1. Bacterial production and Microsystin in Lake Taihu GUANG GAO Nanjing Institute of Geography & Limnology, CAS 2007.03.26

2. Outline Bacterial abundance, biomass and production in Lake Taihu Bacterial abundance, biomass and production in Lake Taihu Microsystin in Lake Taihu Microsystin in Lake Taihu

3. Meiliang Bay, Lake Taihu Main characteristics of this area: Surface area: 120 Km 2 Mean water depth: 1.95 m Mean width: 7.0 Km Mean length: 15.0 Km

5. The river mouth, which was ca. 55% higher than the mean in Meiliang Bay and almost twice as high as the open lake. At river mouth, the total bacterial biomass was 364±225 μg C l -1, i.e. ca. 1.5 and 2.2 times higher than bay and the open lake. The difference between the highest and lowest value was ca. tenfold at the river mouth, only ca. fivefold were in Bay and the open lake. Bacterial abundances and production

6. The mean percentage of active bacteria versus total bacterial abundance varied from 34% to 28% in the river mouth, Meiliang Bay and the open lake. Variation of the active cells between sites was smaller than the variation in abundance and biomass.

7. The relationship between total bacterial abundance and the number of active bacteria

8. The total phosphorus concentration vs the total bacterial abundance (filled circles) or the number of active bacteria (open circles) at different sites of Lake Taihu. The original total phosphorus data were taken from the yearbook of TLLER, CAS.

9. Correlation of bacterial carbon production measured by both [ 3 H]- TdR (filled circles) and [ 14 C]-Leu (open circles) and phytoplankton biomass. ( River mouth, r 2 =0.676, n=13, p=0.001 and r 2 =0.680, n=13, p=0.001, Meiliang Bay, r 2 =0.219, n=39, p=0.003 and r 2 =0.235, n=39, p=0.002) The original phytoplankton biomass data were taken from the yearbook of TLLER, CAS.

10. The Chl-a concentration vs the total bacterial abundance (filled circles) or the number of active bacteria (open circles). The original phytoplankton biomass data were taken from the yearbook of TLLER, CAS.

11. O B R Bacterial cell volumes were rather small !! ( All pictures were taken by using the same sampling time and at the same magnification of 1250 X. Bar = 10 μm. )

12. No significant correlation between the water temperature and bacterial cell volumes was found.

13. The cellular carbon content fluctuated ca. twofold during the year at all sites. No significant changes in the temporal distribution was found.

14. AreaProtozoaRotiferCladoceraCopepoda River Mouth Mean±S.E7.9±2.0 ( n =60) 43.9±4.5 39.0±4.5 9.3±2.4 ( n = 67 ) Meiliang Bay Mean±S.E1.2±0.2 ( n = 180) 12.3±1.7 67.8±2.5 18.2±1.8 Open area Mean±S.E 1.4±0.5 ( n = 60 ) 4.3 ±1.4 ( n =60 ) 58.1 ± 4.5 ( n = 60 ) 36.2 ± 4.4 ( n = 60) The biomass composition in different parts of the lake Grazing Pressure

15. The temp. and spatial distribution of Ciliate abundance

16. The relationship between ciliate abundance and total bacterial abundance (filled circles) and active bacterial abundance (open circles).

17. 32μm16μm1μm1μm 0 1 2 3 4 5 6 0 100 200 300 400 500 600 700 flagellate grazing rate (d -1 ) Bacterial growth rate (d -1 ) Grazing (mgC.m -3.d -1 ) Growing rate (d -1 ) Flagellate are the main bacteria consumer, which can be contributed 90.7% of the grazing.

18. 12 11 8 7 5 3 0 9 Site 11, 12: the area covered by macrophyte Site 9: highly polluted area Site 0: river mouth Site: 3,5 the bay Site 7,8: the open lake Bacterial diversity by using PCR-DGGE method

19. Microsystin in Lake Taihu

20. Temporal distribution of Microsystin in different part of Lake Taihu

21. The whole lake distribution of MicrosystinSeason distribution of Microsystin

22. The spatial distribution of annual mean value of Microsystins

23. The relationship of parameters and the concentration of Microsystin River mouthMeiliang BayOpen LakeWuli Bay Water Temperature 0.593*0.818**0.119-0.002 Transparency0.401-0667*0.3680.060 DO0.448-0.315-0.067-0.310 SS-0.5660.673-0.3570.196 TN-0.853**-0.627*-0.277-0.389 TP 0.692*0.874**-0.3710.077 PO 4 3- 0.1720.0000.0310.559 Chla0.1680.594*0.396-0.644* PH0.3100.755**0.302-0.533 COD MN 0.601*0.846**0.070-0.413 * P<0.05; **P<0.01

24. The relationship of biological parameters and the concentration of Microsystin River mouthMeiliang BayOpen LakeWuli Bay Algal biomass0.0210.818**0.487-0.525 Cyanobacteria biomass 0.593*0.720**0.119-0.002 Rotifer biomass 0.748**0.5050.5220.214 Protozoa biomass 0.3330.4240.2380.294 Cladocera, Copepoda biomass -0.42-0.3080.252-0.165 * P<0.05; **P<0.01

25. The change of MC concentration in the incubation of natural algae bloom

26. (A) Pure culture Microsystis: 5×10 5 cells/ml (B) Mixed culture, Microsystis sp. :2.5×10 3 cells/ml ， Scendesmus obliqaus: 2.5×10 5 cells/ml (C) Mixed culture, Microsystis sp.:2.5×10 5 cells/ml ， scendesmus obliqaus 2.5×10 3 cells/ml

27. Thank you Thank you for your attention! for your attention!