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- Kubeneck, L. Joëlle, et al.
(författare)
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Phosphorus burial in vivianite-type minerals in methane-rich coastal sediments
- 2021
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 231
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Tidskriftsartikel (refereegranskat)abstract
- Sediments are a key sink for phosphorus (P) in coastal systems. This allows coastal areas to act as a filter for P that is transported from land to sea. Recent work suggests that vivianite-type ferrous iron (Fe(II))-P minerals may be more important as a sink for P in coastal sediments than previously thought. Here, we investigate the occurrence of such vivianite-type minerals in sediments of three eutrophic coastal sites with contrasting dynamics with respect to iron (Fe) and sulfur (S), covering a salinity range of 0 to 7. We only find authigenic vivianite-type minerals at the low and intermediate salinity sites, where Fe is available in excess over sulfide production. Sequential extractions combined with SEM-EDS and μXRF analysis point towards substitution of Fe in vivianite-type minerals by other transition metal cations such as magnesium and manganese, suggesting potentially different formation pathways modulated by metal cation availability. Our results suggest that vivianite-type minerals may act as a key sink for P in sediments of many other brackish coastal systems. Climate change-driven modulations of coastal bottom water salinity, and hence, Fe versus S availability in the sediment, may alter the role of vivianite-type minerals as a P burial sink over the coming decades. Model projections for the Baltic Sea point towards increased river input and freshening of coastal waters, which could enhance P burial. In contrast, sea level rise in the Chesapeake Bay area is expected to lead to an increase in bottom water salinity and this could lower rates of P burial or even liberate currently buried P, thereby enhancing eutrophication.
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| 2. |
- Van Helmond, Niels A.G.M., et al.
(författare)
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Removal of phosphorus and nitrogen in sediments of the eutrophic Stockholm archipelago, Baltic Sea
- 2020
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 17:10, s. 2745-2766
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Tidskriftsartikel (refereegranskat)abstract
- Coastal systems can act as filters for anthropogenic nutrient input into marine environments. Here, we assess the processes controlling the removal of phosphorus (P) and nitrogen (N) for four sites in the eutrophic Stockholm archipelago. Bottom water concentrations of oxygen (O2) and P are inversely correlated. This is attributed to the seasonal release of P from iron-oxide-bound (Fe-oxidebound) P in surface sediments and from degrading organic matter. The abundant presence of sulfide in the pore water and its high upward flux towards the sediment surface (4 to 8 mmolm-2 d-1), linked to prior deposition of organic-rich sediments in a low-O2 setting ("legacy of hypoxia"), hinder the formation of a larger Fe-oxide-bound P pool in winter. This is most pronounced at sites where water column mixing is naturally relatively low and where low bottom water O2 concentrations prevail in summer. Burial rates of P are high at all sites (0.03 0.3 molm-2 yr-1), a combined result of high sedimentation rates (0.5 to 3.5 cm yr-1) and high sedimentary P at depth (30 to 50 mol g-1). Sedimentary P is dominated by Fe-bound P and organic P at the sediment surface and by organic P, authigenic Ca-P and detrital P at depth. Apart from one site in the inner archipelago, where a vivianite-type Fe(II)-P mineral is likely present at depth, there is little evidence for sink switching of organic or Feoxide- bound P to authigenic P minerals. Denitrification is the major benthic nitrate-reducing process at all sites (0.09 to 1.7 mmolm-2 d-1) with rates decreasing seaward from the inner to outer archipelago. Our results explain how sediments in this eutrophic coastal system can remove P through burial at a relatively high rate, regardless of whether the bottom waters are oxic or (frequently) hypoxic. Our results suggest that benthic N processes undergo annual cycles of removal and recycling in response to hypoxic conditions. Further nutrient load reductions are expected to contribute to the recovery of the eutrophic Stockholm archipelago from hypoxia. Based on the dominant pathways of P and N removal identified in this study, it is expected that the sediments will continue to remove part of the P and N loads.
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