Climate change and bird impact as drivers of High Arctic pond deterioration

The environmental history since the end of the Little Ice Age of the bird-influenced pond Fugledammen (Hornsund, Svalbard, 77A degrees N) was inferred from a 1-m sediment core using paleolimnological methods. The aim was to track long-term environmental changes and to evaluate the limnological consequences of catchment development in this extremely sensitive landscape. A special focus is given to the impacts of climate change and the observed increase in bird populations in the catchment. The late nineteenth century was characterized by littoral scraping/filtering Cladocera together with vegetation-associated chironomids. The invertebrate community became less diverse towards the twentieth century. Planktonic filter-feeder cladocerans replaced the littoral taxa and collector-gatherers became the most abundant chironomid feeding group. In the more recent sediment layers, invertebrate diversity decreased further but the number of individuals (biomass) increased. Daphnia showed a progressive increase that is typical for similar Arctic ponds in Svalbard, where nutrient loading has increased due to growing bird populations in the catchment. The decreases in vegetation-associated invertebrates, biodiversity, and functional diversity suggest that turbidity has increased and oxygen availability and light penetration decreased in the lake. The paleoecological record is in agreement with the sediment physical and geochemical evidence, indicating that in-lake productivity has strongly increased towards the present. These changes are concurrent with the recent climate warming in Svalbard suggesting that, in addition to longer ice-free season and increased water temperature, the increased air temperatures have various indirect catchment-mediated influences on the aquatic community through changes in bird-population size.