Agronomie 24 (2004) 237-248
DOI: 10.1051/agro:2004021

Soluble phosphorus dynamics in an agricultural watershed

L. Jordan-Meille^a and J.-M. Dorioz<sup>b

a</sup>  ENITA, 1 cours du Général de Gaulle, BP 201, 33175 Gradignan Cedex, France
^b  INRA, 75 avenue de Corzent, BP 511, 74203 Thonon les Bains, France

(Received 3 March 2004; accepted 24 March 2004)

Abstract - Both particulate phosphorus (PP) and soluble phosphorus (SP) contribute to the eutrophication of water bodies. This research focuses on the mechanisms and factors controlling SP exports at the watershed scale in a case study located in Southern France. Variability in the P concentrations and fluxes was analysed over a period of 6 years in a 302-ha rural watershed. During most of the hydrological periods, reservoirs and pathways for PP and SP seemed to be different both in time and space; differences were greatest during storm flows of the early wet season. Their high SP fluxes and concentrations were due to the P released from agricultural soils as shown by a P mass balance downstream/upstream. During these flushing periods, soluble forms of P follow a hydrochemical behaviour quite similar to solutes and are transferred in relationship to subsurface flows, as shown by a detailed monitoring of the transition from dry to wet season on an agricultural sub-watershed.

Key words: soluble phosphorus / watershed / no point source / storm flows / losses

Corresponding author: L. Jordan-Meille l-jordan@enitab.fr

© INRA, EDP Sciences 2004