biogeochemistry of silicon eric struyf, jack middelburg, wim clymans
TRANSCRIPT
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Biogeochemistry of silicon
Eric Struyf, Jack Middelburg, Wim Clymans
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One of 118 elements…
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… on THE table
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Googlability
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• 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
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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
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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
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Who are these minerals?
Quartz
Silicates
Sand Rock
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Tight rasters
Quartz
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The weathering is slow
Butcher et al. 1992
NaCl
CaSO4.2H2OCaSO4
CaCO3
CaMg(CO3)2
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Sink for atmospheric CO2
CO2 + H2O H2CO3
CaSiO3 + 2H2CO3 Ca2+ + 2HCO3 + dissolved Si + H2O
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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
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Diatoms take up dissolved Si (DSi),deposit it as amorphous (biogenic) Si
(ASi) in frustule
Calacademy.org
Astrographics.com
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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
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The ocean Si cycleFriedel, 1991
Diatoms control oceanic Si concentrations
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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
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• Diatom-frustules buried on ocean floor: 1,5 – 3.0 Gton C y-1
• +/- 25 % of yearly anthropogenic CO2 output
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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
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Estuarine ecosystemsHuman interference (global change, habitat loss, pollution)
- Expansion of agricultural activities- Reservoir construction- Urbanization- Industrialization- ...
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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)
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Eutrophication
Phaeocystis sp. blooms:
“foam algae”
Gonyaulax sp. blooms
Toxic “red tides”
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Cloern, 2001
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Not only increase in N and P
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Not only increase in N and PHumborg et al., Nature, 1997
Dams decrease
Si transport
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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
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Recapitulation
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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
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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
After Struyf et al. 2010
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Ocean-continent link
OCEAN SURFACE
EARTH CRUST & SUBSOIL
primary and secondary silicate minerals
Weathering
eolian transport
Net riverine transport
OCEAN FLOOR
diatom ASi in sea- floor 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
After Struyf et al. 2010
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Tectonics
OCEAN SURFACE
EARTH CRUST & SUBSOIL
primary and secondary silicate minerals
Weathering
eolian transport
Net riverine transport
OCEAN FLOOR
diatom ASi in sea- floor sediment
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
After Struyf et al. 2010
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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
EARTH CRUST & SUBSOIL
primary and secondary silicate minerals
Weathering
eolian transport
Net riverine transport
OCEAN FLOOR
diatom ASi in sea- floor sediment
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
After Struyf et al. 2010
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Silica in terrestrial ecosystems
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First...
May 2011, Lecture Dresden
Good for your bones,nervous system, hair and nails!
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Humans and animals
May 2011, Lecture Dresden
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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...
May 2011, Lecture Dresden
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Schoelynck et al. 2013
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58 mg Si L-1
12 mg Si L-1
May 2011, Lecture Dresden
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+Si -Si
Silicon and siliceous structures in biological systems (1981). Simpson, T.L. and B.E. Volcani (eds.), Springer-Verlag
May 2011, Lecture Dresden
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Plants and Si BIOgeochemistry
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Vegetation stores Si
“phytoliths”“silica sheets cells”
- Enhanced strength- Resistence to:
HerbivoresPlant disease
-Reduced water, salt, pollution, stress
- Enhanced productivity
A beneficial element!
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For some it’s essential or crucial
Horsetails
Grasses and sedges
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Si is beneficial – Crop YieldRice, Korndörfer & Leipsch, 2001
Strawberries, Crooks & Prentice, 2012
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Guntzer et al, 2011
Biological stress
Chemical stress
Physical stress
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Rice disease brown spot
Untreated
Silica
Commercial cure
Silica
Commercial cure + silica
Datnoff et al. 1997
Resistance disease
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Vegetation-Soil continuum
Forest Arable
Return of plant litter, straw residue and dying roots
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Vegetation-Soil continuum
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Phytoliths
Diatoms
Sponges
Clarke, 2003
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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:
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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
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Large stock in ecosystems
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Cornelis et al. 2010
Si is accumulated in ecosystem soils
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Plants stimulate the weathering
Hinsinger et al. 2001
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Plants stimulate the weathering…
Hinsinger et al. 2001
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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
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Forests
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Deforestation
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Studies at Hubbard BrookExperimental Forest
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Large-scale experiments!
American beech (Fagus grandifolia)Sugar maple (Acer saccharum)
Yellow birch (Betula alleghaniensis).
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3-yr running mean of average volume weighted“Excess” dissolved silicate
Large increase in exportfollowing whole tree cutand removal (1983-84)
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• 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
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Scheldt watershed
52 river basins
Year-round (2008)
+ 500 observations
Goldschmidt, Knoxville, June 2010
But...
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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
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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
)
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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
exportmineralsilicates
ASi
export export
DSisoil
vegetation
Developing forest Climax forest Early deforested Climax cultivated
TSi-export
soil ASi-pool
mineralsilicates
DSi
ASi
mineralsilicates
DSi
ASi
exportmineralsilicates
DSi
ASi
exportmineralsilicates
ASi
export export
DSisoil
vegetation
Developing forest Climax forest Early deforested Climax cultivated
Goldschmidt, Knoxville, June 2010
![Page 66: Biogeochemistry of silicon Eric Struyf, Jack Middelburg, Wim Clymans](https://reader036.vdocuments.net/reader036/viewer/2022062518/56649e725503460f94b70ea8/html5/thumbnails/66.jpg)
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
exportmineralsilicates
ASi
export export
DSisoil
vegetation
Developing forest Climax forest Early deforested Climax cultivated
TSi-export
soil ASi-pool
mineralsilicates
DSi
ASi
mineralsilicates
DSi
ASi
exportmineralsilicates
DSi
ASi
exportmineralsilicates
ASi
export export
DSisoil
vegetation
Developing forest Climax forest Early deforested Climax cultivated
Goldschmidt, Knoxville, June 2010
![Page 67: Biogeochemistry of silicon Eric Struyf, Jack Middelburg, Wim Clymans](https://reader036.vdocuments.net/reader036/viewer/2022062518/56649e725503460f94b70ea8/html5/thumbnails/67.jpg)
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
exportmineralsilicates
ASi
export export
DSisoil
vegetation
Developing forest Climax forest Early deforested Climax cultivated
TSi-export
soil ASi-pool
mineralsilicates
DSi
ASi
mineralsilicates
DSi
ASi
exportmineralsilicates
DSi
ASi
exportmineralsilicates
ASi
export export
DSisoil
vegetation
Developing forest Climax forest Early deforested Climax cultivated
Goldschmidt, Knoxville, June 2010
![Page 68: Biogeochemistry of silicon Eric Struyf, Jack Middelburg, Wim Clymans](https://reader036.vdocuments.net/reader036/viewer/2022062518/56649e725503460f94b70ea8/html5/thumbnails/68.jpg)
Study Area
Arable Land
Pasture
Grazed Forest Continuous Forest
Clymans et al, 2011
![Page 69: Biogeochemistry of silicon Eric Struyf, Jack Middelburg, Wim Clymans](https://reader036.vdocuments.net/reader036/viewer/2022062518/56649e725503460f94b70ea8/html5/thumbnails/69.jpg)
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