Managing lakes in a changing world

Transcription

1 Managing lakes in a changing world Results from the REFRESH Peeter Nõges Estonian University of Life Sciences

2 Guiding principles Suggested actions Examples

3 Statement 1 Apart from exceptional circumstances, it is not expected that, within the timeframe of WFD implementation (i.e., up to 2027), a climate change signal will become statistically distinguishable from the effects of other human pressures. Why?

4 Global warming reinforces eutrophication Moss et al Eutrophication and climate Regional Stakeholder warming Symposium act along the same pathways

5 Statement 2 It is more likely that indirect pressures arising from human responses to climate change both adaptation and mitigation - will have a greater impact on water bodies than the direct CC pressures. These indirect pressures include: damming and water abstractions for irrigation, new flood defence infrastructure, intense production of energy crops.

6 Acting in conditions of high uncertainty Climate checking of the programme of measures

7 Two most widespread pressures on ecological status of water bodies in the EU: 1. Pressures that originate from hydromorphological modifications to water bodies, 2. Pressures that stem from over-abstraction of water Eutrophication is mentioned only once in the whole document

8 Our aim: Based on REFRESH results Restore the emphasis on needs and costeffective methods to combat eutrophication as the dominating pressure on lakes in Europe Recall some of the basic rules in limnology regarding nutrient limitation, cascading effects in foodwebs, and type-specific differences among lakes If followed, will lead to win-win solutions

9 Guiding principle 1 Critical loading limits for lakes have to be lowered in a future warmer climate as natural mechanisms that control phytoplankton development weaken

10 CC, phosphorus & cyanobacteria Longer periods of thermal stratification lead to oxygen depletion, which enhances phosphorus release from lake sediments Warmer climates boost cyanobacterial dominance in shallow lakes (Kosten et al., 2012) Chlorophyll in Danish lakes is better described by P than by N (Søndergaard et al., 2011). High turbidity caused by phytoplankton gives gives competitive advantage to cyanobacteria which tolerate lower light levels (Kosten et al., 2012)

11 CC, nitrogen & cyanobacteria In northern Europe N loss from soils is primarily associated with vegetationfree periods and excess rainfall. In southern Europe TN concentrations in lakes increase due to higher evaporation. Denitrification becomes limited by organic matter scarcity. In warmer climate, elevated nitrogen concentrations will have a stronger stimulating effect on cyanobacteria. Jeppesen et al Kosten et al. 2012

12 Guiding principle 2 Be aware of the dominant cascading effects in your lakes Rehabilitate zooplankton in lake monitoring schemes Follow changes in fish feeding types and size structure

13 Example

14 Example Mean weight of cladocerans and copepods in a trophic gradient of lakes (Jeppesen et al. 2011)

15 Climate gradient studies N S Changes in diversity Smaller body size Shorter life span Longer and less synchronized spawning period More omnivores Stronger linkage with littoral vegetation Stronger pressure on zooplankton Less control over phytoplankton

16 Guiding principle 3 Consider geographic, and type-specific differences in sensitivity of lakes to pressures for selecting appropriate conservation, adaptation and restoration measures

17 1. Fast and sensitive reaction Võrtsjärv, water temperature AT>0: r = 0.99, p < Tartu Air temperature

18 2. Memorizing of the climate signal by lakes

19 3. Regime switching in lakes resulting from pressure

20 Differences in pressures and lake reactions Latitudinal and altitudinal; Depending on their morphometry and retention time; Depending on eutrophication history

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22 Guiding principle 4: Avoid tradeoffs between measures Attention to: CC adaptation and mitigation measures which endanger water resources, biodiversity and the ecological status of lakes (e.g. energy crops, hydropower) energy-intensive adaptation measures based on continuous use of fossil fuels (e.g. sea water desalinization) energy-intensive restoration measures (e.g. sediment removal, fish removal) if natural processes sustaining the achieved results are not developed.

23 Take home messages Alleviate nutrient pressure on lakes that will be the maximum you can do to help lake ecosystems to cope with climate change impacts. Increase water efficiency measures in water scarce areas Keep an eye on zooplankton because it has the key position in the food web.

24 Thank you!