Nutrients (P, N, Si) in the channel and the dover strait - seasonal and year-to-year variation and fluxes to the north-sea

Abstract

Recent measurements (1986-1988) of the distribution of the concentration of different nutrients (nitrogen, phosphorus and silicate) in the Dover Strait have been used, combined with older results, to calculate the total flux (dissolved and particulate) of nutrients into the North Sea. Special efforts are made to take into account in the fluxes the tidal, geographical and temporal variations in the concentrations of the different nutrients. No vertical gradients in the concentration of the different nutrients were found. Increased nutrient concentration was found in the coastal zones of England and France, compared to the Atlantic water in the central part of the Dover Strait The variation within a single year and between different years in the data available (1930-1988) for the different nutrients was rather large and no clear, annual trends could be distinguished. Average yearly fluxes are, for ammonium, nitrate, nitrite and total nitrogen respectively: 156 +/-29, 364 +/- 68, 26 +/- 6 and 1411 +/- 209 ktonnes N; for ortho-phosphate and total phosphorus, 79 +/- 13 and 192 +/- 32 ktonnes P per year and for dissolved silicate 492 +/- 80 ktonnes Si per year. These fluxes are higher than those published before, because in this study the particulate fraction and the dissolved organic fraction of the nutrients (except Si) are also taken into account.