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

Responses to Climate Change: Where to sample?

Lakes as Sentinels & Integrators of Climate Change

Williamson et al. 2009 Limnol. Oceanogr. 54:2273

Harsch et al. 2009. Ecology Letters 12:1040.

Treeline is advancing to higher elevations (black dots) in 52% of 166 systems sampled worldwide.

Receding treelines observed in only 1% of systems.

DOM Source is Largely Terrestrial

Low – Medium - High

Terrestrial Vegetation

DOM in water

DOM as an Ecosystem Regulator

Low DOM

High transparency

High DOM

Low transparency

DOM Regulates

UV transparency

Compensation depth

Mixing depth

Nutrient cycling

Anoxia

Metal toxicity

Pesticide toxicity

Other …

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)

Beartooth Mountains, MT-WY, USA

Saros et al. 2005 CJFAS 62:1681

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

Central Rocky Mountains, Western USA: Changing Snowfall in Red Lodge, MT

Rose et al. 2009 Photochem. Photobiol. Sci. 8:1244

Changes in Diatoms in the Central Rocky Mtns. Associated with Climate Change

Saros et al. 2003. AAAR 35:18

Central Question:

How will climate-driven increases in DOM influence consumer:producer relationships

in mountain lakes?

Heterotrophic Consumers

Zooplankton (H)

Autotrophic

Phyto. (A)

Climate Change in Montane Ecosystemstemperature, precipitation, treeline --> more DOM

?

HB:AB = 3

(H)

(A)

(H)

(A)

EpilimnionWarm, High Light

HypolimnionCold, Dark

?

?

?

?

(H)

(A)

(H)

(A)

EpilimnionWarm, High Light

HypolimnionCold, Dark

Anoxic

(H)

(A)

(H)

(A)

EpilimnionWarm, High Light

HypolimnionCold, Dark

?

?

?

Experimental Design

(H)

(A) ?

(H)

(A) ?

With DOM

Resource Subsidy

No DOM

Resource Subsidy

(H)

(A) ?

(H)

(A) ?

1.5 m

8.0 m

+/- Zooplankton

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)

Phytoplankton Biomass

Treatment

Initi

al

- DO

M

+ D

OM

- D

OM

+ D

OM

- DO

M

+ D

OM

- D

OM

+ D

OM

Bio

ma

ss

(µ

g L

-1)

0

50

100

150

200

250

300

Epilimnion HypolimnionInitial

DOM p < 0.001

ZP p < 0.001

Depth p = 0.090

DOM*ZP p = 0.187

DOM*Depth p = 0.077

ZP*Depth p = 0.009

DOM*ZP*Depth = 0.65

+ Zoop + Zoop

Phytoplankton Biomass

Treatment

Initi

al

- DO

M

+ D

OM

- D

OM

+ D

OM

- DO

M

+ D

OM

- D

OM

+ D

OM

Bio

ma

ss

(µ

g L

-1)

0

50

100

150

200

250

300

Epilimnion HypolimnionInitial

DOM p < 0.001

ZP p < 0.001

Depth p = 0.090

DOM*ZP p = 0.187

DOM*Depth p = 0.077

ZP*Depth p = 0.009

DOM*ZP*Depth = 0.65

+ Zoop + Zoop

+

-

Total Zooplankton Biomass

Treatment

Initi

al

- DO

M

+ DO

M

- DO

M

+ D

OM

Bio

ma

ss

(µ

g L

-1)

0

200

400

600

800

Epilimnion HypolimnionInitial

DOM p = 0.010 Depth p = 0.003 DOM*Depth = 0.21

Zooplankton:Phytoplankton (H:A) Ratio

Treatment

Initi

al

DO

M -

DO

M +

DO

M -

DO

M +

Zo

op

lan

kto

n B

iom

as

s:P

hyto

pla

nk

ton

Bio

ma

ss

0

5

10

15

20

25

30

Epilimnion HypolimnionInitial

DOM p = 0.002 Depth p =0.216 DOM*Depth = 0.585

No Terrestrial

Resource Subsidy

(-DOM)

With Terrestrial

Resource Subsidy

(+DOM)

(H)

(A)

Initial

(H) (H)

(A)

(H)(H)

(A)

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?

Lake Oesa, Canadian Rocky Mountains UV Transparency July 28, 2008-2009

0

2

4

6

8

10

12

14

16

10 100

Dep

th (

m)

380 nm UV (% of subsurface)

2008

2009

0

5

10

15

20

25

30

35

10 100

Dep

th (

m)

380 nm UV (% of subsurface)

2008

2009

0

5

10

15

20

25

30

35

0 10 20 30

Dep

th (

m)

CDOM fluorescence

2008

2009

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Dep

th (

m)

Turbidity

2008

2009

0

5

10

15

20

25

30

35

0 200 400

Dep

th (

m)

Chlorophyll Fluorescence

2008

2009

Lake Oesa Hesperodiaptomus July 28

0

5

10

15

20

25

30

35

0.00 1.00 2.00 3.00

Dep

th (

m)

Copepods per Liter

2008

2009

Oesa Zooplankton & Chlorophyll July 28

0

5

10

15

20

25

30

35

0.00 1.00 2.00 3.00

Dep

th (

m)

Copepods per Liter

2008

2009

10% UV380

0

5

10

15

20

25

30

35

0 200 400

Dep

th (

m)

Chlorophyll Fluorescence

2008

2009

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

Indirect Effects on Terrestrial DOM?

Low – Medium - High

Terrestrial Vegetation

DOM in water

Indirect Effects of Climate Change: Wildfire

Bark Beetle Damage

Lakes are Good Sentinels & Integrators of Climate Change: Direct & Indirect Effects

Williamson et al. 2009 Limnol. Oceanogr. 54:2273

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.

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

Extra Slides Follow

Net Zooplankton Grazing Effect

Treatment

DOM

-

DOM

+

DOM

-

DOM

+

Ne

t G

razin

g E

ffe

ct

(ml

cle

are

d/u

g z

oo

pla

nk

ton

/we

ek

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Epilimnion Hypolimnion

DOM < 0.001 Depth = 0.992 DOM*Depth = 0.839

Changes in DOC (% yr-1) (up to 100% in past 15-20 yr in some areas)

Monteith et al. 2007

Nature 450:537

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