Seasonal behavior of the upper Rio das Velhas benthic macroinvertebrate communities (Minas Gerais, Brazil) Junqueira, M.V.* & Natividade, J. F. I. L. Fundação Centro Tecnológico de Minas Gerais-CETEC/Setor de Recursos da Água Belo Horizonte-MG CEP 31170-000. *[email protected] Abstract Seasonal behavior of the upper Rio das Velhas benthic macroinvertebrate communities (Minas Gerais, Brazil) This study aims at evaluating the behavior of the zoobenthic communities as regards its diversity and abundance in relation to seasonal variation, which allows for the identification of the period of the year when those communities are more representative at the Rio das Velhas basin. The freshwater macroinvertebrate communities found in both the epifauna and in the infauna had been sampled along the edge of the watercourses and in river beds through the "kicking" method (Macan 1958), with the aid of a 0,3mm mesh net fish trap, ISO 7828 (1985), during three minutes. The samples were kept in formol at 10%, and later sifted with a 0.3 mm-mesh sieve. The material was then selected under a stereomicroscope, and the organisms stored in alcohol at 80%, for further quali-quantitative classification. The structure and composition of the zoobenthonic communities present clear differences in relation to the rainy and dry seasons, as shown in the results of the qualitativequantitative taxonomic analysis. The January campaign registered an average taxa of 4.8 of macroinvertebrates, while April showed 5,4 and July reached 9.3. In October the average was 11.2. These results confirm previous biomonitoring studies developed by CETEC at the Rio das Velhas basin (Junqueira & Campos 1998). Our conclusion is that the variety and amount of zoobenthonic community organisms are drastically reduced during the rainy season. This is due to the effects of the rainy season over the aquatic biota, mainly related to increased outflows and the carriage of sediments to the rivers Resumo Comportamento sazonal da comunidade de macroinvertebrados bentônicos na bacia do alto rio das Velhas (Minas Gerais, Brasil). O estudo proposto visou avaliar o comportamento da comunidade zoobentônica com relação à variação sazonal no que diz respeito a sua diversidade e abundância permitindo identificar e confirmar o período do ano em que a comunidade zoobentônica se torna mais representativa na Bacia do Ato Rio das Velhas. As comunidades de macroinvertebrados aquáticos presentes tanto na epifauna como na infauna bentônica foram amostradas às margens do curso d’água ou no leito do rio, segundo o método de “kicking” (Macan, 1958), com o auxílio de puçá com tela de 0,3mm de poro, ISO 7828 (1985), durante um período de três minutos de coleta. As amostras foram fixadas em formol a 10% e posteriormente triadas com peneira de 0,3 mm de malha. Em seguida procedeu-se a seleção do material através do estereomicroscópio, acondicionando os organismos em álcool a 80%, para posterior classificação quali-quantitativa. Os períodos de chuva e estiagem apresentam diferença na estrutura e composição das comunidades zoobentônicas, mostrada no resultado da análise taxonômica qualiquantitativa. A campanha de janeiro apresentou uma média de 4,8 taxa de macroinvertebrados e a de abril uma média de 5,4 de taxa. Já na coleta de julho obteve-se uma média de 9,3 de diferentes taxa e em outubro esse número subiu para 11,2 taxa coletadas por estação. Tais resultados vêm confirmar os obtidos em trabalhos de biomonitoramento executados anteriormente pelo CETEC no alto Rio das Velhas (Junqueira & Campos 1998). Através do trabalho conclui-se que as comunidades zoobentônicas sofrem acentuada queda tanto na sua variedade quanto na quantidade de organismos nos meses de chuva. Isto decorre de diversos distúrbios provocados pelo período chuvoso sobre a biota aquática, relacionados principalmente ao aumento acentuado das vazões e ao carreamento de sedimentos para os rios. INTRODUCTION The upper Rio das Velhas basin has been used by the Minas Gerais Technology Center Foundation CETEC since 1985 as a pilot basin for studies about the development of lotic ecosystem water quality bioindicator methodologies (Junqueira et al. 2000). These studies were aimed at supporting watershed control and supervision in the state of Minas Gerais. However, despite the increased knowledge resulting from use of bioindicators in this basin , for routine biomonitoring it was necessary to investigate a few other aspects of the seasonal behavior of the aquatic benthonic fauna so as to determine the best time of the year to collect biologic samples. Therefore, this work is aimed at determining the veracity of the assumption that the dry season is the most adequate to be used as reference for the biomonitoring of the water quality of rivers as it is during this season that the zoobenthic communities are expanded. To accomplish this task, we investigated the behavior of the zoobenthic communities of the Upper Rio das Velhas with a focus on their seasonal abundance and varieties during the year of 2003. The seasonal changes of the biological communities are well known. (UNESCO/WO/UNEP 1992) and, according to Friedrich, com.pess. and “Standard Methods for German Rivers” - DIN (1990), many studies have been developed on how to find the best period of the year for zoobenthic collection aimed at biomonitoring German rivers. Those studies will also set up the adequate frequency of the collection for future biomonitoring. It is also worth noting that even in the wealthiest European countries the evaluation of the river water quality takes as reference the biomonitoring data obtained from samples collected during the periods when the macroinvertebrate community is more representative thus being valid for the whole year. The data obtained is used in the elaboration of the annual classification of water (LAWA 1982). This approach allows for cost reduction and the optimization of collection and analysis efforts, without affecting the quality of results but entirely meeting the objectives of water quality monitoring. STUDY AREA The area studied covers the entire upper Rio das Velhas basin, from the neighborhood of its source on the Antônio Pereira mountain range, in the city of Ouro Preto, district of São Bartolomeu, to the neighborhoods of its confluence with the Ribeirão da Prata, in the city of Raposos. The area surveyed covers over 70 km. This region presents a very typical landscape and the sampling site upstream was located at an altitude of 980m, while at downstream it was located at an altitude of 693m. The weather in the region is generally between 18oC and 20oC (annual isothermal lines), the coldest in the state. The southern area, near the city of Ouro Preto, is an isolated nucleus of high rainfall rates, with very high levels of humidity – around 1800-2000mm annually. The exact location of the sampling network stations for the biomonitoring in the upper Rio das Velhas basin can be seen in the map. MAP MATERIALS and METHODS The sampling method used for this study is in line with the one biomonitored by CETEC for the Minas Gerais Water Management (IGAM Instituto Mineiro de Gestão das Águas 2005) in the upper Rio das Velhas basin. Sample gathering was carried out seasonally during the months of January, April, July and October, thus covering the four seasons of the year. The network comprised 14 sampling sites, considered of major relevance in terms of anthropogenic effects for the evaluation of water quality at the upper Rio das Velhas basin. All the areas selected for the zoobenthonic community sampling were similar in terms of habitat, all of them presenting a stony substratum and riffles. These selection criteria were aimed at providing maximum homogeneity for the physical features of the habitat so that the results could be properly compared. The list of sites included in this network, with its respective geographic location is presented in Table I. TABLE I - Biological sampling network sites of the upper Rio das Velhas basin. Coordinates (UTM) Station code Latitude Longitude Height (m) AV005 7753142.67 648719.04 980 Rio das Velhas upstream from São Bartolomeu AV010 7754204.58 644614.55 984 Rio das Velhas upstream from the Rio de Pedras dam AV040 7765067 630940.76 760 Rio das Velhas downstream from the Rio de Pedras dam AV050 7748112.68 614977.6 996 Ribeirão do Silva upstream from Ferteco company AV110 7765743.26 624742.94 800 RCBC* 7786976.05 607910.01 734 Rio Itabirito downstream from the city of Itabirito and Ribeirão do Onça Córrego Capão do Boi at COPASA water station AV200 7774310.99 618189.41 785 Rio do Peixe downstream from Peixes village and from Usina. AV210 7778301.43 626553.05 716 Rio das Velhas downstream from Córrego Mingú, at the seat of Rio Acima. AV240 7780859.01 608506.02 1140 Córrego Seco at COPASA Fechos Reservation AV250 7785099.59 622644.47 746 Ribeirão dos Macacos near the confluence with Rio das Velhas AV300 7790627.92 619026.56 736 Córrego do Cardoso at the city of Nova Lima. AV320 7790385.76 623367.51 726 Córrego da Mina Dágua downstream from Morro Velho reservoir AV330 7789868.96 623714 729 AV345 43047'46''S 19058'25''W 740 AV340 779917.73 625949.6 709 Rio das Velhas downstream from Rio Água Suja and Córrego da Mina Dágua Ribeirão da Prata upstream from the city of Raposos. Ribeirão da Prata at Barracão Amarelo district near the mouth of the river Description AV350 7798558.27 623747.64 693 Rio das Velhas downstream the city of Raposos. * CETEC code Sample collection and analysis The sample collection at the benthic macroinvertebrates communities was performed along the banks of the water courses and/or in the central channel of the river bed, wherever depth made it possible. The “kicking” technique (Macan 1958) was used to sample the macroinvertebrates communities found in the epifauna and in the benthonic infauna. The collection was made with the help of a 0.3mm mesh net during three minutes, as established by the International Standard ISO 7828 (1985), and later fixed in a formaldehyde solution, 10%. Specimen collected manually were fixed in alcohol, 80%. A set of sieves with various mesh sizes was used to wash and screen the material collected, separating the organisms contained in the samples. The material was then sorted by stereomicroscopy and kept in 10 and 20 ml bottles filled with alcohol 70º, for further qualitative and semi-quantitative analysis. This analysis involved the taxonomic identification of the organisms with the help of dichotomic keys (Domingues, et al. 1992; Merrit & Cummins 1996; Heckman 2000a;2000b), comparisons of illustrative plates and the usual optical microscopy techniques. Blade assemblage techniques were also used to allow for better visualization of the anatomical structure of some of the taxonomic groups thus facilitating their identification through microscopy. Concurrently with the biological sampling, water samples were collected for analysis of various physical and chemical parameters. For evaluation, only those parameters with the most meaningful seasonal variations were used, that is, residues in suspension and turbid. The water sample collection were made on the surface of the water, in compliance with the “Standard Methods for Examination of Water and Waste-Water” (APHA 1995). RESULTS AND DISCUSSION Table II shows the results obtained from the taxonomic analysis of the zoobenthonic communities collected during the campaigns carried out in the months of January through April (rainy season), and July through October (dry season) in the biomonitoring sampling network stations of upper Rio das Velhas basin. TABLE II - Composition and total abundance of organisms found in the zoobenthonic communities of the sampling network of the upper Rio das Velhas basin between January and October 2003. (arquivo separado) Due to of the impossibility to reach the borders of some collection stations as a result of floods which occurred in the rainy season, to the collection was made in six stations only during the first campaign, in January. All the fourteen pre-selected stations were available for collection in April, and for the third campaign, in July, two experimental stations were added to the network making a total of sixteen stations. The experimental stations were Córrego Capão do Boi and the Ribeirão do Prata, upstream Raposos). The results obtained indicated a clear difference between the structure and the composition of the samples collected in the zoobenthonics communities at the peak and end of the rainy season (January through April), and during the dry season (July through October). The pluviometric data provided by the CEMIG meteorological station located in the upper Rio das Velhas basin, in the city of Rio das Pedras, in the proximity of the study areas, shows values ranging between 443mm in January, 18mm in April, 1 mm in July and 84mm in October. Fig. I shows this data, which was obtained during the periods of zoobenthonic sample collection in the basin. The average taxa of macroinvertebrates per station reached 4.8 in January, 5.4 in April, 9.3 in July and 11.2 in October. The first campaign showed 21 distinct taxa against 19 in the second collection and 30 different taxa in the third collection. Finally the fourth collection showed a total of 32 taxa of benthonic macroinvertebrates, therefore a growth in the variety of organisms by the end of the rainy season and throughout the dry season, a figure inversely proportional to that obtained at the peak of the wet season. Similar results had been obtained before in the works developed by Junqueira & Campos (1990), in the Rio Grande and Rio Paranaíba basins (Junqueira et al. 1992). The above mentioned taxa were treated as family levels, the class Oligochaeta, Collembola and Hidracarina being considered as one single family. The abundance of macroinvertebrate organisms was obtained per station, and indicated average values of 21 organisms in the first campaign, 62 individuals in the second campaign, and between 344 and 359 individuals in the third and last sampling campaign, demonstrating that the abundance of organisms was raised in the dry season. These qualitative and quantitative findings can be better seen in Figs. I and III. The structure and composition of the benthonic communities observed in the dry season confirm the findings of previous biomonitoring works developed by CETEC at the upper Rio das Velha (Junqueira 2000 op. cit.). Studies by Paprocki (1997) performed in open streams of the Cipó mountain range, which have substratum characteristics similar to those of the upper Rio das Velhas basin stations also showed that the most variety and density of the zoobenthonic fauna is found in the dry season. (June). Besides the effect of the carriage of organisms, this may be associated to the modifications of various abiotic and biotic factors resulting from disturbance caused mainly by the increase of sediments in the water on the aquatic biotics resulting from floods. According to the "Water Resource Management Manual" (FATMA 1999), these flood have a negative impact on the aquatic life as they prevent proper breath and absorption of light. This disturbance is primarily related to the accentuated increase of the outflows of the rivers, caused by the lack of vegetation in their catchment areas, as is the case of the basin herein described. The floods do not allow for proper zoobenthonic collection in some stations and leave many zoobenthonic organisms adrift (Bohle 1995). Another negative factor for aquatic organisms is the great carriage of sediments through flash floods during this period of the year. The lixiviation of sediments carried to the rivers in the wet season may increase the amount of solids dissolved in the water and consequently increase its turbidity. The findings obtained for turbidity and solids in suspension in the water analyzed in the studied stations reached average values of 250,66 NTU and 190,3 mg/l respectively between January and April, as compared to 6,62 NTU and 11.21 mg/l registered between July and October. High levels of solid contents dissolved in the water may result in the decrease of the oxygen dissolved in the water, thus affecting the photosynthetic organisms which are dependent on the transparency of the water, and having an indirect impact on the whole aquatic community (UNESCO/WHO/UNEP op. cit.). Additionally, as Wantzen (1997) states, the solids dissolved in the water may have a negative abrasive affect on aquatic macroinvertebrate organisms. High concentrations of solids endanger the organisms which filter the water to feed, predators depending on water visibility to catch their prey and the most sensitive organisms depending on branquial breathing (Bohle op. cit.) mm FIG. I - Monthly pluviometric data obtained in the CEMIG meteorological station of Rio das Pedras, in the upper Rio das Velhas basin, 2003. 500 450 400 350 300 250 200 150 100 50 0 433 84 1 18 January April July October Concerning the composition of the benthonic fauna, the following taxa: Ceratopogonidae, Dytiscidae, Psephenidae, Veliidae, Gomphidae, Glosossomatidae, Hydroptilidae, Hydrobiosidae, Polycentropodidae, Leptoceridae, Physidae, Hidracarina and Nematoda occurred only in the samples collected between July and October, the dry season. Coenagrionidae, Hydropsychidae, Pyralidae, Collembola and Glossiphoniidae were only observed in the collection which started in April, by the end of the rainy season and in the beginning of the dry season. FIG. II - Composition of the number of taxa found in benthonic macroinvertebrates during the sampling campaigns carried out between January and October, 2003 in the upper Rio das Velhas basin. 12 11,2 taxa number 10 9,3 8 6 5,7 5,4 4,8 4,2 4,6 número de taxa desvio padrão 4 2 1,3 ct ob er O Ju ly pr il A Ja nu ar y 0 FIG. III - Average of the absolute abundance of benthonic macroinvertebrates per station found between the months of January and October, 2003 in the upper Rio das Velhas basin. number of organisms 400 344 359 300 200 100 0 62 21 january April July October CONCLUSION Although the data sampling presented in this work is representative of only one interval of one hydrologic year 2003, it made it possible to detect and evidence that the benthonic communities presented an accentuated decrease in variety and quantity of organisms in the first two collections carried out during wet season. The data provided evidences that the partial absence of rain, typical of the dry season, provides the stability of the climatic conditions necessary to favor the settling of the zoobenthonic community colonies and the growth of its populations, which enriches the fauna and makes it more abundant. This data attests the validity of previous data obtained in the historical series of CETEC projects developed in the upper Rio das Velhas basin (CETEC 1994; 1998). Under these conditions the samplings become more representative and more adequate for the bioindication of water quality for biomonitoring, as a bigger number of zoobenthonic representatives serve as bioindicators of the water quality. Besides, the fact that dissolved substances were found to be more concentrated in the water during the dry season strengthens the advantages of using the samples collected during that period as reference for biomonitoring, for that season is the most adequate to reflect the most critical conditions of the physical and chemical characteristics of the water and the most stable conditions of the coriótopos of lotic ecosystems. We can conclude that in the upper Rio das Velhas basin the best periods to obtain samples of the benthonic fauna are probably between May and October. Such results, which indicate the dry season as the most adequate for collecting benthonic macroinvertebrates of lotic environments, are in agreement with studies previously made in other hydrographic basins of the State, like the one developed by Campos et al. (2002) in the Córrego Rico basin, and comply with the norms of the "Water Resource Management Manual" (op. cit.) These studies also confirm that the periods of collection adopted by CETEC during the development of their water quality biomonitoring methodology were correct and will support the collection plan of future biomonitoring to be made by the CETEC/SEMAD/IGAM in the upper Rio das Velhas basin. However the best period for sample collection in the dry season can be identified by performing a survey of a longer series of historical data about the seasonal behavior of the benthonic communities of this area in shorter intervals. As 2003 was a typical hydrologic year, the findings presented in this work can be considered very representative. BIBLIOGRAPHY AMERICAN PUBLIC HEALTH ASSOCIATION. Standard methods for the determination of water and wastewater. 19.ed.Washington: AWWA/WPCH,1995. BOHLE, H. W. Spezielle Ökologie: liminsche Systeme. Berlin: Springer-Verlag, 1995. 267p. CAMPOS, M. C. S. Macroinvertebrados como bioindicadores de qualidade das águas da bacia do córrego Rico, Paracatu/MG. 4o Encontro Nacional de Biólogos, 2o Encontro de Biólogos da CRBio4 e 1o Encontro de Biologia de Ouro Preto, 2002, Ouro Preto. Biologia: Desafios do Novo Miênio . 96 p. CETEC FUNDAÇÃO CENTRO TECNOLÓGICO DE MINAS GERAIS. Desenvolvimento de métodos e técnicas de bioindicadores de qualidade de água na Bacia do Alto Rio das velhas. Belo Horizonte: Setor de Recursos da Água; FAPEMIG, 1994. 70p. Relatório técnico final. (coord. por Junqueira, M. V.) CETEC FUNDAÇÃO CENTRO TECNOLÓGICO DE MINAS GERAIS. Biomonitoramento da qualidade da água da Bacia do Alto Rio das Velhas. Belo Horizonte: Setor de Recursos da Água; FEAM, 1998. 110p. Relatório técnico final (coord. por Junqueira, M. V.) DIN - DEUTSCHES INSTITUT FÜR NORMUNG 38 410 t1. Deutsche Einheitsverfahren zur Wasser,- Abwasser- und Schlamm-Untersuchung:biologisch-okölogische Gewässerruntersuchnung; (Gruppe M) Allgemeine Hinweise, Planung und Durchführung von Fliessgewässerruntersuchungen (M1). Berlin und Köln. Beuth Verlag, 13 p DOMINGUES, E. , HUBBARD, M. D. , PETERS, W. L. Clave para las ninfas y adultos De las familias y gêneros de Ephemeroptera (Insecta) sudamericanos. Biol Acuatica no 16. La Plata: Instituto de Limnologia. “Dr.Raula Ringuelet, 1992. p. 1-39. FATMA FUNDAÇÃO DO MEIO AMBIENTE DE SANTA CATARINA. Relevância de parâmetros de qualidade das águas aplicados à águas correntes. Parte I: Características gerais, nutrientes elementos traço e substâncias nocivas inorgânicas, características biológicas, Florianópolis: GTZ. 1999. 108p. HECKMAN, C. W. Encyclopedia of South American Aquatic Insects: Ephemeroptera – Ilustrated keys to known famlies, grnrra, and species in South América. London. Kluwer Academic Publishers. 2002a. 419 p. HECKMAN, C. W. Encyclopedia of South American Aquatic Insects: Plecoptera – Ilustrated keys to known famlies, grnrra, and species in South América. London. Kluwer Academic Publishers. 2002b. 419 p. IGAM INSTITUTO MINEIRO DE GESTÃO DAS ÁGUAS. Aperfeiçoamento do monitoramento da qualidade das águas da Bacia do Alto Curso do Rio das Velhas. Belo Horizonte; PNMA II, 2005. 175 p. Relatório 2: Avaliação dos resultados em 2003. JUNQUEIRA, M. V.; AMARANTE, M.; DIAS, C. F.; FRANÇA, E. S. Biomonitoramento da qualidade das águas da bacia do alto Rio das Velhas(MG/Brasil) através de macroinvertebrados bentônicos. Acta Limnológica Brasiliensia. Vol.12. 2000. p. 73-87. JUNQUEIRA, M. V. & CAMPOS, M.S. Adaptation of the “BMWP” method for water quality evaluation to Rio das Velhas watershed (Minas Gerais,Brazil). Acta Limnológica Brasiliensia. Vol.10. n.2. 1998. p.125-135. JUNQUEIRA, M. V. & CAMPOS, M.S.- "Estudo da Macrofauna Bentônica do Rio Grande e Tributários na Ârea de Influência da Futura UHE de Igarapava". In: RESUMOS do VIII Encontro da Associação Mineira de Aqüicultura - Belo Horizonte, MG - 1990. JUNQUEIRA, M. V. et.al.- "Caracterização Limnológica da Área de Influência do Futuro Reservatório Hidrelétrico de Bocaina, MG/GO". In: RESUMOS do II Congresso Latino Americano de Ecologia e do I Congresso da Ecologia do Brasil. Caxambú, MG. 1992. ISO INTERNATIONAL ORGANIZATION FOR STANDARDIZATION – 7828. Water quality; methods of biological sampling, guidance on handnet sampling of aquatic benthic macroinvertebrates. Switzerland, 1985. 6p. LAWA. Landsamt für Wasser und Abfall Nordrheim Westfalen. Richtilinie die Ermittlung der Gewässergüte klasse. Dusseldorf, 1982. (Herrausgeber) 12 p. MACAN, T.T. Methods for sampling of botton fauna of stony streams. Mitt Internat Verein.Limnol., v.8: 121. 1958 MERRIT, R. W. CUMMINS, K. W. An introduction to the aquatic insects of North America. Dubuque: Dendall/Hunt Publ. Co, 1996. 706p. 217.p. PAPROCKI, H. Aspectos da Ecologia de Comunidades de Insetos Aquáticos em Dois Riachos de 1a Ordem na Serra do Cipó, Minas Gerais. Dissertação de Mestrado-FFCLRP. Ribeirão Preto/SP. 1997. UNESCO – WHO; UNEP. Water quality assessments: a guide to the use of biota, sediments and water in environmental monitoring. London: Chapman, & Hall, 1992. 585 p. WANTZEN, K. M . Effects of suspended sediments on aquatic organisms in streams in the Upper Rio Paraguay Basin. Lieberei, R., Voss, K., and Bianchi, H. Proceedings of the 3o SHIFT-Workshop in Manaus 1998. Pp. 519-528. 1999. Hamburg, BMBF. ACKNOWLEDGEMENTS The financial support that made this work possible was provided by the Minas Gerais Research Support Foundation (FAPEMIG), the Minas Gerais Water Management Institute (IGAM) and the Minas Gerais Technology Center Foundation (CETEC). Thanks are also due to Rosa Maria Neves da Silva for proofreading and editing the English text.