Rare earth elements and yttrium (REY) in fjord waters: Comparison between seawater in the Trondheimfjord (Norway), its local riverine REY sources and the North Atlantic

Abstract

The rare earth elements and yttrium (REY) are critical resources increasingly released into the environment due to their pivotal role for an ever-growing number of high-tech products and processes. Fjords, worldwide and particularly in Norway, are not only of high importance for biodiversity but they also have great economic value. Knowledge on the distribution of REY in Norwegian coastal and riverine waters is, however, surprisingly scarce. We here report REY data for water samples from depth profiles from ten stations in the Trondheimfjord, one of Norway’s largest fjords, several Norwegian rivers, and two wastewater treatment plants in Trondheim.Our results show that water from different locations in the Trondheimfjord yield similar REY concentrations that correlate well with dissolved organic carbon. The deepest sample at each station shows the lowest REY concentrations. The shale-normalised (SN) REY patterns of the fjord waters resemble those of North Atlantic seawater, but can be distinguished from open-ocean water by the smaller fractionation between light and middle REY (PrSN/TbSN ≥ 0.5). Stations in the vicinity of a river mouth show considerably higher REY concentrations at shallow depths. The respective REYSN patterns resemble the typically flat patterns of boreal rivers that are often rich in nanoparticles and colloids (NPCs). The REYSN patterns of the four rivers investigated (Nidelva, Orkla, Gaula, Stjørdalselva) show the features of the shallow(er) fjord water samples but have even higher REY concentrations. Ultrafiltration (< 1 kDa) data for the Nidelva corroborate that the typical “REYSN seawater signature” is in fact already present in freshwater where it is, however, usually hidden by the REY associated with NPCs. The local wastewater treatment plants release anthropogenic Gd (from contrast agents used in magnetic resonance imaging) into the Trondheimfjord, but this signal is immediately diluted and thus is not observed in the REYSN patterns of the fjord water. However, our results in general suggest that the slightly elevated Gd/Tb ratios observed in almost all fjord waters relative to North Atlantic marine water may rather be due to the presence of anthropogenic Gd in the southern North Sea and the Baltic Sea, corroborating that anthropogenic Gd can be applied as a sensitive far-field watermass tracer.