Macroinvertebrate Communities of sub

ECOLOGIA BALKANICA2021, Special Edition 4 pp. 49-64

Macroinvertebrate Communities of sub-MediterraneanIntermittent Rivers in Bulgaria: Association withEnvironmental 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, BULGARIA2 - Department of Geography, Ecology and Environmental Protection, Faculty of

Mathematics and Natural Sciences, South-West University “Neofit Rilski”, 66 Ivan MichailovSt. 2700, Blagoevgrad, BULGARIA

*Corresponding author: [email protected]

Abstract. Intermittent rivers and ephemeral streams drain more than 50% of the land surface onEarth. Yet, their ecology remains insufficiently understood. In Bulgaria, temporary rivers aretypically small- or medium-sized rivers (national type R14), flowing in areas with sub-Mediterranean climate. We present the first data focused explicitly on macrozoobenthos fromintermittent rivers in four Bulgarian river basins within the drainage of the Aegean Sea. Weidentified 114 taxa from nine rivers (5÷33 taxa/site), with abundance varying between 61 and 994ind.m-2. The most common were taxa of Ephemeroptera and Chironomidae, followed by the crabPotamon ibericum. There were considerable differences among macroinvertebrates at different sitesat 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 environmentalconditions and local human impacts. Redundancy analysis identified key groups for the sites withfast flow (e.g. Ephemeroptera, Trichoptera, Plecoptera, Coleoptera and Diptera Varia, taxaassociated with altitude and the higher share of stone substrata). Most of the river sites wereclassified as having high ecological status according to the Bulgarian legislation. Only the sites inthe Vrabcha and Dereorman Rivers were with moderate status; these were the sites with the lowesttaxon richness. We could speculate that the structuring of the benthic community was affected byother factors that have not been accounted for in the present study, i.e. great annual fluctuations inriver flow, characteristic for R14, or by loading with nutrients or other pollutants.

Key words: benthic invertebrates, temporary rivers, environmental factors, ecological status, Southern Bulgaria.

IntroductionIntermittent or temporary rivers and

streams have highly variable flow thatperiodically ceases along parts of theircourses (Matthews, 1988; Uys & O’Keeffe,1997). Worldwide, together with ephemeral

streams, intermittent rivers drain more thanhalf of the land surface on our planet (Datryet al., 2014). Nonetheless, their ecology is notsufficiently studied.

In Bulgaria, intermittent rivers arecommon in areas with sub-Mediterranean

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Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria...

climate (Isheva & Ivanov, 2016; Wolfram etal., 2016). These are small- or medium-sizedrivers, classified as R14 under the nationalriver typology (Cheshmedjiev et al., 2013).Bulgarian intermittent rivers belong to thefour Bulgarian river basins (of Struma, Arda,Maritsa and Tundzha Rivers) within thedrainage of the Aegean Sea.

Wolfram et al. (2016) identified twosubtypes within R14 national river type:R14a with low slope and altitude, with lowto medium flow velocity and R14b with highslope and maximum altitude in thecatchment area, with medium high flowvelocity. The authors verified and refinedthe Bulgarian river typology, as well as theclass boundaries for the ecological status ofR14 based on an adapted version of theBiotic index (as described in Cheshmedjiev& Varadinova, 2013), other biological qualityelements and environmental factors.Wolfram et al. (2016) did not provide anydetails on the benthic invertebratecommunities inhabiting rivers of R14national river type.

This is the first faunistic study to focusexplicitly on macrozoobenthos ofintermittent rivers in Bulgaria. Our aimswere to: (i) analyse the basic environmentalparameters (i.e. altitude, water temperature,conductivity, pH, oxygen content andsaturation, substrata), (ii) study the benthicinvertebrate communities (their abundance,diversity and dominant taxa at both lowestpossible taxon level (TL) and at major-groups level (GL), (iii) test for associationsbetween environmental factors andmacroinvertebrate communities (at GL) and(iv) to assess their ecological status based onbenthic macroinvertebrates (at TL).

Material and MethodsStudy areaNine sites representative of intermittent

rivers in Bulgaria were selected and sampledonce in June 2020 (Fig. 1, Table 1). Theselection criteria were defined for thepurposes of a bigger project (seeAcknowledgements), aiming at developing a

new classification system for assessment ofthe ecological status, based on the biologicalquality element macrozoobenthos. Thus, theselected river sections represented variousecological situations: from relativelyunaffected to anthropogenically impacted(as identified by East Aegean RBMP, 2016-2021; West Aegean RBMP, 2016-2021). Allsampled rivers were situated in SouthernBulgaria and belonged to the basins of theStruma (Ludata and Vrabcha Rivers),Tundzha (Fishera and Dereorman Rivers),Arda (Kodzha Dere, Chataldzhevitsa,Kulidzhinska and Aterinska Rivers) andMaritsa (Luda River) Rivers (Fig. 1).

Sample collection and processingBottom habitat structure was described

on site: the presence of stone, gravel, sandand silt was recorded. Physical and chemicalwater parameters, i.e. water temperature(WT), oxygen concentration (DO [mg.dm-3])and saturation (OSat [%]), conductivity(Cond [μS.cm-1]) and pH, were measured insitu using portable Windaus LabortechnikPackage and HANNA multi-parameterinstruments. Water samples were processedfollowing ISO 5667-3: 2018.

Macroinvertebrates were collected bywading in the river for ca. 100 m, followingan adapted version of the pro-rata multi-habitat procedure described inCheshmedjiev et al. (2011) and in accordancewith BDS EN ISO 10870:2012 and EN16150:2012 standards. The method wasregulated by the national water legislationtrough Regulation No H-4 (2012).Invertebrate samples were cleaned fromcoarse substrata, washed through a sieve(500 μm) on site, transferred into containerswith 70% alcohol and transported to thelaboratory. Benthic specimens were sortedby systematic groups, enumerated and thenidentified to the lowest possible level.

AnalysesPearson correlations and their level of

significance among water parameters wereidentified using R 4.0.3. (R Core Team, 2020)and the PerformanceAnalytics package(Peterson et al., 2014). Principal component

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analysis (PCA), based on the correlationmatrix by centring and standardisation, wasused to summarise the major patterns ofvariation of environmental variables (i.e.altitude, physical and chemical waterparameters and substrata).

Log-transformed absolute abundanceswere used in analyses on macroinvertebratecommunities. Cluster analyses wereperformed using Bray-Curtis similarities fortaxa (TL) and major groups (GL) withPRIMER-E Vers. 6. Redundancy analysis(RDA) explored associations among thecorrelation matrices of 16 macroinvertebrategroups and seven environmentalparameters. Parameters identified by RDA tohave the lowest contribution on explainingassociations among environmental factorsand communities were excluded fromfurther statistical analyses. Ordinations(PCA and RDA) were performed usingCANOCO Vers. 5 statistical package forWindows.

The ecological status of the studied riversections was assessed using the Biotic index(BI) and the Total number of taxa (TNT)according to a river-type specific scaledeveloped in the national legislation(Regulation No H-4, 2012).

ResultsEnvironmental factorsThe study sites were situated between

50 and 582 m a.s.l. (Table 1). The lowesttemperature was recorded at the site in theLudata River (13.7°C at 582 m a.s.l.). Thehighest value of conductivity was measuredat the site in the Dereorman River (1332μS.cm-1), followed by the Fishera River (669μS.cm-1). Pearson correlations identified asignificant association (p=0.032) between pHand conductivity and an associationbordering on significance between pH andaltitude (p=0.077; Fig. 2).

According to the results of the PCA, thefirst 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 representedtwo environmental gradients: the first wasrelated to conductivity and silt; this gradientseparated the Dereorman River with thehighest values of these parameters. Thesecond gradient of PC1 was associated withwater temperature and the presence of sandand separated the Vrabcha and Luda Riversfrom the rest of the river sites (Fig. 3). Axis 2was also related to two gradients: the firstwas associated with altitude and stonesubstratum that separated the Ludata,Kodzha Dere and Aterinska Rivers. Thesecond gradient of PC2 was related tooxygen concentration (used also as a proxyfor oxygen saturation as identified by thePCA). The highest values of dissolvedoxygen were measured in Fishera (itsposition on the biplot was associated alsowith the higher conductivity) and LudaRivers. Chataldzhevitsa River was separatedas the site with the highest pH and analtitude of 406 m a.s.l.

Biota: diversity and dominant taxaWe identified 114 taxa of 53 families

and 16 systematic groups of bottominvertebrates in the studied R14 rivers (Table2).

The number of taxa varied between five(Dereorman River) and 33 (KulidzhinskaRiver) taxa per site (Table 2), while theabsolute abundance varied between 61(Vrabcha River) and 994 (KulidzhinskaRiver) ind.m-2 (Fig. 4). The most commonspecies were the mayflies B. rhodani(recorded at six of the nine sites), C. macrura,E. ignita, E. (E.) dispar and the chironomidCr. sylvestris-gr. (all recorded at five sites),followed by the crab P. ibericum and thechironomid Conchapelopia sp. (recorded atfour of the sites). The most abundant wasGammarus sp. with absolute abundance of550 ind.m-2 (or relative abundance of96.32%), recorded from the DereormanRiver. The family Simuliidae (Insecta:Diptera) was recorded at six of the sites.

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Table 1. Rivers with sampling sites, codes and environmental characteristics.

N River Site IDAltitude

Alt [m a.s.l.]

Tempe-rature

Conduc-tivity

pH

Dissolvedoxygen

Oxygensaturation

Substrata presence

WT [°C]

Cond [μS.cm-1]

DO [mg.dm-3]

OSat [%]

Stone Gravel Sand Silt

1 Ludata Yanovski bridge after Senokos site

Luda_YS 582 13.7 443 8.15 7.3 81 x x x

2 VrabchaUpstream of delta, E79 road before Strumyani Town

Vrab_D 129 18.9 442 8.06 7.3 85 x x

3 Fishera 500 m upstream the border with Turkey Fish_B 104 15.6 669 7.66 8.6 89 x x x x

4 Dere-orman

Delta, bridge on Yambol - Elhovo road Der_D 109 15.4 1332 7.71 7.4 74 x x x

5 Luda Before confluence in Byala Rver Luda_C 50 18.3 170 8.01 8.3 74 x x

6 Kodzha Dere

Malko Kamenyane Village Kod_MK 284 17.2 358 8.07 7.2 87 x x

7 Chatal-dzhevitsa

Delta under dam of Borovitsa Reservoir Chat_D 406 16.9 94 8.67 7.3 81 x x x

8 Kuli-dzhinska

Bryagovets Village, 800 m from Ivailovgrad Reservoir

Kuli_D 139 18.1 476 8.02 7.8 86 x x x

9 AterinskaBridge 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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Table 2. List of taxa recorded at each of the sites. Site numbers are as in Table 1.

Group TaxaSites

1 2 3 4 5 6 7 8 9Oligochaeta Oligochaeta indet. x

Lumbricidae Gen. sp. x x xHirudinea Erpobdella octoculata (Linnaeus, 1758) x xHydracarina Lebertia inaequalis (Koch, 1837) x x xGastropoda Belgrandiella sp. x

Radix labiata (Rossmässler, 1835) x x xRadix sp. xPhysella acuta (Draparnaud, 1805) xPlanorbis planorbis (Linnaeus, 1758) xAncylus fluviatilis O. F. Müller, 1774 x x x

Amphipoda Gammarus sp. x x x xIsopoda Asellus aquaticus (Linnaeus, 1758) xDecapoda Potamon ibericum (Bieberstein, 1809) x x x xEphemeroptera Acentrella sinaica Bogoescu, 1931 x

Alainites muticus (Linnaeus, 1758) xBaetis rhodani (Pictet, 1843) x x x x x xB. fuscatus (Linnaeus, 1761) x xB. vernus Curtis, 1834 xB. melanonyx (Pictet, 1843) xB. scambus Eaton, 1870 xB. subalpinus Bengtsson, 1917 xB. vardarensis Ikonomov, 1962 xProcloeon bifidum (Bengtsson, 1912) xCloeon simile Eaton, 1870 xCaenis macrura Stephens, 1835 x x x x xOligoneuriella rhenana (Imhoff, 1852) x x xEphemera danica Müller, 1764 xEphemerella ignita (Poda, 1761) x x x x xEcdyonurus (Ecdyonurus) dispar (Curtis,1834)

x x x x x

Ecdyonurus (E.) insignis (Eaton, 1870) xEcdyonurus (Helvetoraeticus) sp. x xElectrogena affinis (Eaton, 1887) x xE. quadrilineata (Landa, 1969) xRhithrogena bulgarica Braasch, Soldan & Sowa, 1985

x x x

Siphlonurus aestivalis (Eaton, 1903) xHabrophlebia eldae Jacob & Sartori, 1984 x

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Habrophlebia sp. xHabroleptoides sp. x

Plecoptera Leuctra sp. x xNemoura sp. xIsoperla grammatica (Poda, 1761) x x xPerla sp. x

Odonata Anax imperator Leach, 1815 x xCalopteryx splendens (Harris, 1782) xCalopteryx sp. xCordulegaster sp. xGomphus sp. xOphiogomphus sp. xOnychogomphus sp. x

Trichoptera Agapetus orchipes Curtis, 1834 xAgapetus sp. xCyrnus trimaculatus (Curtis, 1834) xPlectrocnemia conspersa conspersa (Curtis, 1834) x

Polycentropus ierapetra Malicky, 1972 xHydropsyche angustipennis (Curtis, 1834)

x

H. bulbifera McLachlan, 1878 x xH. incognita Pitsch, 1993 xH. gr. instabilis xH. gr. incognita xHydropsyche sp. x xHydropsychidae Gen. sp. xSericostoma sp. x xRhyacophila sp. x x xPotamophylax sp. xHalesus digitatus (Schrank, 1781) x xH. tesselatus (Rambur, 1842) xLimnephilidae Gen. sp. xWormaldia sp. x

Megaloptera Sialis lutaria (Linnaeus, 1758) xColeoptera Dytiscidae Gen. sp. x x x

Platambus maculatus (Linnaeus, 1758) xElmidae Gen. sp. x xLimnius volckmari (Panzer, 1793) x xHydraena sp. xLimnichidae Gen. sp. x x

Hemiptera Gerridae Gen. sp. x x x

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Microvelia sp. xVeliidae Gen. sp. x xMesovelia sp. xNepa cinerea Linnaeus, 1758 xAblabesmyia sp. x x

Diptera (Chironomidae)

Aspectrotanypus sp. xCladotanytarsus sp. xChironomus sp. xConchapelopia sp. x x x xCricotopus sylvestris-Gr. x x x x xCricotopus (Isocladius) sp. xCricotopus sp. xDicrotendipes sp. xKiefferulus tendipediformis (Goetghebuer, 1921)

x

Macropelopia sp. xMicrotendipes sp. x x xMicropsectra sp. xOrthocladius sp. xParamerina sp. xParatanytarsus sp. xParatrissocladius sp. xProcladius sp. xPolypedilum convictum (Walker, 1856) x x xPolypedilum sp. x x xProdiamesa olivacea (Meigen, 1818) x xPsectrocladius sp. xTanytarsus sp. xBrillia sp. x x xSimuliidae Gen. sp. x x x x x x

Diptera varia Atherix sp. x x xTipula sp. x xDicranota sp. x xLimoniidae Gen. sp. x x xHexatoma sp. xTabanus sp. x xEmpididae Gen. sp. x x xPsychodidae Gen. sp. xCeratopogonidae Gen. sp. x x

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Fig. 2. Pearson correlations among environmental parameters. Asterisk (*) denotesstatistically significant correlations. Parameter abbreviations are according to Table 1.

Fig. 3. Ordination biplot diagram based on principal component analysis of altitude, waterparameters and four substratum types in the nine river sites (for codes see Table 1).

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Fig. 4. Absolute abundance of macro-invertebrates at each site (for codes see Table 1).

The major groups includedOligochaeta, Hirudinea, Hydracarina,Gastropoda, Amphipoda, Isopoda,Decapoda, Ephemeroptera, Plecoptera,Odonata, Trichoptera, Megaloptera,Coleoptera, Hemiptera, Chironomidae,Diptera Varia (excluding Chironomidae).The most diverse were the groups ofEphemeroptera (25 taxa), Chironomidae(24 taxa) and Trichoptera (19 taxa). Themost frequent were taxa of Chironomidae(recorded at all sites), followed byEphemeroptera and Diptera varia (at eightsites) and by Trichoptera and Gastropoda(at six sites; Table 2).

Mayflies were dominant orsubdominant (based on their abundance)at all but two sites (Fig. 5). Most numerouswere B. rhodani, E. ignita and E. (E.) dispar,but due to a variety of microhabitats wealso found some rare species, e.g. A.sinaica, Pr. bifidum, Electrogena spp., H.eldae, usually occurring in smallpopulations. We recorded six families ofcaddisflies, of which the most commonwere Hydropsychidae (Hydropsyche spp.)at five sites, Polycentropodidae andLimnephilidae at three. Representatives offour subfamilies of Chironomidae wererecorded: Tanypodinae, Orthocladiinae,Prodiamesinae and Chironominae (tribesTanytarsini and Chironomini). From the

sample in the Fishera River, we recordedthe highest number of taxa of the family(14), while at the other sites the number oftaxa varied between one and six. Snails offour families were recorded at six of thesites (Table 2). The most common were thetaxa belonging to Planorbidae (recorded atfour sites).

Taxon-level cluster analyses indicatedthat benthic assemblages were rathervariable at the different sites and thesimilarities among sites were low (max=44.60%; mean=17.42%; Fig. 6A). The mostdistinct from the others were the sites inthe Dereorman, Fishera and VrabchaRivers, while the least different were theKodzha Dere, Kulidzhinska, Aterinska andChataldzhevitsa Rivers. Group-levelcluster analyses suggested highersimilarities among sites (max=75.48%;mean=46.43%; Fig. 6B) and this motivatedus to explore the associations betweenbiota and their environment at GL.

Biota: association with environment andecological status

Three of the parameters (WT, DO andOSat) had similar values among sites andlittle contribution to explaining theassociations among environmental factorsand communities (as demonstrated byRDA), therefore they were excluded fromfurther statistical analyses.

According to the RDA ordination ofbiota and the seven environmentalvariables retained in the analyses (Fig. 7),77.3% of the total variance in benthicinvertebrate communities was explainedby the first three axes (eigenvalues λ1 =0.399; λ2 = 0.273; λ3 = 0.101). Axis 1 waspositively related to conductivity (9.6%explained variation) and silt substratum(29.2% explained variation) and separatedthe Dereorman River, where mostabundant were gammarids of orderAmphipoda (96% of the total abundance,Fig. 4), followed by order Hemiptera.Subdominant at the site in the FisheraRiver was order Hemiptera; that was theonly site where the orders Megaloptera

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and Isopoda were recorded (Figs. 5 and 7).Altitude (9.8% explained variation) andstone substratum (11.3% explainedvariation) were associated with taxa oforders Ephemeroptera, Trichoptera,Plecoptera, Coleoptera and Diptera Varia(i.e. elmids, simuliids), taxa that weremostly recorded in the Ludata,Kulidzhinska, Aterinska and Kodzha DereRivers. The highest abundance of classGastropoda was found in the VrabchaRiver. Taxa of order Odonata were morefrequent on gravel (4.9% explainedvariation) and sand substrata (14.3%explained variation). Shorter gradientsrelated to water mites (Hydracarina) andorder Decapoda were evident along PC2and correlated with the site in the KodzhaDere River. Altitude and pH explained11.6% of the total variation in communitiesand determined the position in theordination of Chataldzhevitsa River; thelowest absolute and relative abundance ofChironomidae were recorded at the samesite.

Our results regarding the ecologicalassessment based on BI and TNT indicatedthat all river sites but two were classifiedas having high ecological status. Bothmetrics and TNT suggested moderateecological status at the sites in theDereorman and Vrabcha Rivers,correspondingly (Fig. 8).

DiscussionIntermittent rivers provide diverse

and dynamic conditions that are associatedwith their intermittence, which in turnshape distinctive invertebrate communities(Datry et al., 2014). Additionally, man-driven climate change or anthropogenicfactors such as pollution or modification ofriverbed morphology and river flowtrigger alterations in the structure anddiversity of macrozoobenthos. Our resultssuggest diverse communities inhabit R14in Southern Bulgaria, with mayfliespredominating in most of them. Cluster

analyses indicated considerable differencesamong macroinvertebrates at differentsites at taxon level, with similarities amongsamples increasing when using group-levelresolution. To some extent, important forthe grouping of rivers was their affiliationto river basins. In addition, seven of themeasured environmental parametersexplained more than 3/4 (grouped ingradients along the first three PCs) of thetotal variation in macrozoobenthiccommunities.

The most taxon-rich was the site in theKulidzhinska River, characterised asundisturbed according to the East AegeanRBMP (2016-2021). This was confirmedalso by the recorded moderate to lowconductivity, high oxygen saturation andits high ecological status (based on both BIand TNT). Relatively taxon-rich were alsothe Ludata and Aterinska Rivers. AterinskaRiver was assessed as having highecological status according to the EastAegean RBMP (2016-2021) and in thepresent study. In 2009–2011, Stoyanova etal. (2014) studied taxa of Ephemeroptera,Plecoptera and Trichoptera (EPT taxa) atsix sites along the Ludata River. Theauthors also recorded high diversity ofthese sensitive taxa at all sites but one thatwas impacted by the toxic compounds inthe seepage waters from a mine upstreamthe site.

The macroinvertebrate communities inthe Dereorman, Fishera and VrabchaRivers, were the least similar to the rest ofthe studied rivers. The lowest taxonrichness was recorded for the DereormanRiver, due to organic pollution fromagriculture as recorded also by Borisova etal. (2013). The lowest macroinvertebrateabundance and the second lowest richnessat the site in the Vrabcha River weattribute to the higher share of sandsubstratum, which is associated with lowerorganic matter and food availability andthe resulting low biotic diversity (Leitao etal., 2014; Tolonen et al., 2001).

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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 attaxon level (A) and at group level (B). Vertical lines denote 50% of similarity between

couples of samples (for codes see Table 1).

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A

B

Fig. 7. Redundancy analysis ordinations of environmental variables and macroinvertebrate groupsat 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).

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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 bethe local anthropogenic impact these sitesare subjected to, as suggested by therecorded high conductivity at the formertwo sites and their moderate ecologicalstatus (East Aegean RBMP, 2016-2021; WestAegean RBMP, 2016-2021). In addition, thesite in the Vrabcha River is impacted by theStruma Motorway, the nearby StrumyaniTown and a factory for the production ofmarble, limestone and granite. We recorded27 taxa at the site in the Fishera River, wherevarious substrata were recorded, thussuggesting a relatively high diversity.However, 14 of the recorded taxa were of thefamily Chironomidae, unlike the othertaxon-rich sites where between one and fourtaxa of Chironomidae were recorded. Acombination among various local impacts atthese sites and the availability of suitablemicrohabitats likely resulted in the lowernumber of the more sensitive taxa.

Wolfram et al. (2016) identified twosubtypes within the R14 national river type:R14a and R14b, as discussed in theIntroduction. The presence of families ofmayflies, caddisflies and stoneflies alongwith elmids and simuliids suggest that the

undisturbed river sites within the Strumaand Arda River Basins (Ludata,Chataldzhevitsa, Kulidzhinska, Aterinskaand Kodzha Dere) are fast-flowing andresemble R14b. High similarities among thefour rivers from the Arda River Basin wererecorded also by Wolfram et al. (2016),where based on macrozoobenthos and otherbiological quality elements the rivers fromthe basin of the Arda River were classified asR14b river subtype within theMediterranean middle-sized R-M2 rivertype. Moreover, typical of this Europeanriver type are Chironomidae, Baetidae,Simuliidae, Heptageniidae, Leuctridae,Elmidae, Ephemerellidae, Hydropsychidae,Gammaridae, Oligochaeta, Hydracarina,Nemouridae, Leptophlebiidae, Limoniidae,Limnephilidae (Feio, 2011). Most of thosetaxa were recorded also during the currentstudy. On the other hand, Fishera andDereorman Rivers of the basin of theTundzha River match the description ofR14a (sensu Wolfram et al., 2016).

R-selected chironomids was the onlygroup that was present at all nine sites,owing to their high motility and tolerance todynamic hydrological conditions (Evtimova

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& Donohue, 2016; Langton & Casas, 1999).However, according to Puntí et al. (2009),they are potentially good indicators ofecological status in Mediterranean rivers onthe Iberian Peninsula and individual taxahave differing requirements toenvironmental conditions. For instance,Micropsectra gr. are found at river sites withgood quality (Marziali et al., 2010), asconfirmed also by the records of this generain the Ludata River at Senokos Village. Thus,it is important to explore the taxonomicstructure of family Chironomidae. The otherabundant group was Ephemeroptera.Mayflies are sensitive to human disturbancesbut the common and widespread species ofthe order are also good colonisers (Brittain,1982). Overall, insect taxa dominated interms of diversity and abundance. Their life-cycle strategies ensure thriving inundisturbed intermittent rivers and streamswith lower intermittence: change betweenlarval aquatic and aerial adult stagespromote survival in relatively naturalwet/dry periods, respectively (Datry et al.,2014; Stubbington et al., 2011).

We found a high association betweenthe environmental factors and the benthicinvertebrate communities (GL) of Bulgarianintermittent rivers. Our RDA identified keytaxa, characteristic of this river type and itstwo subtypes. The distinctness ofcommunities (at TL) was likely a reflectionof the high variability in environmentalconditions and local human impacts. Overthe last century, among the maindisturbances in Medditerranean rivers andstreams are alteration of land use, rivermorphology, water management (Aguiar &Ferreira, 2005; Hooke, 2006). Local impactscould trigger the reduction or evendisappearance of sensitive taxa and theirreplacement by more tolerant ones (e.g.amphipods, isopods, hemipterans andtolerant chironomids). According to ouranalyses, the taxonomic structure of thestudied communities could be explainedonly partially by the measuredenvironmental parameters. While aquatic

invertebrate communities of R14 are type-specific under undisturbed conditions,taxonomic structure is altered when therivers are affected by various anthropogenicpressures. We could speculate that thetaxonomic composition of the studied siteswas affected by factors that have not beenaccounted for in the present study, i.e. thegreat annual fluctuations in river flow,characteristic for R14, or by loading withnutrients or other pollutants.

ConclusionsUnder unaffected conditions of the

aquatic environment in the studiedintermittent rivers, benthic communities arecharacterised by high taxonomic richnesswith a dominant representation ofEphemeroptera, Chironomidae andTrichoptera. The influence of different typesof local impacts (agricultural activity, localindustry and proximity to a highway) hadadverse effects on the integrity of theecosystem, which impacts the taxonomicrichness and ecological status assessedthrough macrozoobenthos.

Further studies incorporating differentseasons, hydrological metrics and organicloading would enable us to better explainthe structure of the macrozoobenthosinhabiting intermittent rivers and will bringadditional clarity regarding this river typeand its representative benthic communities.

Acknowledgments. The study wasfunded by the World Bank, project # 71 95735/17.4.2020, DICON-UBA.

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Received: 29.01.2021Accepted: 29.04.2021

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