Global C cycle with role of Inland Waters

This is a presentation that combines work from Cole’s ECI Book: Cole, J.J. 2013. Freshwater ecosystems and the carbon cycle. In: Kinne O (ed) Excellence in ecology. Book 18. International Ecology Institute, Oldendorf/Luhe 146 pp) and from his chapter in a recent text book on ecosystem ecology (Cole, J.J. 2012. The Carbon Cycle. Chapter 6, pp 109-136 IN: Weathers, K, D. L. Strayer, and G.E. Likens (eds). Fundamentals of Ecosystem Science. Elsevier, New York. 312 pp.

• Both books are available for sale by the publishers. • Cole (2012 at: http://www.int-res.com/book-series/excellence-in-ecology-

books/ee18/ • And Weathers et al. (2012) at: http://store.elsevier.com/Fundamentals-of-Ecosystem-

Science/Kathleen-Weathers/isbn-9780120887743/

• Partial support for Cole in both cases came from the National Science Foundation, (Cole, J.J. OPUS: Terrestrial carbon in Aquatic Ecosystems: A synthesis. NSF-DEB 1256119. 15 February 2013-14 February 2016) and from the Cary Institute of Ecosystem Studies. An earlier version of this talk was presented at a meeting of the Association for the Sciences of Limnology and Oceanography (ASLO), Cole, J. J.; “Terrestrial support of lake food webs: a weight of evidence argument.” (Abstract ID: 13330). Joint Aquatic Science Meeting. Portland Oregon, May, 2014.

• •This presentation may be helpful in teaching about the global C cycle in general and the role of inland waters in that cycle.

Outline • Ecosystem boundaries at the global scale.

• What is a “global” biogeochemical cycle?

• Major pools of C on earth

• C cycle at several time scales:

– Modern (perturbed)

– Pre anthropocene (past 10,000 years)

– Glacial- interglacial scale (400,000 years)

– BREAK

– Earth’s history

• Basics of the C cycle and its links to O

• A counterintuitive idea about atmospheric O2?

• The regulation of a global cycle depends on the time frame considered.

An ecosystem is defined as a spatially

explicit unit of the Earth that includes

all of the organisms, along with all

components of the abiotic

environment within its boundaries

– Likens 1992

When looking at

the Earth as an

ecosystem, most

scientists draw

boundaries between

the “solid” planet

and the

atmosphere. Use

inputs and outputs

from the Earth to

atmosphere as

ecosystem fluxes.

Marine Sediments 20,000,000

At least 9,000,000 is organic C

Land

450 plants

700 detritus

Ocean

5 plants

3000 DOC

38,000 HCO3

Atmosphere 760

102/y 98/y 100/y 100/y

Terrestrial soil - 2150;

Lake sediments - >25,000

Reservoir C mass (Pg) comments Reference

Earth 100,000,000 Poorly known Schlesinger (1997)

Sedimentary rocks - carbonate

65,000,000 Schlesinger (1997)

Sedimenrary rocks- carbonate

16,000,000 Schlesinger (1997)

Marine dissolved carbonates (DIC)

38,000 Sum of dissolved CO2, HCO3 and CO3.

Sundquist and Viser (2005)

Large lake sediments

19,510 Most in African rift lakes

Alin and Johnson (2007)

Fossil fuel (coal, oil, natural gas)

5,200 Known plus likely reserves

Sundquist and Viser (2005)

Terrestrial soils 2,150 Sundquist and Viser (2005)

Atmospheric CO2 750 Modern, industrial, rising

Houghton (2005)

Reactive marine organic C

650 Sundquist and Viser (2005)

Terrestrial vegetation

560 Houghton (2005)

Marine biota 2 Houghton (2005)

Modern- perturbed C cycle

The modern global C balance

• Atmospheric CO2 has risen more rapidly in the past century than at any other time in earth’s history.

• Why is atmospheric CO2 rising?

• What is the evidence for the causes?

• How strong is this evidence?

Suess Effect

Change in 14C (and 13C) in the

atmosphere due to human process.

Named for Hans E. Suess

What changes and why?

Evidence Item #1

Decline in 13C of CO2

Decline in atmospheric 14C

coincides with industrialization.

What happens to this record

after 1950?

From (Levin et al., 2010).

World Climate Report

Evidence Item # 2. Atmospheric CO2 is highly correlated to the

global human population. R2> 0.95

CO2 versus fossil fuel use- global

Fossil fuel use - millions of metric tons per year

0 2000 4000 6000 8000 10000

CO

2 M

aun

a L

oa

(pp

mv

)

260

280

300

320

340

360

380

400

year 1800, extrapolated from other data

Y = 0.013X + 275; r2 = 0.97

Saga Commodities INC

Percent of global CO2 emissions by “country”

Saga Commodities INC

Met

ric

tons

CO

2 p

er c

apit

a per

yea

r

Global C balance in Gt y-1 rough numbers after Schimel et al. 2001

• Emissions to atmosphere 6.5

• Increase in atmosphere 3.1

• Oceanic gas exchange -1.5 (physical)

• Net “terrestrial sink” -1.9 (biological)

• How are these numbers validated?

Modern atmospheric CO2

• Rising rapidly • Fossil fuels as cause of increase supported by: mass balance isotopic evidence (14C and 13C) correlation to human population growth correlation to global fossil fuel use lack of other credible explanations What is the story for the pre-industrial period and

earlier time frames?

Past 1500

years

Past

160,000

years

Years before present-400000 -300000 -200000 -100000 0

180

220

260

300

340

1000 1200 1400 1600 1800 2000

Atm

osp

her

ic p

CO

2 (

atm

)

240

280

320

360

Calendar year

1950 1960 1970 1980 1990 2000 2010 2020

300

320

340

360

380

400

C

B

A

Very long –

400,000,000

years

Past 1000 y

Recent

record

CO2 in the

distant past

has been

nearly as

high a

present- the

rate of

increase at

present is

unique

Past 10,000 years of atmospheric CO2

• Relatively stable.

• Not decreasing. (Falkowski and Raven)

• If organic C was stored on land, where did CO2

come from?

• What C supported terrestrial export production which is near 0.5 Gt C y-1

• Volcanism -not larger than ~0.09 Gt y-1

Atmosphere

Increasing rapidly

3.1 Gt y-1

Ocean

sediment – 0.12 Gt y-1

Modern (50 y)

1.3Gt y-1

~1.9 Gt y-1

Terrestrial NEP > 1

Gt y-1

6.3 Gt y-1

Volcanoes

<0.09 Gt y-1

Atmosphere

Increasing slowly

0.02 Gt y-1

Ocean

ocean sediment buries

0.12 Gt y-1

Post glacial (10,000 y) Volcanoes

<0.09 Gt y-1

??Gt y-1

Values after

Sundquist 1993

Export >

0.4 Gt y-1

Pre-anthropocene balance sheet

in Pg C for past 10,000 years or so

• Inputs to atmosphere:

– Volcanism 0.09

– Change in atmospheric standing stock of CO2 < 0

• Outputs from the atmosphere

– Burial of organic C in marine sediment 0.12

– Terrestrial NEP

• Increase in plant biomass ~0

• Increase in soils and sediments 0.06

• Export of POC and DOC in rivers 0.4

– Sum of Outputs 0.58

• Missing source to atmosphere = 0.58 – 0.09 = 0.49

Where did the missing atmospheric source come

from?

• Need 0.49 Pg C y-1

• Did not come from land

• Did not come from volcanism

• What is left?

• Area of global ocean 361 X 106 km2

• That is 361 X 1012 m2;

• 0.49 Pg C= 0.49 X 1015 g C

• Or an imbalance of 1.4 g C m-2 y-1

• Easily possible for an excess of R over GPP in the ocean

Can we account for that 0.49 Pg y-1 imbalance in

the ocean

• Several steps to get there:

• Review the algebra of GPP, R and NEP

• Rewrite these as a mass balance equation

• Apply this to the ocean

Components of Productivity

CO2 GPP

NPP

Detritus and

exudates

Not

decomposed Exported

Buried (Sediments

and SOM)

Consumers

Ra

Decomposers

Rh Plant biomass

accumulation

NEP

(Rt = Ra + Rh)

GPP review

• GPP = total photosynthesis (> 0)

• R = total respiration (> 0)

• NEP =GPP-R (may be + or -)

• When NEP is +, equals burial plus export

• When NEP is -, net heterotrophy

NEP algebra. • External Import from Outside ( Ie)

• Export from ecosystem (E)

• Burial (export to sediments) (B)

• GPP (gross primary production)

• R (total respiration in the system)

• Total Inputs = GPP + Ie

• Total losses = R+E+B

• Total Inputs = Total Losses (conservation of matter)

NEP Algebra Continued

• Since NEP = GPP-R, we can rearrange

• (GPP-R) = E+B-Ie or:

• NEP = E + B – Ie

• So you do not need to measure GPP or R to get NEP.

• If Ie is > (E+B), NEP is NEGATIVE

Terrestrial

Biosphere

500 -1000 Gt

Terrestrial

detritus

1000-2000 Gt

Marine

Biosphere

2 - 4 Gt

Marine

detritus

500 -1000 Gt

Marine

sediments,

organic

20,000,000 Gt

Atmosphere 760 Gt

~ 48 Gt/y photosynthesis ~52 Gt/y photosynthesis

Biological parts of the C cycle (after

Holland, 1993).

-2 -1 y

0.12 Gt/y 0.4 Gt/y

river

transport

whole ocean net heterotrophy is

Burial + Export - Import 0.12 –0.4 = -0.28 Gt/Y or OR ~0.8 g C m

burial

R ~100-0.12

99.8Gt/y

Let’s make the equation clearer

• Import from land via rivers = 0.4 Gt C/y

• Export from the ocean = ~0

• Burial in marine sediments = 0.12

• NEP = E + B – Ie

• NEP = 0 + 0.12 -0.4 = -0.28 Gt C/y

• This is about 0.8 g C m-2y-1

Correct order of magnitude

• Needed 0.49 Pg C y-1 ( 1.4 g C m-2y-1)

• Calculated that R >GPP by 0.21 Pg C y-1 or about

0.8 g C m-2y-1

• We are very close and easily within error limits.

• Other sources of marine CO2 to the atmosphere:

– Coral reef building

– Precipitation of calcite and aragonite shells

– HOMEWORK- explain how coral reefs, shells and the

manufacture of concrete are all CO2 sources

Are you disturbed?

• The modern ocean is presently a sink for atmospheric

CO2 of about 2 Pg C y-1

• Using modern values, we calculate that R exceeds GPP

by about 0.3 Pg C y-1

• Why is the modern ocean NOT a source of CO2 to the

atmosphere?

• Because atmospheric CO2 is rising! The ocean is a slight

source of CO2 to the ocean but it is trapped.

Outline • Ecosystem boundaries at the global scale.

• What is a “global” biogeochemical cycle?

• C cycle at several time scales:

– Modern (perturbed)

– Pre anthropocene

– Glacial- interglacial scale (400,000 years)

– BREAK

– Earth’s history

• Basics of the C cycle and its links to O

• A counterintuitive idea about atmospheric O2

• What role to freshwater systems play in the global C balance?

• The regulation of a global cycle depends on the time frame considered.

Back to global – let’s link C and O cycles over earth’s history

0.00

0.05

0.10

0.15

0.20

0.25

1 2 3 4

Billions of years before present

pO

2 (

atm

)

cyanobacteria

eucaryotes

Land plants

mammals

Where does oxygen come from?

• Photosynthesis

• Balance between GPP and R

• GPP-R=NEP= org C burial.

• Atmospheric Oxygen comes from org C burial.

• If atmospheric O2 has been “flat” for the past

500,000 years, what does that imply?

What ever controls organic C burial

controls atmospheric O2

• O2 >> 0.2 atm leads to increased fire.

• O2 << 0.2 atm unsuitable for most aerobes

• What controls C burial?

– Mayer hypothesis

– Oxygen hypothesis. (Harnett et al)

Mayer 1994

0

5

10

15

20

25

0 10 20 30 40

Surface area (m2/g)

OC

(m

g/g

)

Clay rules!

Where does clay come from?

Foree and McCarty 1970 and many

others

0

25

50

75

100

0 100 200 300

time (days)

pe

r ce

nt

rem

ain

ing aerobic

anaerobic

Betts and Holand 1992

0

40

80

120

160

0 100 200 300

Bottom water O2 (uM)

Bu

ria

l e

ffic

ien

cy %

Hartnett et al, Nature 1998

• What is the debate they bring up?

• What is the new twist here.

• What is the “experiment”

Oxygen exposure time (yr)

0.01 0.1 1 10 100 1000

10

20

30

40

Hartnet et al.

Hartnett et al, Nature

GAIA (Lovelock, 1991)

• Hypothesis: Earth is kept in a state favorable to living organisms by (in part) living organisms.

• Theory: sees Earth as system in which evolution of organisms is tightly coupled to evolution of the environment. Self regulation of climate and chemistry are emergent properties of this system

Thank you.

• I am willing to meet with you by skype when you have time, if you want to.

Organic C burial in lakes is large

• Natural lake organic C burial – 0.065 Gt y-1 (Mullholland and Elwood 1982)

– 0.034 Gt y-1 (Dean and Gorham 1998; Stallard 1998)

• Lakes sequester 28 to 54% as much organic C as does the global ocean!

• Oceanic organic C burial ~0.12 Gt y-1

• See Cole et al. 2007, Ecosystems

data of Dean and Gorham (1998). Units

are Tg y-1

organic C. Total is 420 Tg y-1

or

0.42 X 1015

g C y-1

Note Ocean may be as low as 60 and Reservoirs >200.

Ocean basin (130)

Reservoirs (160)

Small Lakes (23)Large Lakes (6)

Inland Seas (5)

Peat lands (96)

Why do lakes bury so much organic C?

• Rich theory of C preservation in the sea – Oxygen exposure time hypothesis

– Sorptive preservation hypothesis

• Poorly developed theory in freshwaters. – Low oxygen (a real possibility)

– Low sulfate (especially compared to ocean)

– High lignin (plus low O2) – can be dismissed

• Certainly not close to a universal law of C burial in freshwaters.

High organic C

content in

freshwater

sediments.

This Danish

man from 500

BC (so

somewhat older

than our St.

James) was

preserved in bog

sediment.

Dr. Morten Sondergaard a

living Dane and scientist.

Why did Morten’s progenitor preserve – or why do freshwater sediment have

so much organic C?

• (From the Tollund man web site)

• No oxygen, therefore no bacteria, and no rotting.

• Sphagnum inhibits bacteria

• Special acids inhibit bacteria

• Tannins ‘tan’ the hide.

Burial Efficiency- Oxygen exposure time Hartnett et al. 1998 Nature

Burial Efficiency = Burial / Input = Burial / (Burial + Respiration)

Oxygen exposure time (yr) Org

anic

C B

uri

al E

ffic

ien

cy (

%)

An empirical organic content model

Hakanson 2003

IG = loss on ignition (%DW)

SMTH= 52 week smoothing function

ADA = drainage area; A lake area

Drel = relative depth;

color = water color

Drel is the relative depth (= Dmax · √π/(20 ·

√Area),

Predicted = 0.9024* Observed + 2.4492

R2 = 0.8189

-20

0

20

40

60

0 20 40 60

Observed IG

Pre

dic

ted

IG

NOTE – oxygen is NOT part of this model!!

Whole-lake areation experiment Engstrom and Wright 2003

• 10 lakes in Minnesota • Cores taken before and after aerating 5 • 5 lakes as ‘control’ • Areation was from 8 to 18 Years. Near

continous. • Irregular effect of aeration on total sed

accumulation • Areated lakes did not decrease in organic

content.

Engstrom and Wright 2003

Aerated

Non- Aerated

Carbon in freshwaters – summary so far

• Globally, lakes bury about 40% as much organic C as does the ocean.

• We do not have good models for C preservation in lake sediments. Research opportunity.

• River delivery of organic and inorganic C to the ocean is an important term in the global C balance.

• Lakes and rivers tend to be net heterotrophic – must respire some terrestrial C.

• Does this terrestrial C move up the food web? Research opportunity.

GPP R

sedimentation

Net gas flux

transport

Do Freshwater systems matter in the global C balance?

NCEAS working group

Cole et al. Ecosystems

2007

Integrating Terrestrial and

Aquatic C Cycles (ITAC)

Rob Streigl, Nina Caraco,

Lars Tranvik, Bill

McDowell, Carlos Duarte,

Jack Middleburg, John

Melack, Yves Prairie,

Pirkko Kortalainen, John

Downing, Jon Cole

Rivers also transport “atmospheric” C

• Terrestrial OC in rivers to the ocean (units are Gt y-1 (from Meybeck 87; Sarmiento and Sundquist 92; Stallard 98:

• Dissolved organic C - 0.23

• Particulate organic C - 0.30

• Total organic transport 0.53

• Note implied loss from land is larger by 0.23 number or ~ 0.75 Gt y-1 to balance riverine gas flux.

Dissolved inorganic C (DIC)

• DIC is CO2 +H2CO3 + HCO3 +CO3

• DIC in rivers is dominated by HCO3

• At pH 7.3 HCO3 is 10X CO2 and 100X CO3

• Where does riverine HCO3 come from?

• How does the transport of HCO3 fit into the terrestrial C balance?

Riverine HCO3 is soil respiration in disguise

• The ultimate source of C in HCO3 is (mostly) the atmosphere.

• Alkalinity comes from rock weathering which either consumes atmospheric CO2 directly or consumes CO2 from soil respiration.

• Terrestrial NEE (flux tower) is overestimated by the amount of HCO3 lost

for carbonates

CO2 + H2O + CaCO3 Ca++ + 2HCO3-

2CO2 + 2 H2O + CaMg (CO3)2 Ca++ + Mg++ + 4HCO3-

Carbonate weathering – half the CO2 is atmospheric

for silicates

2 CO2 + 3 H2O + CaSiO3 Ca++ + 2 HCO3- + H4SiO4

2 CO2 + 3 H2O + MgSiO3 Mg++ + 2 HCO3- + H4SiO4

Silicate weathering – all the CO2 is atmospheric

Riverine HCO3 transport units are Gt C y-1

• Total river DIC flux - 0.3 Gt y-1

• From carbonate weathering 0.14

• “atmospheric” C from carbonate

weathering 0.07

• From silicate weathering 0.15

• Total atmospheric C as DIC 0.22

Rivers – summary units are Gt y-1

• CO2 efflux 0.15 • Organic C delivery 0.5 • Atmospherically derived HCO3 (disguised soil R) 0.23 Burial – assumed ~ 0 Loss of terrestrial NEP in rivers 0.87 Note some organic C may be of riverine origin.

Nearly half of the “terrestrial” C sink is in riverine transport.

• Net Terrestrial C sink 2-3 G t/y

• ___________________________

• Riverine transport 0.87

• Burial in lake sediments 0.05

• Reservoir burial 0.22

• ___________________________

• Freshwater components 1.14

0

200

400

600

800

1000

1200

1400

1600

Terrestrial

Biomass Soil

Organic C stores on “land” O

rgan

ic C

(P

g)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Terrestrial pre-

industrial

Terrestrial, industrial

Net

Sto

rage

(Pg y

-1)

Annual Rates of net organic C

storage

-3

-2

-1

0

1

2

River

Flood plain Ocean

abiotic

Terrestrial

biomass

increase CO

2 f

lux (

Pg y

-1) To atmosphere

from atmosphere

Note: pre-industrially biomass

increase approaches 0 and

ocean CO2 flux has opposite

sign

Ocean

Sediment storage

Inland waters

Ocean

Terrestrial NEP

(1-4 Pg C y-1)

Inland waters

CO2 evasion

0.9 0.9

0.9 1.9

0.75

0.23

Passive Pipe Model

Active Pipe Model

Cole et al. Ecosystems 2007

Ecosystem • An ecosystem is defined as a spatially explicit unit

of the Earth that includes all of the organisms, along with all components of the abiotic environment within its boundaries – Likens 1992

• Boundary definition is a big problem! Ideally, boundaries should represent the plane at which short-term exchanges of matter are irreversible relative to the functional ecosystem, ie, where cycling becomes a flux. Likens et al. 1974

OXIDATION STATES OF SULFUROXIDATION STATES OF SULFURS has 6 electrons in valence shell S has 6 electrons in valence shell oxidation states from oxidation states from ––2 to +62 to +6

H2SO4

Sulfuric acid

SO42-

Sulfate

+6

SO2

Sulfur dioxide

+4

FeS2

Pyrite

H2S

Hydrogen sulfide

(CH3)2S

Dimethylsulfide

(DMS)

CS2

Carbon disulfide

COS

Carbonyl sulfide

-2

H2SO4

Sulfuric acid

SO42-

Sulfate

+6

SO2

Sulfur dioxide

+4

FeS2

Pyrite

H2S

Hydrogen sulfide

(CH3)2S

Dimethylsulfide

(DMS)

CS2

Carbon disulfide

COS

Carbonyl sulfide

-2

Decreasing oxidation number (reduction reactions)

Increasing oxidation number (oxidation reactions)

THE GLOBAL SULFUR CYCLETHE GLOBAL SULFUR CYCLE

SO2

H2S

volcanoes industry

SO2

CS2

SO42-

OCEAN

1.3x1021 g S

107 years

deposition

runoff

SO42-

plankton

COS

(CH3)2S

microbes

vents

FeS2

uplift

ATMOSPHERE

2.8x1012 g S

1 week

SEDIMENTS

7x1021 g S

108 years