title: Groundwater control of biogeochemical processes causing phosphorus release from riparian wetlands.
abstract: Because of the high sorption affinity of phosphorus (P) for the soil solid phase, mitigation options to reduce diffuse P transfer usually focus on trapping particulate P delivered via surface flow paths. Therefore, placing riparian buffers between croplands and watercourses has been promoted worldwide, sometimes in wetland areas. To investigate the risk of P-accumulating riparian wetlands (RWs) releasing dissolved P into streams, we monitored molybdate-reactive P (MRP) in the soil pore water of two RWs in an agricultural watershed. Two main mechanisms released MRP under the control of groundwater dynamics. First, soil rewetting after the dry summer period was associated with the presence of a pool of mobile P, limited in size. Its mobilization started under water saturated conditions caused by a rise in groundwater. Second, anoxic conditions at the end of winter caused reductive dissolution of Fe (hydr)oxides along with a release of MRP. Comparison of sites revealed that the first MRP release occurred only in RWs with P-enriched soils, whereas the second was observed even in RWs with low soil P status. Seasonal variations in stream MRP concentrations were similar to concentrations in RW soils. Hence, RWs can act as a key component of the P transfer continuum in agricultural landscapes by converting particulate P from croplands into MRP transferred to streams.
authors.affiliation: Agrocampus Ouest, UMR 1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; INRA, UMR1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; Université européenne de Bretagne, France. Electronic address: rdupas@agrocampus-ouest.fr.
authors.forename: Rémi
authors.initials: R
authors.lastname: Dupas
authors.affiliation: Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118, Géosciences Rennes, Rennes, France.
authors.forename: Gérard
authors.initials: G
authors.lastname: Gruau
authors.affiliation: Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118, Géosciences Rennes, Rennes, France.
authors.forename: Sen
authors.initials: S
authors.lastname: Gu
authors.affiliation: Agrocampus Ouest, UMR 1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; INRA, UMR1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; Université européenne de Bretagne, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Humbert
authors.affiliation: Agrocampus Ouest, UMR 1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; INRA, UMR1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; Université européenne de Bretagne, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Jaffrézic
authors.affiliation: Agrocampus Ouest, UMR 1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; INRA, UMR1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France; Université européenne de Bretagne, France.
authors.forename: Chantal
authors.initials: C
authors.lastname: Gascuel-Odoux
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D053833:Wetlands
chemical_list: D010758:Phosphorus
keywords: Buffer strip; Cell lysis; Groundwater; Phosphorus; Redox processes; Wetland