Combining modelling 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 theoretical development. ong measurements of currents through the Dover Strait 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 component of tidal flow and the wind-forced residual flow resulting in an estimate of the net long term flow into the North Sea of 94,000 m3 s−1—a value in close agreement with the most recent high resolution modelling of Salomon et al. (1993). The temporal variability in these radar and ADCP observations are compared with synoptic wind, tide gauge and numerical model data. uxes of the dissolved metals Cd, Cu, Ni, Pb and Zn through the Straits are then calculated using concentrations in the Strait derived from a study by McManus and Prandle (1994). The latter involved multiple regression of model simulations of dispersion (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 technique depend directly on the net water flux through the Strait. Thus, since 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. ux of suspended sediments is calculated using time and cross-sectionally averaged suspended sediment concentrations obtained during a cruise in June 1990 (Jones et al., 1993). The particulate metal fluxes are calculated by combining these suspended sediment concentrations with the dissolved metal concentrations and publised Kd (partitioning coefficient) values. These dissolved and particulate metal fluxes are also shown to be in reasonable agreement with the values derived by Statham et al. (1993). The net, particulate plus dissolved, flux of these metals through the Strait represents between one-sixth and one-third of the total from all other sources into the southern North Sea.