Modern distribution of Cladocera in lakes of northern China and western Mongolia and its environmental implications

• The first large-scale biogeographical investigation of cladocerans in lakes in northern China and western Mongolia. • Lake level, nutrient, and salinity are the main controls of the structure of modern cladoceran communities. • Subfossil cladoceran-inferred lake level reconstructions are consistent with lake areas extracted from Landsat images. Cladocerans are widely distributed in aquatic ecosystems and are sensitive to environmental changes; hence, they are commonly used to trace ecological changes in aquatic environments. However, the distribution of cladocerans in northern China is poorly known. We investigated the occurrence of cladocerans in 136 water bodies (including lakes and reservoirs), with varying hydro-chemical and climatic gradients, in northern China and western Mongolia. We identified 38 cladoceran taxa in the surface sediments of 88 different water bodies, while the remaining lakes, mainly saline, had no cladocerans. The spatial distribution characteristics of cladoceran species and the environmental factors determining their community composition were investigated using canonical correspondence analysis. The results demonstrate that water depth, trophic status, and water salinity were the top three variables influencing the composition of cladoceran taxa. Transfer functions between the surface sediment cladocerans and lake level and nutrient (NH 4 ) levels in 62 lakes (26 lakes lacked environmental data) were established via multivariate statistical analyses. Using the subfossil cladocerans of Jili Lake, lake level and nutrient values were reconstructed for the past 100 years. The results agree overall with the observational data, and they reveal that the changes in the cladoceran community reflected mainly lake level fluctuations before 1988 CE, and mainly nutrient changes thereafter. Our research clarifies, for the first time, the environmental significance of modern Cladocera in the lakes of northern China and western Mongolia, and it provides a foundation for the future reconstruction of long-term changes in the ecological environment of lakes.