We have produced a comprehensive report on the implications of climate change for ecological reference conditions, thresholds and classification systems for European lakes (Deliverable 3-15-16). The aim of the report was to assess impacts of climate change on reference conditions and ecological thresholds in European lakes, to consider the implications for ecological classification systems (reference values, class boundaries and water body types), and to provide recommendations to river basin managers concerning monitoring programmes and programmes of measures. The EC guidance on river basin management in a changing climate (2009) states that "In general, reference conditions and default objectives should not be changed due to climate change projections over the timescales of initial WFD implementation (up to 2027) unless there is overwhelming evidence to do so" (section 5.4.4. Reference sites). Moreover, one should "avoid using climate change as a general justification for relaxing objectives" (EC 2009, section 5.5 Objectives setting), such as relaxing the Good/Moderate boundary. Nevertheless, although national classification systems are already established and intercalibrated by most EU member states, the six-year River Basin Management planning cycle of the WFD offers an opportunity to review the methods for the adequate assessment of the ecological status of EU water bodies. Moreover, the programme of measures within the River Basin Management Plans should take account of climate change effects in order to achieve the WFD Good status target. In addition, impacts of climate change may affect lake ecosystem services and threaten the implementation of the EU Biodiversity Strategy 2020, especially target 2: Maintain and restore ecosystems and their services. Therefore, although not explicitly mentioned in the WFD, synergies between the WFD and the Biodiversity Strategy may contribute to both maintaining and restoring lake ecosystems and the services they provide.
The following key messages can be extracted from the literature review, new data analyses and case studies presented in this report as a basis for recommendations. In general, our results and recommendations support and expand on those given in the EC guidance (2009), by Moe et al. (2010a - see Fig. 7) and by Nõges & Nõges (2014). With respect to impacts of climate change on reference conditions:
i) shifts in in lake type may occur, ii) changes in reference conditions for phytoplankton are expected for species composition, abundance and the onset and frequency of algal blooms, iii) an increase in reference concentrations of nutrients and cyanobacteria are likely to be required, iv) changes in reference conditions for fish, macroinvertebrate and macrophyte taxonomy based metrics are expected. With respect to impacts of climate change on thresholds and classification systems: i) the probability of exceeding the good/moderate boundaries for one or more biological quality elements will increase, ii) the current good/moderate class boundary for macrophyte metrics and the concentration of cyanobacteria will probably be reached at lower nutrient levels in the future, iii) fish metrics that include salmonids may need adjustment of class boundaries, iv) the current good/moderate boundaries for the BQEs could be retained but nutrient standards will need to be more stringent OR the good/moderate boundaries for the BQEs will need to be relaxed and the current nutrient standards retained.
Potential impacts of climate change on components of ecological status classification, for a biological metric (e.g., EQR based on amount of cyanobacteria) which responds to a nutrient pressure. Ecological status classes: H = high, G = good, M = moderate, P = poor, B = bad. Solid curves: present situation; stippled curves: impact of climate change (CC). (A) CC affects the level of local pressures. (B) CC affects the reference condition of the biological element (i.e. the baseline or
condition found in sites with minimal impact of other anthropogenic pressures). (C) CC affects the biological element's response to increased local pressures, including thresholds used for defining boundaries between ecological status classes. (D) CC affects the biological element's ability to recover when local pressures are decreased due to measures. (From Moe et al. 2010a).
With respect to ecosystem services: i) the costs of treating drinking water supply are likely to increase, ii) water supply for drinking and irrigation will be threatened in Southern Europe, iii) the quality of bathing water will deteriorate, iv) the value of lakes for sportsfishing may be reduced, v) the overall value of lakes for recreation may be reduced. And finally with respect to recommendations for river basin managers: i) monitoring of biological quality assessment metrics in a set of reference lakes to assess the nature and degree of any change will be required, ii) improved monitoring of lakes impacted by eutrophication is crucial to assess whether the nutrient reduction measures and other restoration efforts are sufficient to achieve good status, iii) if only one BQE can be prioritised then phytoplankton should be selected as the BQE responding most strongly to eutrophication, iv) any change in lake type should be considered before the programme of measures is revised, v) climate change impacts on lakes are probably still small enough to be compensated with small to moderate additional restoration efforts in the 2nd RBMPs, vi) climate change impacts are expected to increase in the coming years and may thus require major improvements in nutrient reduction measures for the 3rd RBMP if good status and sufficient provision of ecosystem services are to be achieved in 2027.
We have furthermore established a number of guiding principles concerning various aspects of the WFD such as the risk assessment, status assessment of lakes, objective setting, and the programme of measures (Deliverable 3.21) These include:
Principle 1 assures that reducing external nutrient loading to lakes remains the key for successful lake restoration and meeting water quality targets also in CC conditions. Based on studies made in REFRESH it is shown that critical nutrient loading to achieve and maintain good ecological status in lakes has to be lowered in a future warmer climate as natural mechanisms that support zooplankton grazing weaken. Although in most studies, P is considered the most important limiting nutrient in lakes, several authors advocate consideration of both N and P.
Principle 2 suggests that water managers consider the dominant cascading effects in lake food chains and advocates for using zooplankton in lake monitoring schemes. A number of studies within REFRESH have demonstrated that increasing pressure exerted by planktivorous fish on zooplankton in warmer climates may cause rapid and dramatic increase in phytoplankton including cyanobacteria. Understanding the trophic cascade of a lake is the key for interpreting changes in variables characterizing the WFD ecological status, making future predictions and selecting effective restoration measures.
Principle 3 emphasizes the importance of geographic, and type-specific differences of lakes for selecting appropriate conservation, adaptation and restoration measures and distinguishes between three types of lake sensitivity: fast reaction, “memorizing” of past conditions, and proneness to system shifts exemplified by a number case studies.
Principle 4 stresses the importance of developing clear prioritization principles in order to diminish potential conflicts and trade-offs between management measures. Uncoordinated sectoral responses can be ineffective or even counterproductive, because a response in one sector can increase the vulnerability of another sector and/or reduce the effectiveness of its adaptation responses.