Distribution of rare earth elements and yttrium in fjord waters: evidence for geogenic and anthropogenic sources in Norwegian fjords

The picturesque fjords along Norway’s coastline play an important role for the country’s tourism and aquaculture industry. Despite their economic importance for the country, surprisingly little is known about the occurrence and behaviour of rare earths and yttrium (REY) in Norwegian fjords. We will present dissolved (0.2 µm-filtered) REY data for different sites and depths from several Norwegian fjords with focus on the Seaward Basin in the Trondheimfjord. Our sample set is complemented by data for rivers feeding into the fjord (Orkla, Gaula, Nidelva, Stjørdalselva) and for two waste water treatment plants (WWTPs) releasing their effluents into the Seaward Basin.

All fjordwaters show REY concentrations in a similar range with decreasing concentrations with increasing water depth. Their shale-normalised (_SN) REY patterns share common features with typical seawater patterns, however, light and middle REY are less fractionated compared to open-ocean water. Samples taken close to river mouths have notably higher REY concentrations in surface layers with very flat REY_SN patterns, similar to the rivers investigated and characteristic of boreal rivers with a high nanoparticle and colloid load. In contrast, the truly dissolved (< 1 kDa) REY in river water of the Nidelva show patterns similar to those of seawater.

The effluents of the WWTPs carry a strong anthropogenic Gd signal into the Trondheimfjord, which results from the application of Gd-based contrast agents in magnetic resonance imaging. However, no anomalous enrichment of Gd is detected in the Seaward Basin itself because the large water volume immediately dilutes and obliterates the anthropogenic signal.