Sengupta, M. and Dalwani, R. (Editors). 2008
Proceedings of Taal2007: The 12th World Lake Conference: 1058-1066
Management of Aquatic Exotic Plants: The Case of Elodea Species.
G. Thiébaut, F. Di Nino, M-C. Peltre and P. Wagner
Laboratoire Interactions Ecotoxicité, Biodiversité Ecosystèmes (L.I.E.B.E.), Université Paul Verlaine de Metz,
Umrcnrs 7146, Avenue Général Delestraint, 57070 Metz, France
Email : thiebaut@univ-metz.fr
ABSTRACT
Elodea canadensis Michaux, coming from North America has been introduced in Europe in 1836 and
soon became a widely distributed and troublesome species in Europe, after which it often became
integrated in the biocoenosis. Elodea nuttallii (Planch.) St John was first introduced into Europe in 1939.
Only female plants were observed. Apparently, E. nuttallii is actively spreading in many parts of Europe
and seems to be replacing E. canadensis in many localities.
The impact of several frequencies of hand-pulling on the biomass and on the architecture of E.
nuttallii and of E. canadensis was evaluated by assessment of morphological traits in stream and in a
reservoir respectively. The stream is invaded by E. nuttallii and the reservoir by E. canadensis. Handpulling caused a temporary drastic reduction of biomass of E. nuttallii and of E. canadensis. After handpulling, the spread of E. nuttallii and of E. canadensis was area restricted. The development of native
aquatic plants was favoured two years after the last hand-pulling. Furthermore, no significant difference
was observed in the architecture of Elodea sp. between the reference and experimental areas. Elodea
appeared as disturbance–tolerant species.
Keywords: non indigenous species, freshwaters, France, biological traits, hand-pulling.
INTRODUCTION
In France, biological invasion research in freshwater
systems has focused on a few plants such as
Ludwigia species (Dutartre and Oyarzabal 1993,
Dutartre et al. 1997) or Elodea species (Thiébaut et
al. 1997, Barrat-Segretain 2001, 2004, 2005,
Greulich and Trémolières 2002, Barrat-Segretain et
al. 2002). An indigenous of North America, Elodea
canadensis Michaux, first recorded in the early 19th
century in the British Isles (Simpson 1984, 1990), is
now naturalised and widespread in Europe. Elodea
canadensis became a persistent weed following its
naturalisation, choking waterways before declining
to its present, less-abundant (but still common) level
(Cook and Urmi-König 1985, Thiébaut et al. 1997,
Barrat-Segretain 2001). Another species from North
America, E. nuttallii (Planch.) St John was first
found in Belgium in 1939 and had spread into
northern France by the end of the 1950s. For the past
30 years it has been colonising numerous ponds and
streams in metropolitan France, except in the southeast. Elodea nuttallii is replacing E. canadensis at
many sites (Mériaux and Gehu 1979, Thiébaut et al.
1997, Barrat-Segretain 2001). Although E.
canadensis and E. nuttallii have been spreading for
several years in eastern France, this species is
relatively more problematic in other European
countries (for example in Germany, Switzerland,
Brittany, Belgium, Sweden).
In many bodies of water, it has been necessary
to control overabundant aquatic plants. Large
infestations of plants which cause considerable
environmental impact, such as Ludwigia spp. or
Hydrocharitaceae have the highest priority for
control. There are several methods of managing
aquatic plants: mechanical or manual harvests, handpulling, biological control, changing the aquatic
environment and chemical control. The management
techniques chosen must be appropriate both to the
type of weed problem and to the uses and function of
the body water. To our knowledge, no research on
the impact of hand-pulling of Elodea species (E.
nuttallii and E. canadensis) has been done.
To evaluate the impact of hand-pulling on the
two Elodea species (E. nuttallii, E. canadensis), an
approach based on measurements of morphological
traits was used. In this paper, we aim to determine
the impact of the hand-pulling on E. nuttallii and on
E. canadensis biomass, on Elodea population and
architecture, through measurement of morphological
traits.
MATERIAL AND METHODS
Study area
The study was performed in the Vosges mountains
((NE France). The landscape pattern consists of
sandstone mountains. The regional climate is sub
continental. Two sites were selected: a river and a
reservoir. The first one, located in the Northern
Vosges, is the Falkensteinbach stream. This stream is
characterized by overabundance of E. nuttallii (mean
cover percentage visually estimated between 70 and
90 % in July). The invasive species E. nuttallii
colonized the streams of this area since the end of
1970’s (Muller 1990, Thiébaut and Muller 1999). A
100m length of stream was chosen. Two spot-checks
(Reference site, experimental site E divided in two
sub-units: E1 and E2) located at 45 m intervals
(buffer zone) were selected (Figure 1).
The second one, located in the Donon
mountains, is a reservoir used as a source of supply
for the retaining water (0.5 million cubic metre water
lake). It is also a leisure and nautical centre. The lake
area is 39 ha. This artificial lake is characterized by
overabundance of E. canadensis (mean cover
percentage visually estimated between 70 and 90 %
in July) since 2003. Two spot-checks (Reference site,
experimental site E) located within the littoral zone
were selected. Each area (reference, experimental)
measured 20 x 20 m.
Chemical survey of the water
500 ml of water were collected monthly from the end
of February to the end of October in 2003 and in
2005 in the Falkensteinbach stream. It was collected
in July, August and October 2006 in the lake “La
Plaine”. Analyses were performed immediately upon
returning to the laboratory (less than 24 hours after
sample collection). Alkalinity was determined by
titration (AFNOR 1990). Conductivity and pH were
measured using a combined glass electrode and
corrected for temperature (25°C). Reactive soluble
phosphorus and ammonia were analysed using
spectrophotometer (single reagent ascorbic acid
technique for phosphorus, and indophenol’s
technique for ammonia, AFNOR 1990). Samples for
nitrate, sulfate and chloride analyses were
determined
in
the
laboratory
with
ion
chromatography.
Experimental protocol
Hand-pulling
Hand-pulling involves removing entire plants
(leaves, stems, and roots) from the area of concern
and disposing of them in an area away from the
shoreline. During hand pulling, Elodea plants are
manually removed from the bottom, with care taken
to remove the entire root crown and to not create
fragments. During hand pulling, we dig around and
beneath the plant roots with a tool and gently lift the
entire plant out of the sediment. Elodea plants can be
readily removed from sediments. Once plants are
removed, we place them into bags for transportation
to the surface.
Site 1: Falkensteinbach river
The factor tested was the impact of diffrent
frequencies of hand-pulling in the stream:
- one hand-pulling was practised on E1 and E2 on
February 2003,
- a second hand-pulling was realised on E2 on
May 2003,
Reference site
36 m
Water flow direction
Buffer site
45m
E1
15 m
E2
15 m
1 hand-pulling
3 hand-pulling
February 2003
February & May 2003
Experimental area: 30m
March 2005
Figure 1. Description of the experimental site 1: The Falkensteinbach river.
1059
-
a third hand-pulling was realised on E2 on
March 2005.
The impact of management on the architecture of
plant and on the biomass was assessed each month
until the end of the study.
Impact of the management on the morphology of
Elodea species
Thirty plants were collected each month in site 1
(reference, E1 and E2) from March to October 2003
and from March 2005 to July 2005. They were
removed in July and October 2006 in site 2
(reference, experimental area). Apical shoots of 3cm
length, corresponding to the optimal growth area,
was cut off. Lateral shoots included the initial lateral
which developed from the nodes on the apical
original shoot and the others lateral which was a
development either from the same nodes, or from the
nodes on the lateral shoots (Kunii 1981). Nine
morphological traits were measured of each plant by
a ruler (see for example E. nuttallii: Figure 2):
• trait 1: main shoot length
• 2: lateral shoot length (initial +secondary shoots)
• 3: number of lateral shoots (initial shoot)
• 4: length of total shoot (main + lateral)
• 5: bulk. It corresponded to the ratio between
dried biomass of the plant and length of total
shoot.
• 6: length of ten internodes after the cut of three
cm apex.
• 7: length of a leaf located at the sixth whorl
• 8: width of a leaf located at the sixth whorl
• 9: surface of a leaf located at the sixth whorl.
One leaf on this sixth whorl is cut, fixed on a
paper with sailor tape. Surface was calculated by
using logician Scion image V. 1.63.
Site 2
The lake “La Plaine”, where manual methods are
being used for Elodea canadensis eradication,
typically have Elodea canadensis in small patches
within the littoral zone. Two hand-pulling (one in
July 2006, and a second one in October 2006) were
tested in the litteral zone close to the beach.
Biomass production:
Ten plots (0.2 m2 area/plot) were randomly placed
each month in site 1 (reference, E1 and E2). The
biomass was studied in July, in October 2006 and in
June 2007 in site 2 (reference, experimental area).
The vegetation was dug out manually by species.
Elodea sp. were weighed. Three replicates of E.
nuttallii or E. canadensis were dried at 65° C for
three days. Results were expressed in Dry Mass/m2.
The experiments were realised from March 2003 to
October 2003 in the three areas (Reference, E1, E2)
and from March 2005 to July 2005 in the
Falkensteinbach river (reference site 1, E2). The
biomass was measured in July 2006, in October 2006
and in June 2007 in the Lake La Plaine in the
reference and in the experimental areas.
Sixth whorl leaf
3 cm apex cut
Lateral shoot
Ten apical internodes
Main shoot
Roots
Figure 2. Diagram illustrating E. nuttallii and its morphological traits.
1060
Statistical analysis
After the verification of the normal distribution of
the values and homogeneity of variance, one way
ANOVAs were used to test the management and the
temporal effect. For each significant difference of P
< 0.05, a HDS Tuckey’s posthoc test was performed.
were present in the end of 2003. However at the
beginning of 2005, E. nuttallii have again colonized
the experimental area. A higher biomass was
measured in the reference site 1 in 2005 than in 2003.
The hand-pulling had also a significant impact on the
production of biomass of E. canadensis (Figure 3b).
Table 1. Water chemical composition. Mean annual
values.
RESULTS
Chemical characteristics of the water
The water of the two studied sites was neutral, with
low mineral content (Table 1). The site 1 was
characterized by a high nitrogen concentration
(NNH4+ = 109 ± 40µg/l) and a moderate
concentration of phosphate (PPO43- = 37 ± 10 µg/l),
whereas the site 2 was defined by a moderate nutrient
level (Table 1).
Biomass production
There was a significant difference in the biomass
produced among one, two and three hand-pulling in
site 1. No stands of E. nuttallii were found after July
in site E2 in 2003 (Figure 3a). Only some individuals
La Plaine
pH
conductivity
µScm-1
-1
Faklensteinbach
7.67
±
0.5
6.95
±
0.12
92
±
6.7
71
±
6
alkalinity
µeq L
520
±
7
291
±
29
phosphate
µgPL-1
30
±
10
37
±
10
ammonia
µgNL-1
40
±
10
109
±
40
0.66
±
0.05
0.55
±
0.10
-1
nitrate
mgNL
sulphate
mg L-1
6.50
±
0.26
9.37
±
0.75
chloride
mg L-1
5.73
±
0.78
5.7
±
0.21
1200
Biomass g/m²
1000
800
600
400
reference
E1
E2
200
M
ar
ch
2
Ap 003
ril
20
0
M
ay 3
2
Ju 003
ne
20
Ju 03
ly
Au 20
0
Se gus 3
t
pt
em 200
be 3
r2
O
ct
ob 003
er
M 200
ar
ch 3
2
Ap 005
ril
20
0
M
ay 5
2
Ju 005
ne
20
05
0
Figure 3. Evolution of the biomass of Elodea species in reference site and in hand pulling areas.
1061
Reference
Experimental area
Biomass g/m²
90
80
70
60
50
40
30
20
10
0
July 2006
October 2006
June 2007
Figure 3a. Biomass of E. nuttallii in the Fakensteinbach river;
Main shoot length (cm)
160,00
140,00
120,00
100,00
reference
80,00
E1
60,00
E2
40,00
20,00
M
ar
ch
03
Ap
ril
03
M
ay
03
Ju
ne
03
Ju
ly
Au 03
gu
st
Se
0
pt
em 3
be
r0
O
3
ct
ob
er
03
M
ar
ch
05
Ap
ril
05
M
ay
05
Ju
ne
05
0,00
Figure 3b. Biomass of E. canadensis in the Lake La Plaine.
Impact of management on the architecture of
Elodea species and on the biodiversity
No significant difference was observed in the
architecture of E. nuttallii (Figure 4a) or E.
canadensis (Figure 4b) between the plants collected
in reference and in experimental areas. At the
1062
beginning of the study, the biodiversity was low in
the river Falkensteinbach. E. nuttallii was the
dominant species. The decrease of E. nuttallii stands
allow the development of native aquatic plants such
as Ranunculus peltatus or Callitriche platycarpa two
years after the end of the management in 2007.
Length of 10 internodes(cm)
12,00
10,00
8,00
reference
6,00
E1
E2
4,00
2,00
M
ar
ch
03
Ap
ril
03
M
ay
03
Ju
ne
03
Ju
ly
03
Au
gu
st
Se
03
pt
em
be
r0
O
3
ct
ob
er
03
M
ar
ch
05
Ap
ril
05
M
ay
05
Ju
ne
05
0,00
Leaf width (cm)
0,45
0,40
0,35
0,30
reference
0,25
E1
0,20
E2
0,15
0,10
0,05
M
ar
ch
03
Ap
ril
03
M
ay
03
Ju
ne
03
Ju
ly
03
Au
gu
st
Se
03
pt
em
be
r0
O
3
ct
ob
er
03
M
ar
ch
05
Ap
ril
05
M
ay
05
Ju
ne
05
0,00
Figure 4a : Impact on the hand-pulling on the architecture of E. nuttallii. Example of 3 traits. : trait 1: main
shoot length; trait 6: length of ten internodes; trait 8: width of a leaf located of the sixth whorl.
Main shoot length (cm)
70,00
60,00
50,00
40,00
30,00
20,00
10,00
0,00
Hand-pulling
reference
1063
Leaf width (cm)
0,40
0,35
0,30
0,25
0,20
0,15
0,10
0,05
0,00
Hand-pulling
reference
10 internode length (cm)
10,00
9,00
8,00
7,00
6,00
5,00
4,00
3,00
2,00
1,00
0,00
Hand-pulling
reference
Figure 4b. Impact on the hand-pulling on the architecture of E. canadensis. trait 1: main shoot length; trait 6:
length of ten internodes; trait 8: width of a leaf located of the sixth whorl.
DISCUSSION
Impact of hand-pulling on the E. nuttallii and on
E. canadensis
No significant difference was established for
morphological traits of E. nuttallii /E. canadensis
between plants collected in the experimental and in
the reference areas. Hand-pulling have no impact on
the architecture of Elodea species. Our results didn’t
corroborate the conclusions of Abernethy et al.
(1996) that showed a 44% reduction for length
response after two cuts. Elodea species appeared as a
disturbance-tolerant species. The responses of
1064
Elodea species to the stress (hand-pulling) was
eliminated very quickly, less than one month. The
plants grow fast and reach the water surface only few
weeks after hand-pulling.
In our study, the maximum of biomass of E.
nuttallii was obtained in June 2005. The three
treatments induced a drastic reduction of E. nuttallii
in the stream, less than 2% in the end of the study.
The biomass response of E. canadensis was more
marked in our area (reduction of 63% after one
treatment) than in the study of Abernethy et al.
(1996), which measure biomass reductions of 41 %
after one cut.
Management options
After several hand-pulling the spread of E. nuttallii
and of E. canadensis is area restricted. This method
is efficient. However, due to expense and the time
intensive nature of manual methods, sites suitable for
hand pulling are limited to lakes or ponds only
lightly infested with invasive species. This method
may also be applicable in waterbodies where no
herbicide use can be tolerated such as in a lake used
as a municipal drinking water supply and running
waters.
E. canadensis appeared to be less susceptible to
cutting-based weed control measures than
Myriophyllum spicatum, a native species (Abernethy
et al. 1996). Sabbatini and Murphy (1996) using a
multivariate approach, showed that E. canadensis has
a strong tolerance of management based on
disturbance, such as cutting. Cutting, especially
mechanical control, could induce a reduction of the
biomass of indigenous plants and allow Elodea to
spread to new areas because this management break
up the plant. Stem fragmentation is the main
dispersal mode for Elodea sp. Both Elodea species
showed similar resistance to currents, while fragment
regeneration and colonisation were only slightly
higher in E. nuttallii than in E. canadensis (BarratSegretain et al. 2002). Management such as handpulling or harvests favor the downstream plant
propagation. However harvests can be quite useful in
areas where the weed is already established, or when
the species will disperse into areas unfavourable to
its survival (Bowmer et al. 1995).
The growth of E. canadensis is affected by low
light intensity, contrary to E. nuttallii (BarratSegretain 2004). E. nuttallii and E. canadensis have
wide amplitude in nutrient levels (Robach et al.
1995, Rolland et al. 1999, Thiébaut and Muller 2003,
Thiébaut 2005). Changes in management practices
especially those that have the potential to directly
impact the river will be important to help manage
exotic macrophytes. This includes practices such as
maintaining and enhancing the condition of riparian
vegetation
and,
stormwater
and
nutrient
management. Reduction of nutrients entering the
river is important in the fight against exotic
macrophytes species, as these species grow best in
high nutrient waters.
The biological control of aquatic macrophytes
has received considerable interest all over the world.
Although Elodea species are often preferred food for
waterfowl or crayfish (Lodge 1991), they are avoided
by many insect herbivores (Newman 1991).
However, a slightly higher palatability was
established for E. nuttallii than for E. canadensis by
Limnea stagnalis (Barrat-Segretain et al. 2002). E.
nuttallii is avoided by herbivorous larvae of Acentria
ephemerella (Erhard et al. 2007). No herbivore
damage of apical meristems was observed for E.
canadensis because Acentria ephemerella larvae also
avoid feeding on this species removed leaves below
the apical tips (Gross et al. 2001). In the lake La
Plaine, the spread of E. canadensis may be also
explained by the abundance of this aquatic
lepidopteran in dense mats of Elodea.
An other solution was to do nothing and to
“wait and see”. A noticeable decline of E. canadensis
in European freshwaters (Simpson 1990) and of E.
nuttallii indeed was also reported after the peak of
the outburst in Japan’s lake (Nagasaka et al. 2002).
E. nuttallii populations exhibited a genetic
uniformity that made them vulnerable to attack by
fungi or pathogens.
Further work is needed to improve our
knowledge to estimate the ecological risk of
management on biodiversity and on ecosystem
function. The risk of adverse side-effects for users of
the water and for the ecosystem health must always
be taken into account. Stronger enforcement of
existing laws, coupled with an intensive public
education campaign, is needed to prevent further non
indigenous species introduction.
AKNOWLEDGEMENTS
The assistance of Muriel Julita, Celine Trochain, P.
Rousselle and of the fishermen was greatly
appreciated. This study was funded by the Northern
Vosges Biosphere Reserve, the French water Agency
Rhin-Meuse, the Syndicat Mixte des “Lacs de PierrePercée-La Plaine”. This project is sponsored by the
French Ministry of Ecology and Sustainable
Development Program “Biological Invasions”.
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