title: Phosphorus flux from wetland ditch sediments.
abstract: The accumulation of phosphorus (P) in the bottom sediment of field drainage ditches poses a threat to the ecology both of the ditch water and downstream water courses. We investigated the amounts, forms and internal loading of sediment-bound P along two drainage ditches that regulate water levels in a basin fen (~200 ha) supporting a mixture of restored wetland and drained agricultural fields. Water levels in the Lady's Drove Rhyne are currently managed to enhance the biodiversity of the wetland (Catcott Lows Reserve - an area formerly cultivated for arable crop production); whereas, the East Ditch is managed to drain adjoining land that remains under arable and livestock production. Laboratory-based chemical fractionation schemes were used to characterise the forms and potential mobility of the sediment-bound P, whilst pore-water equilibrators were employed in situ to evaluate the diffusive flux of P through the sediment-water column, and to characterise the corresponding redox conditions. Along both ditches, sediment pore-water profiles indicated conditions ranging from weakly to very reducing conditions with increasing depth, and net fluxes of P from the sediment to overlying water. P flux values ranged from 0.33 to 1.30 mg m(-2) day(-1). Both the degree of P saturation (DPS) of the sediment and NaOH extractable (Fe/Al-bound) P correlated significantly (P<0.05) with P flux. Both in the wetland and agricultural ditches, by far the highest values for P flux were recorded at sites closest to points of drainage water entry from the corresponding, adjoining land. Although the P flux data were obtained from only a single sampling event, this study highlights the contribution of historical as well as ongoing agricultural land use on the sustained elevated P status of ditch sediments in lowland catchments.
authors.affiliation: Department of Geography and Environmental Science, School of Human and Environmental Sciences, The University of Reading, Berkshire RG6 6DW, UK.
authors.forename: C R
authors.initials: CR
authors.lastname: Hill
authors.forename: J S
authors.initials: JS
authors.lastname: Robinson
mesh_terms: D000383:Agriculture; D004739:England; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000032:analysis / Q000737:chemistry*; D010758:Phosphorus / Q000032:analysis / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry; D053833:Wetlands
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus