On the Role of River Systems in the Global Carbon Cycle (with a Twist)

J. RicheyMarch 12

RIVERS IN THE GLOBAL CONTEXT

Riverine C Cycle The River Continuum

… a strategy for taking basic science information and translating it into water resource information and

management at regional scales

GLOBAL RIVER C CYCLE

VEGETATION

SOILS (+)

ATMOSPHERIC CO2

Active SOM,NP (1-2y)

Int. SOM,NP (20-40y)

Pass, SOM,NP (1000y)

Litter

COASTALOCEAN

SHELF SEDIMENTS

~.4 aw

DOC UV Ox?

.1 cw, ~.4aw

.1 cw,~.4aw

.2

.2

MCO3

.2S&S

gigatons/ycw = conventional wisdomaw = alternate wisdomS&S = sensu Sarmiento & Sundquist(+) anthro. effect

RIVERS

ESTUARIE

S

ANTHROPOGENICN,P, Toxics

(+:1.8+1.1)

(P Desorp)

PPR

PPT->Q

DAMSRIP

ARIAN

(1)CO2+H20+M(C,Si)O3->M+2HCO3(2) SOM->CO2

erosion, PPr

leaching

DIC (pCO2,HCO3)

POC (.5uM - 1mm)

DOC (%s < .5uM) Q (N,P,Toxics)

.4 (+)

.2 cw .5aw(++)

.2 (~)

.1 cw, ~.4aw

COASTALOCEAN

POC Loading by Geographic Region (Tg/y)

Oce

AsE

AsSE

SA NE

SA W

SA SE

NA WNA At

NA EGEA At

Eur

Afr W

Afr E

Aust

0

50

100

150

200

250

300

350"Traditional": 200

Area-loading: 350

Calc. Yield: 800

"Best Guess: ~500 ish"

A

SEAs

Discharge1.3 M m3/s

Ocn

Sediment Transport31,000 MT/y

A

SEAs

Are the Humid Tropics a Source or Sink of C?

Uptake (Towers)3-8 Mg C ha-1 y-1

Biomass Accumulation (long-term plots) .7 ± .4

Soil Accumulation (long-term plots) .6 ± .3

Deforestation 1-2 Pg y-1(?)

“…that leaks out of the forest in forms that are not usually measured, … Although this C leakage is thought to be relatively small, surprises cannot be ruled out.” Malhi and Grace (2000)

VOC (??)

Dissolved C

TOC Export (to the Sea)Global .4 - .8 Pg y-1

Amazon 36 Tg y-1 (.06 Mg C ha-1 y-1)

CO2 EVASION Amazon Mainstem 15 Tg y-1

River Corridors ?????

NPP

Evasion(i,t) = km2 * D(pCO2‑Ceq)/z

Richey et al. (in press). Nature.

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PB-1

PB-2

JaruJIP-3

COM-1

COM-2

JIP-1

Rolim

UrupáJIP-2

JIP-4

JIP-5Preto

Machadinho

Streams (< 100 m in width)

15

0

5

10

20

25

J F M A M J J A S O N D

Flo

od

ed A

rea

(x 1

04 km

2 )

T (>100m)

MC

S (<100 m) MF

Inundation in Amazon Rivers

10

15

20

25

%

1.77 x 106 km2

J F M A M J J A S O N D

0

4

8Man

pC

O2

(x 1

03 a

tm)

Dissolved Carbon Dioxide in Amazon Rivers

0

4

8

12

Man

Jt

Jr

Sol

IcMd

Pr

Ng

Jp

atm

15

0

5

10

20

25

30

J F M A M J J A S O N D

CO

2 E

vasi

on

(T

g C

mo

-1)

T (>100m)

S (<100 m)MF

MC

: 1.2 ± . 3 Mg C ha-1 y-1 (basin ~ .5 Gt y-1)

CO2 Evasion from Waters of the Central Amazon

POTENTIAL CO2 SOURCES

~ 1. 2 Mg C ha-1 y-1

0.0

0.4

0.6

Litterfall Plankton MacrophytesSoil DOCSoil CO2

0.2

Extrapolation to Humid Tropics:~0.9 Gt y-1

(3x > previous global)

Schimel et al. (2001) Gurney et al. (2002)

Zonal distribution of terrestrial and oceanic C (deduced from inverse models using different techniques and sets

of atmospheric data, corrected for anthropogenic emissions)

“… A return flux from water to the atmosphere of this (0.9) magnitude comes closer to reconciling independent carbon budgets for the tropics.”