Characterizing spatial and temporal variation in stable hydrogen isotopes (δ 2 H) between two distinct lentic freshwater food webs

We investigated variability in δ 2 H values for two aquatic food webs involving avian consumers (lesser scaup, Aythya affinis Eyton and tree swallow, Tachycineta bicolor Vieillot) foraging from boreal lakes in the Yukon Flats (Alaska, United States) and wetlands in the Prairie Pothole Region (Saskatchewan, Canada), respectively. Generalized linear mixed-effects models were used to decompose sources of variation in water and tissue δ 2 H. We found inter-annual variation in boreal lakes δ 2 H W influenced by surface water connectivity (e.g., open vs. closed basins) and distance to the nearest river. Prairie pothole wetland δ 2 H W displayed intra-annual variability dictated by wetland type (e.g., semipermanent and seasonal) with a range greater than 60‰, which incrementally increased over the summer months. Variance in invertebrate δ 2 H I was explained by taxonomic category, but factors such as the relative distance to the nearest river (boreal model) and wetland type (prairie model) should be explored in future studies. Lesser scaup duckling feather δ 2 H F displayed inter-annual and spatial variability with the top model explaining 86% of the overall variation, including the following fixed effects: basin type (open/closed), year, and calendar date of sampling. Similar spatial patterns with known lesser scaup prey items, such as relative site distance to the nearest river, most closely aligned with Amphipoda δ 2 H I . Variation in tree swallow nestling δ 2 H F was attributed to sampling date with the top model explaining 38% of overall variation, while sampled prey items (e.g., Chironomidae) did not closely follow this pattern. Our findings quantify the extreme temporal and spatial δ 2 H variability in food webs fundamentally linked to seasonal evaporative effects in shallow lentic aquatic ecosystems.