Diatom silicification changes in a high pCO 2 environment: a mesocosm experiment
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Transcript of Diatom silicification changes in a high pCO 2 environment: a mesocosm experiment
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Diatom silicification changes in a high pCO2 environment: a mesocosm
experiment
Kiely ShuttUniversity of Washington
Friday Harbor LaboratoriesSpring 2013
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Diatoms: A Brief Overview
•Major primary producers•Most common phytoplankton•Single celled, some are chain forming•Primary controllers of silica cycling in the ocean•Radial or bilateral symmetry•Diatoms have a silica requirement in order to build frustules
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Silicification
Dissolved H4SiO4
Biogenic Silica SiO2
Upt
ake
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MethodsBiogenic Silica Filtering
Rapid filter method by Paasche (1980)Prepped and ran on spectrometer using
Strickland and Parsons (1968)
Biogenic Silica/Diatom Cell CalculationBiogenic Silica
Liter
( Phytoplankton Cells
Liter
# Diatoms# Cells )
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Research Questions
• Does biogenic silica differ between pCO2 treatments?
• What stressors affected biogenic silica and silica per diatom cell?– Micronutrient limitation? (Iron, Zinc)– Macronutrient limitation? (Nitrate, Silicate)– Microzooplankton grazing pressure?– Light limitation?
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F(2,32)= 5.250, p=0.072
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 202
4
6
8
10
12
14Control
High
Dock
Drift
Time (Days)
Med
ian
Biog
enic
Sili
ca (µ
mol
L-1
)Biogenic silica through time
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
5
10
15
20
25
0
5
10
15
20
25
Time (Days)
Med
ian
Nitr
ate
(µm
ol L-
1)
Med
ian
Biog
enic
Sili
ca (µ
mol
L-1)
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
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20
25
0
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20
25
Control Ni-trate
High Nitrate
Drift Nitrate
Dock Nitrate
Control BioS
High BioS
Drift BioS
Dock BioS
Time (Days)
Med
ian
Nitr
ate
(µm
ol L-
1)
Med
ian
Biog
enic
Sili
ca (µ
mol
L-1)
Statistically strong negative correlations for all treatment groups: ρ= -.923, -.913, -.884
Nitrate and biogenic silica through time
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
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10
15
20
25
30
35
40
45
50
0
5
10
15
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25
30
35
40
45
50
Time (Days)
Med
ian
Silic
ate
(µm
ol L-
1)
Med
ian
Biog
enic
Sili
ca (µ
mol
L-1
)
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
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50
0
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Control BioS
High BioS
Drift BioS
Dock BioS
Control Sil-icate
High Silicate
Drift Silicate
Dock Silicate
Time (Days)
Med
ian
Silic
ate
(µm
ol L-
1)
Med
ian
Biog
enic
Sili
ca (µ
mol
L-1
)
Biogenic silica and dissolved silicate through time
Statistically strong negative correlations for all treatment groups: ρ= -.939, -.897, -.854
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Grazing pressure
Treatment Spearman ρ
Control .382
High -.054
In order to show a significant association between silicification and grazing, our ρ value would need to be closer to -1 or 1.
Previous studies found increase in diatom silicification under grazing pressure (Pondaven et al 2007)
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0 20 40 60 80 100 120 1400.5
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4.5 Irradiance (inside mesocosms) µmol m-2 s-1
Dept
h (m
)
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0 20 40 60 80 100 120 1400.5
1
1.5
2
2.5
3
3.5
4
4.5
T0 ControlT0 HighT0 DriftT11 ControlT11 HighT11 Drift
Irradiance (inside mesocosms) µmol m-2 s-1
Dept
h (m
)
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PAR
(Eie
nste
ins m
-2 d
-1)
Adapted from (Martin-jézéquel et al 2000)
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F(2,30)= 4.200, p=0.122
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
20
40
60
80
100
120
140
160
180ControlHighDrift
Time (Days)
Pico
mol
e Si
lica
Cell
-1Picomole Silica Per Cell Through Time
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Research Questions - Revisited
• Does biogenic silica differ between pCO2 treatments? Nope!
• What stressors affected biogenic silica and silica per diatom cell?– Micronutrient limitation? (Iron, Zinc)– Macronutrient limitation? (Nitrate, Silicate)– Grazing pressure?– Light limitation? Could be!
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Conclusions
• No significant differences between pCO2 treatments for biogenic silica or silicification in diatoms
• Macronutrient limitation and grazing pressure were not affecting silicification in diatoms
• Light limitation likely to be the reason why we see the trends in silicification data as well as other unmeasured variables within our mesocosm system
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Acknowledgements• Jim Murray• Robin Kodner• Kelsey Gaessner • Evelyn Lessard• Mike Foy• Barbara Paul• Amanda Fay• Molly Roberts• Kitae Park• Peers: Phil Gravinese, Kelly Govenar, Jen
Apple, Andrew Turner, Daneil Newcomb, Natsuko Porcino, Amy Stephens
• University of Washington - Friday Harbor Labs
• Mary Gates Endowment• Henry and Holly Wednt Endowment• Educational Foundation of America• Herbs Tavern