Use of benthic macroinvertebrates to assess the biological status ofPampean streams in Argentina
Alberto Rodrigues Capıtulo, Mariana Tangorraa and Carolina Oconb
Instituto de Limnologıa Dr. Raul A. Ringuelet (ILPLA), CC 712, CP 1900 La Plata, Argentina (Phone: 54 1142758564; Fax: 54 11 42757799; E-mail: [email protected])
Accepted 27 February 2001
Key words: biomonitoring, biotic index, Pampean streams, South America, macrozoobenthos
Abstract
Macro-invertebrate communities and environmental variables were assessed seasonally for two years in sevenstreams in North-Eastern of Buenos Aires province (Argentina) in order to analyse changes in their structure andcomposition in relation with the quality of the water. The study includes pristine streams and others affectedby urban and industrial effluents with high conductivity, nitrates, nitrites, phosphates and low oxygen content.Organisms with well-known pollution tolerance were identified to assess biological water quality, using a newBiotic Index (IBPAMP: Biotic Index for PAMPean rivers and streams) in comparison with other existing bioticindices. The usefulness of principal component analysis (PCA) and correlation matrices were examined to evaluatethe efficiency of the method to assess disturbances. In general IBPAMP did well correlate with several classicalmeasures of biological water quality (taxon richness, diversity and several biotic indices). The El Gato stream wasthe most disturbed ecosystem among all studied sites. It was characterised by low dissolved oxygen levels, highturbidity in the middle course, high BOD5 (>30 mg l−1) and COD (>40 mg l−1) values. The Buñirigo stream hasa bad quality in the industrial area, but varying according to the dry and wet periods. In general, in the mountainousareas the water quality of streams was good with the exception of the stations located downstream of cities likeAyacucho on the Tandileofú stream.
Introduction
The Pampean biogeographic province occupies a vastterritory of South America, embracing the plains ofEastern Argentina from 30 to 39 deg South, Uruguayand half the state of Rio Grande do Sul in Brazil. Smallstreams and rivers of the plains have a low-gradientbed carved through cenozoic sedimentary deposits,sediments of loess-mud or clay rich in organic de-tritus, and running waters with slow-currents and ahigh-turbidity (Frengüelly, 1956; Ringuelet, 1962;Rodrigues Capítulo, 1999). In the Argentinian Pam-pean plains streams are usually of the semipermanentor temporary type, with waterflows having semi-desertcharacteristics. In relation with biological character-
aRecipient of a CIC (Provincia de Buenos Aires) grant.bRecipient of a FONCYT grant (PICT 1812).
istics of the region, considering organisms living inPampean streams and rivers, it has been noticed thealmost total absence of typical elements of mountainrivers, except in some streams and rivers having head-waters at Sierras de Tandilia and Ventania. There,a few species of Trichoptera and Ephemeroptera butno Plecoptera can be found. All mentioned taxa, arecommon elements in rivers and streams of Patagonia(Andes), central and north-western Argentina (Albar-iño, 1997). There is a clear dominance of detritivoresowing to the crumbles along the main arms of thelargest rivers with the lowest transparency. This iscomplemented with the occurrence of carnivores whenthe abundance of macrophyte vegetation increases,leading to the development of the typical fauna at theregional level for this kind of rivers and streams.
The objective of this work was to analyse thechanges in the structure and composition of the
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macro-zoobenthos and macro-invertebrates present onmacrophytes in the same habitats in relation with thequality of the water in several streams affected to a dif-ferent extent by urban and industrial perturbations, andcompared with pristine streams of the region. Organ-isms with known pollution tolerance were identified toestablish biological water quality (Hynes, 1971; Hart& Fuller, 1974; Rodrigues Capítulo, 1984a, b; Hakan-son, 1999), using a new Biotic Index (IBPAMP:Biotic Index for PAMPean rivers and streams) incomparison with other biotic indices.
Materials and methods
Study area and characteristics of sampling sites
In this paper only streams were considered whichare located in two hydrographic areas of the Pam-pean biogeographic province according to Fregüelly(1956) (Figure 1): (a) Tributaries of the Río de laPlata river (mean length 36 km approximately): ElGato, El Pescado, Juan Blanco and Buñirigo; (b)Streams of Tandilia gills northeastern slope stream(mean length 60 km approximately): Tandileofú, Na-paleofú and Vivoratá, which have artificial channelsin the downstream section to facilitate drainage tothe Samborombón Bay and the Atlantic Ocean. Thestudy sites have been described by Rodrigues Capí-tulo (1999), the general hydrologic characteristics byRinguelet (1962), Sala et al. (1983), Godz et al. (1983)and Kruse (1986).
Several streams are affected to a certain extent byurban and industrial effluents. Among these, El Gatoand the middle section of Buñirigo are characterisedby high contamination levels. The former is largelypolluted by industrial production (paper mills, ironand steel, and textile) and domestic waste-waters. ElPescado is only moderately disturbed by agriculturaland food processing practices. On the other hand, theJuan Blanco stream is located in the natural reserve ofthe UNESCO Biosfera. Only in the upstream part ofthis stream the quality of the water is affected by someagriculture.
The creeks of the Tandilia system in Buenos Airesprovince have stronger currents, with stony to stony-sandy or clayey (compacted clays) sediments andpools are frequently present. The majority of theseare only impacted by agriculture. However, nearthe small cities as Tandileofú and Napaleofú, urbancontamination was observed and the changes in themacro-invertebrates communities assessed.
Sampling techniques
Seasonally biological samples were taken from 1997till 1999 with Ekman (100 cm2) and Van Veen(470 cm2) grabs in muddy and sandy sediments, anda Surber net in stony areas. Qualitative samples werealways taken with sieves from the macrophytes to ex-amine the presence of macro-invertebrates. Samplingstations were located in the upstream, mid-course anddownstream sections of the streams. The macroinver-tebrates were fixed with formaldehyde (5%).
Temperature ( ◦C), pH, conductivity (µS cm−1),dissolved oxygen (DO mg l−1) and turbidity (UNT)of the water were measured in the field by means ofelectrodes; transparency (cm) by means of a Secchidisk. The flow velocity (cm s−1) was measured witha portable flow-meter (Cole Parmer). Water sampleswere collected for further chemical analysis in the labaccording to standard methods (NO3, NH4, PO4 inmg l−1, BOD5, COD) (Strickland & Parsons, 1968;APHA, 1985). The macro-invertebrates were sorted,identified (species, genus or families) and counted inthe laboratory with a stereo or compound microscope.
Water quality assessment methods
Several existing biotic methods for water quality as-sessment were applied: the diversity index (H′) ofShannon and Weaver (1963); evenness (E) and taxonrichness (Margalef (D) (1955); the biotic score ofChandler (1970) and the BMWP’(Biological Monitor-ing Working Party) score system (Alba Tercedor et al.,1988) adapted to local taxa of the Pampean area inthe Neotropical Region (Rodrigues Capítulo, 1999).Besides two other indices were applied: the IMRP(Macroinvertebrate Index from Pampean Rivers) (Ro-drigues Capítulo, 1999) and a new biotic index:the IBPAMP (Biotic Index for PAMPean rivers andstreams) which is based on the principles proposed byTuffery & Vernaux (1967), De Pauw & Vanhooren(1983), Ghetti (1986), Prat et al. (1986, 1999) andCorigliano (1999), and adapted to locally occurringmacro-invertebrates (Tables 1 and 2).
For the elaboration of the IBPAMP index sevenclasses of horizontal entry were used (Woodiwiss,1978; Ghetti, 1986). The most sensitive taxa, ac-cording to measured physical and chemical parameters(Table 4) and other ecological characteristics observedin the habitats of the sampling sites, were Trichopterawith cases (Leptoceridae), Hydropsychidae, Lestidae,Elmidae and Gomphidae in the rhitron areas (Ta-ble 1) (Rodrigues Capítulo, 1999; Rodrigues Capitulo
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Table 1. Standard table for calculating the IBPAMP index of rhitral zones
Faunistic groups Total numbers of systematic units present
0–1 2–5 6–10 11–15 16–20 21–25 >26
Biotic index
1 Trichoptera with cases > 1 S. U. – – 8 9 10 11 12
(Leptoceridae) Only 1 S.U. – – 7 8 9 10 11
2 Hydropsychidae Lestidae, > 1 S. U. – 6 7 8 9 10 11
Elmidae, Gomphidae Only 1 S.U. – 5 6 7 8 9 10
3 Ancylidae, Decapoda, > 1 S. U. – 4 5 6 7 8 9
Aeshnidae, Simuliidae, Only 1 S.U. – 3 4 5 6 7 8
Other Trichoptera
4 Other Coleoptera All S.U. above – 3 4 5 6 7 –
Ephemeroptera (Caenidae absent
excepted)
5 Coenagrionidae, Caenidae, All S.U. above 2 3 4 5
Heteroptera, Amphipoda absent
6 Tubificidae, red All S.U. above 1 1 2 3
Chironomidae, Physidae, absent
Culicidae
7 Syrphidae, Enchitreidae, All S.U. above – 0 1 2
Psychodidae absent
Table 2. Standard table for calculating the IBPAMP index of potamal zones
Faunistic groups Total numbers of systematic units present
0–1 2–5 6–10 11–15 16–20 21–25 >26
Biotic index
1 Trichoptera with cases > 1 S. U. – – 9 10 11 12 13
(Leptoceridae) Only 1 S.U. – – 8 9 10 11 12
2 Other Trichoptera Lestidae, > 1 S. U. – 6 7 8 9 10 11
5 Coenagrionidae, Caenidae, All S.U. above 2 3 4 5
Heteroptera, Amphipoda absent
6 Tubificidae, red All S.U. above 1 1 2 3
Chironomidae, Physidae, absent
Culicidae
7 Syrphidae, Enchitreidae, All S.U. above – 0 1 2
Psychodidae absent
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Figure 1. Geographical map with location of sampled streams. 1 – El Gato, 2 – El Pescado, 3 – Buñirigo, 4 – Juan Blanco, 5 – Tandileofu, 6 –Napaleofu, 7 – Vivorata.
et al., in press) Tangorra et al. 1998, Tangorra et al.,1999). For the potamon were added Mollusca (Union-idae) at the first levels of water quality (Table 2).Furthermore the Pampean organisms are in accor-dance with the regional tolerance values for benthicmacro-invertebrates of EPA (Barbour et al., 1999).
For this index five classes (I–V) of water quality,from unpolluted to very heavily contamination, wereestablished according to the previously mentionedauthors (Table 3).
Statistical analyses
For the statistical analyses a ln(x + 1) transformationwas used for the values of biological, physical andchemical parameters in order to reduce the effect ofseasonal variations. The correlation matrix was ob-tained including those parameters and the biotic index.Principal component analysis (PCA) was applied for
the examination of multivariate data to evaluate theefficacy of the biotic indices and to assess the impactof human activity on the rivers and streams of BuenosAires province (Zitko, 1994). Furthermore, the par-tial correlation (p < 0.05) between the biotic index(IBPAMP) and Factor 1 (which grouped physico-chemical parameters) was analysed (Pla, 1986).
Results
In general the effluent discharges caused an impor-tant decrease in dissolved oxygen levels of the streamwaters, and a significant increase in nitrites, nitrates,phosphates, BOD5 and COD. The most affected siteswere those of El Gato stream in all seasons of theyear (DO <2 mg l−1; high turbidity (>200 UNT inthe middle part); high BOD5 (>30 mg l−1) and COD(>40 mg l−1). The Buñirigo stream only presented
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Table 3. Classes of water quality based on IBPAMP index
Class Biotic index Significance Colour
IBPAMP
I 10–13 Unpolluted Blue
II 8–9 Slightly polluted Green
III 6–7 Moderately polluted Yellow
IV 4–5 Heavily polluted Orange
V 1–3 Very heavily polluted Red
a bad quality in the industrial area, with changesaccording to the seasons.
In the mountainous part, in general the quality ofthe stream waters was good except for the stationslocated downstream of the cities. For example theTandileofú stream showed, in general, a good physi-cal, chemical and biological quality along its courseexcept downstream of Ayacucho city.
A total of 118 invertebrate taxa including micro-crustaceans were recorded from the seven streamsexamined. The taxa found in the plain (potamon) areaof El Gato, El Pescado, Buñirigo and Juan Blanco aredescribed in Tangorra et al. (1999). In the present pa-per only the macro-invertebrate fauna was considered.The most abundant taxa registered during the study pe-riod in the potamon were the oligochaetes belonging tothe family of the Naididae (Dero sp., Pristina sp., Naissp., Chaetogaster sp. and Stylaria sp.) and the Tubifi-cidae (Limnodrilus hoffmeisteri), the snails Pomaceacanaliculata, Biomphalaria peregrina and Heleobiaparchappei and the amphipod Hyalella curvispina.Among the insects the main taxa recorded were thechironomids Chironomus sp. and Goeldichironomussp. followed by the coleopterans Hydrophilidae, Elmi-dae and Dytiscidae. The more sensitive species toantropogenic disturbances were registered in the JuanBlanco stream and in the upper sections of Buñirigoand El Pescado: Palaemonetes argentinus and Mac-robrachium borelli (Decapoda Natantia), Diplodondelodontus delodontus (Pelecypoda), Campsurus sp.(Ephemeroptera), Aeshna bonariensis (Odonata), Cyr-nellus sp. and Oecetis sp. (Trichoptera). In pollutedareas these taxa disappear or their numbers are signif-icantly reduced.
El Gato stream presented a low diversity, mainlyin the middle part where the industrial discharges aremore important. In this section of the stream onlyDero sp., Limnodrilus claparedianus, Colembola andTardigrada were observed.
The streams of the Tandilia hills had in generalthe best water quality (flow >60 cm s−1 and hightransparency and low turbidity) and enabled the es-tablishment of populations of sensitive species; themore typical ones recorded were cased Trichoptera(Leptoceridae), Trichoptera without cases (Hydropsy-chidae: Smicridea pampeana), Ephemeroptera (Cally-baetis sp.), Lestidae and other Zygoptera, Coleoptera(Elmidae), Molluscs (Ancylidae) and Gordioidea.
In Table 4 the major taxa recorded are listed as wellas the mean and standard deviation of the physical andchemical parameters measured in sampling sites.
The taxonomic levels and the total number of sys-tematic units (S.U.) that determine the vertical entry inthe table for the IBPAMP index are shown in Table 5.Biotic index scores obtained for the different samplingsites are given in Table 6.
The distributions of the scores over the IB-PAMP quality classes were the following: unpolluted(14.4%); slightly polluted (38.4%); moderately pol-luted (21.6%); heavily polluted (13.2%); and veryheavily polluted (12%) (Table 6).
One can see that the low values correspond with ahigh degree of pollution of the El Gato stream fromup to downstream in all the seasons. In the El Pescadostream the water quality was very bad in the upper partof the basin especially during summer and fall.
The IBPAMP score proved to be a very in-teresting tool for the assessment of the Pampeanstreams examined. The scores correlated well with allphysico-chemical parameters (dissolved oxygen ex-cepted) (Figure 2). The IBPAMP index had a goodcorrelation with the diversity indices of Shannon &Weaver and Margalef, as well as the biotic indicesBMWP’, Chandler and the IMRP.
The correlation matrix was made up by 15 vari-ables (the physico-chemical parameters and the bioticindices) and 52 valid cases. In the PCAs the first prin-cipal component explained 45.4% of the variance andthe second 14.6%. In Figure 2 one can see three dis-tinct groups. One group is formed by diversity andbiotic indices at the left of the axis one; the sec-ond group on the other side of the axis is made upby the parameters indicating antropogenic disturbance(BOD5, COD, conductivity); and the third group inthe upper part of the axis two by NO3, PO4 andNH4. For the DO, pH and E (evenness) the correla-tion coefficient is low. Only the calculated correlationbetween the IBPAMP index and the factor 1 only(physico-chemical parameters) had a good statisticalsignificance (r = −0.77) (Figure 3; Table 7).
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Table 4. Main taxa of macroinvertebrates recorded and corresponding mean and standard deviation of the physical-chemical parameters
DO (mg 1) Conductivity BOD (mg 1) COD (mg 1 PO4 (mg 1) NH4 (mg 1)
Figure 2. Principal component analyses (PCAs). At the left of axis 1 are grouped the biologic indices (IBPAMP, diversity, Chandler, IMRP,BMWP′); at the right are grouped the physical and chemical parameters used to assess the water quality (conductivity, BOD5, PO4, NO3, andNH4).
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Figure 3. Relation between IBPAMP index and Factor 1 grouping the physico-chemical parameters.
Table 5. Taxonomic levels to define the systematic units(S.U.) for the IBPAMP index. Columns 3 and 4 show themost common numbers recorded in the rhitral and potamalzones of Pampean streams
The studied environments presented different varia-tions in their watercourses owing to seasonal changesin precipitation and, in the lower sector, to the actionof tidal waves from the Río de la Plata river, con-
nected to the Atlantic Ocean. Under natural conditionsthe sources of some streams such as Juan Blanco,Buñirigo and Pescado do not frequently present wa-ter flow during the dry period (mainly in summer),forming pools where the fauna must adapt to the lenticconditions of the environment. However other streamswhich receive urban and industrial effluents, as isthe case of El Gato stream, during dry periods, havecertain continuity due to this influence, producing astrategic change in the life cycles of the inhabitantspecies. This aspect was previously considered byWilliams (1987), Morais (1995) and lately by Coimbraet al. (1996) for European rivers in the Mediterraneanarea. The species which remain in these disturbedsystems are more tolerant in general, to adverse con-ditions, as is the case for some Gastropods (Physidae),Oligochaeta (Tubifícidae) and Hirudinea.
In general the registered values of the dissolvedoxygen in the water were lowest in polluted sectorsof the studied streams. However, remarkable are thechanges in the values of the DO observed in the sec-tors with high contents of nutrients, low content ofsuspended solids, and high densities of algal masses.These recorded variations are probably the reason ofthe low correlation with the IBPAMP index. On theother hand pH values are relatively uniform in all stud-ied streams related with neutral or slightly alkalinesoils (pH = 7.0 − 8.5) of the region, independent ofthe biotic communities.
Férnández and Schnack (1977) worked out a firstlist of invertebrates tolerant to some pollution fac-tors in the Rodriguez and Carnaval streams (in thesampling area studied), the former being related tothe effluents coming from a meat processing plant.
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Table 6. Biotic index (IBPAMP) scores of sampled streams
Streams Summer Autumn Winter Spring
El Gato Upstream 3 5 3 5
Midstream 6 1 2 1
Downstream 3 4 7 6
El Pescado Upstream 6 6 5 4
Midstream 8 6 6 8
Downstream 5 3 8 7
Buñirigo Upstream dry stream 4 7 9
Downstream 8 9 5 5
Juan Blanco Upstream 7 9 9 9
Downstream 10 9 9 10
Tandileofu Upstream 8 9 7 7
Midstream 1 10 10 10 9
Midstream 2 3 4 3 3
Downstream 7 8 8 9
Napaleofu Upstream 9 9 10 7
Midstream 1 9 10 9 9
Midstream 2 8 7 8 9
Downstream 5 6 6 5
Vivorata Upstream 9 9 8 9
Midstream 10 10 9 10
Downstream 10 10 8 9
These authors observed significant differences in thebacteriological contamination of the stream sections,which are directly connected to the cattle plant wastes.The invertebrates mentioned in this study are rela-tively coincident to the ones found in the samplesfrom the potamal zone where the described bioticindices were applied. Modenutti (1987) studied thezooplankton of the Rodriguez stream in order to de-termine spatial variation of the species composition ofthis community. They reported in polluted sections aconsiderable increase in the proportion of Ciliata andRotifera Bdelloidea, and a decrease in species andindividual numbers of Rotifera Monogononta and Rhi-zopoda Testacea. The unpolluted sections and pollutedones of this stream were coincident with the men-tioned results of Fernández and Schnack (1977) basedon Sladecek (1973).
However, in the mountainous environments theconditions are different with a constant water flowcoming from spring and flows. Although agricultureand cattle raising are present in the region, the al-teration in the source areas (rhitron) and middle partis not significant. This is proved by the presence ofhigh densities of sensitive species belonging to the Hy-dropsychidae, Hydroptilidae, Leptoceridae, Simuli-
idae, etc. Nevertheless in downstream direction thefield slope decreases but the supply of pesticides, thenutrients coming from agriculture and urban sewageincreases. In several streams and canals from this areathe fauna becomes poor in favour of tolerant speciesbelonging to the Chironomidae and Oligochaeta.
With regard to the index values itself, unpublishedinformation about invertebrate samples of preliminarystudies on rithral zones from Ventania Hills rivers(Sauce Grande River) allowed observing scores ofthe IBPAMP index between 10 to 13. In the TandilHills, however none of the analysed streams reachedan index > than 10.
Gómez (1999) and Gómez and Licursi (2001),used an index based on benthic diatoms (with classes0-IV following the Dell’Uomo (1991) criterion, inaccordance with Sládecek (1973), that correlated sig-nificantly with the data of the aquatic invertebrates,which supports the validity of the applied indices inthe present work.
This coincides with the opinion and considera-tions of De Pauw and Hawkes (1993), Ravera (1998),Corigliano (1999) and Prat et al. (1999) about theadvantages of biological monitoring to obtain infor-mation on the global situation of the environment
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Table 7. Factor Loadings (Unrotated) ofthe principal component analysis (PCA) forphysico-chemical parameters only
integrated over time. The community characteristicsare the result of various environment factors influenc-ing the community structure. The anomalies recordedby biological monitoring, indicate that stress condi-tions occurred in the past which appear not to beevidenced by chemical monitoring. However, thesebiological methods may not be applied in all situa-tions, and chemical monitoring is important to identifyand quantify the potential causes of biological effects.Both, biological and chemical monitoring are thuscomplementary to each other.
Conclusions
(1) The use of the biotic indices allowed to differen-tiate between sections of streams which are moreor less affected by urban and industrial distur-bance. The polluted El Gato stream is charac-terised by the following tolerant taxa: Limnodrilushoffmeisteri, Lumbriculus variegatus, Helobdelatriserialis, Biomphalaria peregrina, Stenophysamarmorata, Pomacea canaliculata, Chironomussp. Goeldichironomus sp., etc.; the middle courseof the Tandileofú stream is dominated by Nema-toda and Parachironomus sp. In other sectionswith better environmental conditions the follow-ing sensitive species were found in the potamal
zone: the dragonflies Aeshna bonariensis, Mi-crathyria didyma, the mayflies Callybaetis sp.and Campsurus sp., the caddisfly Oecetys sp.,the shrimps Palaemonetes argentinus and Mac-robrachium borelli and the bivalve Diplodon de-lodontus delodontus. In the rhitral zone othersensitive taxa are Hydropsychidae, Hydroptilidae,Leptoceridae, Simuliidae.
(2) The IBPAMP showed a positive highly significantcorrelation with the other biotic and diversity in-dices, except eveness, and a negative one equallysignificant with most of the physical-chemical wa-ter quality parameters that were considered (con-ductivity, BOD5, PO4, NO3, NO2 and NH4),however not dissolved oxygen and pH.
(3) The correlation between factor 1 in which onlyphysico-chemical parameters were considered,and the IBPAMP index was highly significant.
Acknowledgements
This study was financed by the following Projects:4740/97 of the National Council of Scientific andTechnological Research (Argentine); 1812/97 of theNational Agency for Scientific and Technological Pro-motion, and 216 of the National University of La Plata,Argentina). We are grateful to Carlos Roldán for as-sistance in the field and Jorge Donadelly for wateranalyses in the laboratory. Special thanks go to thereferees for their suggestions and comments.
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