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.

沉积物是沿海系统中磷（P）的主要汇。这使得沿海地区可以作为从陆地运输到海洋的磷的过滤器。最近的工作表明，维维石型亚铁（Fe（II））-P矿物作为沿海沉积物中P的吸收剂可能比以前认为的更为重要。在这里，我们调查了3种富营养化沿海地区沉积物中这种云母型矿物的发生，这些矿体相对于铁（Fe）和硫（S）的动态变化相反，盐度范围为0至7。我们仅发现自生的云母-低盐度和中等盐度的矿物，其中铁的含量超过硫化物的生产。连续萃取与SEM-EDS和μXRF分析相结合，表明在Vivianite型矿物中的Fe被其他过渡金属阳离子（例如镁和锰）取代，这表明潜在的不同形成途径受到金属阳离子可用性的调节。我们的研究结果表明，Vivianite型矿物可能是许多其他咸淡沿海系统沉积物中P的关键汇。气候变化驱动的沿海底水盐度调节，以及沉积物中铁与硫的可利用性可能会在未来几十年内改变vi石类矿物作为P葬库的作用。对波罗的海的模型预测指出，河水输入量的增加和沿海水域的新鲜化将增加磷的埋藏量。相比之下，