and one-third of the total from all other sources in to the southern North Sea.