nutrients and photoinhibition as controls on lake …

NUTRIENTS AND PHOTOINHIBITION AS CONTROLS ON LAKE ERIE PHYTOPLANKTON

AND THEIR FLUORESCENCE PROPERTIES

G. Silsbe1, K. Rattan1, R. Smith1

([email protected]), S. Guildford1, R. Hecky1, M. Twiss2 .

1 Biology Dept., U. Waterloo, Waterloo, ON

2 Biology Dept., Clarkson U., Potsdam, NY

Station 78M - September (24h)

Time (h) 22:00 02:00 06:00 10:00 14:00 18:00

Dep

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)

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2.00 2.25 2.50 2.75 3.00 3.25 3.50

Purpose

• Identify nature and scope of nutrient limitation of phytoplankton

• Assess fluorescence methods as means of characterizing nutrient status, physiological condition, and productivity

• Assess vertical structure and photoinhibitionas influences on surface layer phytoplankton characteristics

The NT/IFYLE Project – Study Sites

June 2005

May 2005 July 2005

September 2005

83 Wo 82 Wo 81 Wo 80 Wo 79 Wo 83 Wo 82 Wo 81 Wo 80 Wo 79 Wo

42 No

43 No

o41 N

42 No

43 No

o41 N

42 No

43 No

o41 N

42 No

43 No

o41 N

4 “Lakewide” Cruises (below) and 1 diel survey (not shown) in Central basin

The NT Project – What we did

~180 CTD Profiles

~135 Optical Profiles (Fast Repetition Rate Fluorometry, Fluoroprobe, PAR)

~115 Water Chemistry Suites (Chl –a, PAB spectra, TP, TDP, SRP, Part. C, Part. N, Part. P, SRSi, NH3, N03, Phytoplankton and Bacterial Samples)

Greg: ~113 14C Photosynthetic Irradiance Curves and 226 Alkalinity Titrations

Kim: ~ 200 Nutrient Assays

Maggie: ~15 C02 Production Experiments

4 Spatial/Diurnal Surveys in the Bay of Quinte

4 5 6 7 8 9 10MONTH

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25303540

TP (u

g l- 1

)

westerneasterncentral-westcentral

BASIN

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810

SR

P (u

g l-1

)


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4 5 6 7 8 9 10MONTH

5

10152025

Chl

a (u

g l-1

)


BASIN

Nutrient status indicators

Assay Nutrient Moderate Extreme Deficient

Deficiency Deficiency

N debt N >0.15

P debt P >0.075

APA P 0.003-0.005 >0.005

C:N N 8.3-14.6 >14.6

C:P P 129-258 >258

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0.001

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P d

ebt (

umo l

P u

g C

hl a

- 1)


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0.0001

0.0010

0.0100

AP

A (u

mo l

P u

g C

h l a

-1 h

-1)


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4 5 6 7 8 9 10MONTH

0.001

0.010

0.100

N d

ebt (

umol

N u

g C

hl a

- 1)


BASIN

4 5 6 7 8 9 10MONTH

0.0

0.1

0.2

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0.7Fv

/Fm

4321

BASIN

0.001 0.010 0.100P debt (umol P ug Chl a -1)

0.1

0.2

0.30.40.50.6

Fv/F

m


BASIN

0.050.10

0.150.20

0.250.30

0.350.40

N debt (umol N ug Chl a -1)

0.1

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0.40.50.60.7

Fv/F

m


BASIN

Date and Time

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Temperature (Deg C)

PAR (µmol.m-2.s-1)

Fv'/Fm'

09:00 12:00 15:00 18:00 21:00 24:00 03:00 06:00 09:0016-Jun-05 17-Jun-05

Date and Time

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PAR (µmol.m-2.s-1)

Fv/Fm Dark Chamber

09:00 12:00 15:00 18:00 21:00 24:00 03:00 06:00 09:0016-Jun-05 17-Jun-05

Chl-a Fluorescence(µg.L-1)

Fv/Fm

0.0 0.1 0.2 0.3 0.4 0.5 0.6

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Sigma PSII0 100 200 300 400

Fm

0 2 4 6 8 10 12 14 16

Fv/Fm DarkFv/Fm LightSigma PSIIFm Dark (Biomass)

Dark Adaptionfrom 2 m sample

Time

14:00 14:20 14:40 15:00 15:20 15:40 16:00

Sigm

a PS

II

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Fv/F

m

0.0

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Sigma PSIIFv/Fm

Time of Profile13:50

Conclusions to date

• Diel photoinhibition is a very significant complication but

• Moderate (15-20 minutes) periods of dark adaptation may remove most such effects

• N and P (and Si) deficiency symptoms occur in Lake Erie and

• Fv/Fm (dark adapted PAM) shows promise in detecting nutrient stress

To do:

- cross-reference vertical profile results with horizontal surveys (assess photoinhibition effects, verify inferred stress levels, assess potential bias in areal standing crop estimates)

- use ELCOM to interpret sampling pattern relative to dominant circulation features before and during expeditions (is between-station variability explicable by circulation features?)

Fluoroprobe: Theory•All phytoplankton contain chlorophyll-a, the pigment that upon absorption of irradiance mediates the passage of electrons to the photosynthetic electron transport chain.

Chl-a core

antenna

Photosynthesis

FluorescenceIrradiance

Thermal Decay


•Phytoplankton also have accessory pigments that absorb irradiance at different l than chl-a, and pass electrons to the chl-a in the core antenna.

Fluoroprobe: Theory•The fluoroprobe contains 5 alternating LEDs that excite the water sample at specific wavelengths.

•At each excited wavelength, chl-a fluorescence is measured and the relative response of the 5 wavelengths is processed through an algorithm to assess the contribution of each phytoplankton group

FRRF: Theory

Φ F = kf/(kf + kd + kp)

The quantum fluorescence yield can be defined by the rate constants of each process

Where Φ F = Fluorescence yieldkf = rate constant of fluorescencekd = rate constant of thermal deactivationkp = rate constant of photochemistry

Φ P = kp/(kf + kd + kp)The quantum yield of photochemistry can also be expressed through these rate constants.

FRRF: Theory

Φ Fo = kf/(kf + kd + kp) Φ FM = kf/(kf + kd)

If Fv = Fm – Fo then these equations can be rearranged

Fv/Fm = kp/(kf + kd + kp) = Φ P

3. Fluorescence InductionFluorescent Probes

0 100000 200000 300000Cumulative Excitation Energy (a.u.)

1000

1500

2000

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Fluo

resc

ence

(a.u

.)

Depth = 83.69m, 06:01:13, 03/08/99

00.20.40.60.81

(F -

F 0)/F

V

FV/FM = 0.449σPSII = 624 (± 89) (Å2 quanta-1)R2 = 0.860

The primary advantage of using a sequence of saturating pulses (FRRF) is you can obtain an instantaneous induction curve. The slope of the curve is represented mathematically using a poisson formula.

[F(E) – Fo] / Fv = 1 – e σPSII E

Where σPSII is the effective absorption cross-section of Photosystem II

4 5 6 7 8 9 10MONTH

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NO

3 (u

g l -1

)


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NH

3 (u

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SR

Si (

ug l-

1)


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nutrients and photoinhibition as controls on lake …

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