Journal
MARINE CHEMISTRY
Volume 231, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.marchem.2021.103948
Keywords
Phosphorus cycle; Vivianite; Iron; Sediments
Categories
Funding
- NWO-Vici grant [865.13.005]
- Netherlands Earth System Science Center (NESSC)
- Swedish Agency for Marine and Water Management (Havs-och vattenmyndigheten, DNR 1960-2018)
- EU Seventh Framework Programme [2112932-1]
- Formas (Sweden) (BONUS/COCOA) [2112932-1]
- Olaf Schuiling Fund
- Utrecht University
- Horn Point Laboratory
- NSF [OCE1756877]
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Recent studies have found that vivianite-type minerals may play a significant role in the sink for phosphorus in eutrophic coastal sediments, particularly in areas with an excess of iron. Analysis comparing the dynamics of iron and sulfur indicates that vivianite-type minerals occur at low and intermediate salinity sites, potentially influenced by the availability of metal cations.
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 mu XRF 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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