Abstract: Implications of climate change for ecological reference conditions, thresholds and classifiation systems for European lakes
This report focuses on the potential effects of climate change on ecological reference conditions and on ecological responses to nutrient pressures in lakes, especially threshold-type and non-linear responses. Reference conditions and thresholds responses are both fundamental for national ecological classification systems required by the European Water Framework Directive (WFD), for defining reference values and management targets (Good/Moderate class boundary). The potential effects of climate change on these components therefore have important implications for assessment of ecological status and management of lakes.
We have looked at the potential effects of climate change on lakes using an extensive literature review, as well as by analysing palaeolimnological datasets, large-scale European datasets and long-term time series for four individual lakes in Norway, Estonia and Germany (case studies). Climatic changes considered include increased temperature, increased precipitation (and consequently increased content of organic matter) and reduced precipitation (and consequently reduced water levels and increased salinity). The literature review describes the effects of climate change on reference conditions for each biological quality element (BQE; phytoplankton, macrophytes, macroinvertebrates and fish); of these phytoplankton and fish tend to be most sensitive to climate change.
Results from new palaeolimnological analyses suggest that nutrients are the dominant driver of diatom compositional change, and there is insufficient evidence to suggest how reference conditions should be modified in light of climate change. Nonetheless further work is required to explore the relationships between diatoms and climate change in more detail. Analysis of chlorophyll a (chl-a) in European reference lakes suggest that, under future climatic conditions, increased temperature in combination with increased TP (due to increased winter precipitation) will lead to increased chl-a concentrations, although the effects will vary with the lake type (notably humic level). Large-scale analysis of cyanobacteria in North-European lakes, considering both lake typology and climate variables, suggest that the risk of exceeding regulatory thresholds for cyanobacteria will increase with future higher temperature, but also that this tendency may, to some degree, be compensated by increased precipitation.
The four case studies provide more detailed examples of interactions between climatic factors and nutrient pressures on plankton communities, and demonstrate some of the complexity involved in ecological responses to climate change in lakes. Finally, the report provides a set of recommendations for river basin management, considering impacts of climate change on reference conditions and ecological thresholds, and the implications for WFD-based classification systems.
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