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ECOLOGIA BALKANICA
2021, Special Edition 4 pp. 49-64
Macroinvertebrate Communities of sub-Mediterranean
Intermittent Rivers in Bulgaria: Association with
Environmental Parameters and Ecological Status
Vesela Evtimova1, Violeta Tyufekchieva1*, Emilia Varadinova1,2, Yanka Vidinova1,
Mila Ihtimanska1, Galia Georgieva1, Milcho Todorov1, Rabia Soufi1
1 - Department of Aquatic Ecosystems, Institute of Biodiversity and Ecosystem Research,
Bulgarian Academy of Sciences, 1 Tsar Osvoboditel Blvd., 1000 Sofia, BULGARIA
2 - Department of Geography, Ecology and Environmental Protection, Faculty of
Mathematics and Natural Sciences, South-West University “Neofit Rilski”, 66 Ivan Michailov
St. 2700, Blagoevgrad, BULGARIA
*Corresponding author: vtyufekchieva@yahoo.com
Abstract. Intermittent rivers and ephemeral streams drain more than 50% of the land surface on
Earth. Yet, their ecology remains insufficiently understood. In Bulgaria, temporary rivers are
typically small- or medium-sized rivers (national type R14), flowing in areas with sub-
Mediterranean climate. We present the first data focused explicitly on macrozoobenthos from
intermittent rivers in four Bulgarian river basins within the drainage of the Aegean Sea. We
identified 114 taxa from nine rivers (5÷33 taxa/site), with abundance varying between 61 and 994
ind.m-2. The most common were taxa of Ephemeroptera and Chironomidae, followed by the crab
Potamon ibericum. There were considerable differences among macroinvertebrates at different sites
at taxon level, with similarities among samples increasing when using lower taxonomic resolution.
The distinctness of communities was likely a reflection of the high variability in environmental
conditions and local human impacts. Redundancy analysis identified key groups for the sites with
fast flow (e.g. Ephemeroptera, Trichoptera, Plecoptera, Coleoptera and Diptera Varia, taxa
associated with altitude and the higher share of stone substrata). Most of the river sites were
classified as having high ecological status according to the Bulgarian legislation. Only the sites in
the Vrabcha and Dereorman Rivers were with moderate status; these were the sites with the lowest
taxon richness. We could speculate that the structuring of the benthic community was affected by
other factors that have not been accounted for in the present study, i.e. great annual fluctuations in
river flow, characteristic for R14, or by loading with nutrients or other pollutants.
Key words: benthic invertebrates, temporary rivers, environmental factors, ecological status, Southern Bulgaria.
Introduction
Intermittent or temporary rivers and
streams have highly variable flow that
periodically ceases along parts of their
courses (Matthews, 1988; Uys & O’Keeffe,
1997). Worldwide, together with ephemeral
streams, intermittent rivers drain more than
half of the land surface on our planet (Datry
et al., 2014). Nonetheless, their ecology is not
sufficiently studied.
In Bulgaria, intermittent rivers are
common in areas with sub-Mediterranean
© Ecologia Balkanica
http://eb.bio.uni-plovdiv.bg
Union of Scientists in Bulgaria – Plovdiv
University of Plovdiv Publishing House
Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
climate (Isheva & Ivanov, 2016; Wolfram et
al., 2016). These are small- or medium-sized
rivers, classified as R14 under the national
river typology (Cheshmedjiev et al., 2013).
Bulgarian intermittent rivers belong to the
four Bulgarian river basins (of Struma, Arda,
Maritsa and Tundzha Rivers) within the
drainage of the Aegean Sea.
Wolfram et al. (2016) identified two
subtypes within R14 national river type:
R14a with low slope and altitude, with low
to medium flow velocity and R14b with high
slope and maximum altitude in the
catchment area, with medium high flow
velocity. The authors verified and refined
the Bulgarian river typology, as well as the
class boundaries for the ecological status of
R14 based on an adapted version of the
Biotic index (as described in Cheshmedjiev
& Varadinova, 2013), other biological quality
elements and environmental factors.
Wolfram et al. (2016) did not provide any
details on the benthic invertebrate
communities inhabiting rivers of R14
national river type.
This is the first faunistic study to focus
explicitly on macrozoobenthos of
intermittent rivers in Bulgaria. Our aims
were to: (i) analyse the basic environmental
parameters (i.e. altitude, water temperature,
conductivity, pH, oxygen content and
saturation, substrata), (ii) study the benthic
invertebrate communities (their abundance,
diversity and dominant taxa at both lowest
possible taxon level (TL) and at major-
groups level (GL), (iii) test for associations
between environmental factors and
macroinvertebrate communities (at GL) and
(iv) to assess their ecological status based on
benthic macroinvertebrates (at TL).
Material and Methods
Study area
Nine sites representative of intermittent
rivers in Bulgaria were selected and sampled
once in June 2020 (Fig. 1, Table 1). The
selection criteria were defined for the
purposes of a bigger project (see
Acknowledgements), aiming at developing a
new classification system for assessment of
the ecological status, based on the biological
quality element macrozoobenthos. Thus, the
selected river sections represented various
ecological situations: from relatively
unaffected to anthropogenically impacted
(as identified by East Aegean RBMP, 2016-
2021; West Aegean RBMP, 2016-2021). All
sampled rivers were situated in Southern
Bulgaria and belonged to the basins of the
Struma (Ludata and Vrabcha Rivers),
Tundzha (Fishera and Dereorman Rivers),
Arda (Kodzha Dere, Chataldzhevitsa,
Kulidzhinska and Aterinska Rivers) and
Maritsa (Luda River) Rivers (Fig. 1).
Sample collection and processing
Bottom habitat structure was described
on site: the presence of stone, gravel, sand
and silt was recorded. Physical and chemical
water parameters, i.e. water temperature
(WT), oxygen concentration (DO [mg.dm-3])
and saturation (OSat [%]), conductivity
(Cond [μS.cm-1]) and pH, were measured in
situ using portable Windaus Labortechnik
Package and HANNA multi-parameter
instruments. Water samples were processed
following ISO 5667-3: 2018.
Macroinvertebrates were collected by
wading in the river for ca. 100 m, following
an adapted version of the pro-rata multi-
habitat procedure described in
Cheshmedjiev et al. (2011) and in accordance
with BDS EN ISO 10870:2012 and EN
16150:2012 standards. The method was
regulated by the national water legislation
trough Regulation No H-4 (2012).
Invertebrate samples were cleaned from
coarse substrata, washed through a sieve
(500 μm) on site, transferred into containers
with 70% alcohol and transported to the
laboratory. Benthic specimens were sorted
by systematic groups, enumerated and then
identified to the lowest possible level.
Analyses
Pearson correlations and their level of
significance among water parameters were
identified using R 4.0.3. (R Core Team, 2020)
and the PerformanceAnalytics package
(Peterson et al., 2014). Principal component
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Evtimova et al.
analysis (PCA), based on the correlation
matrix by centring and standardisation, was
used to summarise the major patterns of
variation of environmental variables (i.e.
altitude, physical and chemical water
parameters and substrata).
Log-transformed absolute abundances
were used in analyses on macroinvertebrate
communities. Cluster analyses were
performed using Bray-Curtis similarities for
taxa (TL) and major groups (GL) with
PRIMER-E Vers. 6. Redundancy analysis
(RDA) explored associations among the
correlation matrices of 16 macroinvertebrate
groups and seven environmental
parameters. Parameters identified by RDA to
have the lowest contribution on explaining
associations among environmental factors
and communities were excluded from
further statistical analyses. Ordinations
(PCA and RDA) were performed using
CANOCO Vers. 5 statistical package for
Windows.
The ecological status of the studied river
sections was assessed using the Biotic index
(BI) and the Total number of taxa (TNT)
according to a river-type specific scale
developed in the national legislation
(Regulation No H-4, 2012).
Results
Environmental factors
The study sites were situated between
50 and 582 m a.s.l. (Table 1). The lowest
temperature was recorded at the site in the
Ludata River (13.7°C at 582 m a.s.l.). The
highest value of conductivity was measured
at the site in the Dereorman River (1332
μS.cm-1), followed by the Fishera River (669
μS.cm-1). Pearson correlations identified a
significant association (p=0.032) between pH
and conductivity and an association
bordering on significance between pH and
altitude (p=0.077; Fig. 2).
According to the results of the PCA, the
first three principal components (PCs)
explained 81.91% of the total variance in
environmental data (eigenvalues λ1 = 0.362;
λ2 = 0.321; λ3 = 0.137). Axis 1 represented
two environmental gradients: the first was
related to conductivity and silt; this gradient
separated the Dereorman River with the
highest values of these parameters. The
second gradient of PC1 was associated with
water temperature and the presence of sand
and separated the Vrabcha and Luda Rivers
from the rest of the river sites (Fig. 3). Axis 2
was also related to two gradients: the first
was associated with altitude and stone
substratum that separated the Ludata,
Kodzha Dere and Aterinska Rivers. The
second gradient of PC2 was related to
oxygen concentration (used also as a proxy
for oxygen saturation as identified by the
PCA). The highest values of dissolved
oxygen were measured in Fishera (its
position on the biplot was associated also
with the higher conductivity) and Luda
Rivers. Chataldzhevitsa River was separated
as the site with the highest pH and an
altitude of 406 m a.s.l.
Biota: diversity and dominant taxa
We identified 114 taxa of 53 families
and 16 systematic groups of bottom
invertebrates in the studied R14 rivers (Table
2).
The number of taxa varied between five
(Dereorman River) and 33 (Kulidzhinska
River) taxa per site (Table 2), while the
absolute abundance varied between 61
(Vrabcha River) and 994 (Kulidzhinska
River) ind.m-2 (Fig. 4). The most common
species were the mayflies B. rhodani
(recorded at six of the nine sites), C. macrura,
E. ignita, E. (E.) dispar and the chironomid
Cr. sylvestris-gr. (all recorded at five sites),
followed by the crab P. ibericum and the
chironomid Conchapelopia sp. (recorded at
four of the sites). The most abundant was
Gammarus sp. with absolute abundance of
550 ind.m-2 (or relative abundance of
96.32%), recorded from the Dereorman
River. The family Simuliidae (Insecta:
Diptera) was recorded at six of the sites.
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Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
Table 1. Rivers with sampling sites, codes and environmental characteristics.
N River Site ID
Altitude
Alt
[m a.s.l.]
Tempe-
rature
Conduc-
tivity pH
Dissolved
oxygen
Oxygen
saturation Substrata presence
WT
[°C]
Cond
[μS.cm-1]
DO
[mg.dm-3]
OSat
[%] Stone Gravel Sand Silt
1Ludata Yanovski bridge after
Senokos site Luda_YS 582 13.7 443 8.15 7.3 81 x x x
2Vrabcha
Upstream of delta, E79
road before Strumyani
Town
Vrab_D 129 18.9 442 8.06 7.3 85 x x
3Fishera 500 m upstream the
border with Turkey Fish_B 104 15.6 669 7.66 8.6 89 x x x x
4Dere-
orman
Delta, bridge on
Yambol - Elhovo road Der_D 109 15.4 1332 7.71 7.4 74 x x x
5Luda Before confluence in
Byala Rver Luda_C 50 18.3 170 8.01 8.3 74 x x
6Kodzha
Dere
Malko Kamenyane
Village Kod_MK 284 17.2 358 8.07 7.2 87 x x
7Chatal-
dzhevitsa
Delta under dam of
Borovitsa Reservoir Chat_D 406 16.9 94 8.67 7.3 81 x x x
8Kuli-
dzhinska
Bryagovets Village, 800
m from Ivailovgrad
Reservoir
Kuli_D 139 18.1 476 8.02 7.8 86 x x x
9Aterinska
Bridge between
Ivailovgrad Town and
Svirachi Village
Ater_IS 180 14.2 406 7.96 7.3 71 x x x x
Fig. 1. Map of Bulgaria with sampling area and sites. See Table 1 for site numbers.
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Evtimova et al.
Table 2. List of taxa recorded at each of the sites. Site numbers are as in Table 1.
Group Taxa Sites
123456789
Oligochaeta Oligochaeta indet. x
Lumbricidae Gen. sp. x x x
Hirudinea Erpobdella octoculata (Linnaeus, 1758) x x
Hydracarina Lebertia inaequalis (Koch, 1837) x x x
Gastropoda Belgrandiella sp. x
Radix labiata (Rossmässler, 1835) x x x
Radix sp. x
Physella acuta (Draparnaud, 1805) x
Planorbis planorbis (Linnaeus, 1758) x
Ancylus fluviatilis O. F. Müller, 1774 x x x
Amphipoda Gammarus sp. x x x x
Isopoda Asellus aquaticus (Linnaeus, 1758) x
Decapoda Potamon ibericum (Bieberstein, 1809) x x x x
Ephemeroptera Acentrella sinaica Bogoescu, 1931 x
Alainites muticus (Linnaeus, 1758) x
Baetis rhodani (Pictet, 1843) x x x x x x
B. fuscatus (Linnaeus, 1761) x x
B. vernus Curtis, 1834 x
B. melanonyx (Pictet, 1843) x
B. scambus Eaton, 1870 x
B. subalpinus Bengtsson, 1917 x
B. vardarensis Ikonomov, 1962 x
Procloeon bifidum (Bengtsson, 1912) x
Cloeon simile Eaton, 1870 x
Caenis macrura Stephens, 1835 x x x x x
Oligoneuriella rhenana (Imhoff, 1852) x x x
Ephemera danica Müller, 1764 x
Ephemerella ignita (Poda, 1761) x x x x x
Ecdyonurus (Ecdyonurus) dispar (Curtis,
1834) xxxxx
Ecdyonurus (E.) insignis (Eaton, 1870) x
Ecdyonurus (Helvetoraeticus) sp. x x
Electrogena affinis (Eaton, 1887) x x
E. quadrilineata (Landa, 1969) x
Rhithrogena bulgarica Braasch, Soldan
& Sowa, 1985 x x x
Siphlonurus aestivalis (Eaton, 1903) x
Habrophlebia eldae Jacob & Sartori, 1984 x
53
Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
Habrophlebia sp. x
Habroleptoides sp. x
Plecoptera Leuctra sp. x x
Nemoura sp. x
Isoperla grammatica (Poda, 1761) x x x
Perla sp. x
Odonata Anax imperator Leach, 1815 x x
Calopteryx splendens (Harris, 1782) x
Calopteryx sp. x
Cordulegaster sp. x
Gomphus sp. x
Ophiogomphus sp. x
Onychogomphus sp. x
Trichoptera Agapetus orchipes Curtis, 1834 x
Agapetus sp. x
Cyrnus trimaculatus (Curtis, 1834) x
Plectrocnemia conspersa conspersa
(Curtis, 1834) x
Polycentropus ierapetra Malicky, 1972 x
Hydropsyche angustipennis (Curtis,
1834) x
H. bulbifera McLachlan, 1878 x x
H. incognita Pitsch, 1993 x
H. gr. instabilis x
H. gr. incognita x
Hydropsyche sp. x x
Hydropsychidae Gen. sp. x
Sericostoma sp. x x
Rhyacophila sp. x x x
Potamophylax sp. x
Halesus digitatus (Schrank, 1781) x x
H. tesselatus (Rambur, 1842) x
Limnephilidae Gen. sp. x
Wormaldia sp. x
Megaloptera Sialis lutaria (Linnaeus, 1758) x
Coleoptera Dytiscidae Gen. sp. x x x
Platambus maculatus (Linnaeus, 1758) x
Elmidae Gen. sp. x x
Limnius volckmari (Panzer, 1793) x x
Hydraena sp. x
Limnichidae Gen. sp. x x
Hemiptera Gerridae Gen. sp. x x x
54
Evtimova et al.
Microvelia sp. x
Veliidae Gen. sp. x x
Mesovelia sp. x
Nepa cinerea Linnaeus, 1758 x
Ablabesmyia sp. x x
Diptera
(Chironomidae)
Aspectrotanypus sp. x
Cladotanytarsus sp. x
Chironomus sp. x
Conchapelopia sp. x x x x
Cricotopus sylvestris-Gr. x x x x x
Cricotopus (Isocladius) sp. x
Cricotopus sp. x
Dicrotendipes sp. x
Kiefferulus tendipediformis
(Goetghebuer, 1921) x
Macropelopia sp. x
Microtendipes sp. x x x
Micropsectra sp. x
Orthocladius sp. x
Paramerina sp. x
Paratanytarsus sp. x
Paratrissocladius sp. x
Procladius sp. x
Polypedilum convictum (Walker, 1856) x x x
Polypedilum sp. x x x
Prodiamesa olivacea (Meigen, 1818) x x
Psectrocladius sp. x
Tanytarsus sp. x
Brillia sp. x x x
Simuliidae Gen. sp. x x x x x x
Diptera varia Atherix sp. x x x
Tipula sp. x x
Dicranota sp. x x
Limoniidae Gen. sp. x x x
Hexatoma sp. x
Tabanus sp. x x
Empididae Gen. sp. x x x
Psychodidae Gen. sp. x
Ceratopogonidae Gen. sp. x x
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Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
Fig. 2. Pearson correlations among environmental parameters. Asterisk (*) denotes
statistically significant correlations. Parameter abbreviations are according to Table 1.
Fig. 3. Ordination biplot diagram based on principal component analysis of altitude, water
parameters and four substratum types in the nine river sites (for codes see Table 1).
56
Evtimova et al.
Fig. 4. Absolute abundance of macro-
invertebrates at each site (for codes see Table 1).
The major groups included
Oligochaeta, Hirudinea, Hydracarina,
Gastropoda, Amphipoda, Isopoda,
Decapoda, Ephemeroptera, Plecoptera,
Odonata, Trichoptera, Megaloptera,
Coleoptera, Hemiptera, Chironomidae,
Diptera Varia (excluding Chironomidae).
The most diverse were the groups of
Ephemeroptera (25 taxa), Chironomidae
(24 taxa) and Trichoptera (19 taxa). The
most frequent were taxa of Chironomidae
(recorded at all sites), followed by
Ephemeroptera and Diptera varia (at eight
sites) and by Trichoptera and Gastropoda
(at six sites; Table 2).
Mayflies were dominant or
subdominant (based on their abundance)
at all but two sites (Fig. 5). Most numerous
were B. rhodani, E. ignita and E. (E.) dispar,
but due to a variety of microhabitats we
also found some rare species, e.g. A.
sinaica, Pr. bifidum, Electrogena spp., H.
eldae, usually occurring in small
populations. We recorded six families of
caddisflies, of which the most common
were Hydropsychidae (Hydropsyche spp.)
at five sites, Polycentropodidae and
Limnephilidae at three. Representatives of
four subfamilies of Chironomidae were
recorded: Tanypodinae, Orthocladiinae,
Prodiamesinae and Chironominae (tribes
Tanytarsini and Chironomini). From the
sample in the Fishera River, we recorded
the highest number of taxa of the family
(14), while at the other sites the number of
taxa varied between one and six. Snails of
four families were recorded at six of the
sites (Table 2). The most common were the
taxa belonging to Planorbidae (recorded at
four sites).
Taxon-level cluster analyses indicated
that benthic assemblages were rather
variable at the different sites and the
similarities among sites were low (max=
44.60%; mean=17.42%; Fig. 6A). The most
distinct from the others were the sites in
the Dereorman, Fishera and Vrabcha
Rivers, while the least different were the
Kodzha Dere, Kulidzhinska, Aterinska and
Chataldzhevitsa Rivers. Group-level
cluster analyses suggested higher
similarities among sites (max=75.48%;
mean=46.43%; Fig. 6B) and this motivated
us to explore the associations between
biota and their environment at GL.
Biota: association with environment and
ecological status
Three of the parameters (WT, DO and
OSat) had similar values among sites and
little contribution to explaining the
associations among environmental factors
and communities (as demonstrated by
RDA), therefore they were excluded from
further statistical analyses.
According to the RDA ordination of
biota and the seven environmental
variables retained in the analyses (Fig. 7),
77.3% of the total variance in benthic
invertebrate communities was explained
by the first three axes (eigenvalues λ1 =
0.399; λ2 = 0.273; λ3 = 0.101). Axis 1 was
positively related to conductivity (9.6%
explained variation) and silt substratum
(29.2% explained variation) and separated
the Dereorman River, where most
abundant were gammarids of order
Amphipoda (96% of the total abundance,
Fig. 4), followed by order Hemiptera.
Subdominant at the site in the Fishera
River was order Hemiptera; that was the
only site where the orders Megaloptera
57
Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
and Isopoda were recorded (Figs. 5 and 7).
Altitude (9.8% explained variation) and
stone substratum (11.3% explained
variation) were associated with taxa of
orders Ephemeroptera, Trichoptera,
Plecoptera, Coleoptera and Diptera Varia
(i.e. elmids, simuliids), taxa that were
mostly recorded in the Ludata,
Kulidzhinska, Aterinska and Kodzha Dere
Rivers. The highest abundance of class
Gastropoda was found in the Vrabcha
River. Taxa of order Odonata were more
frequent on gravel (4.9% explained
variation) and sand substrata (14.3%
explained variation). Shorter gradients
related to water mites (Hydracarina) and
order Decapoda were evident along PC2
and correlated with the site in the Kodzha
Dere River. Altitude and pH explained
11.6% of the total variation in communities
and determined the position in the
ordination of Chataldzhevitsa River; the
lowest absolute and relative abundance of
Chironomidae were recorded at the same
site.
Our results regarding the ecological
assessment based on BI and TNT indicated
that all river sites but two were classified
as having high ecological status. Both
metrics and TNT suggested moderate
ecological status at the sites in the
Dereorman and Vrabcha Rivers,
correspondingly (Fig. 8).
Discussion
Intermittent rivers provide diverse
and dynamic conditions that are associated
with their intermittence, which in turn
shape distinctive invertebrate communities
(Datry et al., 2014). Additionally, man-
driven climate change or anthropogenic
factors such as pollution or modification of
riverbed morphology and river flow
trigger alterations in the structure and
diversity of macrozoobenthos. Our results
suggest diverse communities inhabit R14
in Southern Bulgaria, with mayflies
predominating in most of them. Cluster
analyses indicated considerable differences
among macroinvertebrates at different
sites at taxon level, with similarities among
samples increasing when using group-level
resolution. To some extent, important for
the grouping of rivers was their affiliation
to river basins. In addition, seven of the
measured environmental parameters
explained more than 3/4 (grouped in
gradients along the first three PCs) of the
total variation in macrozoobenthic
communities.
The most taxon-rich was the site in the
Kulidzhinska River, characterised as
undisturbed according to the East Aegean
RBMP (2016-2021). This was confirmed
also by the recorded moderate to low
conductivity, high oxygen saturation and
its high ecological status (based on both BI
and TNT). Relatively taxon-rich were also
the Ludata and Aterinska Rivers. Aterinska
River was assessed as having high
ecological status according to the East
Aegean RBMP (2016-2021) and in the
present study. In 2009–2011, Stoyanova et
al. (2014) studied taxa of Ephemeroptera,
Plecoptera and Trichoptera (EPT taxa) at
six sites along the Ludata River. The
authors also recorded high diversity of
these sensitive taxa at all sites but one that
was impacted by the toxic compounds in
the seepage waters from a mine upstream
the site.
The macroinvertebrate communities in
the Dereorman, Fishera and Vrabcha
Rivers, were the least similar to the rest of
the studied rivers. The lowest taxon
richness was recorded for the Dereorman
River, due to organic pollution from
agriculture as recorded also by Borisova et
al. (2013). The lowest macroinvertebrate
abundance and the second lowest richness
at the site in the Vrabcha River we
attribute to the higher share of sand
substratum, which is associated with lower
organic matter and food availability and
the resulting low biotic diversity (Leitao et
al., 2014; Tolonen et al., 2001).
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Evtimova et al.
Fig. 5. Relative abundance (%) of the benthic groups at each of the nine sites
(for codes see Table 1).
A B
Fig. 6. Bray-Curtis similarity among samples based on macroinvertebrate communities at
taxon level (A) and at group level (B). Vertical lines denote 50% of similarity between
couples of samples (for codes see Table 1).
59
Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
A
B
Fig. 7. Redundancy analysis ordinations of environmental variables and macroinvertebrate groups
at the studied river sites. (A) associations among the seven environmental variables and the
distribution patterns of benthic groups and (B) ordination of river sites (for codes see Table 1).
60
Evtimova et al.
Fig. 8. Ecological status at each of the studied sites. Circles denote values of the Biotic index,
triangles - of the Total number of taxa per site, blue - high ecological status and yellow -
moderate ecological status (for codes see Table 1).
Another possible explanation could be
the local anthropogenic impact these sites
are subjected to, as suggested by the
recorded high conductivity at the former
two sites and their moderate ecological
status (East Aegean RBMP, 2016-2021; West
Aegean RBMP, 2016-2021). In addition, the
site in the Vrabcha River is impacted by the
Struma Motorway, the nearby Strumyani
Town and a factory for the production of
marble, limestone and granite. We recorded
27 taxa at the site in the Fishera River, where
various substrata were recorded, thus
suggesting a relatively high diversity.
However, 14 of the recorded taxa were of the
family Chironomidae, unlike the other
taxon-rich sites where between one and four
taxa of Chironomidae were recorded. A
combination among various local impacts at
these sites and the availability of suitable
microhabitats likely resulted in the lower
number of the more sensitive taxa.
Wolfram et al. (2016) identified two
subtypes within the R14 national river type:
R14a and R14b, as discussed in the
Introduction. The presence of families of
mayflies, caddisflies and stoneflies along
with elmids and simuliids suggest that the
undisturbed river sites within the Struma
and Arda River Basins (Ludata,
Chataldzhevitsa, Kulidzhinska, Aterinska
and Kodzha Dere) are fast-flowing and
resemble R14b. High similarities among the
four rivers from the Arda River Basin were
recorded also by Wolfram et al. (2016),
where based on macrozoobenthos and other
biological quality elements the rivers from
the basin of the Arda River were classified as
R14b river subtype within the
Mediterranean middle-sized R-M2 river
type. Moreover, typical of this European
river type are Chironomidae, Baetidae,
Simuliidae, Heptageniidae, Leuctridae,
Elmidae, Ephemerellidae, Hydropsychidae,
Gammaridae, Oligochaeta, Hydracarina,
Nemouridae, Leptophlebiidae, Limoniidae,
Limnephilidae (Feio, 2011). Most of those
taxa were recorded also during the current
study. On the other hand, Fishera and
Dereorman Rivers of the basin of the
Tundzha River match the description of
R14a (sensu Wolfram et al., 2016).
R-selected chironomids was the only
group that was present at all nine sites,
owing to their high motility and tolerance to
dynamic hydrological conditions (Evtimova
61
Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...
& Donohue, 2016; Langton & Casas, 1999).
However, according to Puntí et al. (2009),
they are potentially good indicators of
ecological status in Mediterranean rivers on
the Iberian Peninsula and individual taxa
have differing requirements to
environmental conditions. For instance,
Micropsectra gr. are found at river sites with
good quality (Marziali et al., 2010), as
confirmed also by the records of this genera
in the Ludata River at Senokos Village. Thus,
it is important to explore the taxonomic
structure of family Chironomidae. The other
abundant group was Ephemeroptera.
Mayflies are sensitive to human disturbances
but the common and widespread species of
the order are also good colonisers (Brittain,
1982). Overall, insect taxa dominated in
terms of diversity and abundance. Their life-
cycle strategies ensure thriving in
undisturbed intermittent rivers and streams
with lower intermittence: change between
larval aquatic and aerial adult stages
promote survival in relatively natural
wet/dry periods, respectively (Datry et al.,
2014; Stubbington et al., 2011).
We found a high association between
the environmental factors and the benthic
invertebrate communities (GL) of Bulgarian
intermittent rivers. Our RDA identified key
taxa, characteristic of this river type and its
two subtypes. The distinctness of
communities (at TL) was likely a reflection
of the high variability in environmental
conditions and local human impacts. Over
the last century, among the main
disturbances in Medditerranean rivers and
streams are alteration of land use, river
morphology, water management (Aguiar &
Ferreira, 2005; Hooke, 2006). Local impacts
could trigger the reduction or even
disappearance of sensitive taxa and their
replacement by more tolerant ones (e.g.
amphipods, isopods, hemipterans and
tolerant chironomids). According to our
analyses, the taxonomic structure of the
studied communities could be explained
only partially by the measured
environmental parameters. While aquatic
invertebrate communities of R14 are type-
specific under undisturbed conditions,
taxonomic structure is altered when the
rivers are affected by various anthropogenic
pressures. We could speculate that the
taxonomic composition of the studied sites
was affected by factors that have not been
accounted for in the present study, i.e. the
great annual fluctuations in river flow,
characteristic for R14, or by loading with
nutrients or other pollutants.
Conclusions
Under unaffected conditions of the
aquatic environment in the studied
intermittent rivers, benthic communities are
characterised by high taxonomic richness
with a dominant representation of
Ephemeroptera, Chironomidae and
Trichoptera. The influence of different types
of local impacts (agricultural activity, local
industry and proximity to a highway) had
adverse effects on the integrity of the
ecosystem, which impacts the taxonomic
richness and ecological status assessed
through macrozoobenthos.
Further studies incorporating different
seasons, hydrological metrics and organic
loading would enable us to better explain
the structure of the macrozoobenthos
inhabiting intermittent rivers and will bring
additional clarity regarding this river type
and its representative benthic communities.
Acknowledgments. The study was
funded by the World Bank, project # 71 957
35/17.4.2020, DICON-UBA.
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