title: Internal Loading and Redox Cycling of Sediment Iron Explain Reactive Phosphorus Concentrations in Lowland Rivers.
abstract: The phosphate quality standards in the lowland rivers of Flanders (northern Belgium) are exceeded in over 80% of the sampling sites. The factors affecting the molybdate reactive P (MRP) in these waters were analyzed using the data of the past decade (>200 000 observations). The average MRP concentration in summer exceeds that winter by factor 3. This seasonal trend is opposite to that of the dissolved oxygen (DO) and nitrate concentrations. The negative correlations between MRP and DO is marked (r = -0.89). The MRP concentrations are geographically unrelated to erosion sensitive areas, to point-source P-emissions or to riverbed sediment P concentration. Instead, MRP concentrations significantly increase with increasing sediment P/Fe concentration ratio (p < 0.01). Laboratory static sediment-water incubations with different DO and temperature treatments confirmed suspected mechanisms: at low DO in water (<4 mg L-1), reductive dissolution of ferric Fe oxides was associated with mobilization of P to the water column from sediments with a molar P/Fe ratio >0.4. In contrast, no such release was found from sediments with lower P/Fe irrespective of temperature and DO treatments. This study suggests that internal loading of the legacy P in the sediments explains the MRP concentrations which are most pronounced at low DO concentrations and in regions where the P/Fe ratio in sediment is large.
authors.affiliation: Division Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
authors.forename: Erik
authors.identifier: 0000-0003-3054-2444
authors.initials: E
authors.lastname: Smolders
authors.affiliation: Division Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
authors.forename: Evert
authors.initials: E
authors.lastname: Baetens
authors.affiliation: Division Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
authors.forename: Mieke
authors.initials: M
authors.lastname: Verbeeck
authors.affiliation: Division Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
authors.forename: Sophie
authors.initials: S
authors.lastname: Nawara
authors.affiliation: Division Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium.
authors.forename: Jan
authors.initials: J
authors.lastname: Diels
authors.affiliation: Flanders Environment Agency VMM, Dokter De Moorstraat 24-26, B-9300 Aalst, Belgium.
authors.forename: Martin
authors.initials: M
authors.lastname: Verdievel
authors.affiliation: Flanders Environment Agency VMM, Dokter De Moorstraat 24-26, B-9300 Aalst, Belgium.
authors.forename: Bob
authors.initials: B
authors.lastname: Peeters
authors.affiliation: Flanders Environment Agency VMM, Dokter De Moorstraat 24-26, B-9300 Aalst, Belgium.
authors.forename: Ward
authors.initials: W
authors.lastname: De Cooman
authors.affiliation: European Copper Institute, Avenue de Tervuren 168 b-10, B-1150 Brussels, Belgium.
authors.forename: Stijn
authors.initials: S
authors.lastname: Baken
mesh_terms: D019015:Geologic Sediments; D007501:Iron; D010084:Oxidation-Reduction; D010758:Phosphorus; D045483:Rivers; D014874:Water Pollutants, Chemical
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus; D007501:Iron