SAME 8 Applications of Aquatic Microbial Ecology Section 8: water quality
Toxic cyanobacterial proliferations in response to re-oligotrophication: The paradox of large lake restoration ? S Jacquet, JF Humbert, C Leboulanger, JF Briand O Anneville, B Leberre, G Paolini, JP Bosse
Congress hall, Taormina, Italy, 29 October 2002
Location of interest
Geneva lake The largest natural O European lake km2;
Lmax = 72 km; S = 582 V = 89 Zmax = 310 m ; SCA = 7974 km2
km3
Lake Bourget The largest natural French lake Lmax = 18 km; S = 42 km2; V = 3.5 km3 Zmax = 145 m ; SCA = 560 km2
Nutrient pollution: total phosphorus Bourget
120
P. tot. (µg.l-1)
100
Geneva 80
60
40
20 0 1960
1965
1970
1975
1980
1985
Time (years)
1990 1
1995
2000
Water quality restoration process The case of Lake Bourget 180
1969 - 2002
-1
P-PO4 (µg.l )
150 120 90 60 30 0
Year 2001 PO4 ~ 18 µg.l-1 Ptot ~ 26 µg.l-1
Water quality restoration process The case of Lake Bourget 7
Chl a (µg.l-1.year-1)
Transp. (m)
1984 - 2001
6
5
4
Spring months
10 9 8 7 6 5 4
Year 2001 Transp mean ~ 6.2 m Transp min ~ 3.3 m Chloro ~ 7.7 mg.m-3
1988 - 2001
However, since 1996 Depth (m)
0
20
40
Fluoroprobe (µg / L chlorophylle a)
Fluoroprobe
Depth (m)
0
Cell counting (Number of cells / mL)
20
40
Planktothrix rubescens
Cell counts Summer 2000
Autumn 2000
Winter 2000 / 2001
Spring 2001
03 -A ug 31 -99 -A u 13 g-9 -S 9 e 29 p-9 -S 9 ep 14 -99 -O c 03 t-9 -N 9 o 16 v-9 -N 9 o 29 v-9 -N 9 o 07 v-9 -D 9 e 22 c-9 -D 9 e 05 c-9 -J 9 an 18 -0 -J 0 an 31 -00 -J an 15 -00 -F eb -0 0
Conc. (µg.l-1)
Bloom and toxin production
0m
50 m July 99
3
April 00 July 00 April 01
Eq. MCYS LR (µg.l-1)
6
WHO drinking water 5 guideline conc. of 1µg.l-1 10 m
4 15 m
20 m
2
1
July 01 April 02
Lab experiments OD (570nm)
Population growth
2
1
0 0
20
40
60
80
100
Eq MC-LR (µg.l-1)
Time (d)
extra intra
600 400 200 0 2
Toxin production
6
20
64
Time (d)
87
112
Why ? Cyanobacterial blooms result from competitive situations between phytoplanktonic species
Environmental factors favoring these situations : ! Nutrient pollution (54 % of eutrophic lakes in Europe) ! Stability of the water column (blooms occur principally in summer)
Why cyanobacteria are often the winner in competitive situations ? - Control of their buoyancy - Heterocysts - Storage capacity
The particular case of P. rubescens (lab exp., in situ dynamics, literature) # low light, low temperature, low nutrient adapted # enhanced by P pulses # late summer – early autum species # requires stable water column # able to regulate its buoyancy # filamentous and toxic and hence little grazed # probably little affected by viral control #… Years 0 P +++
