Phosphorus Cycling and Burial in Sediments of a Seasonally Hypoxic Marine Basin |
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| Authors: | Fatimah Sulu-Gambari Mathilde Hagens Thilo Behrends Dorina Seitaj Filip J R Meysman Jack Middelburg Caroline P Slomp |
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| Institution: | 1.Department of Earth Sciences (Geochemistry), Faculty of Geosciences,Utrecht University,Utrecht,the Netherlands;2.Department of Estuarine and Delta Systems,NIOZ Royal Netherlands Institute for Sea Research,Yerseke,the Netherlands;3.Utrecht University,Utrecht,the Netherlands;4.Department of Analytical, Environmental and Geochemistry,Vrije Universiteit Brussel (VUB),Brussels,Belgium |
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| Abstract: | Recycling of phosphorus (P) from sediments contributes to the development of bottom-water hypoxia in many coastal systems. Here, we present results of a year-long assessment of P dynamics in sediments of a seasonally hypoxic coastal marine basin (Lake Grevelingen, the Netherlands) in 2012. Sequential phosphorus extractions (SEDEX) and X-ray absorption spectroscopy (XAS) indicate that P was adsorbed to Fe-(III)-(oxyhydr)oxides when cable bacteria were active in the surface sediments in spring. With the onset of summer hypoxia, sulphide-induced dissolution of the Fe-(III)-(oxyhydr)oxides led to P release to the pore water and overlying water. The similarity in authigenic Ca-P concentrations in the sediment and suspended matter suggest that Ca-P is not formed in situ. The P burial efficiency was ≤ 32%. Hypoxia-driven sedimentary P recycling had a major impact on the water-column chemistry in the basin in 2012. Water-column monitoring data indicate up to ninefold higher surface water concentrations of phosphate in the basin in the late 1970s and a stronger hypoxia-driven seasonal P release from the sediment. The amplified release of P from the sediment in the past is attributed to the presence of a larger pool of Fe-bound P in the basin prior to the first onset of hypoxia. Given that P is not limiting, primary production in the basin has not been affected by the decadal changes in P availability and recycling over the past 40 years. The changes in P dynamics on decadal time scales were not recorded in sediment profiles of total P or organic C/total P. |
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