Functional group classification based on the morphological,physiological and ecological characteristics of diatoms is advanced in describing the tolerance and sensibility of diatoms to environmental stressors.In this study,we examined the spatial distribution of diatom functional groups in surface sediments of Haixi Lake and explored the relationships between diatom distributions and environmental variables using multivariate analyses.Principal components analysis (PCA) and redundancy analysis (RDA) results showed that water depth and total nitrogen (TN) were the key drivers for the heterogeneous distribution of diatom functional groups.Water depth of ca.8 m was the threshold depth in influencing diatom functional group structures linking with thermal stratification.These results provided a basis for fossil record interpretation of the short core.Diatom functional groups fluctuated over the last century,in keeping with mean annual temperature,sediment TN,and median grain size.Climate warming,accelerated nutrient enrichment and intensified hydrological changes led to the dominance of functional group D,MP and P.Additionally,climate warming and nutrient enrichment led to increased diatom functional group diversity,while increased water depth (led by damming and reservoir reinforcement) contributed to diversity loss around 1957 and 1990 AD,respectively.