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The annual cycle of phytoplankton pigment composition, optical properties and photosynthetic quantum efficiency (PQE) in the western English Channel
Jim Aiken1, James Fishwick1, Gerald Moore1
and Katharine Pemberton2
1Plymouth Marine Laboratory, Plymouth, Devon, U.K.2now at UWAEG, Dept. Biology, University of Waterloo, Ontario, CANADA
MAG workshop, Villefranche, Mar 2004
Main objective:To monitor the variation and co-variation of pigments, carbon, phytoplankton absorption and photosynthetic quantum efficiency (PQE) over a seasonal cycle.
Prior knowledge driving the study:• Preferential Chla synthesis in healthy algae and vice versa.
• Ratio of optical absorption of phytoplankton extracts atdifferent wavelengths reflects pigment concentrations and the “health” ofcells:
- 430/665nm (Tpig/Chla) – increased at low nutrients - Margalef, 1967 - 480/665nm (red to blue, Car.:Chla) – increased as cells aged -Jeffrey &
Hallegraeff, 1980 and Heath et al., 1990.• Co-variance of a480/a665 and Cph/Chla – low in “healthy cells” –
Heath et al., 1990.
• This study: a674/a443 and a674/a490• Link to an indicator of photosynthetic quantum efficiency.
Overview of presentation• Introduce the study site
• Methods and materials
• Overview of seasonal variation at the site
• Relationships between:• PAR and other parameters• PQE, pigments and pigment ratios• Absorption ratios, pigments and PQEm• Phytoplankton carbon pigments and PQEm
• SummaryReference for this work: Jim Aiken, James Fishwick, Gerald Moore and Katharine Pemberton (2004) The annual cycle of phytoplankton photosynthetic quantum efficiency, pigment composition and optical properties in the western English Channel. J. Mar. Biol. Ass, U.K. 84: 1-13.
Case study - the siteStation ‘L4’
• Weekly sampling in 2001 (n = 44)
• 10 km off the coast of Plymouth in the Western English Channel
• 51m depth• Seasonally stratified• Succession of blooms
from Mar to Sep
L4
(50º15’N,
4º13’W)
Methods 1. Parameters measured:
• Photosynthetic quantum efficiency (PQE) – FRRF• CTD measurements• Optical profilers in 7 wavebands• HPLC analysis for pigments (surface)• Nutrient analysis (surface)• Phytoplankton particle absorption spectra (surface)• Phytoplankton species counts – converted to carbonusing formulae of Strathmann (1967). (surface)
Methods 2. Calculation of phytoplankton photosynthetic quantum efficiency (PQE)
PQE’ = Fv’ / Fm’
where Fv’ = Fm’ – F0’
- Reflects the efficiency of photosystem II in the light adapted state. - FRRF Dark chamber 0.2 to 1.0s flushing time allow relaxation ofphotochemical but not non-photochemical quenching.
Methods 3. Derivation of daily values of PQEma) Typical FRRF profiles during “non-stratified” part of year
PAR (µmol photons m-2 s-1)
1 10 100
1000
Dep
th (m
)
0
10
20
30
Temp (C)
10.2 10.4 10.6 10.8
PARTemp
Fm
0.6 0.8 1.0 1.2
FmLFmD
PQE
0.2 0.3 0.4 0.5
Temp (C)
10.2 10.4 10.6 10.8
PQELPQEDTemp
•PQE used was subsurface value where constant value had been obtained and L and D chamber values converged.
Methods 3b. Derivation of daily values of PQEmb) Typical FRRF profiles during summer stratification
PAR (µmol photons m-2s-1)
1 10 100
1000
1000
0
Dep
th (m
)
0
10
20
30
40
50
60
Temp (C)
10 12 14 16
PARTemp
Fm
0 4 8 12
FmLFmD
PQE
0.0 0.2 0.4 0.6
Temp (C)
10 12 14 16
PQELPQEDTemp
•PQE derived for both surface and thermocline layer where possible.•Not possible when quenching extended below surface layer.
Seasonal variation of parameters: Overview
Pigm
ent (
mg
m- 3
)
0
2
4
6
8
10
12
Chla TPig
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
0
10000
20000
30000
µΜ
0
1
2
3
4
5
6PAR Nitrate Phosphate
Nut
rient
s (
)
Pig
men
t con
cent
ratio
n (m
g m
)
Jan Feb Mar Apr May
Pig
men
t con
cent
ratio
n (m
g m
3 )
0
2
4
6
8
10
12Chla Total Pig
Jan Feb Mar Apr May
Sig
maD
0
100
200
300
400
500
600
700
PQ
Em
& C
hla/
Tota
l pig
0.3
0.4
0.5
0.6
0.7
SigmaD PQEm Chla/TPig
Jan Feb Mar Apr May
Tota
l Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
010
000
2000
030
000
Nut
rient
s (µ
mol
l-1)
0
1
2
3
4
5
6
PAR Nitrate Phosphate
Jan Jun Nov
Chl
a (m
g m
-3)
0
3
6
PAR
030
000
Seasonal variation of parameters:Mid Winter to Spring Bloom (MWSB)
Seasonal variation of parameters:Summer Stratification (SS)
May Jun Jul Aug
Pig
men
t con
cent
ratio
n (m
g m
3 )
0
2
4
6
8
10
12Chla Total Pig
May Jun Jul Aug 0
100
200
300
400
500
600
700
PQ
Em
& C
hla/
Tota
l pig
0.3
0.4
0.5
0.6
0.7
SigmaD PQEm Chla/TPig
May Jun Jul Aug
Tota
l Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
010
000
2000
030
000
Nut
rient
s (µ
mol
l-1)
0
1
2
3
4
5
6
PAR Nitrate Phosphate
Jan Jun Nov
Chl
a (m
g m
-3)
0
3
6
PAR
030
000
Sig
maD
Seasonal variation of parameters: Autumn bloom to Early Winter (ABEW)
Jan Jun Nov
Chl
a (m
g m
-3)
0
3
6
PAR
030
000
Sep Oct Nov Dec
Pig
men
t con
cent
ratio
n (m
g m
3 )
0
2
4
6
8
10
12Chla Total Pig
Sep Oct Nov Dec
Sig
maD
0
100
200
300
400
500
600
700
PQ
Em
& C
hla/
Tota
l pig
0.3
0.4
0.5
0.6
0.7
SigmaD PQEm Chla/TPig
Sep Oct Nov Dec
Tota
l Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
010
000
2000
030
000
Nut
rient
s (µ
mol
l-1)
0
1
2
3
4
5
6
PAR Nitrate Phosphate
Relationship with PAR – Chla/Tpig
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Chl
a/Tp
ig
0.40
0.45
0.50
0.55
0.60
0.65
0.70
Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
010
000
2000
030
000
Chla/TPig PAR
MWSB ABEW
Significant relationship between - 4 day PAR and Chla/Tpig for MWSB (R2 = 0.96)- 1 day PAR and Chla/Tpig for ABEW (R2 = 0.83)
Relationship with PAR – a674/a443
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
a674
/a44
3
0.0
0.2
0.4
0.6
0.8
1.0
Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
010
000
2000
030
000
a674/a443 PAR
MWSB ABEW
Significant relationship between - 4 day PAR and a674/a443 for MWSB (R2 = 0.76)- 4 day PAR and a674/a443 for ABEW (R2 = 0.80)
Relationship with PAR – PQEm
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
PQ
Em
0.36
0.38
0.40
0.42
0.44
0.46
0.48
0.50
0.52
0.54
Dai
ly P
AR
(µm
ol p
hoto
ns m
-2)
010
000
2000
030
000
PQEmPAR
MWSB ABEW
Significant relationship between - 1 day PAR and PQEm for MWSB (R2 = 0.90)- 1 day PAR and PQEm for ABEW (R2 = 0.71)
Relationship between pigments and pigment ratios
Pigments throughout 2001
Pigm
ent (
mg
m-3
)
02468
1012
Pigment ratios through 2001
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Chl
a/Tp
ig &
AC
/Tpi
g
0.3
0.4
0.5
0.6
0.7
Chl
a/A
C
0
1
2
3
Chla/Tpig Chla/AC AC/Tpig
Chla Tpig AC
Relationship between pigments and pigment ratiosTpig vs Chla/Tpig
0 2 4 6 8 10 120.4
0.5
0.6
0.7
Tpig vs Chla/AC
TPig (mg m-3)
0 2 4 6 8 10 120.4
0.8
1.2
1.6
2.0
Chla vs Chla/TPig
0 2 4 6 8
Chl
a / T
pig
0.4
0.5
0.6
0.7
Chla vs Chla/AC
Chla (mg m-3)
0 2 4 6 8
Chl
a / A
C
0.4
0.8
1.2
1.6
2.0
TPig (mg m-3)Chla (mg m-3)
Chl
a / T
pig
Chl
a / A
C
R2 = 0.69
R2 = 0.62R2 = 0.68
R2 = 0.62
Relationship between PQEm and Chla or TPig
Tpig vs PQEm
Chla (mg m-2)0 2 4 6 8 10 12
PQ
Em
0.4
0.5
Chla vs PQEm
Chla (mg m-2)0 2 4 6 8
PQEm
0.4
0.5
R2 = 0.78 R2 = 0.81
TPig
Relationship between PQEm and Pigment ratiosAll data
Chla/TPig0.4 0.5 0.6 0.7
PQ
Em
0.35
0.40
0.45
0.50
0.55
Mid Jan - Mid Aug exc. DCM(MWSB & SSur)
Chla/TPig
0.4 0.5 0.6 0.7
PQ
Em
0.35
0.40
0.45
0.50
0.55
Jan - Mid May (MWSB)
Chla/TPig0.4 0.5 0.6 0.7
PQ
Em
0.35
0.40
0.45
0.50
0.55
Sep - Dec (ABEW)
Chla/TPig
0.4 0.5 0.6 0.7
PQ
Em
0.35
0.40
0.45
0.50
0.55
R2 = 0.59 R2 = 0.89
R2 = 0.85 R2 = 0.76
Relationship between absorption ratios and other parameters
• Absorption ratios showed similar patterns to cycles of Chla/Tpig and PQEm• Fewer data and low signal to noise• Ratios low in winter, peaked in spring bloom, fluctuated through summer,peaked again in autumn and declined in winter
250.490.3790.293Lineara674/a443Chla/AC
250.65-0.5962.819Lineara674/a443PQEm
250.52-0.2231.322Lineara674/a443Chla/Tpig
250.63-0.6132.347Lineara674/a443PQEm
250.670.4190.130Loga674/a443Tpig
250.660.4990.115Loga674/a443Chla
NRInterceptSlopeType relationship
Dependent variable
Independent variable
Relationship between phytoplankton carbon (Cph) and other parameters
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Cph
(mg
m-3
)
0
50
100
150
200
250Small phytoplanktonLarge phytoplankton
•Similar pattern to pigments: low in winter, peak in spring, summer andautumn blooms and declining from autumn to winter
•Original phytoplankton data condensed into 2 groups:• small (picoplaknton and flagellates) and •large (coccolithophores, dinoflagellates, diatoms and other).
Relationship between carbon and other parameters:
Carbon (mg m-3)
0 100 200 300
TPig
(mg
m-3
)0
2
4
6
8
10
12
Carbon (mg m-3)
0 100 200 300
Chl
a (m
g m
-3)
0
1
2
3
4
5
6
7
R2 = 0.88 R2 = 0.86
Cph vs Chla Cph vs TPig
• Chla and Tpig significantly correlated to carbon • Outliers occurred when high proportion of flagellates
Relationship between carbon and other parameters:
Chla/TPig0.50 0.55 0.60 0.65
Chl
a/C
ph
0.00
0.01
0.02
0.03
0.04
PQEm0.44 0.46 0.48 0.50 0.52 0.54
Chl
a/C
ph0.00
0.01
0.02
0.03
0.04
0.05
0.06
R2 =0.65 R2 =0.62
Chla/Tpig vs Chla/Cph (Spring to Summer)
PQEm vs Chla/Cph (Spring to Early winter)
• Chla/C and Tpig/C significantly correlated to PQEm outside of periods with high flagellates in the population.
SummaryChla and Tpig• closely correlated for whole year• correlated to CphChla/TPig • low in winter and higher during blooms• correlated to recent light fluxes, PQEm, optical absorption
ratios and for most of year to Chla/CphOptical absorption ratios• correlated with Chla/Tpig and PQEm
Final notes...•PQEm, Chla/Tpig, Chla/Cph and a674/a443 are greater whenplants are growing actively
• When nutrients sufficient, PQEm, Chla/Tpig and a674/a443are linear functions of light
Acknowledgements
We’d like to thank the following people for their collaboration:
Ian Joint, Roger Harris,Angel Lopez-Urrutia,Tania Smith,Carole Llewellyn, Denise Cummings, Malcolm Woodward,the crews of RV Squilla and Sepiaand special thanks to Derek Harbour
This work was part funded by the Natural Environment Research Council.