Contrasting effects of little auk colonies on potentially toxic and rare earth elements in Arctic soils.

Seabirds like little auks (Alle alle) transfer chemical elements to terrestrial environments through faeces and other biological material, enriching Arctic soils with nutrients, organic matter and marine-derived contaminants. We quantified Potentially Toxic Elements (PTEs) and Rare Earth Elements (REEs) in seabird-influenced soils at varying distances from colonies at four Svalbard locations: Hornsund, Isfjorden, Aasefjellet and Magdalenefjorden, and examined their relationships with soil physicochemical properties (moisture, pH, conductivity, total nitrogen and carbon content). Contrary to our initial expectations, most PTEs (13 of 19) and REEs (12 of 13) had lower concentrations in seabird-influenced soils compared to control areas, suggesting that the presence of little auks may contribute to their reduction in soil. Only certain PTEs (e.g., Co, Ni, Sr, Se, V, Zn) and one REE (Sc) showed elevated concentrations in some colonies. Despite the nutrient gradient, distance from colonies did not significantly affect elemental concentrations. Seabird presence accounted for a small but significant portion of the variance in PTEs (2.5 %) and REEs (3.2 %), while geographical location explained the greatest proportion of variation (41 % and 52 %, respectively). Hornsund, Aasefjellet and Magdalenefjorden showed significant differences in element concentrations between seabird and control soils, whereas Isfjorden - hosting a smaller colony - showed minimal differences. Soil properties were strong predictors of elemental variability: pH, moisture and total nitrogen explained almost 24 % of PTE variability, while conductivity and total nitrogen explained 14 % of REE variability. Our findings suggest that seabird activity does not universally increase soil element concentrations, and that local environmental conditions and biogeochemistry play dominant roles in shaping elemental patterns. Further research on soil-plant transfer of PTEs and REEs is recommended to clarify the mechanisms driving elemental dynamics in Arctic ecosystems.