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Use of epipelic diatoms for evaluation of water quality in the Matanza-Riachuelo (Argentina), a pampean plain river
PII: S0043-1354(97)00448-X
Wat. Res. Vol. 32, No. 7, pp. 2029±2034, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/98 $19.00 + 0.00
USE OF EPIPELIC DIATOMS FOR EVALUATION OF WATER QUALITY IN THE MATANZA-RIACHUELO (ARGENTINA), A PAMPEAN PLAIN RIVER NORA GOÂMEZ* Instituto de LimnologõÂ a Dr. R.A. Ringuelet, C.C. 712, 1900 La Plata, Argentina (First received January 1997; accepted in revised form October 1997) AbstractÐEpipelic diatom assemblages have been used to evaluate water quality in the Matanza-Riachuelo river basin. Twenty-three sites were sampled in April, May, June and August 1995, before the setup of restoration programs. The Matanza-Riachuelo river basin is located in N.E. Buenos Aires province. It runs across one of the most industrialized and populous zones of Argentina, for which it is subject to strong anthropogenic disturbances. A total number of 97 taxa were identi®ed of which only 37 were abundant. Navicula cryptocephala, Nitzschia palea and N. umbonata occur in the whole basin though more frequent downstream; Stephanodiscus hantzschii and Cyclotella meneghiniana develop where the river becomes wider and deeper. The distribution of the diatomological ¯ora in the MatanzaRiachuelo basin was aected by the increasing concentration of organic matter carried by the river and downstream for the input of chemical compounds, several of which are toxic to aquatic life (i.e. heavy metals, phenols, hydrocarbon, etc.). The assemblage was dominated by pollution-tolerant species, which implies strong to very strong contamination in a great portion of the basin. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐdiatoms, epipelic, ecology, river, water quality, pampean plain, Argentina
INTRODUCTION
The Matanza-Riachuelo is a typical river of plains with a gentle river bed gradient and meandering. It runs across one of the most industrialized and crowded zones of Argentina, for which it is subject to strong anthropogenic disturbances. In recent years, a multidisciplinary research group has been working out a plan for the restoration of the rivers's water quality. The use of diatoms as water quality indicators has been recognized in a number of articles (Coste, 1978; Descy, 1979; Lange-Bertalot, 1979; Sladecek, 1986; Sabater et al., 1987, Sabater and Sabater, 1988; Descy and Coste, 1990, 1991; Whitton et al., 1991; Whitton and Rott, 1995). Considering epipelic algae from Argentina, these were studied only by Claps (1996), but there is no precedent on the use of benthic diatoms to evaluating water quality in this country. The objective of this article is to describe epipelic diatom assemblages in the Matanza-Riachuelo river basin and relate them with environmental factors before the setup of restoration programs, contributing toward the assessment of water quality. The approach used in this study will be applied to other pampean plain river basins and will provide a valu*Author to whom all correspondence should be addressed.
able baseline for future water quality assessment eorts. MATERIAL AND METHODS
Twenty-three sites in the Matanza-Riachuelo river basin (Fig. 1) were sampled in April, May, June and August 1995. In areas where the depth was above 30 cm, triplicate samples of the more super®cial layer (5±10 mm in depth) were collected by using a core 3 cm in diameter. Material was observed by inspected cytoplasmatic contents. Samples were ®xed in 4% formalin. The organic matter fraction was removed with acids (Barber and Haworth, 1981). Clean diatoms were mounted in Naphrax, counting up to 300 valves in each sample (Sabater et al., 1987) with an optical microscopy BH Olympus with phase contrast at a magni®cation of 1250, assessing the relative abundance of each identi®ed taxa. The identi®cation of taxa was based on studies by previous authors (Hustedt, 1930; Frenguelli, 1941; Patrick and Reimer, 1966, 1975; Krammer and Lange-Bertalot, 1986, 1991; Lange-Bertalot and Krammer, 1987). The initial data matrix for the principal component analysis included only species with relative abundance higher than 5%. Variance normality was attained by logarithmic transformation of data (X = log(X + 1); X = percent). The richness index (R) was obtained by using Margalef's formula (Ludwig and Reynolds, 1988). STUDY AREA
The basin of the Matanza-Riachuelo river is located between 35806'S±58849'W and 34838'S±
2029
2030
Nora GoÂmez
Fig. 1. Map showing Matanza-Riachuelo basin, the sampling sites and the main industrial activity.
58821'W and has a surface of nearly 2240 km2. The river has a length of 85 km, a width ranging from 10 m (in the upper basin) to 150 m (at the RõÂ o de la Plata river mouth) and a mean gradient of 0.35 m/ km. The river bed sediments have a composition of slime±clay soil in most of the basin (except at the mouth where slime±sand soils predominate) with some CaCO3 concretions (``caliche''). Depth ranges from 0.60 to 7.70 m. Nearly one half of the river course has been altered thus changing the original landscape. Annual mean discharge varies from 2.89 m3 sÿ1 up to maximum values of 1000 m3 sÿ1. The hydrological cycle of the river depends mainly on precipitation, and along the lower stretch of the basin receives further contribution of underground water. The mean annual rainfall in the basin is around 800±1000 mm, 40% from December to March. The discharge capacity of the RõÂ o de la Plata varies by the eect of tides. Mean annual temperature is approximately 178C.
Of the 23 sampling stations selected for the present study, 5 were located along streams subject to the impact from agricultural, cattle and industrial activities (Fig. 1). Humane population living throughout the basin is about 2 720 000. Main contaminating factors in the region are: industrial euents discharge without previous adequate treatment,
Table 1. Physico±chemical features in the Matanza-Riachuelo river, average, maximum and minimum in brackets, upstream and downstream from station 10
Cond. (mS cmÿ1) Oxy. (mg lÿ1) pH TSS (mg ÿ1) Secchi disk (cm) BOD5 (mg lÿ1) COD (mg lÿ1)
Upstream from station 10 (n = 36)
Downstream from station 10 (n = 56)
1824.2 (4990±495) 4.7 (8.6±0.8) 8 (8.5±7) 56.5 (179.9±4) 39.7 (60±15) 20.2 (156±3) 55.7 (180±18)
1970 2.7 7.8 280.7 22.5 50.2 98.1
(9370±645) (7±0.2) (8.45±6.9) (787±10) (50±11) (254±9) (655±17)
Water quality evaluation using diatoms Table 2. List of the species with an abundance over 5% in Matanza-Riachuelo river basin Achnanthes lanceolata BreÂb. (ACHL) A. minutissima Kutz. (ACHM) Amphora coeaeformis (Ag.) Kutz. (AMPC) A. veneta Kutz. (AMPV) Anomoeoneis sphaerophora (Ehr.) P®tzer (ANOS) Aulacoseira. granulata (Ehr.) Simonsen (AUGR) Bacillaria paradoxa Gmelin (BACP) Cocconeis placentula Ehr. (COCP) Cyclotella meneghiniana Kutz. (CYCM) Cymbella silesiaca Bleisch. (CYSI) Fragilaria ulna (Nitzsch.) Lange-B. (FRAU) Gomphonema clavatum Ehr. (GOMC) G. parvulum Kutz. (GOMP) Melosira varians Ag. (MELV) Navicula accomoda Hust. (NAVA) N. atomus (Kutz) Grun. (NAAT) N. capitata Ehr. (NACA) N cryptocephala Kutz. (NAVC) N. cuspidata Kutz. (NACU) N. erifuga Lange-B. (NAER) N. goeppertiana (Bleisch) H.L. Smith (NAGO) N. pupula Kutz. (NAPU) N. pygmaea Kutz. (NAPY) N. subminuscula Manguin (NASU) Nitzschia amphibia Grun. (NIAM) N. amphiboides Hust. (NIAMP) N. fonticola Grun. (NIFO) N. heu¯eriana Grun. (NIHE) N. hungarica Grun. (NIHU) N. Iinearis (Ag.) W.M. Smith (NILI) N. palea (Kutz.) W. Smith (NIPA) N. sigma (Kutz.) W.M. Smith (NISI) N. umbonata (Ehr.) Lange-B. (NIUM) Pinnularia gibba Ehr. (PIGI) P. microstaurum (Ehr.) Cleve (PIMI) Rhoicosphenia curvata (Kutz.) Grun. (RHCU) Stephanodiscus hantzschii Grun. (STEH)
sewage discharge insuciently treated and harbor activities with no environmental control. The distribution of main industrial activities is shown in Fig. 1 (CEAMSE, 1983).
2031
Physical±chemical characteristics of the river The main physical±chemical features of the river are shown in (Table 1), which is based on data gathered during the INCHYT-CETUAA-ILPLA (1995) agreement. Suspended solids (TSS), biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) increased downstream. Dissolved oxygen, pH and transparency increased upstream. Conductivity was variable along the basin, reporting the highest values at sampling site 11. It decreased at sampling station 23 for the eect of the less mineralized waters of the RõÂ o de la Plata. The rivers of the depressed pampean plain present semidesert-like drainage (Dangavs, 1973), thus introducing transitory changes in the mineralization. The substrate type (calcium rich), the mineralized nature of underground water and the industrial in¯uence explain the relative high conductivity in the Matanza-Riachuelo river. RESULTS
A total of 97 diatom species were identi®ed; only 37 had a relative abundance higher than 5% in at least one sample (Table 2). The principal components analysis allowed us to assess the characteristics of the species as well as trends in their distribution and associations (Fig. 2). The ®rst axis, which accounted for 21% of the variance, arranged the species along a left-to-right gradient which can be related to increasing BOD5, COD, decreasing dissolved oxygen, transparency and pH. The most pollution-tolerant species are separated toward the right end of the axis: Navicula cryptocephala, Nitzschia palea and N. umbonata. These species
Fig. 2. Principal component analysis (PCA) of the 37 selected species. Three group of species can be made according to the dierences in the water quality (see the explanation in the text). The abbreviations of species are indicated in Table 2.
Nora GoÂmez
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Table 3. Species grouped in relation to their tolerance to dierent concentrations of organic matter according to Lange-Bertalot (1979) Pollution-sensitive taxa
Less tolerant taxa
Most tolerant taxa
Achnanthes minutissima Cocconeis placentula Cymbella sileciaca Nitzschia heu¯eriana N. linearis N. sigmoidea
Achnanthes lanceolata Anomoeoneis sphaerophora Melosira varians Navicula capitata N. cuspidata N. pupula N. pygmaea Nitzschia amphibia N. hungarica N. levidensis N. sigma N. tryblionella Pinnularia microstaurum Surirella ovalis
Amphora veneta Fragilaria ulna Gomphonema parvulum Navicula accomoda N. atomus N. cryptocephala N. goeppertiana Nitzschia palea N. umbonata
occur in the whole basin but are found more frequently downstream from station 10. Other species found in this group are Stephanodiscus hantszcchii and Cyclotella meneghiniana, which occur downstream from station 12, where the river is wider and deeper. Toward the left end of the ®rst axis, the species separated are Gomphonema clavatum, Achnanthes minutissima, A. lanceolata, Nitzschia fonticola, N. amphibia, N. amphiboides, N. hungarica, Navicula erifuga, N. capitata and Rhoicosphaenia curvata. These species are particularly frequent at stations 7, 2 and 8, which correspond to the upper basin. The second axis, which accounts for 11% of the variance, arranged the species in relation to water mineralization, separating toward the superior end the species Navicula pygmaea, N. pupula, N. atomus, Amphora coeaeformis, A. veneta, Bacillaria paradoxa and Nitzschia sigma. These species are particularly frequent at the sampling stations 3, 6, 11 and 13, where conductivity is relatively high (2440±9370 mS cmÿ1).
Based on data about taxa autoecology and following the Lange-Bertalot (1979) criteria, the species were grouped according to their tolerance to dierent concentrations of organic matter (Table 3; Fig. 3). The pollution-sensitive species, were scarce throughout the basin and reached highest abundance values at station 7. Less tolerant species also showed low occurrence, decreasing downstream from station 10. Finally, the most tolerant group were present all throughout the basin with relative abundance values above 35%, except at station 7 where there is a decline in its percentage. This station corresponds to the Las Ortegas stream, a sampling station slightly less mineralized (495± 1314 mS cmÿ1), relatively low BOD5 (3±17 mg lÿ1). This stream runs across a zone of ``banÄados'' (area with submerged soils and emergent macrophytes) before discharging into the Matanza-Riachuelo river. Finally, it has to be noted that downstream from the sampling station 10, the density and richness of
Fig. 3. Percentages of the three species groups of gradual tolerance to pollution, along the MatanzaRiachuelo basin.
Water quality evaluation using diatoms
2033
Fig. 4. Distribution of the BOD5, COD and richness species (R). Richness species assemblage decreased downstream from sampling station 10, with input of the important chemical compounds products by industries: tannery, paper, textiles, metallurgy and chemical.
species assemblage decreased (less than 45% of the species recorded upstream occurred downstream) and BOD5 and COD increased (Fig. 4). Also, downstream observations of material without acid treatment showed that more than 65% of diatoms cells were cytoplasmatic with contents modi®ed or were empty.
DISCUSSION
The distribution of the studied diatom assemblage was variable in species composition, density and relative abundance of the involved taxa. The assemblage was dominated by pollution-tolerant species, which implies high to very high contamination in a great portion of the basin. Frequent or intense disturbance reduces the community to a few species, coincident with the polysaprobic group of species of the saprobic system (Prat and Ward, 1994). The distribution of the diatomological ¯ora found in the Matanza-Riachuelo basin was aected by the increasing concentration of organic matter carried by the river and for the increase of phenols, hydrocarbon, oil, heavy metals (chromium, cadmium, lead, copper, mercury, arsenic), pesticide (CEAMSE, 1983), downstream from station 10. These include mainly industrial by-products (tannery, paper, textiles, metallurgy, chemical industries), which explain to a great extent the assemblage impoverishment toward the basin mouth. Chemical pollution can cause a strong perturbation of the algae ¯ora (Cazaubon, 1991). The group of sensitive taxa and less tolerant taxa, scarcely occurring throughout the basin, decrease downstream from the outlets of the above mentioned industries, which is a similar situation to that described for the Main river by Lange-Bertalot (1979). Pollution-sensitive species reached the highest proportion at station 7. Toward the headwaters of Las Ortegas stream there are settlements of indus-
tries related to production of meat, milk, grains, sweets and free-alcohol drinks (CEAMSE, 1983). So the autopurifying capability of this stream would be enhanced as it runs across inundated zones with emerged vegetation. The role of the macrophytes for the removal of nutrients and other pollutants from wastewater has been documented (Brix and Schierup, 1988; Pullin and Hammer, 1991). Also soils bear mechanical, physicochemical and biological characteristics that contribute to water puri®cation, which depend on the type of soil (Margalef, 1955). Cazaubon (1991) consider the epipelon as a memory of stress that represents a warning of severe danger for water quality. This consideration is applicable to the epipelic diatomological ¯ora of the Matanza-Riachuelo basin, which serve as a good descriptor of those perturbations aecting this pampean plain river. AcknowledgementsÐI am grateful to anonymous referees for their valuable comments on the manuscript and for linguistic improvement in the text. Financial support for this study has been provided by the INCHYT-CETUAAILPLA agreement.
REFERENCES
Barber, H. G. and Haworth, E. Y. (1981) A guide to the morphology the diatom frustrule. Freshwat. Biol. Assoc. Sci. Publ. 44. Brix H. and Schierup H. (1988) The use of aquatic macrophytes in water pollution control. Ambio 18(2), 100±107. Cazaubon, A. (1991) Problems and objectives of sampling river algae for monitoring. In Use of Algae for Monitoring Rivers, eds. B. A. Whitton, E. Rott, G. Friedrich, 183 pp. Austria. CEAMSE (1983) Propuesta para el saneamiento de la cuenca del Rio Matanza-Riachuelo. Report. Buenos Aires, 420 p. Claps M. C. (1996) Structure and dynamics of epipelic algae from a plain river (SamboromboÂn river, Argentina). Arch. Hydrobiol. 137(2), 221±263. Coste, M. (1978) Sur l'utilisation des diatomeeÂs benthiques pour l'appreÂciation de la qualite biologique des eaux courantes. These Biol. veÂget., Univ. Besancon, 150 p.
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Dangavs N. V. (1973) Estudios geoloÂgicos en la laguna de San Miguel del Monte. Rev. Museo de la Plata VIII, 281±313. Descy J. P. (1979) A new approach to water quality estimation using diatom. Beih. Nov Hedw. 64, 305±323. Descy, J. P. and Coste, M. (1990) Utilisation des diatomeÂes benthiques pour l'evaluation de la qualite des eaux courantes. Contrat CEE B-71-23. Rapport ®nal. Cemagref, 60 p. Descy J. P. and Coste M. (1991) A test of methods for assessing water quality based on diatoms. Verh. Int. Verein. Limnol. 24, 2112±2116. Frenguelli J. (1941) Diatomeas del Rõ o de la Plata. Rev. Mus. La Plata Bot. 2, 213±334. Hustedt, F. (1930) Bacillariophyta (Diatomeae) In: Die Susswaser¯ora Mitteleuropas, ed. A. Pascher, Vol 10. Jena, 465 p. INCHYT-CETUAA-ILPLA (1995) EvaluacioÂn de la cuenca Matanza-Riachuelo a partir del estudio de la comunidad bentoÂnica (macroinvertebrados-diatomeas bentoÂnicas). Report. Buenos Aires, 150 p. Krammer, K. and Lange-Bertalot, H. (1986) Bacillariophyceae, Naviculaceae. Die Susswaser¯ora von Mitteleuropa Teil 2/1 Stuttgart. 876 p. Krammer, K. and Lange-Bertalot, H. (1991) Bacillariophyceae, Centrales, Fragilariaceae, Eunotiaceae. Die Susswaser¯ora von Mitteleuropa. 2/3 Stuttgart, 576 p. Lange-Bertalot H. (1979) Pollution and tolerance of diatoms as criterion of water quality estimation. Nova Hedwigia 64, 285±304. Lange-Bertalot, P. and Krammer, K. (1987) Bacil-
lariophyceae, Epithemiaceae, Surirellaceae. Bibliotheca. Diatomologica, Stuttgart, 289 p. Ludwig, J. A. and Reynolds, J. F. (1988) Statistical Ecology. John Wiley, New York. 337 p. Margalef, R. (1955) Los organismos como indicadores en la limnologõÂa. Inst. Forestal Inv. Exp., Madrid. 300 p. Patrick, R. and Reimer, C. W. (1966) The Diatom of the United States, Exclusive of Alaska and Hawaii, Vol. I, No. 13. Academy of Natural Sciences of Philadelphia, 668 p. Patrick, R. and Reimer, C. W. (1975) The Diatom of the United States, exclusive of Alaska and Hawaii, Vol. II, No. 13. Academy of Natural Sciences of Philadelphia, 213 p. Prat, N. and Ward, J. W. (1994) The tamed river. In: Limnology Now: A Paradigm of Planetary Problems, ed. R. Margalef. Barcelona. Pullin B. P. and Hammer B. (1991) Aquatic plants improve wastewater treatment. Wat. Environ. Technol. 3(3), 36±40. Sabater S., Sabater F. and Tomas X. (1987) Water quality and diatom communities in two catalan rivers (N.E. Spain). Wat. Res. 20(8), 901±911. Sabater S. and Sabater F. (1988) Diatom assemblages in the river Ter. Arch. Hydrobiol. 111(3), 397±408. Sladecek V. (1986) Diatoms as indicators of organic pollution. Acta Hydrochim. Hydrobiol. 14(5), 555±566. Whitton, B. A., Rott, E. and Friedrich, G. (eds.) (1991) Use of Algae for Monitoring Rivers. Austria, 183 p. Whitton, B. A. and Rott, E. (eds.) (1995) Use of Algae for Monitoring Rivers, Vol. II. Austria, 196 p.
Wat. Res. Vol. 32, No. 7, pp. 2029±2034, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/98 $19.00 + 0.00
USE OF EPIPELIC DIATOMS FOR EVALUATION OF WATER QUALITY IN THE MATANZA-RIACHUELO (ARGENTINA), A PAMPEAN PLAIN RIVER NORA GOÂMEZ* Instituto de LimnologõÂ a Dr. R.A. Ringuelet, C.C. 712, 1900 La Plata, Argentina (First received January 1997; accepted in revised form October 1997) AbstractÐEpipelic diatom assemblages have been used to evaluate water quality in the Matanza-Riachuelo river basin. Twenty-three sites were sampled in April, May, June and August 1995, before the setup of restoration programs. The Matanza-Riachuelo river basin is located in N.E. Buenos Aires province. It runs across one of the most industrialized and populous zones of Argentina, for which it is subject to strong anthropogenic disturbances. A total number of 97 taxa were identi®ed of which only 37 were abundant. Navicula cryptocephala, Nitzschia palea and N. umbonata occur in the whole basin though more frequent downstream; Stephanodiscus hantzschii and Cyclotella meneghiniana develop where the river becomes wider and deeper. The distribution of the diatomological ¯ora in the MatanzaRiachuelo basin was aected by the increasing concentration of organic matter carried by the river and downstream for the input of chemical compounds, several of which are toxic to aquatic life (i.e. heavy metals, phenols, hydrocarbon, etc.). The assemblage was dominated by pollution-tolerant species, which implies strong to very strong contamination in a great portion of the basin. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐdiatoms, epipelic, ecology, river, water quality, pampean plain, Argentina
INTRODUCTION
The Matanza-Riachuelo is a typical river of plains with a gentle river bed gradient and meandering. It runs across one of the most industrialized and crowded zones of Argentina, for which it is subject to strong anthropogenic disturbances. In recent years, a multidisciplinary research group has been working out a plan for the restoration of the rivers's water quality. The use of diatoms as water quality indicators has been recognized in a number of articles (Coste, 1978; Descy, 1979; Lange-Bertalot, 1979; Sladecek, 1986; Sabater et al., 1987, Sabater and Sabater, 1988; Descy and Coste, 1990, 1991; Whitton et al., 1991; Whitton and Rott, 1995). Considering epipelic algae from Argentina, these were studied only by Claps (1996), but there is no precedent on the use of benthic diatoms to evaluating water quality in this country. The objective of this article is to describe epipelic diatom assemblages in the Matanza-Riachuelo river basin and relate them with environmental factors before the setup of restoration programs, contributing toward the assessment of water quality. The approach used in this study will be applied to other pampean plain river basins and will provide a valu*Author to whom all correspondence should be addressed.
able baseline for future water quality assessment eorts. MATERIAL AND METHODS
Twenty-three sites in the Matanza-Riachuelo river basin (Fig. 1) were sampled in April, May, June and August 1995. In areas where the depth was above 30 cm, triplicate samples of the more super®cial layer (5±10 mm in depth) were collected by using a core 3 cm in diameter. Material was observed by inspected cytoplasmatic contents. Samples were ®xed in 4% formalin. The organic matter fraction was removed with acids (Barber and Haworth, 1981). Clean diatoms were mounted in Naphrax, counting up to 300 valves in each sample (Sabater et al., 1987) with an optical microscopy BH Olympus with phase contrast at a magni®cation of 1250, assessing the relative abundance of each identi®ed taxa. The identi®cation of taxa was based on studies by previous authors (Hustedt, 1930; Frenguelli, 1941; Patrick and Reimer, 1966, 1975; Krammer and Lange-Bertalot, 1986, 1991; Lange-Bertalot and Krammer, 1987). The initial data matrix for the principal component analysis included only species with relative abundance higher than 5%. Variance normality was attained by logarithmic transformation of data (X = log(X + 1); X = percent). The richness index (R) was obtained by using Margalef's formula (Ludwig and Reynolds, 1988). STUDY AREA
The basin of the Matanza-Riachuelo river is located between 35806'S±58849'W and 34838'S±
2029
2030
Nora GoÂmez
Fig. 1. Map showing Matanza-Riachuelo basin, the sampling sites and the main industrial activity.
58821'W and has a surface of nearly 2240 km2. The river has a length of 85 km, a width ranging from 10 m (in the upper basin) to 150 m (at the RõÂ o de la Plata river mouth) and a mean gradient of 0.35 m/ km. The river bed sediments have a composition of slime±clay soil in most of the basin (except at the mouth where slime±sand soils predominate) with some CaCO3 concretions (``caliche''). Depth ranges from 0.60 to 7.70 m. Nearly one half of the river course has been altered thus changing the original landscape. Annual mean discharge varies from 2.89 m3 sÿ1 up to maximum values of 1000 m3 sÿ1. The hydrological cycle of the river depends mainly on precipitation, and along the lower stretch of the basin receives further contribution of underground water. The mean annual rainfall in the basin is around 800±1000 mm, 40% from December to March. The discharge capacity of the RõÂ o de la Plata varies by the eect of tides. Mean annual temperature is approximately 178C.
Of the 23 sampling stations selected for the present study, 5 were located along streams subject to the impact from agricultural, cattle and industrial activities (Fig. 1). Humane population living throughout the basin is about 2 720 000. Main contaminating factors in the region are: industrial euents discharge without previous adequate treatment,
Table 1. Physico±chemical features in the Matanza-Riachuelo river, average, maximum and minimum in brackets, upstream and downstream from station 10
Cond. (mS cmÿ1) Oxy. (mg lÿ1) pH TSS (mg ÿ1) Secchi disk (cm) BOD5 (mg lÿ1) COD (mg lÿ1)
Upstream from station 10 (n = 36)
Downstream from station 10 (n = 56)
1824.2 (4990±495) 4.7 (8.6±0.8) 8 (8.5±7) 56.5 (179.9±4) 39.7 (60±15) 20.2 (156±3) 55.7 (180±18)
1970 2.7 7.8 280.7 22.5 50.2 98.1
(9370±645) (7±0.2) (8.45±6.9) (787±10) (50±11) (254±9) (655±17)
Water quality evaluation using diatoms Table 2. List of the species with an abundance over 5% in Matanza-Riachuelo river basin Achnanthes lanceolata BreÂb. (ACHL) A. minutissima Kutz. (ACHM) Amphora coeaeformis (Ag.) Kutz. (AMPC) A. veneta Kutz. (AMPV) Anomoeoneis sphaerophora (Ehr.) P®tzer (ANOS) Aulacoseira. granulata (Ehr.) Simonsen (AUGR) Bacillaria paradoxa Gmelin (BACP) Cocconeis placentula Ehr. (COCP) Cyclotella meneghiniana Kutz. (CYCM) Cymbella silesiaca Bleisch. (CYSI) Fragilaria ulna (Nitzsch.) Lange-B. (FRAU) Gomphonema clavatum Ehr. (GOMC) G. parvulum Kutz. (GOMP) Melosira varians Ag. (MELV) Navicula accomoda Hust. (NAVA) N. atomus (Kutz) Grun. (NAAT) N. capitata Ehr. (NACA) N cryptocephala Kutz. (NAVC) N. cuspidata Kutz. (NACU) N. erifuga Lange-B. (NAER) N. goeppertiana (Bleisch) H.L. Smith (NAGO) N. pupula Kutz. (NAPU) N. pygmaea Kutz. (NAPY) N. subminuscula Manguin (NASU) Nitzschia amphibia Grun. (NIAM) N. amphiboides Hust. (NIAMP) N. fonticola Grun. (NIFO) N. heu¯eriana Grun. (NIHE) N. hungarica Grun. (NIHU) N. Iinearis (Ag.) W.M. Smith (NILI) N. palea (Kutz.) W. Smith (NIPA) N. sigma (Kutz.) W.M. Smith (NISI) N. umbonata (Ehr.) Lange-B. (NIUM) Pinnularia gibba Ehr. (PIGI) P. microstaurum (Ehr.) Cleve (PIMI) Rhoicosphenia curvata (Kutz.) Grun. (RHCU) Stephanodiscus hantzschii Grun. (STEH)
sewage discharge insuciently treated and harbor activities with no environmental control. The distribution of main industrial activities is shown in Fig. 1 (CEAMSE, 1983).
2031
Physical±chemical characteristics of the river The main physical±chemical features of the river are shown in (Table 1), which is based on data gathered during the INCHYT-CETUAA-ILPLA (1995) agreement. Suspended solids (TSS), biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) increased downstream. Dissolved oxygen, pH and transparency increased upstream. Conductivity was variable along the basin, reporting the highest values at sampling site 11. It decreased at sampling station 23 for the eect of the less mineralized waters of the RõÂ o de la Plata. The rivers of the depressed pampean plain present semidesert-like drainage (Dangavs, 1973), thus introducing transitory changes in the mineralization. The substrate type (calcium rich), the mineralized nature of underground water and the industrial in¯uence explain the relative high conductivity in the Matanza-Riachuelo river. RESULTS
A total of 97 diatom species were identi®ed; only 37 had a relative abundance higher than 5% in at least one sample (Table 2). The principal components analysis allowed us to assess the characteristics of the species as well as trends in their distribution and associations (Fig. 2). The ®rst axis, which accounted for 21% of the variance, arranged the species along a left-to-right gradient which can be related to increasing BOD5, COD, decreasing dissolved oxygen, transparency and pH. The most pollution-tolerant species are separated toward the right end of the axis: Navicula cryptocephala, Nitzschia palea and N. umbonata. These species
Fig. 2. Principal component analysis (PCA) of the 37 selected species. Three group of species can be made according to the dierences in the water quality (see the explanation in the text). The abbreviations of species are indicated in Table 2.
Nora GoÂmez
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Table 3. Species grouped in relation to their tolerance to dierent concentrations of organic matter according to Lange-Bertalot (1979) Pollution-sensitive taxa
Less tolerant taxa
Most tolerant taxa
Achnanthes minutissima Cocconeis placentula Cymbella sileciaca Nitzschia heu¯eriana N. linearis N. sigmoidea
Achnanthes lanceolata Anomoeoneis sphaerophora Melosira varians Navicula capitata N. cuspidata N. pupula N. pygmaea Nitzschia amphibia N. hungarica N. levidensis N. sigma N. tryblionella Pinnularia microstaurum Surirella ovalis
Amphora veneta Fragilaria ulna Gomphonema parvulum Navicula accomoda N. atomus N. cryptocephala N. goeppertiana Nitzschia palea N. umbonata
occur in the whole basin but are found more frequently downstream from station 10. Other species found in this group are Stephanodiscus hantszcchii and Cyclotella meneghiniana, which occur downstream from station 12, where the river is wider and deeper. Toward the left end of the ®rst axis, the species separated are Gomphonema clavatum, Achnanthes minutissima, A. lanceolata, Nitzschia fonticola, N. amphibia, N. amphiboides, N. hungarica, Navicula erifuga, N. capitata and Rhoicosphaenia curvata. These species are particularly frequent at stations 7, 2 and 8, which correspond to the upper basin. The second axis, which accounts for 11% of the variance, arranged the species in relation to water mineralization, separating toward the superior end the species Navicula pygmaea, N. pupula, N. atomus, Amphora coeaeformis, A. veneta, Bacillaria paradoxa and Nitzschia sigma. These species are particularly frequent at the sampling stations 3, 6, 11 and 13, where conductivity is relatively high (2440±9370 mS cmÿ1).
Based on data about taxa autoecology and following the Lange-Bertalot (1979) criteria, the species were grouped according to their tolerance to dierent concentrations of organic matter (Table 3; Fig. 3). The pollution-sensitive species, were scarce throughout the basin and reached highest abundance values at station 7. Less tolerant species also showed low occurrence, decreasing downstream from station 10. Finally, the most tolerant group were present all throughout the basin with relative abundance values above 35%, except at station 7 where there is a decline in its percentage. This station corresponds to the Las Ortegas stream, a sampling station slightly less mineralized (495± 1314 mS cmÿ1), relatively low BOD5 (3±17 mg lÿ1). This stream runs across a zone of ``banÄados'' (area with submerged soils and emergent macrophytes) before discharging into the Matanza-Riachuelo river. Finally, it has to be noted that downstream from the sampling station 10, the density and richness of
Fig. 3. Percentages of the three species groups of gradual tolerance to pollution, along the MatanzaRiachuelo basin.
Water quality evaluation using diatoms
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Fig. 4. Distribution of the BOD5, COD and richness species (R). Richness species assemblage decreased downstream from sampling station 10, with input of the important chemical compounds products by industries: tannery, paper, textiles, metallurgy and chemical.
species assemblage decreased (less than 45% of the species recorded upstream occurred downstream) and BOD5 and COD increased (Fig. 4). Also, downstream observations of material without acid treatment showed that more than 65% of diatoms cells were cytoplasmatic with contents modi®ed or were empty.
DISCUSSION
The distribution of the studied diatom assemblage was variable in species composition, density and relative abundance of the involved taxa. The assemblage was dominated by pollution-tolerant species, which implies high to very high contamination in a great portion of the basin. Frequent or intense disturbance reduces the community to a few species, coincident with the polysaprobic group of species of the saprobic system (Prat and Ward, 1994). The distribution of the diatomological ¯ora found in the Matanza-Riachuelo basin was aected by the increasing concentration of organic matter carried by the river and for the increase of phenols, hydrocarbon, oil, heavy metals (chromium, cadmium, lead, copper, mercury, arsenic), pesticide (CEAMSE, 1983), downstream from station 10. These include mainly industrial by-products (tannery, paper, textiles, metallurgy, chemical industries), which explain to a great extent the assemblage impoverishment toward the basin mouth. Chemical pollution can cause a strong perturbation of the algae ¯ora (Cazaubon, 1991). The group of sensitive taxa and less tolerant taxa, scarcely occurring throughout the basin, decrease downstream from the outlets of the above mentioned industries, which is a similar situation to that described for the Main river by Lange-Bertalot (1979). Pollution-sensitive species reached the highest proportion at station 7. Toward the headwaters of Las Ortegas stream there are settlements of indus-
tries related to production of meat, milk, grains, sweets and free-alcohol drinks (CEAMSE, 1983). So the autopurifying capability of this stream would be enhanced as it runs across inundated zones with emerged vegetation. The role of the macrophytes for the removal of nutrients and other pollutants from wastewater has been documented (Brix and Schierup, 1988; Pullin and Hammer, 1991). Also soils bear mechanical, physicochemical and biological characteristics that contribute to water puri®cation, which depend on the type of soil (Margalef, 1955). Cazaubon (1991) consider the epipelon as a memory of stress that represents a warning of severe danger for water quality. This consideration is applicable to the epipelic diatomological ¯ora of the Matanza-Riachuelo basin, which serve as a good descriptor of those perturbations aecting this pampean plain river. AcknowledgementsÐI am grateful to anonymous referees for their valuable comments on the manuscript and for linguistic improvement in the text. Financial support for this study has been provided by the INCHYT-CETUAAILPLA agreement.
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