Phosphorus flux from wetland ditch sediments

► Bottom sediment-bound phosphorus (P) levels in basin fen drainage ditches were comparable with those in eutrophic lakes. ► Diffusive flux of the internally bound P to the ditch water represents a serious threat to water quality. ► Spatial variation, both in sediment P status and flux values, was largely explained by the proximity of drainage inputs. ► Peak P values were recorded immediately downstream of the drainage pump in the (former agricultural) wetland reserve.