28Arctic freshwater ponds are typically pristine and oligotrophic, however, seabird biovectors can markedly alter 29 water quality via enrichment with marine-derived nutrients and bioaccumulated metals. These ornithogenic inputs 30 can be the dominant factor structuring aquatic biota and the surrounding island flora. Here, we measured a suite 31 of limnological water chemistry variables and sediment geochemistry from 21 freshwater ponds influenced by 32 Common Eiders (Somateria mollissima) in Hudson Strait, near the northern communities of Cape Dorset (Nunavut) 33 and Ivujivik (Quebec). Nest counts and sedimentary δ 15 N values were used as proxies of bird abundance. Nutrient-34 rich guano from the nesting eiders visibly promoted the growth of catchment vegetation. Elevated metal (Al, Cd, 35 Zn), metalloid (Se), and nutrient concentrations (N, P) in the water of eider-affected sites were recorded (Sign test;36 p = 0.004), but the proximity of many sites to the coast meant that variables related to ocean spray (conductivity, 37 Na + , Mg 2+ , Cl -, Sr) confounded the effects of birds on pond water chemistry. In contrast, sediment geochemistry 38 appeared to more clearly characterize sites according to the level of eider activity in their catchments by tracking 39 Pb, Cd, N, and P sedimentary concentrations (Sign test; p = 0.02). These results have direct implications for 40 reconstructing historical eider population trends using sediment archives, which is necessary to inform effective 41 conservation management strategies. 42

Seabirds are thought to provide ecological services such as the movement of nutrients between marine and terrestrial ecosystems, which may be especially critical to productivity and diversity in nutrient-poor environments. Most Arctic ecosystems are unaffected by local human impacts and are naturally nutrient poor and especially sensitive to warming. Here, we assessed the effects of nesting common eider ducks (Somateria mollissima) on soil, vegetation, and pond sediments on island archipelagoes in Hudson Strait between Nunavut and Québec, Canada. Soil, moss, and pond sediments were significantly higher in nitrogen on islands with large numbers of nesting eiders compared to sites with no nesting birds. The highest concentrations of nitrogen in soils and moss occurred at the margins of ponds on eider islands, which correspond to the areas of highest eider use. δ15N and δ34S values in soils, moss, and sediments indicated substantial marine-derived organic matter inputs at the higher nutrient sites. We propose that by foraging on coastal marine benthic invertebrates and returning to islands to nest, eider ducks bio-transport and concentrate marine-derived nutrients to their colony islands, fertilizing Arctic island ecosystems in the process. As common eiders nest on thousands of low to mid-latitude islands throughout the circumpolar Arctic, these nutrient inputs likely dramatically affect biota and ecosystem functioning throughout the tundra biome.

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