Water transparency to UV radiation in montane lakes: consequences of climate-driven changes in terrestrial inputs. Presented by Craig Williamson at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.

1. Water transparency to UV radiation in montane lakes:
consequences of climate-driven changes in terrestrial inputs.
Craig Williamson, Carrie Kissman, Kevin Rose
Miami University Global Change Limnology Lab
Jasmine Saros
University of Maine Climate Change Institute
Janet Fischer & Jennifer Everhart
Franklin & Marshall College

2. Responses to Climate Change:
Where to sample?

3. Lakes as Sentinels & Integrators
of Climate Change
Williamson et al. 2009 Limnol. Oceanogr. 54:2273

6. Treeline is advancing to higher elevations (black dots)
in 52% of 166 systems sampled worldwide.
Receding treelines observed in only 1% of systems.
Harsch et al. 2009. Ecology Letters 12:1040.

7. DOM Source is Largely Terrestrial
Terrestrial
Vegetation
Low – Medium - High
DOM in
water

8. DOM as an Ecosystem Regulator
Low DOM High DOM
High transparency Low transparency
DOM Regulates
UV transparency
Compensation depth
Mixing depth
Nutrient cycling
Anoxia
Metal toxicity
Pesticide toxicity
Other …

9. DOM Has Doubled in 15-20 yr in Many Lakes & Rivers
Evans et al. 2006. Global Change Biology 12:2044
(See also Findlay 2005. FEE 3:133; Monteith et al. 2007. Nature 450:537)

10. Beartooth Mountains, MT-WY, USA
Saros et al. 2005
CJFAS 62:1681

11. Ganguly et al. 2009. Proc. Nat. Acad. Sci. U.S. 106:15555

12. Central Rocky Mountains, Western USA:
Changing Snowfall in Red Lodge, MT
Rose et al. 2009 Photochem. Photobiol. Sci. 8:1244

13. Changes in Diatoms in the Central Rocky
Mtns. Associated with Climate Change
Saros et al. 2003. AAAR 35:18

14. Central Question:
How will climate-driven increases in DOM
influence consumer:producer relationships
in mountain lakes?

15. Climate Change in Montane Ecosystems
temperature, precipitation, treeline --> more DOM
?
Heterotrophic Consumers
Zooplankton (H)
HB:AB = 3
Autotrophic
Phyto. (A)

16. Epilimnion (H)
Warm, High Light
(A) ?
Hypolimnion (H)
Cold, Dark
(A) ?

17. Epilimnion (H)
Warm, High Light
(A) ?
Hypolimnion (H)
Cold, Dark
(A) ?
?
Epilimnion (H)
Warm, High Light
(A) ?
Hypolimnion (H)
Cold, Dark
Anoxic (A) ?

18. Experimental Design
With DOM No DOM
Resource Subsidy Resource Subsidy
(H) (H)
1.5 m
(A) ? (A) ?
+/- Zooplankton
(H) (H)
8.0 m
(A) ? (A) ?

19. Experimental Design
• 3 week field microcosms
• 3.8 L transparent bags
• Natural phytoplankton
• Treatments (3 replicates):
 +/- Zooplankton grazers
 +/- DOM
 2 depths to give different light & temperature:
– 1.5 m (epilimnion)
– 8 m (hypolimnion)

20. Phytoplankton Biomass
300
Initial Epilimnion Hypolimnion
250
Biomass (µg L )
200
-1
DOM p < 0.001
ZP p < 0.001
150 Depth p = 0.090
DOM*ZP p = 0.187
100 DOM*Depth p = 0.077
ZP*Depth p = 0.009
DOM*ZP*Depth = 0.65
50
0
l
tia M M M M M M M M
Ini -D
O DO DO DO O DO O DO
+ - + -D + -D +
+ Zoop + Zoop
Treatment

21. Phytoplankton Biomass
300
Initial Epilimnion Hypolimnion
250
Biomass (µg L )
200
-1
DOM p < 0.001
ZP p < 0.001
150 Depth p = 0.090
DOM*ZP p = 0.187
100
+ DOM*Depth p = 0.077
ZP*Depth p = 0.009
DOM*ZP*Depth = 0.65
50
-
0
l
tia O
M M O
M M M M M M
Ini -D DO -D DO O DO O DO
+ + -D + -D +
+ Zoop + Zoop
Treatment

22. Total Zooplankton Biomass
800
Initial Epilimnion Hypolimnion
600
Biomass (µg L )
-1
DOM p = 0.010
400 Depth p = 0.003
DOM*Depth = 0.21
200
0
al M M M M
n iti DO DO DO DO
I - + - +
Treatment

23. Zooplankton:Phytoplankton (H:A) Ratio
Zooplankton Biomass:Phytoplankton Biomass
30
Initial Epilimnion Hypolimnion
25
DOM p = 0.002
Depth p =0.216
20 DOM*Depth = 0.585
15
10
5
0
al - + - +
iti M M M M
In DO DO DO DO
Treatment

24. No Terrestrial With Terrestrial
Resource Subsidy Resource Subsidy
(-DOM) (+DOM)
(H) (H)
(A)
Initial
(H)
(A)
(H)
(H)
(A)

25. DOM & Transparency: Vertical overlap of
Consumers and their Resources
• Do we see variations in DOM and transparency in alpine
lakes among years?
• What are the implications of these transparency
changes for vertical overlap of consumers and their
resources?

26. Lake Oesa, Canadian Rocky Mountains
UV Transparency July 28, 2008-2009
380 nm UV (% of subsurface)
10 100
0
2
4
Depth (m)
6
8
10
12 2008
14 2009
16

27. 380 nm UV (% of subsurface) CDOM fluorescence
10 100 0 10 20 30
0 0
5 5
10 10
Depth (m)
Depth (m)
15 15
20 20
25 25
2008 2008
30 30
2009 2009
35 35
Chlorophyll Fluorescence Turbidity
0 200 400 0 10 20 30 40 50 60
0 0
2008
2008 5
5 2009
2009
10 10
Depth (m)
Depth (m)
15 15
20 20
25 25
30 30
35 35

28. Lake Oesa Hesperodiaptomus July 28
Copepods per Liter
0.00 1.00 2.00 3.00
0
5
10
Depth (m)
15
20
25
2008
30
2009
35

29. Oesa Zooplankton & Chlorophyll July 28
Copepods per Liter
Chlorophyll Fluorescence
0.00 1.00 2.00 3.00
0 200 400
0
0
5 2008
5
2009
10 10
Depth (m)
Depth (m)
15 15
20 20
25 2008 25
30 2009 30
35 10% UV380 35

30. Lake Oesa Transparency vs. Precipitation
(PRELIMINARY: N= 4 only!!!)

31. Indirect Effects on Terrestrial DOM?
Terrestrial
Vegetation
Low – Medium - High
DOM in
water

32. Indirect Effects of Climate Change: Wildfire

33. Bark Beetle Damage

34. Lakes are Good Sentinels & Integrators of
Climate Change: Direct & Indirect Effects
Williamson et al. 2009 Limnol. Oceanogr. 54:2273

35. Specific Conclusions
 Higher DOM will stimulate producer biomass more than
consumer biomass, reducing consumer regulation of
autotrophic production and fate of fixed carbon.
 Shorter, interannual climate-induced variations in DOM
and other variables can alter transparency and
consumer-resource interactions.

36. Acknowledgements
Field and Laboratory Assistance:
– Jeremy Mack, Kevin Rose, E. Overholt, R. Moeller, S. Lee, A. Nurse,
N. McCulligh, M. Collado, A. Tucker and M. Cohen
Funding:
– USA National Science Foundation, Miami University

37. Extra Slides Follow

38. Net Zooplankton Grazing Effect
Net Grazing Effect (ml cleared/ug zooplankton/week)
2.0
Epilimnion Hypolimnion
1.8
1.6
1.4
1.2 DOM < 0.001
Depth = 0.992
1.0
DOM*Depth = 0.839
0.8
0.6
0.4
0.2
0.0
- + - +
D OM OM OM OM
D D D
Treatment

39. Changes in DOC (% yr-1)
(up to 100% in past 15-20 yr in some areas)
Monteith et al. 2007
Nature 450:537

40. Template