Freshwater cyanobacterial blooms and toxin production S. Jacquet & J.-F. Humbert

1. Freshwater cyanobacterial blooms and toxin production S. Jacquet & J.-F. Humbert UMR CARRTEL Thonon EC, Brussels, 29 May 2002

2. Cyanobacterial blooms result from competitive situationsbetween phytoplanktonic species Environmental factors favoring these situations : F Nutrient pollution (54 % of eutrophic lakes in Europe) F Stability of the water column (blooms occur principally in summer)

3. Why cyanobacteria are often the winner in competitive situations ? - Control of their buoyancy - Heterocysts - Accessory pigments (phycoerythrin…) nutrient/light uptake - Multicellular organization (filament, colony) - Synthesis of toxins defense against predation

4. … and the winner is:

5. Predicting cyanobacteria dominance in lakes ? Causes Insufficiently treated sewage Manure, effluent from livestock industries Runoff from roads Runoff from fertilized agricultural areas Effects Fertilization of water, chiefly with P Consequences Mass developments of potentially toxic cyanobacteria Low N/P is not a key parameter The risk is more associated to total P or total N Enhancing factors: Shallow waters Long RT

6. Most common cyanobacterial toxins F Cyclic peptides - Microcystins - Nodularin F Alkaloids - Anatoxin –a, -a(S) - Saxitoxins - Cylindrospermopsins Hepatotoxicity F Lipopolysaccharides Potential irritant for any exposed tissue Hepatotoxicity Neurotoxicity

7. Impacts of cyanobacteria • Ecological impact - Perturbations of the ecosystem functioning - Shade - Trophic chains - Anoxia at the end of the bloom • Sanitary impacts - Mortality and morbidity in aquatic and terrestrial invertebrates and vertebrates Example: In Switzerland, more than 100 cattle deaths were attributed during the last two decades to cyanotoxin poisoning - Human contamination

8. Human poisoning by cyanotoxins • Short term effects - Gastrointestinal and hepatic illness - Death of kidney dialysis patients in Brazil • Chronic term effects - Hepatic carcinoma Principal routes of exposure F Oral exposure through drinking water, F Oral and dermal exposure trough recreational water use F Oral exposure through consommation of contamined products ? F Haemo-dialysis

9. Nutrient control of toxin production Environmental control is little known • Microcystis aeruginosa, microcystins LR (MC-LR) • Several lakes investigated in US, Canada • Ptot  MC-LR production • N (N03, NO2, NH4)   MC-LR production • light   MC-LR production High MC content at the later exponential and stationary phase of growth MC production = f(growth rate, cell division) Caution : N2 fixing vs. not fixing cyanobacteria Species dependence  case studies

10. % cyanobacterial blooms associated to toxin Production : UK : up to 60% Sweeden: up to 53% Finlande : up to 45% Denmark : up to 80% Norway: up to 45% Germany : up to 70% • Biological significance, functional role of toxins : • - ‘ fine-tunning’ metabolism and balancing uptake • - assimilation and incorporation of nutrients for growth • - beneficial associations with other microbes • protective role from zooplankton, bacteria, viruses, fungi • reserve pools of metabolites

11. Preventive/remedial measures F Reduction of nutrients: Phosphorus principally (< 10 µg/l) Permissible and dangerous inputs for P and N in lakes Permissible inputs Dangerous inputs Mean Depth (m) P N P N (g m-2 a-1) (g m-2 a-1) (g m-2 a-1) (g m-2 a-1) < 5 < 0.07 < 1.0 > 0.13 > 2.0 < 10 < 0.1 < 1.5 > 0.2 > 3.0 < 50 < 0.25 < 4.0 > 0.5 > 8.0 < 100 < 0.4 < 6.0 > 0.8 > 12.0 < 150 < 0.5 < 7.5 > 1.0 > 15.0 < 200 < 0.6 < 9.0 > 1.2 > 18.0 Renewal time of 2 m3 m-2 a-1 Vollenweider/OECD Reduction of dissolved inorganic nitrogen alone supports the dominance of heterocystic species (Anabaena and Aphanizomenon)

12. Preventive/remedial measures • In small lakes - In-lake phosphorus precipitation - Construction of pre-reservoir to retain P - Sediment dredging and P binding - Physical and chemical treatments - Vertical mixing - Copper sulfate !!! - Biomanipulation - Fish, virus…

13. The case of Planktothrix rubescens in Lake Bourget Decrease of P from 120 µg/l to 30 µg/l in the last 20 years BUT problems with the toxic cyanobacteriumP. rubescens since 1996-97

14. MCYS-RR (µg/l) 6 10 m 15 m 20 m 5 4 3 2 1 0 m 50 m 0 14-oct-99 07-déc-99 22-déc-99 03-nov-99 16-nov-99 29-nov-99 13-sept-99 29-sept-99 15-févr-00 03-août-99 31-août-99 05-janv-00 18-janv-00 31-janv-00 July 99 April 00 July 00 April 01 July 01 April 02 The case of Planktothrix rubescens in Lake Bourget orthoP < 3 µg.l-1 ! WHO drinking water guideline conc. of 1µg/l

15. Eutrophic conditions Meso-trophic conditions P +++ P - 24 °C P +++ P + 7 °C P +++ P +++ How to explain P. rubescens bloom since 4 years ? • P. rubescens is • low light, low temperature, low nutrient adapted • filamentous and toxic and hence little grazed • able to regulate its buoyancy • enhanced by P pulses • …

16. How to survey the development of P. rubescens ? • Counting filaments • Use of a fluorimetric probe

17. Why P. rubescens in lake Bourget and not Léman? 1 - Original species diversity  Competition Lake Léman > 800 Phytopk species described to date ~ 150 phytopk species observed each year Clearly less for Lake Bourget ~ 100 phytopk species 2 - Water column stability (IDH), depth and timming • Bourget is highly stratified in summer compared to Léman • There is a clear delay of stratification for Léman (> September) • Metalimnion is deeper in Bourget than in Léman • Stability of epilimnion = vertical migration • Stability of metalimnion = refuge from continuous entrainment

18. Conclusions Still efforts are required to continue the reduction of nutrients (especially P) in small and deep lakes Probably efforts should be rewarded when P < 10 µg.l-1 In the whole trophic zone  real P limitation Particular case: P. rubescens that grows with < 3 µg.l-1 Importance of global change to account for  Modelisation to predict future changes of lake water quality