Drivers and consequences of shifting seasons in lake ecosystems

Background/Question/Methods: As is the case in terrestrial ecosystems, seasonal events in freshwaters are also highly sensitive to climate change. However, there are important questions regarding how seasonality is quantified in these systems, and the role of non-climate drivers in also bringing about phenological change. Here, I present analyses of plankton and fish seasonal events using data from a multi-decadal monitoring scheme in the English Lake District. These analyses quantify the extent to which seasonality has shifted at different levels in the food chain, and what potential drivers and consequences of these shifts might be.

Results/Conclusions: Data from the Cumbrian lakes show that seasonal events such as plankton blooms and fish spawning have been shifting earlier at multi-decadal scales, and that rates of change vary considerably among species. We show that these changes are correlated with rising water temperatures and other environmental stressors, such as nutrient enrichment. Furthermore, rates of change vary systematically with species traits, but only in part, with much variation within trait groupings. While we can detect effects of mismatching in freshwaters, such as reductions in fish recruitment, there are still many unknowns. Key among these are impacts at the scale of food webs based upon a variable mixture of resources, rather than simplified food chains, and the potential for trophic generalism to offset negative consequences for consumers. Future research on mismatching in fresh waters should combine experimentation, modelling and monitoring with a clear mechanistic framework that articulates likely ecosystem-scale effects of changing seasonality.