DIAGENETICALLY FORMED VIVIANITE (FE3(PO4)2 · 8H2O) PRESENT IN URBAN POND SEDIMENT: A POTENTIAL MARKER OF ANTHROPOGENIC CONTAMINATION

Lakes are important archives of sedimentological, environmental and neotectonic changes. This study examines lake sediments from NW England to determine local environmental change. Anthropogenic activities have contributed to the records of lakes sediments most notably since the start of the industrial revolution. Lakes have been used previously to derive pollution histories and thus extend the record of modern air quality monitoring (1). Long-term exposure to pollutants are a major health concern for populations in areas of large-scale industrial activity. Levels of particulates generated by industrial activities found in lacustrine sediments, have garnered significant interest as proxies demarcating the Anthropocene (2).

Here, urban pond sediments, from locations near Halton in NW England, an area known for its chemical industry since the early 1800’s, have been investigated. Mineral magnetic studies and ²¹⁰Pb,¹³⁷Cs dating suggests that the sediments are from 1800s-2000s (1). We have analyzed the sediment particle content at selected depths by computer controlled scanning electron microscopy (CCSEM). Changes in particle assemblages have been of principal interest. Abundances of particle types that are considered representative of anthropogenic emissions (metal bearing particles and high temperature industrial spherules) decreased with sediment depth. This anthropogenic record is superimposed on non-industrial inputs to the sediment and is modified by diagenetic alterations in the sediment. At depth, we identified abundant framboidal pyrite (FeS₂) suggesting an anoxic sulfur rich environment, while in surface sediments we observed digenetic vivianite (Fe₃(PO₄)₂ · 8H₂O), indicating an anoxic environment with excess phosphorus. We posit vivianite formation was facilitated by the input of phosphorus into the pond via wash-off of (NPK) fertilizer from local farmland. We consider the presence of vivianite in this type of setting can be used as an anthropogenic activity proxy.

1. Powers, A. and Worsley, A. (2008) Using urban manmade ponds to reconstruct a 150 year history of air pollution in NW England. Env. Geochem. Health, 31:327-338

2. Oldfield, F., Gedye, S.A., Hunt, A. et al. (2015) The magnetic record of fly ash deposition in lake sediments and ombrotrophic peats. Holocene, 25(1):215–225.