REGULATED RIVERS: RESEARCH & MANAGEMENT
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
INTERSTITIAL FAUNA IN NEWLY-CREATED FLOODPLAIN CANALS
OF A LARGE REGULATED RIVER
PIERRE MARMONIERa,*, CECILE CLARETb AND MARIE-JOSE DOLE-OLIVIERb
a
GRETI (and ESA-CNRS no. 5023, Villeurbanne), Uni6ersité de Sa6oie, 73376 Le Bourget-du-Lac Cedex, France
ESA-CNRS no. 5023 ‘Ecologie des Eaux Douces et des Grands Fleu6es’ -HydroBiologie et Ecologie Souterraines,
Uni6ersité Claude-Bernard Lyon I, 69622 Villeurbanne Cedex, France
b
ABSTRACT
Artificial drainage canals are often dug in large river floodplains to prevent winter inundation when groundwater level
increases. Nothing is known about the biodiversity of the interstitial fauna of these artificial aquatic systems. The
water chemistry and interstitial fauna of four drainage canals along the River Rhône (dug 11 – 15 years ago) were
sampled in July during 3 years (1995–1997). A total of 53 taxa were found, with both epigean and hypogean
organisms, and some rare phreatobites previously considered as absent from this sector of the Rhône. The faunal
assemblage is characterized by limited temporal variations between the 3 successive years. Differences in interstitial
fauna composition between the four drainage canals were mostly linked to oxygen availability and to heterogeneity
in water origin (true ground water or surface water infiltration through embankment). Low oxygen content results in
poorly diversified assemblages, which are always dominated by the same small set of species. In contrast,
heterogeneity in water origin resulted in elevated faunal diversity. Copyright © 2000 John Wiley & Sons, Ltd.
KEY WORDS:
diversity; drainage canals; ground water; invertebrates; River Rhône
INTRODUCTION
Agricultural practices, urban development, river engineering and especially hydroelectric production are
major causes of floodplain degradation (Henry and Amoros, 1995). In floodplains, these activities alter
groundwater flowpaths and the level of the water table. When the riverwater level is decreased,
groundwater inputs to backwaters downstream of the power plant decrease (Bravard et al., 1986).
Whereas, upstream of power plants, groundwater inputs increase when the water table is maintained at
a high level (Henry et al., 1995; Claret et al., in press). In this latter case, seasonal inundation of the
floodplain may occur. In such cases, drainage canals may be dug to drain the water that infiltrates
through the embankment and thus prevent groundwater overflows.
These drainage canals are early successional or ‘juvenile’ aquatic systems. They are vegetation-poor and
thus structurally very homogeneous, which contrasts with the great ecological and geomorphological
diversity of the surrounding floodplain channels. The natural backwaters have high heterogeneity and
high connectivity (surface and subsurface) with other floodplain annexes, making these habitats biodiversity ‘hot spots’ with respect to vegetation (Bornette et al., 1998; Bornette et al., in press), benthos (Castella
and Amoros, 1988; Obrdlik et al., 1995), and interstitial invertebrates (Stanford and Ward, 1993;
Marmonier et al., 1997).
In contrast to natural backwaters, nothing is known about the composition, taxonomic richness and
diversity of interstitial assemblages in artificial drainage canals. The present study aimed to address this
lack of knowledge in two ways: (1) to evaluate the colonization of these young artificial aquatic systems
by interstitial fauna, for both epigean and hypogean invertebrates, and (2) to highlight the groundwater
fauna diversity of different apparently homogeneous drainage canals (similar origin, location and
features). In view of the canals age (11 – 15 years since creation) and their apparent homogeneity, we
* Correspondence to: GRETI (and ESA-CNRS no. 5023, Villeurbanne), Université de Savoie, 73376 Le Bourget-du-Lac Cedex,
France.
CCC 0886–9375/2000/010023 – 14$17.50
Copyright © 2000 John Wiley & Sons, Ltd.
Recei6ed 20 December 1998
Re6ised 8 March 1999
Accepted 16 April 1999
24
P. MARMONIER ET AL.
expected that temporal changes would still be occurring in their interstitial fauna, whereas differences
between canals would be weak. To test this hypothesis, four drainage canals were sampled for water
chemistry and interstitial fauna every summer over 3 successive years.
STUDY SITES
The four study canals were situated in two alluvial plains of the Upper River Rhône (France), at
Brégnier-Cordon and at Belley. Hydroelectric facilities were completed in these two floodplains in 1983
and 1984, respectively. The upper stretches of both were impounded by regulation dams, which divert
water flow into a headrace canal that leads to a power plant, by-passing the main river channel (Figure
1(a)). At Brégnier, base flow in the by-passed channel is maintained at 80 m3 s − 1 from December to
March; 150 m3 s − 1 from June to August; and 100 m3 s − 1 during the remaining periods. At Belley, the
base flow varies between 25 and 60 m3 s − 1 according to the season. The capacity of the impoundments
is restricted to 700 m − 3 s − 1 (Bravard, 1987; Savey and Cottereau, 1991; Dessaix et al., 1995). In both
cases, drainage canals were dug along the foot of the reservoir and the headrace.
Three sampling points were established in the upstream part of each canal (except canal D, which had
four points) and visited in July 1995, 1996 and 1997. At Belley (BE, Figure 1(b)), one canal (A) was
located close to the dam, at the foot of the retention canal embankment, between the retention canal and
the by-passed channel. The three sampling points in canal A were located at the upstream end of the canal
at 0 m (A1), at 100 m (A2) and 210 m downstream (A3). The three other canals are located at Brégnier
Figure 1. (a) Scheme of the hydroelectric facilities built on the River Rhône: the upstream dam diverts most of the water flow into
a headrace canal that leads to a power plant; the former channel is by-passed. (b) Location of the two sectors, Belley (BE) and
Brégnier (BR) on the River Rhône. Location of the four drainage canals (A, B, C, D) and the points () sampled on each
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
INTERSTITIAL FAUNA
25
(BR, Figure 1(b)). Canal B was located on the left side of the River Rhône, at the foot of the reservoir
embankment, with B1 at 0, B2 at 300, and B3 at 600 m, respectively from the upstream end of the canal.
Canal C was located on the right side of the river, at the foot of the headrace canal embankment; C1 was
at 0, C2 at 300, and C3 at 600 m, respectively from the upstream end. Canal D was located on the left
side of the river, between the retention canal and the by-passed channel. Two sections can be distinguished
in this canal: the upstream part is separated from the retention canal by a karstic hill (the ‘Mont Cordon’)
with D1 and D2 located at 20 and 120 m, respectively from the upstream end; the downstream part was
located just at the foot of the retention canal embankment, with D3 located at 600 and D4 at 800 m from
the upstream end, respectively.
MATERIAL AND METHODS
At each sampling point, a perforated metal pipe of 23 mm inside-diameter (9 rows of 5 mm diameter holes
in a 13-cm band, 4 cm from the distal end of the pipe) was driven into the sediment to a depth of 0.5 m
from the sediment surface. Water temperature and specific conductance were then measured in situ with
a thermo-conductimeter (WTW LF 92) using a peristaltic hand pump (Willy A. Bachofen type).
Additional surface and interstitial water samples were taken, stored in 1 mL hemolyse tubes and kept in
insulated containers cooled with ice for the 30 min required to return to the laboratory. In the laboratory,
sulphate, chloride and nitrate concentrations (9 0.1 ppm) were measured with a Capillary Ion Analyser
(Waters). Hydraulic head difference between surface water and interstitial water was measured using a
hydraulic potentiomanometer (Freeze and Cherry, 1979; Winter et al., 1988). The amount of fine sediment
in the interstices was estimated from the volume of sediment pumped in the 10 L samples. The amount
of particulate organic matter (POM) in sediments was measured by loss on ignition after invertebrate
sorting (4 h at 550°C; see discussion about ignition temperature in Bretschko and Leichtfried, 1987). The
POM concentrations were probably underestimated because the Bou–Rouch method samples only the
finest fraction of the sediment (B 5 mm), but this underestimation is weak because interstitial POM is
generally of small size (Leichtfried, 1985; Marmonier et al., 1995).
Interstitial invertebrates were collected at the same sampling point using the Bou–Rouch sampler (Bou
and Rouch, 1967; Bou, 1974); 10 L of water and sediment were pumped and then, filtered through a 300
mm mesh net. Samples were preserved in the field in a 5% formaldehyde solution and stained with Bengal
Pink. Invertebrates were sorted in the laboratory by sieving. Some groups were identified to species or
genus (Planaria, Acheta, Bivalvia, Gastropoda, Ostracoda, Cladocera, Amphipoda, Isopoda,
Ephemeroptera, Trichoptera, Plecoptera, Coleoptera). Syncarida and most diptera were identified to
family level, copepods were separated into cyclopids and harpacticids. Other groups (Nematoda,
Oligochaeta, and Hydracarina) were not identified further.
Three different biodiversity measures were used in this study (Claret et al., in press): (1) the taxonomic
richness and the Shannon – Weaver diversity index (Shannon and Weaver, 1962), (2) biological traits, and
(3) habitat-based groups. Biological traits considered here and their different categories (Table I) were
chosen because they are documented for most groundwater (i.e. hypogean) organisms, which are still
poorly studied compared to surface (i.e. epigean) fauna. They categorize animals according to size, feeding
and movement. Habitat-based classification of the fauna derives from the affinity of species for
groundwater environments (Table II), including their frequency in different types of subterranean systems
and their behavioural, morphological, and physiological specializations to ground waters (Marmonier et
al., 1993; Gibert et al., 1994).
The physical and chemical characteristics of interstitial water (seven variables× 39 samples) were
submitted to principal components analysis, whereas the faunal data matrix (33 taxa×39 samples) was
submitted to correspondence analysis using the Statistica/W (version 4.5) statistical package (StatSoft Inc.,
Tulsa, USA, 1997). Abundances, mean taxonomic richness, and Shannon–Weaver index were compared
between sites using the Kruskal – Wallis non-parametric rank test.
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
26
P. MARMONIER ET AL.
Table I. Species traits and categories used for interstitial fauna classification (Claret et al., in press)
No. Species traits
No.
Abbreviations Categories and characteristics
1
Trophic
I
ii
iii
iv
C
H
D
O
Carnivores, animal consumers
Herbivores, vegetation feeders (macrophytes, algea, periphyton)
Detritivores on fine or coarse organic matter
Omnivores, opportunists, feed on all source of food
2
Mobility
I
ii
F
Sl
iii
iv
W
Sw
Fixed, buried or with very low mobility
Sliders, slow mobility using a muscular foot, cilia and mucus, or
setae
Walkers, need frictional surface and employ legs
Swimmers, propel themselves inside water using limbs or carapace
movement
I
ii
iii
Ma
Me
m
3
Body size
Macrofauna (maximum attainable length\2000 mm)
Mesofauna (500–2000 mm)
Meiofauna (B500 mm)
RESULTS
Principal components analysis of the physical and chemical data explained 56.7% of the total variability
by the first two components, with C1 (32.4%) accounting for sediment volume, oxygen content,
temperature and specific conductance and C2 (24.3%) for chloride, sulphate, and nitrate concentrations.
The physical and chemical differences between the four canals revealed by the principal components
analysis are reflected in the mean concentrations of solutes in each canal (Figure 2). The interstitial water
of canal A had significantly lower oxygen (p B0.1%), nitrate (pB0.1%), and fine sediments (p= 0.01%)
than sites B, C, and D. In canal D, oxygen content always exceeded 4 mg L − 1, but a high heterogeneity
was found between sampling points, with high nitrate contents at the two upstream points and high fine
sediment content in the two downstream points. In canal C, oxygen and fine sediment contents were
rather low in 1995 and increased to medium values in 1996 and 1997. Other physical and chemical
characteristics (i.e. specific conductance, chloride, sulphate, and POM contents) reached rather similar
values in the four canals (p \10%) with little change between years (p\ 5% for all stations).
The composition of the interstitial fauna, 53 taxa sampled in the four canals (Table III), was
characterized by Crustacea (the most diversified group), with four species of Cladocera, seven Ostracoda,
and seven Amphipoda. A Syncarid of the family Parabathynellidae and two amphipods (Salentinella
juberthiae and Crangonyx sp.) were sampled for the first time in these sectors of the Upper River Rhône.
Table II. Habitat-based groups and categories used for interstitial fauna classification (Marmonier et al., 1993;
Gibert et al., 1994)a
No.
Groups
1
Stygoxenes
2
Stygophiles
3
a
Stygobites
No.
Abbreviations Categories and characteristics
Stx
Stygoxenes: epigean organisms, incidentally found in ground waters
I
Stt
ii
Stp
Occasional hyporheos: epigean organisms, life cycle with an obligate
epigean stage in surface stream
Permanent hyporheos: epigean organisms, whole life cycle possible
in surface water as well as in ground water
I
Stub
ii
Phr
Ubiquitous stygobites: hypogean organisms that colonize all types
of groundwater systems (caves, interstitial habitats, stable and unstable zones)
Phreatobites: hypogean organisms that colonize stable environments
(deep, porous aquifers)
Amphibites were absent.
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
INTERSTITIAL FAUNA
27
Figure 2. Principal component analysis ordination (C1 × C2) of the 39 sampling points by 7 physical and chemical measures. (T°C:
temperature; Cond.: specific conductance in mS cm − 1; Cl − : chloride concentrations in mg L − 1; SO4− − : sulphate concentrations in
mg L − 1; NO3− : nitrate concentrations in mg L − 1: O2: dissolved oxygen concentrations in mg L − 1; Sed.: fine sediment volume in
cm3 10 L − 1)
After preliminary analyses, the initial matrix was reduced by eliminating taxa represented by less than
three individuals. Correspondence analysis of the interstitial faunal data, with 26.3% of the total
variability explained by the two axes (Figure 4), revealed strong differences between canals, with only
three species common to all four sites (the Planaria Polycelis sp., the Mollusca Potamopyrgus antipodarum
and the Amphipoda Niphargus rhenorhodanensis). The interstitial fauna of canal A was dominated by the
Mollusca Val6ata cristata and the Isopoda Asellus aquaticus, associated with the Ostracoda Pseudocandona lobipes and the Coleoptera Haliplus lineatocolis. Another characteristic of the canal A assemblage
was the lack of epigean Amphipoda, both Gammarus fossarum and G. pulex were absent. Over the 3 years,
few rare taxa were collected, i.e. only 37% of taxa were present during a single sampling period. The
resulting assemblage at canal A has low diversity and was dominated by the same small set of species,
from 1 year to another.
The two upstream points in canal D (Figure 4; Table III) were characterized by deep groundwater
dwellers (the Amphipoda Niphargus fontanus and Syncarida Parabathynellidae) and some epigean
organisms frequently found in small oligotrophic rivers or groundwater fed streams (such as the Planaria
Dugesia sp., the Ephemeroptera Caenis sp., the Plecoptera Protonemura sp., and the Coleoptera Esolus
parallelepipedus). At the two downstream points of canal D, insect larvae generally found in slow flowing
streams with fine bottom sediments (such as the Ephemeroptera Ephemera sp. or the Trichoptera
Limnephilidae) or gravel bed (such as the Trichoptera Silo cf. pallipes) dominated the assemblages. In this
canal, rare taxa represented 53% of the total taxonomic richness.
Samples from canals B and C (Figure 4; Table III) were characterized by cyclopoids, harpacticoids,
Nematoda and Oligochaeta (unidentified groups) and two hypogean taxa, Niphargopsis casparyi (stygobite,
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
28
P. MARMONIER ET AL.
sampled in canals B and C) and Salentinella juberthieae (phreatobite, sampled in canal C only). The
occurrence of the Amphipoda Gammarus fossarum and the two Coleoptera Elmis maugetii and Limnius
6olkmari, in all Brégnier canals (B – D) results in some sample points of canals B and C being ordinated
close to those of canal D. Rare taxa represented 72% (canal B) and 55% (canal C) of the total taxonomic
richness; however, dominant taxa did not change from 1 year to the next. Temporal changes between
years were thus lower than spatial differences between canals (Figure 4).
Canal D had the largest number of taxa (34), with high mean taxonomic richness (S) and high mean
diversity index (H%, Kruskal – Wallis test p B0.1 in 1996; Figure 5). Canal A had the lowest number of
taxa (16), and intermediate values for S and H%, which varied little between years (Figure 5). The two
remaining canals (B and C) had intermediate total taxonomic richness (with 22 and 20 taxa, respectively).
S and H% values displayed high interannual change, with a significant increase in canal C from 1995 to
1996 and 1997 (S: p B5% and H%: p B10%). When all samples from the four canals were grouped (Table
IV), abundances did not significantly differ according to oxygen or POM contents, whereas species
richness and H% diversity reached highest values in well oxygenated areas (\ 6 mg L − 1) and in areas with
intermediate POM content (between 10 and 100 mg L − 1; Table IV).
Similar distributions of species among species trait modalities were observed for the four canals, with
detritivores (except in canal B), walking species, and large sized animals dominating (Figure 6). For
diversity of habitat-based groups, canals B – D showed a progressive decrease of relative species richness
from the stygoxenes to the phreatobites, whereas in canal A, the decreasing gradient disappeared with
high percentages of stygoxenes and permanent stygophiles compared to other groups, and a complete lack
of phreatobites.
Figure 3. Physical and chemical variables (mean + S.E.; n= 3 for canals A, B and C and n =4 for canal D) in each canal for each
sampling year (1995, 1996 and 1997)
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
29
INTERSTITIAL FAUNA
Table III. List of interstitial fauna of drainage canals sampled in Belley and Brégnier sectors
Ecological statusa
Stx
Planaria
Nematoda
Oligochaeta
Acheta
Gastropoda
Bivalvia
Hydracarina
Cladocera
Ostracoda
Copepoda
Syncarida
Amphipoda
Isopoda
Ephemeroptera
Plecoptera
Trichoptera
Coleoptera
Diptera
Dugesia sp
Polycelis sp.
Div. sp.
Div. sp.
Helobdella stagnalis
Hauffenia minuta
Val6ata cristata
Potamopyrgus antipodarum
Radix sp.
Planorbis carinatus
Pisidium sp.
Div. sp.
Alona guttata
Alona quadrangularis
Chydorus sphaericus
Cryptocandona 6a6rai
Candona candida
Pseudocandona lobipes
Pseudocandona albicans
Ilyocypris sp.
Herpetocypris reptans
Prionocypris zenkeri
Harpacticoida
Cyclopoida
Parabathynellidae
Salentinella juberthiae
Crangonyx sp.
Niphargus fontanus
Niphargus rhenorhodanensis
Niphargopsis casparyi
Gammarus pulex
Gammarus fossarum
Asellus aquaticus
Ephemerella ignita
Baetis sp.
Caenis sp.
Ephemera sp.
Protonemura sp.
Limnephilidae
Odontocerum albicorne
Leptoceridae
Silo cf. pallipes
Sericostomatidae
Elmis maugetii
Haliplus lineatocolis
Hydroporus sp.
Limnius 6olkmari
Esolus parallelepipedus
Chironomidae
Simulidae
Empididae Atalantinae
Ceratopogonidae
Tipulidae
Stt
Stp
Canalsb
Stub
Phr
C
D
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
B
*
*
A
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
a
Ecological status of the taxa: stx—stygoxene, stt — occasional hyporheos, stp — permanent hyporheos, stub —
ubiquitous stygobites, phr—phreatobites.
b
A: Belley canal, B–D: Brégnier canals (see locations in Figure 1).
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
30
P. MARMONIER ET AL.
DISCUSSION
The composition of interstitial assemblages in the four drainage canals of the Upper River Rhône varied
little between 1995 and 1997, but significant between-canal differences were observed (Table IV). The
temporal stability was certainly linked to a rapid colonization of the canals (which were 11–15 years old
between 1995 and 1997), whereas the spatial heterogeneity observed in faunal composition was linked to
subtle physical and chemical differences between the canals. When these drainage canals were dug in 1983
and 1984, they were probably mostly free of interstitial fauna, whereas we observed a total of 53 taxa 10
years later. In particular, we found a Syncarid Parabathynellidae and two Amphipoda (Salentinella
juberthieae and Crangonyx sp.), that were previously thought to be limited to the Jons sector (55 km
downstream). A few hypogean organisms were probably present in the ground waters surrounding the
canals when they were dug, but densities of stygofauna in both Belley and Brégnier sectors are so low
(Ginet, 1982; Marmonier and Creuzé des Châtelliers, 1992) that interstitial habitats directly in contact
with the canals could be considered as uncolonized.
Colonization of empty niches has been frequently discussed at a variety of spatial scales. At the
continental scale, biogeographical models of colonization have been proposed for a long time (see for
review Blondel, 1986; Cox, 1990), or for subterranean animals Christiansen and Culver (1987). At the
microhabitat scale, many studies have highlighted the different refugia available for aquatic fauna during
disturbance and their potential pathways of recolonization (Williams and Hynes, 1976; Palmer, 1990;
Palmer et al., 1992; Dole-Olivier et al., 1997). At the intermediate scale, colonization processes of different
aquatic systems inside the same floodplain have been poorly documented, especially for interstitial
assemblages (Gibert et al., 1990). At this latter scale, connectivity between water bodies is a basic factor
influencing colonization, but pathways were certainly different for epigean and hypogean taxa.
Figure 4. Correspondence analysis (F1 × F2) ordination of the 39 sampling points on the basis of their taxonomic composition (33
taxa). (Duge: Dugesia sp.; Poly: Polycelis sp.; Nema: Nematoda; Olig: Oligochaeta; Hauf: Hauffenia sp.; Pant: Potamopyrgus
antipodarum; Vcris: Val6ata cristata; Pisi: Pisidium sp.; Hydc: Hydracarina; Aqua: Alona quadrangularis; Ccand: Candona candida;
Plob: Pseudocandona lobipes; Palb: Pseudocandona albicans; Harp: Harpactocoida; Cycl: Cyclopoida; Nfon: Niphargus fontanus;
Nrhe: Niphargus rhenorhodanensis; Gfos: Gammarus fossarum; Asel: Asellus aquaticus; Baet: Baetis sp.; Eign: Ephemerella ignita;
Limn: Limnephilidae; Seri: Sericostomatidae; Silo: Silo cf. pallipes; Elmi: Elmis sp.; Hali: Haliplus lineatocolis; Hydp: Hydroporus
sp.; Limu: Limnius 6olkmari; Chir: Chironomidae; Cera: Ceratopogonidae)
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
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INTERSTITIAL FAUNA
Figure 5. Taxonomic richness and Shannon–Weaver index (mean + S.E.; n = 3 for canals A, B and C and n =4 for canal D) in each
canal for each sampling year (1995, 1996 and 1997)
For epigean fauna with an aerial stage, such as insects (e.g. Ephemerella ignita, Odontocerum albicorne,
or Silo cf. pallipes), flight dispersal of adults is the most common process (Milner, 1994). Epigean taxa
without flying adults can colonize interstitial habitats by two ways: anemo- or zoochorie and upstream
migrations. In the drainage canals, the transport of eggs or adults (in living or torpid conditions) by wind,
birds or amphibians has been documented for many micro-crustaceans (Löffler, 1964; Sohn and
Kornicker, 1979; Seidel, 1989; Sohn, 1996) and can be evoked for most epigean ostracods that live and
lay eggs on muddy or sandy sediments (e.g. Candona candida, Prionocypris zenkeri, Herpetocypris
reptans). Upstream migrations are well known for some Amphipoda (Gammarus roeseli, Meijering, 1972).
In the Brégnier and Belley sectors Gammarus fossarum and G. pulex are abundant in the by-pass channels
of the river (Perrin and Roux, 1978; Dessaix et al., 1995) and they could easily colonize the drainage
Table IV. Relationships between interstitial assemblages characteristics (abundances, species richness, H% diversity)
and environmental characteristics (oxygen and POM content), with results of Kruskal–Wallis ANOVA of ranks
Abundances
Species richness (S)
Diversity index (H%)
n.s.
Oxygen K–W testb
contenta highest values Class 3 (\ 6 mg L−1)
H =5.72 (p = 0.05)
Class 3 (\ 6 mg L−1)
n.s.
Class 3 (\ 6 mg L−1)
POM
K–W test
n.s.
contentc highest values Class 3 (50–100 mg L−1)
n.s.
Class 3 (50–100 mg L−1)
H =8.51 (p= 0.04)
Classes 2 and 3 (10–100 mg L−1)
Samples of all sites and of all sampling series were grouped.
a
Oxygen content classes: 1— B 4 mg L−1; 2—between 4 and 6 mg L−1; 3 —\ more than 6 mg L−1.
b
Kruskal–Wallis test. n.s. = non significant.
c
POM classes: 1 — B 10 mg L−1; 2—between 10 and 50 mg L−1; 3 — between 50 and 100 mg L−1; 4 —\ 100 mg L−1.
Copyright © 2000 John Wiley & Sons, Ltd.
Regul. Ri6ers: Res. Mgmt. 16: 23 – 36 (2000)
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P. MARMONIER ET AL.
Figure 6. Distribution of taxa among species trait and habitat-affinity categories in each canal. See Tables I and II for abbreviations
canals from downstream. The connectivity between drainage canals and abandoned channels (e.g. canals
B and D) can explain the occurrence of molluscs (e.g. Radix sp.), crustaceans (e.g. Asellus aquaticus), or
insect larvae (e.g. Baetis sp., Caenis sp., or Trichoptera Limnephilidae) by upstream migrations from
stagnant water bodies.
For hypogean organisms, the absence of flying adults eliminates the probability of aerial transport and
strongly limits dispersion (see Danielopol et al., 1994). The most frequently evoked process for recolonization is intragravel migration, which can occur over a few meters (Marmonier, 1991) or several kilometers
(Magniez, 1993). In drainage canals, colonization may occur through subterranean water from populations located in the main channel (e.g. Niphargus rhenorhodanensis, Niphargopsis casparyi ), from scarce
patches of fauna in deep groundwater of the floodplain (e.g. Niphargus fontanus, Salentinella juberthiae,
Crangonyx sp., Parabathynellidae), or from lateral karstic systems (e.g. Niphargus fontanus, Reygrobellet
et al., 1975). However, the hypogean fauna of our study canals was species poor (Table IV), probably
because of the biogeographical location of the floodplains. These areas were covered by ice during the last
glaciation and their potential biodiversity has been reduced by this major climatic disturbance (Ginet,
1983).
Eleven to 15 years after their creation, the canals exhibited rather stable faunal assemblages over the
short term of our study. The little changes observed in interstitial assemblage composition between 1995
and 1997 lead us to believe that colonization processes have slowed down or ended. In canal A, a total
of 34 taxa were sampled over the study, reaching exactly the same taxonomic richness observed in a
Copyright © 2000 John Wiley & Sons, Ltd.
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INTERSTITIAL FAUNA
33
natural side channel spring (Plenet and Gibert, 1995). The increase of taxonomic richness and H% diversity
observed in canal C from 1995 to 1996 – 97 was certainly linked to increased oxygen concentrations.
Rather than a long term faunal shift, the changes observed in canal C probably reflected fluctuations in
environmental constraints.
Despite their similar origin, similar location in the floodplain and similar aspects, the faunal assemblages in the four canals were consistently different. Two major environmental characteristics could
explain these differences in faunal composition: oxygen availability and origin of interstitial water. For
example, the low amounts of fine sediment, medium organic matter content, but low oxygen concentrations of the interstitial habitats in canal A permitted anaerobic processes and denitrification (Figure 3).
These features seems to contradict the pattern generally observed in floodplains, i.e. low oxygen content
and denitrification processes associated with fine sediment deposits and high organic matter content
(Cooke and White, 1987; Claret et al., 1997). In fact, the characteristics observed in the canal result from
upstream microbial processes, oxygen consumption and denitrification occurring inside the reservoir’s
embankment. These environmental constraints result in a poorly diversified interstitial fauna dominated
by Val6ata cristata and Asellus aquaticus, this latter being resistant to mild hypoxia (Hervant et al., 1996).
The assemblage contained few rare taxa and lacked organisms that need high–medium oxygen content
(e.g. Gammarus fossarum, Hervant et al., 1995).
In contrast, the interstitial water in canals B–D contained enough oxygen (Figure 3) to maintain
aerobic processes and prevent denitrification. In these conditions, taxonomic richness and diversity of
fauna were high, with Gammarus fossarum present or dominant at most sampling points, and higher
percentages of rare taxa. Oxygen concentrations also explained temporal changes observed in canal C.
Low discharges of the River Rhône during the summer of 1995 certainly led to a decrease in water supply
to canal C, a reduction in oxygen concentrations in the interstices (Figure 3), and a decline in taxonomic
richness and H% diversity (Figure 5). Similar influences of oxygen content on groundwater fauna
composition have been highlighted for both spatial and temporal changes by Danielopol (1989) and
Pospisil et al. (1994) in the Danube floodplain.
In their predictive model of hyporheos density, Strayer et al. (1997) assumed that oxygen content takes
precedence, and hyporheos density would be linked to available organic matter when oxygen is not
limiting. The present study supports the first part of this predictive model (the link between oxygen
content and the abundance of invertebrates), but fails to support the second part—the highest species
richness and H% index values were observed with intermediate POM levels, which seems to represent
optimal conditions for interstitial fauna. Interstitial water movement is low in floodplains compared to the
active channel and high organic matter would induce a decrease in oxygen levels.
The origin of interstitial water my also explain some variations in interstitial fauna composition, such
as for canal D: the downstream part, fed mostly by seepage water from the River Rhône through the
reservoir embankments and by surface water in downwelling zones, harboured a small stream epigean
fauna (e.g. Silo cf. pallipes, Limnephilidae, Ephemera sp.) and two ubiquitous stygobites (i.e. Niphargus
rhenorhodanensis and Hauffenia cf. minuta, Ginet, 1982; Marmonier et al., 1992; Dole-Olivier et al., 1993).
In contrast, the upstream part of canal D was fed mostly by deep groundwater, the hypogean fauna
consisted of one ubiquitous stygobite (i.e. Hauffenia cf. minuta) and two phreatobites (i.e. Niphargus
fontanus and Parabathynellidae; Dole-Olivier et al., 1993; Claret et al., 1997). The total taxonomic
richness for the entire canal was high because of the distinct interstitial water origins. Relationships
between water origin and the composition of interstitial assemblages have been well documented in the
main channels of both large temperate rivers (such as the River Rhône, Marmonier and Dole, 1986;
Dole-Olivier and Marmonier, 1992a,b) and small desert streams (Boulton et al., 1992; Stanley and
Boulton, 1993; Boulton and Stanley, 1995). In floodplains, Marmonier et al. (1992) showed that the origin
of groundwater had a weak influence on interstitial assemblages compared to the location of the sampling
point in the alluvial plain (i.e. distance to the main channel, frequency of floods). In the present study, all
four canals had similar location (i.e. close to the river channel) and were weakly influenced by floods
because of embankments; in such conditions, the origin of interstitial water plays a major role in the
composition and diversity of interstitial fauna.
Copyright © 2000 John Wiley & Sons, Ltd.
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P. MARMONIER ET AL.
Finally, among the different ways of measuring biodiversity, the diversity in habitat-based groups was
the most efficient for highlighting differences between the four canals. This is not surprising because this
classification includes behavioural, biological, physiological, and ecological characteristics of the species
(Claret et al., in press). Modification in the decreasing gradient from stygoxenes to phreatobites (as
observed in the poorly oxygenated canal A) may be an efficient description of disturbance in floodplain
interstitial assemblages.
ACKNOWLEDGEMENTS
This work was supported by grants from the ‘Ministère de l’Environnement’ (subvention No. 94049) and
the ‘Ministère de l’Enseignement Supèrieur et de la Recherche’ (Subvention No. 96N60/0014). We would
like to thank G.H. Copp (University of Hertfordshire, UK) for editing the English text, Y. Giuliani
(Compagnie Nationale du Rhône, France) for his authorization to sample in the drainage canals, S.
Crommer for his help in the field, R. Ginet (Université Lyon I, France) for identification of Niphargides
and Ph. Richoux (Université Lyon I, France) for identification of Coleoptera.
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