Organic Matter Sources and Transformations Along a Headwater Stream-River Continuum

S. Leigh McCallister and Eric HallVirginia Commonwealth University

Reevaluation of the global carbon model (Takahashi et al., 2002)

From Sabine et al., 2004

Cole et al. 2007

Nature (2009)

Swift River Watershed and Connections to Quabbin Reservoir

Eddy Covariance Data

• Relatively high nighttime CO2 flux from the northwest sector of the footprint of the Wofsy group’s EMS tower measured for over 12 years

• Where did this CO2 come from?

01

23456

789

Ave

rage

nig

ht C

flux

(µm

ol m

-2 s

-1 )

1992 1994 1996 1998 2000 2002 2004

SW wind

NW wind

Slide by Jenny McInnis, 2005

What Drives Bioavailability

• Discharge• OM source• Inorganic Nutrients• OM quality• Photochemical Interactions

Can we discern the input of different sources of OM and their respective ecological fates along a stream contiuum?

0

20004000

60008000

1000012000

1400016000

18000

-800 -600 -400 -200 0 200

Distance from the Swamp (m)

[CO

2] (p

pm)

BigelowBrookUpstream

BeaverSwamp

BigelowBrookDownstream

Stream Carbon Dioxide [ ]

Stream Colored Dissolved Organic Matter

Conceptual Model Baseflow conditions

deep water table and dry soil

stream fed by deep groundwater depleted in DOM, leading to low stream-water DOC concentrations (C).

streamwater table

litter layer

upper soil horizon

lower soil horizon

streambed gravelwater movement

Stormflow conditions

water table elevation and soil moisturerise in response to rainfall

flow initiated in shallow soil horizonsrich in organic matter (OM)

shallow subsurface stormflow leaches OM and enters stream, which raises C.

stream water table

litter layer

upper soil horizonlower soil horizon

streambed gravelwater movement

DOC from Headwaters to the Quabbin

May ‘10

Seasonal Changes in Quality

Distance from Headwaters0 5000 10000 15000 20000 25000 30000

DO

C:D

ON

10

20

30

40

50

60

70

80

90Sept '09March '10May '10

Distance from Headwaters (m)0 5000 10000 15000 20000 25000

% L

abile

(28

days

)

0

5

10

15

20

25

% Lability with Distance from Headwaters

DOC Lability

Distance from Headwaters0 5000 10000 15000 20000 25000 30000

% L

abili

ty

0

5

10

15

20

25

30

35

40Sept '09

March '10

May '10

NO relationship with C:N

Photochemical Enhancement of DOC consumption

Sampling locationsL.B. Brook Swamp Pond Quaker

% L

abili

ty

0

10

20

30

40

50DarkUV exposed

Various facets of DOC bioavailability

k 0

Guillmette and del Giorgio 2011

% DOC consumed 2 vs 28 days

Distance from Headwaters0 5000 10000 15000 20000 25000

% L

abili

ty0

4

8

12

16

20

0-28 days0-2days

0 5000 10000 15000 20000 250000

10

20

30

40

% L

abili

ty

Distance from Headwaters

Sept ‘09 discharge 20 (cubic ft/s) ‘March ‘10 discharge 265 (cubic ft/s)

DOC concentration controls LTCC

DOC (mg/L)0 2 4 6 8 10 12

k (L

TCC

)

-0.06-0.05-0.04-0.03-0.02-0.010.000.01

r2= 0.65

p < 0.0001

13C-DOC

Distance from Headwaters0 5000 10000 15000 20000 25000 30000

13C

(per

mil)

-33

-32

-31

-30

-29

-28

-27

-26

Sept '09March '10May '10

Deciduous -27.6Coniferous -31.2Soil -26.8SAV -38.2Algal (slime) -36.7Marsh -28.9

Watershed Controls

Mixed Forest best predictor for stream DOC concentration

Sept ’10 and ’11, Deciduous land cover best predictor for both the amount and % of DOC consumed

May ’09 and May ’10 Open water best predictor for the rate and amount of DOC consumed

The Boundless Carbon Cycle.

How can we combinediverse data sets tounderstand the flux and fate of terrestrial OM intoaquatic ecosystems?

Future Research ???OM Characterization

Thanks to NSF-DEB

Harvard Forest

Emery Boose

Bill Sobzcak