biogeochemistry of silicon eric struyf, jack middelburg, wim clymans

Biogeochemistry of silicon

Eric Struyf, Jack Middelburg, Wim Clymans

One of 118 elements…

… on THE table

Googlability

• Silicon is the eighth most common element in the universe by mass

• Silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen

• Silicon has a large impact on the world economy. Highly purified silicon is used in semiconductor electronics: a great deal of modern technology depends on it.

A bit of wiki

Basic Chemistry of SiBasic Chemistry of Si

• Numerous Si-bearing minerals (mineralogy, Numerous Si-bearing minerals (mineralogy, petrology: disciplines within geology).petrology: disciplines within geology).– SiOSiO22: Quartz, glass : Quartz, glass

– Silicates:Silicates:• olivines: (Mg, Fe)olivines: (Mg, Fe)22SiOSiO44

• pyroxenes: Ca(Mg,Fe)Sipyroxenes: Ca(Mg,Fe)Si22OO66

• feldspars: (Na,K)AlSifeldspars: (Na,K)AlSi33OO88 to CaAl to CaAl22SiSi22OO88

• mica’s: KAlmica’s: KAl22(AlSi(AlSi33OO1010)(OH))(OH)22

• clay minerals: e.g. Alclay minerals: e.g. Al22SiSi22OO55(OH)(OH)44

Weathering of silicates is ultimate source of all dissolved Si in water: mineral Si to dissolved Si.

Transport and cycling in riverine continuum

Butcher et al. 1992

Who are these minerals?

Quartz

Silicates

Sand Rock

http://en.wikipedia.org/wiki/Image:Towering_Sand_Dunes.jpg

http://upload.wikimedia.org/wikipedia/commons/e/e7/Quartz_Crystal.jpg

http://upload.wikimedia.org/wikipedia/commons/9/94/KaolinUSGOV.jpg

Tight rasters

Quartz

The weathering is slow

Butcher et al. 1992

NaCl

CaSO4.2H2OCaSO4

CaCO3

CaMg(CO3)2

Sink for atmospheric CO2

CO2 + H2O H2CO3

CaSiO3 + 2H2CO3 Ca2+ + 2HCO3 + dissolved Si + H2O

http://upload.wikimedia.org/wikipedia/commons/9/90/Bicarbonate-resonance.png

DiatomsDiatoms

• Diatoms dominate coastal and Diatoms dominate coastal and oceanic biogenic Si productionoceanic biogenic Si production

• > 10.000 species> 10.000 species• Pelagic and benthic forms Pelagic and benthic forms

Thalassiosira

Diatoms take up dissolved Si (DSi),deposit it as amorphous (biogenic) Si

(ASi) in frustule

Calacademy.org

Astrographics.com

DiatomsDiatoms

• Centric forms:Centric forms:– radial or concentricradial or concentric– most pelagic are centricmost pelagic are centric

• Pennate forms:Pennate forms:– bilaterally symmetricalbilaterally symmetrical– more heavily silicifiedmore heavily silicified– most benthic are pennatesmost benthic are pennates

The ocean Si cycleFriedel, 1991

Diatoms control oceanic Si concentrations

Si, diatoms and the C cycleSi, diatoms and the C cycle

• Diatoms sink fast:Diatoms sink fast:– they are largethey are large– they aggregatethey aggregate

• An efficient transfer of labile C from photic An efficient transfer of labile C from photic zone to benthos and ocean interiorzone to benthos and ocean interior

• Diatom-frustules buried on ocean floor: 1,5 – 3.0 Gton C y-1

• +/- 25 % of yearly anthropogenic CO2 output

Productivity240 Tmol y-1

Silica Burial6.3 Tmol y-1

Eolian input0.5 Tmol y-1

Seafloor input0.6 Tmol y-1

Groundwater0.4 Tmol y-1

Rivers: DSi: 6.2 Tmol y-1

ASi: 1.1 Tmol y-1

The Oceanic Si Cycle – Biological Si Pump

Weathering1.9 Tmol y-1

Sponges3.1 Tmol y-1

Reverse weathering: 1.5 Tmol y-1

(based on Tréguer & De La Rocha, 2012)

DSi: Dissolved Silica / ASi: Amorphous Silica

Estuarine ecosystemsHuman interference (global change, habitat loss, pollution)

- Expansion of agricultural activities- Reservoir construction- Urbanization- Industrialization- ...

Si and eutrophication

Expansion of agricultural activities

- Increased input of N and P- Ratio of N/Si/P disturbed- Ratio determines composition of phytoplankton- Ideal molar ratio 16/16/1

Changes in composition of coastal phytoplankton

Si-limitation: shift to non-diatom species

Risk of collapse of foodwebs (supported by diatoms)

Eutrophication

Phaeocystis sp. blooms:

“foam algae”

Gonyaulax sp. blooms

Toxic “red tides”

Cloern, 2001

Not only increase in N and P

Not only increase in N and PHumborg et al., Nature, 1997

Dams decrease

Si transport

Conley et al., L&O, 2000

The lake effect is observed worldwide!

The “dam-effect” is one of the best known human impacts on the Si cycle

Recapitulation

Dissolved silica essential for diatom growth in the ocean

Diatoms constitute 50+ % of ocean primary productivity

OCEAN SURFACE

DSi diatom ASi

240Tmole yr-1

After Struyf et al. 2010

The C-pump

OCEAN SURFACE

OCEAN FLOOR

diatom ASi in sea-floor sediment

ASi burial

DSi diatom ASi

240Tmole yr-1

6.5 Tmole yr-1

Diatom shells buried on ocean floor: 1,5 – 3.0 Gton C y-1

Ocean C-pump ~ Si-pump: +/- 25 % of yearly human CO2 output


Ocean-continent link

OCEAN SURFACE

EARTH CRUST & SUBSOIL

primary and secondary silicate minerals

Weathering

eolian transport

Net riverine transport

OCEAN FLOOR

diatom ASi in seafloor sediment

ASi burial

DSidiatom

ASi240

Tmole yr-1

6 Tmole yr-1 (*)

0.5 Tmole yr-1

6.5 Tmole yr-1

Terrestrial export of Si essential to sustain diatoms

Traditional view: export controlled by bedrock weathering


Tectonics

OCEAN SURFACE



Weathering

eolian transport


OCEAN FLOOR


ASi burial

DSidiatom

ASi240

Tmole yr-1

6 Tmole yr-1 (*)

0.5 Tmole yr-1

6.5 Tmole yr-1

Hydro- thermal

input

&

Seafloor weathering

plate tectonics

Tectonical processes close the cycle


A new paradigm

Recently discovered: bio-buffer between Si weathering and export

Regulates Si transport between land and ocean

ECOSYSTEM SOIL

60-200Tmole yr-1

OCEAN SURFACE



Weathering

eolian transport


OCEAN FLOOR


ASi burial

DSidiatom

ASi240

Tmole yr-1

6 Tmole yr-1 (*)

0.5 Tmole yr-1

6.5 Tmole yr-1

Hydro- thermal

input

&

Seafloor weathering

plate tectonics


Silica in terrestrial ecosystems

First...

May 2011, Lecture Dresden

Good for your bones,nervous system, hair and nails!

Humans and animals


Good for students and scientists?

Anderson, I.W., Molzahn, S.W., Roberts, N.B., Bellia, J. and Birchall, J.D., Proc. Eur. Brew. Conv., Brussels, 1995, 543-551

Silica gives stronger bones…And is good for the brain…

Even we are filters...


Schoelynck et al. 2013

58 mg Si L-1

12 mg Si L-1


+Si -Si

Silicon and siliceous structures in biological systems (1981). Simpson, T.L. and B.E. Volcani (eds.), Springer-Verlag


Plants and Si BIOgeochemistry

Vegetation stores Si

“phytoliths”“silica sheets cells”

- Enhanced strength- Resistence to:

HerbivoresPlant disease

-Reduced water, salt, pollution, stress

- Enhanced productivity

A beneficial element!

For some it’s essential or crucial

Horsetails

Grasses and sedges

Si is beneficial – Crop YieldRice, Korndörfer & Leipsch, 2001

Strawberries, Crooks & Prentice, 2012

Guntzer et al, 2011

Biological stress

Chemical stress

Physical stress

Rice disease brown spot

Untreated

Silica

Commercial cure

Silica

Commercial cure + silica

Datnoff et al. 1997

Resistance disease

Vegetation-Soil continuum

Forest Arable

Return of plant litter, straw residue and dying roots

Vegetation-Soil continuum

Phytoliths

Diatoms

Sponges

Clarke, 2003

The Si in biota is AMORPHOUS

Not ordered in a tight crystal raster, like minerals

It dissolves more than 1000 times faster

Amorphous matrix of hydrated silica (SiO2•nH2O).

A bit like:

The “bio” in Si biogeochemistry- Yearly production of plant ASi, 60 – 200 Tmole

comparable to ocean ASi production (Conley 2002)

a multitude is in soil organic matter

- High solubility range, REACTIVE on biological timescales

NEW CONCEPT:

Ecosystems control Si-concentrations in rivers

Large stock in ecosystems

Cornelis et al. 2010

Si is accumulated in ecosystem soils

Plants stimulate the weathering

Hinsinger et al. 2001

Plants stimulate the weathering…

Hinsinger et al. 2001

The ecosystem Si filter

SOIL

Silicate minerals

Mineral weathering

bio-Si export

Dissolved Si export

VEGETATION

Riv

er E

stuary

Oce

an

Size of bio-Si stock

Land use

Bio-Si reactivity

HydrologyHydrology

February 2011, seminar Nottingham

Forests

Deforestation

Studies at Hubbard BrookExperimental Forest

Large-scale experiments!

American beech (Fagus grandifolia)Sugar maple (Acer saccharum)

Yellow birch (Betula alleghaniensis).

3-yr running mean of average volume weighted“Excess” dissolved silicate

Large increase in exportfollowing whole tree cutand removal (1983-84)

• Release from the biologically derived BSi pool

• Highest Si fluxes when plant materials left on the soil surface after deforestation

• Deforestation appears to enhance land-ocean flux of biogenically reactive Si

Deforestation

Scheldt watershed

52 river basins

Year-round (2008)

+ 500 observations

Goldschmidt, Knoxville, June 2010

But...

0

10

20

30

40

0 10 20 30 40 50

Forest coverage (%)

TS

i fl

ux

(µ

mo

l h

a-1 s

-1)

-50

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60

% transformed into forest

% i

nc

rea

se

in

TS

i fl

ux

GrassHumanCrop

Si and long-term deforestation

Cultivation lowered base-flow Si fluxes

-50

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60

% anthropogenic ecosystem transformed into forest

% in

cre

as

e in

TS

i flu

x

Forest vs. human

Forest vs. crop

Forest vs. grassland

Mixed multiple regression

(soil texture, lithology, drainage capacity,

land use)

‘forests vs. cropland’

(p < 0,001)

‘forest vs. grassland’

(p< 0.003)

‘forest vs. agriculture

(grassland + cropland)’ (p<

0,005) Goldschmidt, Knoxville, June 2010

1.0

10.0

100.0

0 10 20 30 40 50

Forestation (%)

TS

i fl

ux

(µm

ol.

ha-1

.s-1

)

New conceptual model

Si - fluxes

Soil ASi pool

0

100

0

100

TSi exportTSi-export

soil ASi-pool

mineralsilicates

DSi

ASi

mineralsilicates

DSi

ASi

exportmineralsilicates

DSi

ASi


ASi

export export

DSisoil

vegetation

Developing forest Climax forest Early deforested Climax cultivated

TSi-export

soil ASi-pool

mineralsilicates

DSi

ASi

mineralsilicates

DSi

ASi


DSi

ASi


ASi

export export

DSisoil

vegetation

Developing forest Climax forest Early deforested Climax cultivated

Goldschmidt, Knoxville, June 2010

Study Area

Arable Land

Pasture

Grazed Forest Continuous Forest

Clymans et al, 2011

Human impact on Si pools

Fig. Representation of the land use sequence in the study area, southern Sweden. Values indicate measured means (±standard errors) for total biogenic silica pool (PSia) and easily soluble silica pool (PSie) in the soils.

ca. 500 yrs human disturbance => 87±51 kg SiO2 ha-1

Clymans et al, 2011

biogeochemistry of silicon eric struyf, jack middelburg, wim clymans

Documents

mineral si

dissolved si dsi

tmol y1sponges3

tmol y1groundwater0

gton c y

oceanic si concentrationssi

amorphous biogenic si

oceanic biogenic si