Bird impacts on ecological structure, composition and function in Arctic ponds

Sammendrag

Small ponds and lakes and their surrounding riparian zone are ecological hot spots in the Arctic landscape. They are important for biogeochemical cycling and habitats for terrestrial and aquatic organisms. Arctic birds may have strong impact on these small aquatic ecosystems. In particular, the increasing populations of Arctic geese are strongly associated with ponds and can significantly influence the physico-chemical properties and ecological communities of these waterbodies. Birds supply nutrients via feces, grubbing and physical disturbance leading to increased erosion and run-off. We examined how the pond ecosystems, including phytoplankton and zooplankton communities respond to increased bird impact. Six ponds on Svalbard differentially impacted by birds were sampled in summer 2022. Bird-impacted ponds were characterized by higher nutrient concentrations, especially of phosphorus. They also had significantly higher phytoplankton biomass with a different phytoplankton community. Although mixotrophic species constituted a substantial part of the community in all ponds, we observed increased dominance of both cryptophytes and cyanobacteria at high bird impact. High bird impact was also associated with low metazoan zooplankton abundance and high ciliate abundance. Phytoplankton and metazoan zooplankton taxa richness was much lower in the most impacted pond compared to the other waterbodies. Bird impact did not significantly relate to diffusive CO 2 and methane fluxes from the ponds. Thus, high bird impact was associated with hypereutrophic pond conditions characterized by decreased diversity and a likely stimulation of the microbial loop. The results may hint at some of the future changes in Arctic ecosystems in ponds increasingly influenced by birds.