The role of grain dissolution and diagenetic mineral precipitation in the cycling of metals and phosphorus: A study of a contaminated urban freshwater sediment

The most abundant authigenic mineral in the sediments is vivianite (Fe3(PO4)2 · 8H2O), containing a significant level of redlingite (Mn32+(PO4)2·8H2O), with minor framboidal pyrite (FeS2). Electron microprobe analysis shows the vivianite to contain Zn, Cu and Pb, suggesting that vivianite acts as a long-term sink for these metals in this sediment. This implies that authigenic vivianite in freshwater sediments may act as a long-term sink for metals, in a similar manner to sulphides in marine sediments. This study highlights that the nature of detrital and diagenetic mineralogy, in addition to porewater and sediment chemistry, needs to be considered in assessing contaminated sediments.