Rare earth element distribution patterns in Lakes Huron, Erie, and Ontario

Rare earth elements (REE) are increasingly used in industrial applications, consumer electronics and green technologies, but their baseline concentrations and distribution patterns in the North American Great Lakes remain poorly understood. Here, we report dissolved REE concentrations in > 70 surface water samples from Lakes Huron, Erie, and Ontario (2021 and 2022) and assess their spatial distribution patterns and governing biogeochemical controls. Dissolved (<0.22 µm-filtered) REE concentrations were spatially heterogeneous (up to 3 orders-of-magnitude) across the lakes and did not systematically increase upstream-to-downstream through the basin. Nearshore-to-offshore decreases in dissolved REE levels were observed for all lakes and appeared the result of REE adsorption to colloids and subsequent sedimentation. Combined with enrichment of light over heavy REE, particularly in samples closer to shore, our data suggests that riverine input is a major pathway by which REE are loaded to the lakes. Finally, we used normalization and pattern-filling to assess REE anomalies in the lake surface waters. Anomalies for Gd (>20 % across the lakes) were notably higher than those of the other REE but varied significantly spatially, and also showed enrichment nearshore, particularly near urban centers and in Lake Ontario. This work provides new surveillance data to further develop our understanding of REE dynamics in the Great Lakes.