NUTRIENT FLUXES BETWEEN THE ENGLISH-CHANN EL AND THE NORTH-SEA - ACTUAL SITUATION AND EVOLUTION SINCE 10 YEARS

As part of the MAST I-FluxManche initiative, a monthly (September 1990 to November 1991) sampling programme has been carried out in the Dove r Strait. Samples were taken (weather permitting) at two depths at eac h of six standard stations between Folkestone and Cap Gris-Nez. Data f rom all surveys, in conjunction with estimates of water movement deriv ed from hydrodynamic numerical model, have been used to calculate flux es of nutrients between the Channel and the North Sea. Results demonst rate that although nutrient concentrations are lower in the central ch annel-waters than in the coastal zone, the dissolved nutrient flux to the North Sea is mom important for stations of the central part of the Dover Strait as water. Current concern about possible increases in ni trogen and phosphate discharges to seawater, apparently confirmed for the southern North Sea by Dutch workers, prompted a comparison of the present data set with values obtained by sampling from car-ferries dur ing the period 1979-81. That long time scale investigation does not sh ow more important increase than interannual variability can do (+ 0,85 mumol/l N-NO2 + NO3, + 0,1 mumol/l P-PO4, + 1,1 mumol/l Si from 1979- 1980 to 1990-1991).