Dynamics and Biogeochemistry of River Corridors and Wetlands (Proceedings of symposium S4 held during the Seventh IAHS Scientific Assembly at Foz do Iguaçu, Brazil, April 2005). IAHS Publ. 294, 2005, 37-45

1 Catchment Science Centre, Groundwater Protection and Restoration Group, Department of Civil and Structural Engineering, University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield S1 3JD, UK

2 The Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK

3 Department of Geography, Queen Mary, University of London, Mile End, London E1 4NS, UK

Abstract Phosphorus (P) is generally viewed as the main element driving eutrophication risk in freshwaters. In this paper we examine the release of P from riparian wetland sediments to pore water and surface water. The research was conducted at Strumpshaw Fen in the Norfolk Broads region of the UK. We show that substantial quantities of bioavailable P may be released into solution from the sediments at Strumpshaw Fen. This release is physicochemically controlled, and involves the reductive-dissolution of P complexed at the surface of ferric hydroxide. Maximum concentrations of molybdate-reactive P (MRP) in 0.45 m m filtered solutions can reach up to 1 mg l^-1 P in surface water, and up to 4.5 mg l^-1 P in pore water. Such high concentrations of MRP indicate that riparian wetlands may act as sources of P with the potential to threaten the chemical and ecological quality of receiving water bodies.