Abstract. Surface sediments from 30 mountain lakes in south-eastern Switzerland (Engadine, Grisons) were analysed for subfossil diatom, chironomid, and cladoceran assemblages. Ordination techniques were used to identify relevant physical and chemical environmental parameters that best explain the distribution of these biota in the studied lakes. Diatom assemblage composition showed a strong relationship with physical (e.g., lake depth, temperature, organic content of surface sediments) and chemical variables (e.g., lake-water pH, alkalinity, silica concentration). The greatest variance in chironomid and cladoceran assemblages is explained by dissolved organic carbon (DOC) content of lake water, temperature, and the organic content of surface sediments, all parameters which are highly correlated with lake elevation. Increasing lake depth is refl ected in diatom and cladoceran assemblages by higher percentages of planktonic species, whereas chironomid assemblages in the deep Engadine lakes are characterised by a high proportion of lotic taxa. In contrast to similar studies in the Northern and Southern Alps, subfossil assemblages in the Engadine mountain lakes showed a strong relationship with DOC, which in these weakly buffered lakes is negatively correlated with altitude. According to our fi ndings, chironomid and cladocera remains have a considerable potential as quantitative palaeotemperature indicators in the Engadine area. This potential is somewhat weaker for diatoms which seem to be more strongly infl uenced by water chemistry and lake bathymetry.

In our study, we focused on littoral Cladocera living and feeding in shallow shore parts of 46 mountain lakes in the Tatra Mountains (Slovakia and Poland). The studied lakes underwent a major acidification event in the 1980s and are now in the process of recovery. Lakes were divided into three categories based on their sensitivity to acidification: 5 extremely sensitive (ES), 11 acid sensitive (AS), and 30 non-sensitive (NS) lakes. In our study, we included historical data from the literature, and data from sediment core and littoral samples, which together represent the evolution of the littoral communities from a pre-industrial period up to the present. In total, 11 littoral species were found belonging to three cladoceran families. Most of the species were members of the family Chydoridae: Alona affinis, A. quadrangularis, A. rectangula, A. guttata, Acroperus harpae, Alonella excisa, A. nana, Chydorus sphaericus, and Eurycercus lamellatus. One species belonged to each family Daphniidae (Ceriodaphnia quadrangula) and Polyphemidae (Polyphemus pediculus). The most numerous littoral taxa were Alona affinis, Acroperus harpae, and Chydorus sphaericus. All species reacted to decreased pH levels during peak acidification in the 1980s by disappearing from most of the lakes of all categories; the only persisting species was Chydorus sphaericus. Most species returned to the lakes when pH started to increase in the 1990s, although their return was noticeably slower in AS lakes. Alona quadrangularis decreased its distribution range over the studied period; Polyphemus pediculus was mostly detected in the 1910s only. The number of species was highest in all lake categories when dwarf pine was present in the lake catchment. On the whole, the littoral community was richest in NS lakes.