significant seasonal and event- driven changes of carbon and nutrient fluxes to first-order streams...

Significant seasonal and event-driven changes of carbon and nutrient fluxes to first-order streams of an Amazon forest

Mark S. Johnson, Johannes Lehmann, Evandro Carlos Selva, Eduardo Guimarães Couto, Mara Abdo, Erick C.M. Fernandes,

Susan Riha

Cornell UniversityUniversidade Federal do Mato Grosso

Why study tiny catchments?

Clearly reflect land surface processesImportant measurements for determining

C balances and fluxes across interfacesOnce you get a bit (~50 m) downstream,

instream processes begin to strongly influence the aquatic picture

Site Description

Four perennial headwater catchments

Small streams originating as seeps (minas d’agua ou nacentes)

Juruena, MT

0.85 Ha1.69 Ha0.78 Ha0.62 Ha

N0 50 100 Meters

1

2

3

4 IKONOS Panchromatic Image(Courtesy EOS-Webster)

Headwater watersheds

1

234

0.85 Ha1.69 Ha0.78 Ha0.62 Ha

N0 50 100 Meters

1

2

3

4 IKONOS Panchromatic Image(Courtesy EOS-Webster)

Headwater watersheds

1

234

Jun-03 Aug-03 Oct-03 Dec-03 Feb-04 Apr-04 Jun-04

0

100

200

mm

d-1 throughfall

Site Description

Four perennial headwater catchments

Small streams originating as seeps (minas d’agua ou nacentes)

Juruena, MT

May-03 Jul-03 Sep-03 Nov-03 Jan-04 Mar-04 May-04

4.5

5.0

5.5

6.0

6.5

7.0

Streamwater pH- Seasonal Dynamics As dry season

progresses, streamflow pH rises.

Hypothesis: High GPP during rainy-season leads to higher soil CO2, and lower ground-water and stream water pH.

n=4 watersheds

100

mm d-1

Jul 03 Sep 03 Nov 03 Jan 04 Mar 04 May 04

Co

nd

uct

ivity

(S

cm

-1)

0

20

40

60

80

100

1200

100

Electrical Conductivity- Seasonal Dynamics As dry

season progresses, streamflow becomes more concentrated

Streamflow becomes more dilute as rainy season progresses.

n=4 watersheds

Carbon fluxes to forest floor

Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04

Litt

erfa

ll (g

C /

m2 )

and

Thr

ough

fall

(g C

/ m

2 )

0

25

50

75

100

Litter (g/m^2) TF (g/m2)

For period presented, 23X more C fell as litter than as DOC in throughfall

Selva et al., 2004 LBA poster 27.7-P for C in litterfall fractions

Mean ± SE, n=4 watersheds

DOC concentrations in surface runoff (enchurrada) Litter build up

during dry season leads to very large DOC values for surface runoff

Throughfall-DOC followed a similar pattern

01-Sep-03 01-Nov-03 01-Jan-04 01-Mar-04 01-May-04

0

100

200

0

10

20

30

40

50

60

70

DO

C (

mg

L-1)

Surface ponding- late in wet season

Rainfall-discharge-DOC flux relationship

DOC flux Discharge

Ra

infall (m

m d

-

1)

01-Sep-03 01-Nov-03 01-Jan-04 01-Mar-04 01-May-04

0

100

200

0

100

200

300

Dis

char

ge (

x 1

03 L

da

y-1)

and

DO

C fl

ux (

g d

ay-1

)

Ra

infall (m

m d

-1)

DOC stream export Discharge (vazão)

High surface DOC concentrations during dry to wet transition leads to high DOC export

Lower surface DOC concentrations during late rainy season leads to lower DOC export

Baseflow and storm flow DOC DOC (mg/L)

Baseflow Storm flow Ratio

Oct-03 5.7 10.0 1.7

Nov-03 3.1 9.9 3.2

Dec-03 2.4 7.5 3.1

Jan-04 2.1 7.3 3.5

Feb-04 1.9 5.8 3.1

Mar-04 1.1 3.6 3.3

Apr-04 0.7 3.8 5.3

Baseflow and storm flow CPOC

Intact leaves transported during baseflow

Fragmented material transported during storm flow

Evandro Selva et al., 2004, LBA poster 27.7-P

Rapid surface runoff, rapid stream response

Overland flow present

Percolation present at 10 cm

13:00 14:00 15:00 16:000

20

Ra

infall (m

m) p

er 5 m

inu

tes

0

10

20

Discharge

rainfall D

isch

arge

(L

s-1)

Time of Day, 28 April 2004

24 April 2004, Watershed 4

12:00 13:00 14:00 15:00 16:00 17:00

pHD

O (

mg

L-1)

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

EC

( S

cm

-1)

0

5

10

15

20

25

30

pH Dissolved OxygenElectrical Conductivity

Storm dynamics- pH, DO, EC

Storm water shows initial surficial contribution

Then, increasing contribution of subsurface lateral flow More anoxic More acidic More dilute

Groundwater seeps pH = 4.56 EC = 7 µS cm-128 April 2004, Watershed 2

pH Dissolved OxygenElectrical Conductivity

CO

2(aq

) pp

m

Lateral flow delivering CO2 pulse

28 April 2004, Watershed 2 12:00 13:00 14:00 15:00 16:00 17:00

Dis

char

ge (

L s-1

)

-1)

0

10

20

0

2000

4000

6000

8000

Discharge CO2(aq)

CO

2 (aq) p

pm

Initial CO2 decrease due to surface contributions

Storm water pulse of free CO2 flushed out of soil profile with interflow (rapid subsurface flow)

Terrestrial-aquatic organic C flux

DOC84.6%

POC12.1%

CPOC3.3%

DOC84.6% POC

12.1%

CPOC3.3%

Jan - May 2004

Dissolved C exports are 5.5X solid C exports

Large losses of CO2 from emergent groundwater

Forested Ultisol-OxisolSouthern Amazon, Juruena, MTN=30(from 4 watersheds)

Distance from spring (m)

0 20 40 60 80 100 120 140 160 25000

5000

10000

15000

20000

25000

30000

35000

y=24489.9/(1+0.1189X)r=0.79

pC

O2 (

pp

m)

Johnson et al. (unpublished data)

Terrestrial-aquatic C flux components

Jan - May 2004

DOC6.6%

HCO3- C15.7%CO2-C(aq)

10.5%

CO2-C outgas evasion66.0%

CPOC0.3%

POC0.9%

Solid Phase1.2%

Conclusions Solid inputs >> dissolved inputs Gaseous outputs >> dissolved outputs >> solid

outputsAboveground DOC fluxes become more dilute

over the course of the wet season If soil DOC are in equilibrium, aboveground fluxes are

important driver of variability within DOC system

Nested temporal scales are an important feature of the terrestrial-aquatic interface

AgradecimentosLBA and organizing committeeRohden Indústria Lígnea Ltda. for site access

and support (parabens pela sua certificação!)Jeff Richey, Alex Krusche and Paulo Nunes

for conceptual and logistical support Benedito Silveira de Andrade and Elielton

Anterio da Souza for field assistanceAo povo Brasileiro e Juruenense