The influence of climate-induced alterations in dissolved organic matter on metal toxicity and UV radiation in

Rocky Mountain streams

William H. Clements, Dept. of Fishery and Wildlife BiologyJill S. Baron, Natural Resource Ecology Laboratory

Colorado State University, Fort Collins, CO

Diane M. McKnight, Institute of Arctic and Alpine ResearchUniversity of Colorado, Boulder, CO

Joseph S. Meyer, Department of Zoology and PhysiologyUniversity of Wyoming, Laramie, WY

Resp

onse

Variab

le

Time

Recoverya

b

c

New steady state

New steady state

Disturbance of an impaired system

Paine et al. 1998

Compound Perturbations & Ecological Surprises

Hypothetical recovery trajectory

Two disturbance events

Heavy Metal Pollution

Year

1960 1970 1980 1990 2000 2010

CO

2 (µ

L/L)

310

320

330

340

350

360

370

380 Climate Change

UV Radiation

Climate-induced changes in hydrology and biogeochemistryUV-b Radiation

Toxicity & bioavailability of metals

Penetration ofUV-b radiation

Structure and function of benthic communities

Quality & quantity of DOM

Fulvic AcidHumic AcidHumin

Field Monitoring

Spatiotemporal variation in physicochemical characteristics of 21 Colorado streams along a gradient of metal contamination

Assess the relationship between discharge and DOC quality/quantity

Characterize the influence of DOC on UV-b attenuation

Measure effects of photobleaching on DOC quality/quantity

Fairplay

Eagle

Breckenridge

Georgetown

Winter Park

Buena Vista

Leadville

Field Monitoring

April-October, 2003

Routine phys-chemDischargeDOCNutrientsCations, anionsHeavy metals

Co

nce

ntr

atio

n (

mg

/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6Zinc

Station

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

DOC

Approx. Criterion Value

0

1

2

3

4

5

6

7 Arkansas

0

2

4

6

8

10

12

14

m3/s

DOC

Eagle

Apr 19

May 5

May 19

June 8

July

1Aug 5

Sept 7Oct 1

1

0

1

2

3

4

5

6 Chalk

Apr 19

May 5

May 19

June 8

July

1Aug 5

Sept 7Oct 1

1

0

1

2

3

4

5

6 Tennessee

Log10 Discharge (cms)

-2 -1 0 1 2

Log 1

0 D

OC

-2

-1

0

1

R2 = 0.29

Percent Forested Area10 20 30 40 50 60 70 80

Mean D

OC

(m

g/L

)

-2

-1

0

1

2

3

4

5

6

R2 = 0.59

Prusha and Clements (2004)

TerrestrialVegetation

DOC

Discharge

Zn

ZnZnVariable

βr2

[Zn] in water 0.20 0.42

[DOC] -1.69 0.25

Zn

ZnZn

Vertical attenuation coefficients (Kd)

Eagle River, ColoradoUV-B, 6-21-03

mW cm-2

0.0 0.1 0.2 0.3

Dep

th (

m)

0.00

0.10

0.20

0.30z

EE

ln

K 0

Z

d

Where: z = depth Ez = irradiance at depth E0 = irradiance at surface Kd = vertical attenuation coefficient

Mean Summer [DOC] mg/L2.42.22.01.81.61.41.21.00.80.6

UV

-B A

tten

uat

ion

(K

d)

10

8

6

4

2

0

y = 4.39x-1.78R2 = 0.8898

DOC and UV-b Attenuation

Zuellig & Brooks, unpublished

Fractionation (XAD-8 resin) to determine quantity of fulvic acids

2-D fluorescence (Fluorescence Index) to determined source

(ie., allochthonous vs. autochthonous

Spatiotemporal variation in DOM quality

DateApr 1

9May 5

May 19

June 8

July

1Aug 5

Sept 7

Oct 11

Flu

ores

cenc

e In

dex

1.3

1.4

1.5

1.6

1.7

1.8

Per

cent

Ful

vic

Aci

d

0

10

20

30

40

50

60

70

Eagle Clear Snake

TerrestrialOrigin

MicrobialOrigin

Appel & McKnight,unpublished

DOM Composition

Photobleaching DOM

Irradiated with Solar Simulator

Concentrated with RO

Exposure (h)

0 12 24 36 48

[DO

C]

(mg

L-1

)

20

30

50

60

70

80HomestakeEagleEF5 WetlandEF5 RiverDeerSnakeX

~ 13.4% reduction

Brooks et al., unpublished

Microcosm Experiments

Assess effects of UV radiation and metals on benthic communities with different metal exposure histories

Hypotheses:

Effects of UV-B radiation + metals will be greater than either stressor alone

Effects of metals will be greater on naïve communities (ie., no prior metal exposure)

West Tennessee Creek(reference)

Arkansas River

Trays colonized in field

Transferred to microcosms

2 x 2 factorial (metals x UV) for 10 d

Stream flow

Trays

Drift net

Measured drift, metabolism, community structure

UV-b Lamps

Num

ber

of M

ayfli

es D

riftin

g pe

r S

trea

m

0

20

40

60

80

100

120

140

Treatment

C UV M UV+M0

5

10

15

20

25

30

Arkansas River

West Tennessee Creek

MacroinvertebrateDrift

Kashian & Clements, unpublished

CommunityMetabolism

Kashian & Clements, unpublished

Field Experiments

Hypothesis:

Benthic communities from metal-polluted streams are more susceptible to ambient UV-b radiation than those from unpolluted streams

Study Design

12 sites

• Split plot: UV-B excluded and ambient

• 60-day duration (July-September)

• Estimated UV-B exposure at stream bed

• Chlorophyll a and community structure

UV-b No UV-b

~ 2.5 tons cinderblock~ 1000 feet PVC~7500 miles

UV-b Dosimeters

UV-B Quantification

• Dosimeters replaced every 4 to 6 days

•Absorbance calibrated to UV-B exposure

•Measured depth, DOC, and Kd

• Estimated total UV-B exposure at streambed

UV-B at the streambed

StationTenness

eeCotto

n

West Clear

EF510Mile

4Mile

Bucksk

inClear

Mosquito AR3

FrenchChalk

UV

-b a

t S

trea

mbe

d (J

/cm

2 )

0

50

100

150

200

250

300

Zuellig et al. unpublished

0

0.05

0.10

0.15

0.20

0.25

Background Low Med High

Ch

loro

ph

yll a

ug

/ L/c

m2

Metals Gradient

ANOVA Sig.Treat 0.047Metals 0.937Treat*Metals 0.991

NoUV

UV

Power Analysis Treat 0.516Metals 0.074Treat*Metals 0.056

0

20

40

60

80

100

120

Background Low Med High

Scr

aper

Ab

un

dan

ce

Metals Gradient

ANOVA Sig.Treat 0.832Metals 0.001Treat*Metals 0.640

NoUV

UV

Power Analysis Treat 0.110Metals 1.00Treat*Metals 0.412

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6N

et C

om

mu

nit

y M

etab

oli

sm

FrenchW Tenn 4-mile Mosquito Chalk

No UV

UV

Kashian et al. unpublished

Summary- Monitoring Results

•DOC increased with discharge & vegetation

•DOC strongly influenced UV-B attenuation

•Spatial and temporal variation in DOC quality

•Photobleaching reduced [DOC]

Summary- Microcosm Experiments

•Metal effects greater on communities with no history of metal exposure

•Drift in reference communities responded to UV-b and metals

•Effects of metals & UV-b greater than either stressor alone

Summary- Field Experiments

• Chlorophyll a increased when UV was eliminated at reference sites

• Macroinvertebrate response to UV was weak low statistical power

•Community metabolism responded to bothmetals and UV-b

Implications

•Benthic communities in shallow, alpine streams exposed to intense UV-b

•Climate-induced changes in DOC are likely to increase UV-b exposure & metal

bioavailability

•Potential for interaction between metals and UV-b in structuring benthic communities

Future Research

• Model relationship between climate change, stream hydrology and DOC

• Photodegradation of DOC and metal bioavailability

• Larger scale experiments to address statistical power

Acknowledgements

Bob Zuellig, Donna Kashian, Marjorie Brooks

Oliver Cox, Walter Johnston, Lea Ann Zuellig, Jeremiah Davis, Bryn Johnson, Dan Kashian, Cindy Kipley, Heather Lyons, Katy Mitchell, Jeremy Monroe, Joe Nicholson, Lorie Peterson, Blair

Prusha, Travis Schmidt, Ted Soileau, Richard Thorp, Crystal Van Cutsem, Nicole Vieira, Rudy Zuellig Sr., Colorado Mountain

College, Bureau of Land Management, Arapahoe National Forest, Pike National Forest, San Isabel National Forest, B + B Mines, Clear Creek County, Milam Family, Edith Seppi, Sondra Dirks

R829640