Riparian wetlands, sinks or sources of phosphorus in agricultural landscapes?

Abstract

The grass-covered buffer zones placed in riparian wetlands are used for interception and retention of agricultural pollutants, such as phosphorus transferred by erosion from upland fields. The aim of this study is to assess the risk of remobilisation of phosphorus (P) accumulated in the wetlands of a catchment area in Brittany. It consisted in monitoring the concentrations of dissolved P and particulate P in the river and in the wetland soil water. The role of riparian wetlands was then placed in the context of the continuum of P transfer along a catchment (area), taking into account P arrivals from upland plots (by erosion) and the risk of transfer to the river (by solubilisation). As shown by the results of this study, wetlands behave like bioreactors that can convert particulate phosphorus accumulated in grass-covered buffer zones to dissolved phosphorus. Over time, riparian wetlands can evolve from sinks of particulate phosphorus to sources of dissolved phosphorus that is more mobile and more bioavailable.