Nutrient fluxes to the Bay of Biscay from Cantabrian rivers (Spain)

Nutrient fluxes to the Bay of Biscay from the Cantabrian basin have been quantified for the first time. Data between 1981 and 1995 of the main 16 Cantabrian rivers from the COCA monitoring programme have been used. Values of water flow and dissolved inorganic nitrogen (DIN), phosphate and silicate concentrations have been taken. Equations are proposed to quantify the fluvial nutrient contributions to the Cantabrian Sea. The annual average of continental outputs to the Bay of Biscay from the Cantabrian basin is 16.1 × 10⁹ m³ of freshwater, 1.0 × 10⁹ mol of N in DIN, 0.062 × 10⁹ mol of phosphate and 1.2 × 10⁹ mol of silicate. In comparison with the French rivers, those of the Cantabrian have small fluxes and their outflow is very disperse, not forming large coastal plumes. From April to September, when the primary production is relatively important, the DIN contribution to the Cantabrian coastal reservoir is 10%. Coastal fertilisation due to continental waters could be considered as negligible and only influences areas very close to river mouths, except for the Nalón River. Its flux represents 33 % of nitrate, 39 % of phosphate and 15 % of silicate of the total continental inputs of nutrients to the Cantabrian Sea.