coupled biogeochemical cycles

Coupled Biogeochemical Cycles

William H. Schlesinger

Millbrook, New York

1. Some basic stoichiometry for life―in biomass

First articulated by Liebig (1840)and later advanced by Redfield (1958), Reiners (1986), Sterner and Elser (2002), and Cleveland and Liptzin (2007)

Complementary Models for Ecosystems

Reiners, W.A. 1986

145

100 + ?Δ

121

40

The Global Nitrogen Cycle - Modern

48-59

18

<5

IF NPP = 60 x 1015 g C/yr

60 X 1015 g C x 1 N = 1.2 x 1015 g N 50 C

= 1200 x 1012 g N/yr

From: Magnani et al. 2007

Townsend et al. 1996. Ecological Applications 6(3):806-814.

Spatial Distribution of the 1990 Carbon Sink Resulting from Fossil-fuel N Deposition between 1845 and 1990

Coupling of biogeochemical cycles, due to:

2. The flow of electrons in the oxidation/reduction reactions―

First articulated by Kluyver (1926),and later advanced by Morowitz, Nealson, Falkowski, and many others

Schlesinger, W.H. 1997

H2O/O2 C N S FeH

2O/O

2

X

PhotosynthesisCO2 CH2O O2

C

RespirationC CO2O2 H2O X

DenitrificationC CO2NO3 N2

Sulfate reductionC CO2SO4 H2S

Iron reduction- organic C oxidation4a or

AOM4b

C CO2FeIII FeII

N

Heterotrophic nitrification

NH4 NO3O2 H2O

Chemoautotrophy(nitrification)

NH4 NO3CO2 C

AnammoxNH4 + NO2N2+H2O

Sulfate reduction7

NH4 N2/ NO3SO4 H2S

Feammox 5a,b,c

NH4 NO2/N2/NO3FeIII FeII

S

Sulfur oxidationS SO4

O2 H2O

Chemoautotrophy(sulfur-based

photosynthesis)S SO4CO2 C

Autotrophic DenitrificationS SO4

NO3 N2/NH4

X

Iron reducing and sulfur oxidizing

bacterial consortium 6

S SO4FeIII FeII

Fe

Chemolithotrophic(Iron oxidizing

bacteria) 1

FeII FeIIIO2 H2O

Autotrophic or mixotrophic (iron

oxidizing bacteria) 2

FeII FeIIICO2 C

iron oxidizing archaeum3a or nitrate-

reducing, Fe(II)-oxidizing bacteriums3b

FeII FeIIINO3 N2/NH4

X X

Oxidized ReducedO

xidi

zed

R

educ

ed

Table 1. Matrix of redox reactions via microbial metabolisms as updated and modified from Schlesinger et al (2011).

Mikucki et al. 2009

Coupled Metabolism & The Sulfur Wars

Howarth and Teal 1979report 75 moles/m2of sulfate reduction annually

2H+ + SO4= + 2CH2O 2CO2 + H2S + 2H2O

implies 150 moles of C is oxidized

150 mols C = 1800 g C/m2/yr

Howes et al. 1984

NPP nowhere near that high!

145

100 + ?Δ

121

40

The Global Nitrogen Cycle - Modern

48-59

18

<5

Denitrification

5CH2O + 4H+ + 4NO3- →

2N2 + 5CO2 + 7H20

Intermediates include NO and N2O

Hirsch et al. 2006Hirsch et al. 2006

∆ N20= TOTAL

N20 __________________

N2 + N20

Schlesinger 2009

Calculation of change in denitrification from N2O

124 Tg (0.37) + 110 Tg (0.082) = 234 Tg (0.246)

4 TgN2O/yr / 0.25 = 17 TgN/yr

145

116-124

121

40

The Global Nitrogen Cycle - Modern

48-59

18

150+9

<5

Land-sea Transport48

3. Coupling of biogeochemical cycles to carbon through chelation

Fig. 2. The fractional amount of Pb loss calculated over the study period is significantly correlated with the thickness (cm) of the forest floor at each site. A logarithmic fit to these data give r2 = 0.65.

Kaste et al. 2006.

Principles of coupled biogeochemical cycles apply to geo-engineering

For example, if we wanted to sequester a billion metric tons of C in the oceans by enhancing NPP with Fe fertilization

Current marine NPP = 50 x 1015 g C/yr

F-ratio of 0.15 means that 7.5 x 1015 g C/yr sinks through the thermocline

An additional 1 x 1015 g C/yr sinking would require ~7 x 1015 g C/yr additional NPP, so

7 x 1015 g C x 23 x 10-6 Fe/C = 1.6 x 1011 g Fe (Lab uptake), or x 6 x 10-4 = 4.2 x 1012 (Field observation) Buesseler & Boyd (2003)

Versus, the global production of Fe annually (1900 x 1012 g Fe/yr)

For example, to provide a sink for 1 x 1015 gC/yr in the world’s soils by

fertilizing them:

Current terrestrial NPP = 50 x 1015 g C/yr

Preservation ratio of 0.008; i.e., global NEP – 0.4 g C/yr (Schlesinger 1990)

To store an additional 1.0 x 1015 g C in soils would require adding125 x 1015 g C/yr to terrestrial NPP

125 x 1015 g C/yr x 1 N/50 C = 2.5 x 1015 g N as fertilizer each year

2.5 x 1015 g C @ 0.857 g C released as CO2 per g N = 2.14 x 1015 g C/yr released in fertilizer production

The Global Phosphorus Cycle

Natural Biogeochemical Cycle in Surface Biosphere (terrestrial & oceanic)Element Flux (1012 g/yr) Biospheric Flux/Sedimentary Flux

C 107000 446N 9200 368P 1000 500S 450 5.6Cl 120 0.46Ca 2300 3.7Fe 40 5.3Cu 2.5 23.6Hg 0.003 4.3

Comparison of Biogeochemical Cycle to Anthropogenic Cycle (Flux in 1012 g/yr)

Element Biospheric Flux Anthropogenic Flux Anthro/Sedimentary Anthro/Biospheric

C 107000 8700 36.3 0.081

N 9200 221 8.8 0.024

P 1000 25 12.5 0.025

S 450 130 1.6 0.29

Cl 120 170 0.65 1.42

Ca 2300 65 0.10 0.028

Fe 40 1.1 0.14 0.028

Cu 2.5 1.5 14.3 0.60

Hg 0.003 0.0023 3.3 0.77

My final message today:

There is an increasing role for biogeochemists

to contribute to the understanding and fruitful

solutions to global environmental problems.

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