Changes in subfossil chironomid and cladoceran assemblages along water depth in Swiss lowland lakes

Abstract Aquatic invertebrate remains in lake sediments can potentially be used to provide information on past changes in water depth based on sediment records. However, only limited data are available on the distribution of invertebrate remains across varying water depths in stratified Central European lowland lakes. We analysed fossil chironomid and cladoceran assemblages from surface sediments sampled along ten transects of six Swiss lowland lakes with the aim of exploring the relationship between the distribution of species assemblages of these indicator groups and water depth. Subfossil assemblages of chironomids and cladocerans in the surface sediments differed markedly between and within the studied lakes of different sizes, depths, and trophic states. For nine of ten transects, relatively strong shifts in the assemblages associated with water depth were detected. However, the strength and pattern of change in assemblages along the depth gradient differed between cladocerans and chironomids. Cladoceran assemblages showed clear changes along the entire surveyed depth gradient, with more pronounced changes in the shallower samples. On the contrary, the chironomid assemblages, which also showed notable changes across the entire depth gradient, showed more pronounced changes across the estimated thermocline position and in the deeper transect parts. These results imply that the choice of indicator group in future studies aiming to reconstruct changes in water depth based on chitinous aquatic invertebrate remains could depend on the expected palaeowater depth, and that both groups analysed together can be expected to react more sensitively over a broader range of water depths than one of the groups analysed individually.