1. A number of studies have shown that spring biological events have advanced in recent decades,\udand concluded that these changes in phenology are driven by climatic change. Freshwater lakes are\udsensitive indicators of climate change, where direct effects of climate on physical processes can affect\udthe seasonal timing of planktonic communities. However, many lake ecosystems have also\udexperienced long-term changes in other ecological pressures that could affect phenology.\ud2. In this study, long-term (1955–2003) physical, chemical and biological data from Windermere\ud(UK) were analysed in order to assess the relative effects of a number of coincident pressures on\udthe phenology of two spring diatom taxa. The analysis provides a detailed case study, highlighting\udthe species-specific drivers that affect the phenology of dominant members of the phytoplankton\udcommunity.\ud3. The results showed that, whilst the spring peak biomass of one taxon (Cyclotella) appeared to be advancing as a result of earlier thermal stratification, the advancement of the other (Asterionella) was closely linked with both progressive nutrient enrichment and lake warming. Furthermore, nutrient enrichment explained more variation in phenology than water temperature. Both taxa also\udreached their peak abundance earlier when the over wintering biomass at the end of the previous\udyear was higher.\ud4. Patterns of change in phenology and ecological pressures were markedly nonlinear in time, as\udwere the effects of some drivers of seasonal timing. This highlighted a need to relax the restriction\udof linearity in our analyses of biological seasonality.\ud5. Synthesis. Phenological shifts may be brought about by local processes, such as eutrophication,\udas well as by climate change. Even in the same ecosystem different mechanisms may alter the phenology\udof different species.
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