ANNUAL GEOCHEMICAL MASS BALANCES IN WATERS OF THE FIRTH-OF-CLYDE

A first-order mass balance of twelve minor and trace elements in the c oastal sea area of the Firth of Clyde is presented for the period Augu st 1989-July 1990. It is based on our own four sets of chemical data c ollected in the Clyde Estuary and Firth of Clyde over that period, com plemented by independent information relating to water column hydrogra phy, rainfall, wind speed, river discharge, as well as sewage sludge a nd dredged material disposed of at sea. Terrigenous inputs were measur ed or estimated as continuous functions of time. Mean exchange rates w ith the open shelf were calculated over four periods representative of 77 % of the one-year period considered here. All these fluxes were su bsequently converted to monthly values to facilitate intercomparison. Sedimentation rates were estimated by difference. The trapping efficie ncy (%) of the system over the study period was 80 +/- 8 for Pb, 75 +/ - 10 for Fe, 70 +/- 9 for Co, 68 +/- 12 for Mn, 50 +/- 14 for Zn, 34 /- 31 for P, 33 +/- 20 for N, 33 +/- 25 for Cu, 26 +/- 30 for Ni, 20 /- 46 for Si, 15 +/- 16 for Cd, 14 +/- 26 for organic C, and -14 +/- 1 3 for inorganic C. Most elements exhibited a close correspondence betw een their annual import and export fluxes across the marine boundary. The implication is that physical transport is the dominant process in the region adjoining the North Channel, i.e. the outermost part of the Firth of Clyde. By extension, the inner Firth and near-shore zone mus t act as a trap for metal-bearing particles. Such an understanding of the present-day state of the system with regard to trace metal and nut rient cycles would enable one to predict the response of the system to any scenario of modification of the metal/nutrient inputs only to the extent that the system responds linearly to input variability.