global changes incidence on phytoplankton, with special
TRANSCRIPT
I.S.RIVERSLYON 2018
• 8 main significant genera with the highest biomass contribution of
Limnothrix, Oscillatoria and Aphanizomenon
• Possible relationships with physical-chemical parameters
• Rising water temperature, decreasing P, stable NO3-
• Discussion
• Time scale - phytoplankton biomass decreased along the years
together with cyanobacterial contribution.
• Longitudinal scale – cyanobacteria biomass increased along the
Loire: consequence of increased residence time, water
temperature and lateral inputs from slow flow tributaries
• Planktic cyanobacteria do not form blooms in the R. Loire,
contrary to earlier reports (Larroudé et al, 2013). On rare
occasions, some cyanobacteria reached high abundance in the
main river, but they were exported from slow-flowing tributaries
• Although part of the phytoplankton decrease may be explained
by significant P-limitation of growth, it is likely that predation by
benthic filter-feeders, particularly the invasive Asiatic clams
(Corbicula spp.), has been a key loss process for phytoplankton
in the R. Loire. This has been the case in other large European
rivers.
• More investigations are still necessary to tell apart the effects of
increased temperature, discharge variations, reduced
eutrophication and predation by invasive species on the
phytoplankton of the River Loire
• Introduction• Climate change and eutrophication are expected to affect phytoplankton
growth, with an increased risk of potentially harmful cyanobacterial
blooms
• Few papers reported an increase of cyanobacterial abundance in rivers,
that could be related to climate change
• In this study, based on phytoplankton monitoring data, we examine
long-term trends in phytoplankton development in the R.Loire, with a
focus on the contribution of cyanobacteria to total phytoplankton
biomass
• Material & Methods
• Results• Overall long term decrease of chlorophyll-a and cyanobacteria biomass
• Total phytoplankton biomass decreased highly since late 90’s
• Cyanobacteria biomass occurred in 38% of the samples
• Cyanobacteria were most of the time a very small fraction of total
phytoplankton (~1%), except on rare occasions
• 63 cyanobacteria taxa ; 2/3 of them have filamentous morphology
• Cyanobacteria were the most abundant in downstream station
(Montjean)
Global changes incidence on phytoplankton, with special reference to
cyanobacteria, in the R. Loire (France)
Impact des changements globaux sur le phytoplancton
et les cyanobactéries de la Loire (France)
Maria Leitao1; Andràs Abonyi4; Jean-Pierre Descy2; Anne Marie Lançon1; Camille
Minaudo3; Florentina Moatar3
Longitudinal change in the mean annual biomass of the main cyanobacteria taxa (1991-2011)
0
20
40
60
80
Mal
vale
tte
Nev
ers
Gie
n
Orlé
ans-
Jarg
eau
Cha
umon
t
Mon
tjean
µg
C L
-1
Anabaena / Dolichospermum
Planktothrix
0
50
100
150
200
Mal
vale
tte
Nev
ers
Gie
n
Orlé
ans-
Jarg
eau
Cha
umon
t
Mon
tjean
µg
C L
-1
Phormidium
Oscillatoria
0
100
200
300
400
500
Mal
vale
tte
Nev
ers
Gie
n
Orlé
ans-
Jarg
eau
Cha
umon
t
Mon
tjean
µg
C L
-1
Aphanizomenon
Limnothrix
0
20
40
60
80
100
Mal
vale
tte
Nev
ers
Gie
n
Orlé
ans-
Jarg
eau
Cha
umon
t
Mon
tjean
µg
C L
-1
Merismopedia
Microcystis
• Loire : 6 stations (km 138 – km 830)
• Monthly sampling: 1991 – 2011
(monitoring Loire-Bretagne Agency)
• Chemical analysis: standard methods
• Phytoplankton: Utermöhl &
biovolume for biomass
• Phytoplankton samples: n = 1 024
• Biomass calculated when the taxon > 4 individuals (>1% counting)
• Trends of nutrients were analysed in parallel with phytoplankton
0
3 000
6 000
9 000
12 000
15 000
18 000
21 000
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2005 2006 2007 2008 2009 2010 2011
Bio
mas
se C
(µg
C L
-1)
Biomasse C Cyano Biomasse C total Malvalette Chaumont Montjean