Subfossil chironomid assemblage shifts indicate Little Ice Age termination, deforestation, and human impact in a subalpine lake catchment

Abstract

Paleoenvironmental reconstruction was conducted on a short sediment core from a subalpine lake (Low Tatra Mountains, Slovakia) spanning the past ~ 300 years, and aimed to assess the impact of climatic oscillations and the well-documented human activities in the catchment. An analysis of subfossil chironomid remains was applied, supported by a land cover reconstruction using historical maps and orthoimagery. Two main phases of lake development were identified: the first, preceding major anthropogenic pressure and the second, which followed the opening of the first hotel in the lake vicinity in 1950, characterised by massive infrastructure and tourism expansion. The oldest assemblages date to the coldest period of the Little Ice Age (LIA) and were dominated by Derotanypus and Paratanytarsus austriacus-type, indicating very cold and oligotrophic conditions. Warming following the end of LIA caused a gradual shift in the taxonomic composition, with previously dominant taxa disappearing or decreasing in abundance. Dominance of Tanytarsus lugens-type, Zavrelimyia and Heterotrissocladius marcidus-type still reflects relatively cold temperatures and low productivity. Taxonomic composition remained mostly stable until the middle of the twentieth century, when construction work in the catchment caused deforestation, the number of year-round tourists increased, and the lake was dammed to improve conditions for boating and angling. The resulting increased nutrient loading, oxygen depletion and macrophyte development are evident from the rising abundances of taxa tolerant of high trophy. The increase of thermally plastic taxa in the twenty-first century reveals recent climate warming, which will likely only exacerbate the already considerable negative human influence, making lake recovery improbable.