Release of dissolved phosphorus from riparian wetlands: Evidence for complex interactions among hydroclimate variability, topography and soil properties

Sen Gu; Gérard Gruau; Rémi Dupas; Cornélia Rumpel; Alexandra Crème; Ophélie Fovet; Chantal Gascuel-Odoux; Laurent Jeanneau; Guillaume Humbert; Patrice Petitjean

doi:10.1016/j.scitotenv.2017.04.028

Release of dissolved phosphorus from riparian wetlands: Evidence for complex interactions among hydroclimate variability, topography and soil properties

Sci Total Environ. 2017 Nov 15:598:421-431. doi: 10.1016/j.scitotenv.2017.04.028. Epub 2017 Apr 25.

Authors

Affiliations

¹ Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Campus de Beaulieu, 35042 Rennes, France. Electronic address: gu.sen@univ-rennes1.fr.
² Observatoire des Sciences de l'Univers de Rennes, CNRS, UMR 6118 Géosciences Rennes, Campus de Beaulieu, 35042 Rennes, France.
³ INRA, UMR 1069 Sol Agro et hydrosystème Spatialisation, 35042 Rennes, France; Department Aquatic Ecosystem Analysis, UFZ - Helmholtz-Centre for Environmental Research, Brueckstr. 3a, 39114 Magdeburg, Germany.
⁴ CNRS, Institut d'Ecologie et des Sciences de l'Environnement de Paris, Campus AgroParisTech, 78850 Thiverval-Grignon, France.
⁵ INRA, UMR 1069 Sol Agro et hydrosystème Spatialisation, 35042 Rennes, France.

PMID: 28448934
DOI: 10.1016/j.scitotenv.2017.04.028

Abstract

In agricultural landscapes, establishment of vegetated buffer zones in riparian wetlands (RWs) is promoted to decrease phosphorus (P) emissions because RWs can trap particulate P from upslope fields. However, long-term accumulation of P risks the release of dissolved P, since the unstable hydrological conditions in these zones may mobilize accumulated particulate P by transforming it into a mobile dissolved P species. This study evaluates how hydroclimate variability, topography and soil properties interact and influence this mobilization, using a three-year dataset of molybdate-reactive dissolved P (MRDP) and total dissolved P (TDP) concentrations in soil water from two RWs located in an agricultural catchment in western France (Kervidy-Naizin), along with stream P concentrations. Two main drivers of seasonal dissolved P release were identified: i) soil rewetting during water-table rise after dry periods and ii) reductive dissolution of soil Fe (hydr)oxides during prolonged water saturation periods. These mechanisms were shown to vary greatly in space (according to topography) and time (according to intra- and interannual hydroclimate variability). The concentration and speciation of the released dissolved P also varied spatially depending on soil chemistry and local topography. Comparison of sites revealed a similar correlation between soil P speciation (percentage of organic P ranging from 35-70%) and the concentration and speciation of the released P (MRDP from <0.10 to 0.40mgl^-1; percentage of MRDP in TDP from 25-70%). These differences propagated to stream water, suggesting that the two RWs investigated were the main sources of dissolved P to streams. RWs can be critical areas due to their ability to biogeochemically transform the accumulated P in these zones into highly mobile and highly bioavailable dissolved P forms. Hydroclimate variability, local topography and soil chemistry must be considered to decrease the risk of remobilizing legacy soil P when establishing riparian buffer zones in agricultural landscapes.

Keywords: Biogeochemical processes; Groundwater; Hydroclimate; Phosphorus; Riparian wetland; Topography.