Quantifying impacts of nutrient inputs on basal resources and carbon cycling in Arctic lake food webs

Climate change is altering carbon and nitrogen cycling in freshwater ecosystems, potentially generating ecosystem–climate feedback loops. In the Arctic, warming promotes tundra greening and herbivore expansion. Herbivores supply nitrogen-rich inputs to lakes, modifying basal resource quality, potentially affecting their consumption, carbon transfer within food webs and lake carbon sink capacity. We assessed nine lakes in Svalbard using a space-for-time substitution to evaluate how climate-driven increase in migratory geese affects nutrient enrichment, resource quality, consumer trophic niches, and carbon transfer in lake food webs. Stable isotope analyses and Bayesian mixing models revealed that goose-derived inputs contributed up to 22% of sediment organic matter and increased nitrogen in sediments and vegetation. Improved resource quality drove a dietary shift in the abundant tadpole shrimp Lepidurus arcticus from carnivory in nitrogen-poor lakes to herbivory–detritivory in enriched lakes. Consequently, carbon extraction from basal resources, which act as long-term storage pools, rose from 2.62 ± 0.25 to 1054.93 ± 152.73 mgCm −2 during summer. Isotopic patterns in aquatic vegetation, the contribution of excreta to sediment organic matter, and the trophic response of L. arcticus served as effective ecological indicators of herbivore-mediated organic enrichment and its impact on carbon retention. Our findings suggest that managing migratory birds in the Northern Hemisphere has significant consequences for food webs and carbon cycling in high-latitude freshwater ecosystems, with potential consequences for their carbon sink capacity. Stable isotopes and mixing models applied to sediments and key food-web components could detect causes of organic enrichment and its effects on carbon cycling across diverse lentic ecosystems.