Prsentation PowerPoint

1
Dynamics and diversity of the microbial
communities in the Reservoir Marne (Seine
catchment area, France) A project began in 2006
Anne ROLLAND and Stéphan JACQUET INRA UMR
CARRTEL, Group of Aquatic Microbial Ecology, BP
511, 74203 Thonon-les-Bains, Cedex, FRANCE
Context and Question
Phytoplankton can be considered as a
bio-indicator of changes in aquatic ecosystems
and may thus constitute an excellent marker of
water quality. Assessing biological, chemical and
physical influence on phytoplankton regulation
constitute a key step to understand population
dynamics and to ensure, when necessary and if
possible, a human-hand control before any algal
bloom. Preventing such proliferations is
typically what will be required to satisfy the
good ecological state recommended by the Water
Framework Directive.
The first objective of our research is to
describe precisely, in time and space, both the
dynamics and the diversity of phytoplanktonic
organisms in the Reservoir Marne located in the
Seine catchment area. In a second time, the role
of the various environmental factors (physical,
chemical and biological) and processes (i.e.
predation, viral lysis, competition) implied in
their distribution will be analyzed.
Reservoir Marne
Sampling methods

• One of the major artificial lake in Europe
• Regulation of the Seine river flow
• Surface area 48 km2
• Capacity 350 millions of m3
• Two lakes
• A small one lake Champaubert
• (0,5 km2, mean depth 4 m)
• A larger one lake Der
• (47,5 km2, mean depth 8 m)

The reservoir has been sampled between March and
September 2006 every two weeks. For the first
time, Six stations have been investigated and
water has been collected at various depths to
analyze major nutrients and chlorophyll a (chla)
concentrations, phytoplankton and zooplankton
abundance and diversity, bacterial and viral
abundance. Also, a submersible fluorescence
Probe (the Fluoroprobe) was used to discriminate
and quantify the major algal classes in situ
(i.e. the chlorophyceae, the Bacillariophyceae,
the cyanobacteria and the cryptophyceae).
2 - The reservoir is not uniform as revealed by
the phytoplankton abundance which varies
significantly from one station to another at any
sampling date
3 257 phytoplankton species have been
identified mostly represented by Chlorophyceae
and Diatoms taxa.
4 The chla concentration varies from 4 to 16
µg.L-1 among sampling stations. Thus, the
Reservoir Marne can be considered as a
meso-eutrophic ecosystem.
Preliminary results
1 The Fluoroprobe constitutes for this
reservoir an excellent monitoring tool for total
chla concentration
5 A clear seasonal dynamics can be observed for
the different microbial communities (here at 3 m
for the a) phyto-, b) bacterio- and c)
virioplankton for 3 of the 6 sampling stations
from March to June 2006)
a)
b)
c)
Perspectives
Acknowledgments

• Multivariate statistics will be used
• to determine phytoplankton evolution through a
  multi-points comparative analysis and on a depth
  gradient
• to evaluate bottom-up, top-down and side-in
  controls.
• Integration of our data into pre-existing models
  on the Reservoir Marne (BARMAN) functioning seems
  to be interesting to improve them.
• The results from the submersible fluorescence
  probe will be compared to 2 other identical
  probes and with the taxonomic composition to
  validate unambiguously the whole dataset.
• The average chla concentration seems to
  highlight the meso-eutrophic status of the
  Reservoir Marne. However, discrete concentrations
  can reach 35 µg.L-1, so special attention will be
  paid on these samples.

Dominique Amon-Moreau, Gérard Beaudoin, Stéphanie
Brault-Breton, Pascal Chatel, Michelle Declercq,
Jean-Claude Druart, Josette Garnier, Yannick
Guillemin, Philippe Prompt and Christophe Saleur.