Phytoplankton Community Composition, Abundance, and

Health on the International Section of the St. Lawrence

River

Jessica Harold

Advisor: Dr. Michael Twiss

Clarkson REU Program

August 2, 2007

Outline

• Importance– Hypothesis

• Methods– Instruments

• Results &

Discussion

Why Study Phytoplankton of the St. Lawrence River?

• The Great Lakes-St. Lawrence River System holds 18% of the world’s freshwater (Thorp et al. 2005)

• Phytoplankton form the basis of aquatic food chains

Hypothesis • Phytoplankton biomass will decrease upon entry

into the St. Lawrence River from Lake Ontario– Disruption of phytoplankton physiology (Lewis et al.

1984)– Increased predation by zooplankton and benthic

grazers– Decreased nutrient availability– Cell loss from the water column due to increased

flocculation (Ruiz et al. 2004)

• Phytoplankton community composition will change due to changing environmental factors

Materials and Methods• 19 stations were sampled over a two day

period

• Phytoplankton– Health and composition determined by a

FRRF and a FluoroProbe, respectively– Abundance determined using chlorophyll-a

abundance

Fast Repitition Rate Fluorometer (FRRF)

• Determines photosynthetic efficiency of whole phytoplankton samples (Fv/Fm)

• Photosynthetic efficiency is a measure of phytoplankton health

FluoroProbe• Measures phytoplankton biomass in each of four divisions

• Nutrients– Water collected from a depth of 6 m

using a 2 L Niskin bottle– Analyzed water to determine total

phosphorus and dissolved silicate

• Chlorophyll-a– Water is filtered and then chlorophyll-

a is extracted from the filter paper using acetone

– Fluorometer is used to determine abundance

Results

• No significant changes in phytoplankton community composition were found along the transect

•Dominated by Chlorophyta (green algae) and Euglenophyta

• Both groups are typically abundant under eutrophic conditions (Kalff 2002).

0102030405060708090

100

3.1

21.4

39.2

58.3

77.3

95.9

114.

6

132.

9

152.

1

179.

0

Distance from the Moses-Saunders Dam (km)

Per

cent

age

of P

hyto

plan

kton

D

ivis

ion

%Cryptophyta and PErich cyanobacteria

%Heterokontophyta andDinophyta

% PC richCyanobacteria

% Chlorophyta andEuglenophyta

Phytoplankton Abundance and Health

• Photosynthetic efficiency remained relatively constant• Distinct trends seen in phytoplankton abundance

0.00

0.50

1.00

1.50

2.00

2.50

0.0 50.0 100.0 150.0 200.0

Distance from Moses-Saunders Dam (km)

Co

nce

ntr

atio

n o

f C

hlo

rop

hyl

l-a

(µm

)

Total (>0.22µm)

Micro (>20 µm)

Nano (2-20µm)

Pico (0.22-2µm)

Nutrients

• Total dissolved phosphorus remains constant• Dissolved silicate exhibits an interesting trend

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.0 50.0 100.0 150.0 200.0

Distance from the Moses-Saunders Dam (km)

SiO

2 (µ

M)

Discussion• Total dissolved phosphorus and chlorophyll-

a are not correlated– Phosphorus is not limiting

• Silicate concentrations– Increase due to elevated turbulence as the

river becomes isothermal

• Phytoplankton abundance initially decreases, but then recovers

– The decrease is not due to poor health

• Hypothesis: decrease is due to increased predation or disrupted physiology

– Increase in abundance• Hypothesis: phytoplankton have

adapted to new environment, or predation has decreased

Acknowledgements

• Advisor Dr. Michael Twiss

• Tiffany Basara and Dave Page

• Co-worker Kyleigh Gloska

• Cristina Gauthier and all the REUs!

Questions?

LiteratureRuiz, J., Macias, D, Peters, F. 2004. Turbulence increases the average settling

velocity of phytoplankton cells. Proc. Nat. Acad. Sci. 101:17720-17724.

Lewis, M. R., E. P. W. Horne, J. J. Cullen, N.S. Oakley & T. Platt. 1984. Turbulent motions may control phytoplankton photosynthesis in the upper ocean. Nature 311: 49-50; doi 10.1038/311049a0.

Thorp, J.H., Lamberti, G.A., and Casper, A.F. 2005. St. Lawrence River Basin. In Rivers of North America, eds. A.C. Benke and C.E. Cushing, pp. 983-1018. Boston: Elsevier Academic Press.

Kalff, Jacob. 2002. The Phytoplankton. In Limnology, p. 316. Upper Saddle River, New Jersey: Prentice Hall.

Basu, B.K., Klaff, J., Pinel-Alloul, B. 2000. Midsummer plankton development along a temperate river: the St. Lawrence River. Can. J. Fish. Aquat. Sci. 57 (Suppl.1): 7-15.

FRRF details

• The FRRF was programmed to measure the ratio of variable chlorophyll-a fluorescence (Fv) to maximal chlorophyll-a fluorescence (Fm)

• Fo=basal chlorophyll-a fluorescence