Selenium trophodynamics in Lahontan cutthroat trout and its aquatic and terrestrial prey from the unpolluted saline-alkaline Omak Lake

Selenium (Se) is an essential micronutrient that, in excess, is toxic. In water, Se is relatively mobile, and toxicity occurs through transfers across trophic levels in food webs. Se trophodynamics in unpolluted alkaline watersheds remain understudied. Saline-alkaline lakes may expedite Se speciation, potentially facilitating its uptake and assimilation. Se was investigated in the unpolluted Omak Lake, the largest saline-alkaline lake in Washington state, U.S., which hosts Lahontan cutthroat trout (LCT, Oncorhynchus henshawi ) sport fishery. This research aimed to: (1) explore Se across LCT’s different life stages, (2) investigate Se trophodynamics in LCT, (3) examine LCT’s feeding and prey habitats, potentially influencing Se transfer, and (4) explore Se-content differences between aquatic and terrestrial prey. Total-Se was assayed via ICP-MS, and stable isotope analysis (δ 15 N) assigned trophic positions. Se concentrations in all fish and invertebrates (0.01-2.54 µg g -1 dry weight [dw]) were below protective thresholds, as expected in unpolluted waters. Trophic transfer factors for LCT ranged from 1.17 to 1.61 (Se: 0.1-0.69 µg g -1 dw) and were likely influenced by specific prey species, including fish and both aquatic and terrestrial invertebrates. For example, Sculpin ( Cottus spp. ) contained up to 2.54 µg g -1 dw, odonates up to 0.70 µg g -1 dw, and hymenopterans up to 0.92 µg g -1 dw. Se-levels in Omak Lake confirmed its unpolluted status. Se-content variability among benthic and littoral species suggested that Se-transfers were prey-specific. Terrestrial invertebrates may contribute to Se inputs into the lake. These findings provided insights into Se trophodynamics within remote, pristine, saline-alkaline lakes.