Flow of nutrients from agriculture to the roadstead of Brest

Abstract

Nitrogen and phosphorus are used in large quantities for agriculture to increase production. A part of them is then found in water where they can increase eutrophication. Nitrogen and phosphorus transfer from agricultural lands and farms to water occur by several ways. Various physical, chemical and biological mechanisms works in those transfer. In order to observ observe, to understand and to quantify them, the Cemagref is studying the Kerouallon, a small watershed in north-west of Brittany, France. Those transfer depend, of course, on agricultural practices, on the characteristics of the basin and on meteorological and hydrological conditions: Nutrients concentrations and flows vary a lot in the stream at the outlet of a basin according to all these mechanisms. In order to quantify nutrients flows from agricultural activity to water, it is necessary to collect data about discharge and concentrations in water with a small and pertinent enough timestep to monitor all the variations. It is important also to put them in relation with hydrological conditions. That is done now on the Kerouallon basin and we will try to use the results now on larger basins.