Environmental changes affecting light climate in Andean Patagonian mountain lakes: implications for the plankton community. Presented by Beatriz Modenutti at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.

1. ENVIRONMENTAL CHANGES AFFECTING
LIGHT CLIMATE IN ANDEAN PATAGONIAN
MOUNTAIN LAKES: IMPLICATIONS FOR THE
PLANKTON COMMUNITY
Beatriz Modenutti
E. Balseiro, M. Bastidas Navarro, M.S. Souza,
C. Laspoumaderes, F. Cuassolo
Lab. Limnología. INIBIOMA-CONICET. Universidad Nacional
del Comahue, Bariloche, Argentina.

2. Andean Lakes from
Chile and Argentina
(Araucanian lakes)

4. • Oligotrophic. TP less than 5 µg L-1
• DOC concentration (0.5 mg L-1)
• High PAR & UVR transparency (KdPAR: 0.09 m-1 and Kd305: 0.52 m-1)
Euphotic zone up to 55 m.

5. Field Studies

6. Field Experiments

7. Laboratory experiments

8. Temperature, Light and Clorophyll a profiles

9. Stentor araucanus Foissner & Wölfl

10. Stentor araucanus
•Mainly inhabits upper epilimnetic levels (Modenutti et al 2005).
•High UVR resistance (Modenutti et al 1998).
•Prey on long bacterial rods (Foissner and Woelf, 1994).

11. Photosynthetic efficiency
100
Stentor araucanus
Ophrydium naumanni
ng C (ng Chla)-1 / mol photons m-2
Picocyanobacterias
10
1
0.1
0.01
0 500 1000 1500 2000
-2 -1
µmol photons m s

12. Ophrydium naumanni Pejler
• Inhabit mainly the metalimnion and
preys on bacteria and
picocyanobacteria(Modenutti and
Balseiro 2002).

13. Photosynthetic efficiency
100
Stentor araucanus
Ophrydium naumanni
ng C (ng Chla)-1 / mol photons m-2
Picocyanobacterias
10
1
0.1
0.01
0 500 1000 1500 2000
-2 -1
µmol photons m s

14. Picocyanobacteria in the DCM
Lago Espejo Lago Gutiérrez Lago Moreno

15. Photosynthetic efficiency
100
Stentor araucanus
Ophrydium naumanni
ng C (ng Chla)-1 / mol photons m-2
Picocyanobacterias
10
1
0.1
0.01
0 500 1000 1500 2000
-2 -1
µmol photons m s

16. Changing scenarios:

17. In temperate lakes:
• Wind action is important in determining
mixing depth.
• Epilimnion can undergo periods of heating
during hot and calm weather and periods of
strong mixing by wind.

18. Vertical mixing can lead to a shortage of light if
planktonic organisms are frequently mixed down to
the bottom, whereas stratification enhances light
supply by decreasing mixing depth.
Depth

19. Interannual variability in wind speed may produce changes in the
summer thermocline depth and consequently in the epilimnetic
mean irradiance
1998-99 2003-04 t d.f. P
Zterm 27.7 ± 0.92 15.8 ± 0.71 9.339 13 P<0.001
Kd PAR 0.141 ± 0.003 0.161 ± 0.002 4.175 13 P=0.001
Kd 305 0.667 ± 0.017 0.772 ± 0.005 4.889 13 P<0.001
Im PAR 199.35 ± 20.68 542.0 ± 48.3 7.380 13 P<0.001
Im 305 0.05 ± 0.01 0.165 ± 0.018 6.152 13 P<0.001
Nutrient variations were statistically not significant (P> 0.05)

20. In the water column:
-2 -1 -2 -1
PAR (µmol m s ) PAR (µmol m s )
1 10 100 1000 1 10 100 1000
0 0
305
320
340
10 10
380
Depth (m)
Depth (m)
20 PAR < 100 µmol Photons m-2 s-1 PAR
20
30 30
40 40
6 8 10 12 14 16 18 6 8 10 12 14 16 18
Temperature ºC Temperature ºC
•The shallower thermocline depth implies an increase in light supply favouring
Stentor araucanus which has higher critical light level, and higher resistance
to UVR.
•The vertical segregation gives Stentor araucanus the advantage of driving
light availability for other phototrophs located lower in the water column.
•Ophrydium naumanni has a lower critical light intensity consequently it is a
superior light competitor. However, the sharp decrease in Ophrydium PE may
result also from the incidence of UVR.
Modenutti et al 2008. Limnology and Oceanoraphy 53: 446-455

21. UVR and Bacteria Morphology
• The solar radiation and particularly ultraviolet
radiation (UVR) have strong effects on the production,
activity, and abundance of bacterioplankton (Helbling
et al. 1995; Sommaruga et al. 1997;Tranvik and
Bertilsson 2001).
• However, up to now few studies have shown evidence
of the effects of UVR on bacterial community
composition and morphological distribution.

22. Rivadavia
Gutiérrez 3
2
A Correntoso
Mascardi Cat
Prok
TPP
KdPAR
Kd380
B 2
Mascardi Tron
RDA Axis 3
TP
PCA Axis 3
1 Nahuel Huapi Kd305
1
Kd340
Espejo TN Kd320
0 Futalaufquen 0
Chl TDP
NF
-1 -1
Ophry -2
-2 DOC
-1 1
2 -3
0 1 -2 0 2
PC -1 is
A
1 0
2 RD
0
1
-1 Ax
Ax 2
xis AA A
is -1 A xis 2 -2 RD
1 3
-2 P CA 1 3
50%
The overall bacterial community composition 10%
was similar in all lakes and over depth in each
lake
1%
Actinobacteria β-Proteobacteria (banda 6) α-
Proteobacteria Cytophaga-Flavobacterium-
Bacteroides (CFB) were present in the sampled
strata.

23. 103 Filaments mL-1 % Fuctional morphologies
0
5
10
15
20
25
100
0
20
40
60
80
Espejo 50%
A
C
Espejo 10%
Espejo 1%
Correntoso 50%
Correntoso 10%
Correntoso 1%
Nahuel Huapi 50%
Nahuel Huapi 10%
Nahuel Huapi 1%
Nahuel Huapi 0.1%
Gutierrez 50%
Gutierrez 10%
Gutierrez 1%
Morphology
Masc. Cat 50%
Masc. Cat 10%
Masc. Cat 1%
Masc. Tro 50%
Masc. Tro 10%
Masc. Tro 1%
Rivadavia 50%
Rivadavia 10%
Rivadavia 1%
Futalaufquen 50%
Futalaufquen 10%
Futalaufquen 1%
50 10
Depth (% surface PAR)
1
B
D
0
10
12
14
16
18
20
40
60
80
100
Filament length ( m) % Fuctional morphologies
Corno et al. 2009. Limnology and Oceanography 54: 1098-1112.

24. µmol fotones m s
100 101 102 103 104
•The relative proportion of filaments to total 0
bacterial biovolume was higher in the upper
10
layers, which have higher UVR intensities
(305–340 nm). 20
•We obtained a direct relationship between
Profundidad
mean UVR in the epilimnion and 30
filamentation. 40
305 nm
• Filament mean length in the upper layers 320 nm
340 nm
380 nm
was also significantly greater than at deeper 50 PAR
levels.
60
10-1 100 101 102 103
305 nm 320 nm
60
R2=0.56 R2=0.52
60
Radiación UV (µW cm-2 nm-1)
% Filaments
% Filaments
40 40
20 20
0 0
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
W cm-2 nm-1 W cm-2 nm-1
60 340 nm 380 nm
2 60
R2=0.49 R =0.46
% Filaments
% Filaments
40 40
20 20
Corno et al. 2009. Limnology and
0
0 1 2 3 4 5 6 0 5 10 15 20 25
0 Oceanography 54: 1098-1112.
W cm-2 nm-1 W cm-2 nm-1

25. Laboratory experiments:
PAR UVR
Modenutti et al 2010. Photochemistry and Photobiology 86: 871–881

26. Epilimnetic levels of UVR induce filamentation and that this response is not a feature of a
particular cluster. However, β-Proteobacteria exhibited a high relative importance in filament
formation while Actinobacteria were almost absent among filaments.
Modenutti et al 2010. Photochemistry and Photobiology 86: 871–881

27. Consequences in the C transfer within the microbial loop
•The biovolume of bacteria that became inedible (cells >
7 μm) increase significantly in the epilimnion.
•In the epilimnion nanoflagellates and ciliates encounter
prey assemblage composed by a large extent of inedible
cells. Thus, bacterivory would be reduced with a
consequent decrease in epilimnetic trophic energy
transfer.

28. Climate change
Masiokas et al (2008) indicated a
significant warming and decreasing
precipitation
•Glacier recession
•Changes in light climate in lakes

29. BLACK GLACIER
2009
1942

30. LAGO MASCARDI
•Gradient of turbidity in Tronador Arm

31. PAR (µmol Photon m-2 s-1)
10-1 100 101 102 103
0
The effect of the glacial clay
decreases with the distance from the
10
river mouth, and consequently the
lake turns more transparent from P1
Depth (m)
to P7 with a monotonically decrease 20
in Kd values
30
P1
P2
P3
P4
40 P5
P6
P7

32. 0
P1
P2
P3
10 P4
P5
P6
P7
DCM increase in depth and
Depth (m)
20
magnitude along the
30
gradient from P1 to P7.
40
50
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-1 2.0
Chla (µg L )
DCM (Chla µg L )
1.5
Magnitude of DCM -1
(concentration of Chla) has a 1.0
negative relationship with
Total Suspended Solids. 0.5
0.0
0.1 1 10
-1
STS (mg L )

33. 2.5 35
30
2.0
TSS (mg L )
-1
25
Picy (10 cell mL )
1.5
20
3
15
1.0
10
0.5
-1
5
0.0 0
0 2 4 6 8 10 12 14 16 18
40
Distance from source (km)
PICY (10 cel mL )
-1
30
Picocyanobacteria were very 20
3
sensitive to changes in light
climate 10
0
0.5 1.0 1.5 2.0
TSS (mg L-1)

34. Conclusions
•Climate change (warming, wind, precipitations)
caused changes in lake light supply.
•Microbial food web was observe to be very
sensitive to changes in light supply.
•These changes may occur in scenarios were
anthropogenic deposition of nitrogen or
increase in phosphorus by dust was not
recorded.
•This situation is of particular importance for
lacustrine food webs.

35. Thank you
C O N IC E T