Effects of natural and human impacts on large European lake Case study Lake Peipsi

Transcription

1 Effects of natural and human impacts on large European lake Case study Lake Peipsi Külli KANGUR Estonian University of Life Sciences , Living Lakes Eastern Europe Network Conference, Tartu

2 Outline 1. Large lakes and the EU Water Framework Directive 2. The comparison of most important parameters (P, chlorophyll, transparency) of open water 3. Fish and fisheries 4. Conclusion

3 Lake size an important characteristic in typology WFD requires the determination of type-specific ecological status of water bodies (CIS, 2003a). Large lakes react differently to pressure factors than small lakes. Physically large lakes have similarities to seas. The WFD requires reference state for all waterbodies Large lakes often do not have reference sites

4 Peipsi and Võrtsjärv - large lakes in Estonia The Water Framework Directive (2000) considers lakes with a surface area >100 km 2 as very large lakes

5 According to the Estonian lake typology, Peipsi and Võrtsjärv belong to separate types Võrtsjärv VÕRTSJÄRV surface area km 2 catchment area - 3,374 km 2 mean depth m water residence time ~ 1 year volume km 3 PEIPSI surface area 3555 km 2 catchment area 47,800 km 2 mean depth 7.1 m water residence time ~ 2 years volume 25 km 3

6 Different parts of large lakes may belong to different lake types and have different ecological quality (CIS, 2003b). Photo H. Mäemets Lake Peipsi consists of three limnologically different parts Photo A. Kangur

7 II Long-term studies of Lake Peipsi Peipsi has extended limnological data series : Hydrochemistry since 1950s Biota since 1960s Water level and temperature since 1924 Advanced statistical methods and mathemathical models are needed

8 Narva R. Sampling Estonian- Russian joint expeditions L. Peipsi s.s. In summer since 2001 Emajõgi R. L. Lämmijärv In winter since 2004 L. Pihkva National monitoring on Peipsi Velikaja j.

9 Estonian-Russian joint expeditsion in summer 2007

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11 a2*ip*ip(l) General linear model for large lakes Dr. Tõnu Möls a4*t35(l) pl*ip*t53(l) Legend: Factor Factor transformations used in model terms Year: a1, a2, a3, a4, a5, a6 Day of the year: t35, t44, t53 Longitude: pl Latitude: ip Sampling depth: sg Definition of transformations: a1 to a6 are calculated from the year number by using six Gaussian curves with specifically selected parameters: pl*pl*pl(l) pl*ip*t44(l) a3*t53(l) a2*ip(l) ip*pl(l) ip*ip(l) a1*pl*ip(l) pl*ip*t35(l) a3*t44(l) a1*ip*ip(l) pl*pl(l) ip*ip*t53(l) a3*t35(l) ip*ip*t44(l) a2*t53(l) a1*ip(l) ip(l) a6*pl*pl(l) ip*ip*t35(l) a2*t44(l) pl(l) a6(l) a6*pl(l) a2*t35(l) ip*t53(l) ip*t44(l) a1*t53(l) a5(l) a5*pl*pl(l) a4(l) a1*t44(l) ip*t35(l) a5*pl(l) a3(l) a4*pl*pl(l) a1*t35(l) pl*pl*t53(l) a2(l) pl*pl*t44(l) a4*pl(l) a6*pl*ip(l) a1(l) a3*pl*pl(l) a6*ip*ip(l) pl*pl*t35(l) sg*t53(l) a3*pl(l) a6*ip(l) pl*t53(l) sg*t44(l) a5*pl*ip(l) a2*pl*pl(l) pl*t44(l) a2*pl(l) pl*t35(l) a5*ip*ip(l) sg*t35(l) sg*ip*ip(l) sg*ip(l) a1*pl(l) t53(l) a4*pl*ip(l) a4*ip*ip(l) a6*t44(l) a6*t35(l) Year sg*pl*ip(l) a1*pl*pl(l) a5*ip(l) a6*t53(l) sg*pl*pl(l) sg*pl(l) sg*sg(l) sg(l) L t44(l) t35(l) ip*ip*ip(l) pl*ip*ip(l) pl*pl*ip(l) a4*ip(l) a3*pl*ip(l) a3*ip*ip(l) a3*ip(l) a2*pl*ip(l) a5*t53(l) a5*t44(l) a5*t35(l) a4*t53(l) a4*t44(l) The three transforms of seasonal time are calculated like the beta-functions: IJsselmeer (L=1) and Peipsi (L=2) Terms of the joint linear model for lakes t35=t 3 (1-t) 5, t44=t 4 (1-t) 4, t53=t 5 (1-t) 3 where t=(day number within year) / 365. are explained in the Legend. properties in East-West direction. Model terms more complex changing of the L. IJsselmeer added to the initial Peipsi model to describe the were terms Blue parameters. linear 2 92=184 has The sampling depth is presented by its square root denoted by sg. model. In the case of two lakes (L=1,2), the model Table fixed terms of the general linear

12 What is more important: human impact or climate change? The WFD assessments fail to take into account the modifying effects of weather and ice conditions or variations in water residence time.

13 Mean annual water level in Lake Peipsi from 1920 to 2006

14 Range of natural water level fluctuations 3.04 m over the last 80 years average annual range of 1.15 m Lake Peipsi, Photo Karin Kangur

15 Temperature of water, o C Water level, cm A Simultaneous effect of high temperature and low water level B In shallow L. Peipsi the effect of warm weather is especially strong when it syncronizes with low water level

16 Algal bloom in Lake Peipsi 9 August 2002 Photo Peeter Unt

17 Strong cyanobacterial bloom, high water temperature and progressive water level reduction led to fish-kill L. Peipsi, August 2002 Photo Peeter Unt

18 Ice conditions Photo Karin Kangur Duration of ice-covered period (days with water temperature <1 o C) has significantly decreased.

19 III Comparison of the most important water parametrs in Peipsi s.s. Lämmijärv Pihkva Peipsi s.s. Peipsi s.s. Pihkva Pihkva

20 Eutrophication is the most serious environmental problem for Peipsi Water characteristics and biological communities in the lake change from north to south. Peipsi, August 2002

21 Long-term changes of total phosphorus content (mg P m -3 ), calculated from the Model, referenced to the selected geographical points, and the 220 th day (8 th August) of year. Dashed lines correspond to 95% confidence limits for the real TP value.

22 Chlorophyll-a

23 Water transparency 5 S 4 E C C H I year Scatterplot of Secchi in L. Peipsi ss. Measurements of early days of a year are coloured lilac to blue, the late autumn observation are coloured red, green dots denote the summer observations (spectral colour scale).

24 Spatial gradients Transparency in the lake reflects phosphorus content in the lake The high P-load from the south is the main course of water quality gradients from South-East to the North Delta of Velikaya River August 2002

25 Water transparency

26 The biomass of cyanobacteria Microcystis sp. in July Sept Peipsi s.s. Lämmijärv+Pihkva j g m Biomass of M. viridis has increased in Lake Peipsi.

27 Abundance of zooplankton during open water period Peipsi s.s. L. Pihkva+L. Lämmijärv ind. uhat m t Abundance of zooplankton has drastically decreased.

28 Fish community of L. Peipsi react distinctly to changes in water quality and biota Räpina rand, Jõepera, Karin Kanguri foto

29 IV Fish and fisheries The fish stocks of the lake are heavily exploited 37 fish species inhabit Peipsi

30 Freshwater fish catch of Estonia L. Peipsi (Estonian part) %, L. Võrtsjärv %, other inland water bodies - 1 2%.

31 Dominant fishes in commercial catches from Lake Peipsi in Catch, 10 6 kg 2,5 2 1,5 1 0,5 0 Smelt Vendace Whitefish Roach Small rough fishes Bream Pike Perch Pikeperch

32 Total commercial catch 10 6 kg Total catch

33 Catch, 10 6 kg Smelt yield in Peipsi Smelt, the previous dominant in the fish community has strongly decreased on a long-term scale.

34 The fish community of Peipsi has shifted from clean- and coldwater fish species (vendace, whitefish, burbot) towards more pikeperch and bream, which prefer productive warm and turbid waters. Burbot Vendace

35 Catch, 10 6 kg Climate change and predator - prey interactions in Peipsi 3,5 3 Vendace Pikeperch 2,5 2 1,5 1 0, The flourishing of pikeperch preceeded the collapse of vendace. The main reason collapse of vendace was cumulative effect of sequential extreme weather events (extraordinary hot summer and earliest ice-off dates).

36 10 6 kg 10 6 kg Smelt 1 0 3, ,5 Pikeperch Great changes occurred in the predator-prey relationship (mainly pikeperch versus smelt) 2 1,5 1 0,

37 Over-explotation has caused significant decrease of the abundance of larger specimens pikeperch in Peipsi Main prey fish for young pikeperch (Sl 25 cm) is smelt.

38 CPUE, ind. per trawlhour Length frequency distribution of pikeperch (Sander lucioperca) according to experimental trawling in autumn Sl, cm Legal size

39 What is the main food of young pikeperch (Sl>10 cm) in Peipsi? Chironomus larvae

40 Conclusion State of Lake Peipsi ecosystem is unstable. Eutrophication is still the main environmental problem for Lake Peipsi. Great changes occurred in different trophic levels of the ecosystem. Climate change may have stronger effect on Peipsi ecosystem than smooth changes in nutrients load.

41 Thank you!