Temporal and bathymetric distribution of benthic macroinvertebrates in the Ponte Nova Reservoir, Tietê River (São Paulo, Brazil). - PDF

Temporal and bathymetric distribution of benthic macroinvertebrates in the Ponte Nova Reservoir, Tietê River (São Paulo, Brazil). PAMPLIN 1, P.A.Z. & ROCHA 2, O. 1 Universidade Federal do Piauí, Campus

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Temporal and bathymetric distribution of benthic macroinvertebrates in the Ponte Nova Reservoir, Tietê River (São Paulo, Brazil). PAMPLIN 1, P.A.Z. & ROCHA 2, O. 1 Universidade Federal do Piauí, Campus Profa. Cinobelina Elvas, Rodovia BR-135 km 03, , Bom Jesus, PI, Brasil. 2 Universidade Federal de São Carlos, Departamento de Ecologia e Biologia Evolutiva, Rodovia Washington Luis km 235, , São Carlos, SP, Brasil. ABSTRACT: Temporal and bathymetric distribution of benthic macroinvertebrates in the Ponte Nova Reservoir, Tietê River (São Paulo, Brazil). The structure of macroinvertebrate benthic fauna in the Ponte Nova Reservoir, Tietê River, was investigated in January, April, July and November of Samplings of the benthic fauna and measurements of temperature, ph, electrical conductivity and dissolved oxygen concentration were carried out in 90 randomly selected sites of the reservoir. Ponte Nova is a warm-monomictic reservoir in which temperature ranges from 16.9ºC to 29.0 ºC and hypolimnion is anoxic ( 8 meters of depth) in January. Benthic community was composed of 36 taxa, and Chironomidae was the richest group, with 21 taxa. Chaoboridae (Chaoborus) was the dominant taxon, representing almost 70% of the total benthos, and the highest density of benthic fauna, 851 ind.m -2, was registered in July. Bathymetrically, the highest densities were usually observed in the deepest areas of the reservoir ( 8 meters) due to the greater abundance of Chaoborus. Chironomidae and Oligochaeta occurred at low densities and preferentially inhabited the shallowest areas. On the other hand, diversity indexes (Shannon-Wiener and Margalef) decreased with increased depth. Stepwise Multiple Regression analysis indicated that depth (b = -0.39, p for Chaoborus; b = , p for chironomids; b = , p for oligochaetes), temperature (b = , p = for Chaoborus; b= , p for oligochaetes), fine sediment fraction (b = 0.218, p = for oligochaetes), organic matter (b = , p for Chaoborus; b = , p for oligochaetes) and dissolved oxygen concentrations (b = 0.156, p for Chaoborus; b = , p = for chironomids) were the major predictors of benthos distribution. The Ponte Nova reservoir has a diversified community of benthic invertebrates, with high taxonomic richness and low population densities. Key-words: benthos, macroinvertebrate composition, depth distribution, Chironomidae, tropical reservoir. RESUMO: Distribuição temporal e batimétrica dos macroinvertebrados bentônicos na represa Ponte Nova, rio Tietê (São Paulo, Brasil). A estrutura da fauna de macroinvertebrados bentônicos na represa Ponte Nova, rio Tietê, foi investigada em janeiro, abril, julho e novembro de Amostragens da fauna bentônica e medidas da temperatura, do ph, da condutividade elétrica e da concentração de oxigênio dissolvido foram realizadas em 90 pontos amostrais distribuídos randomicamente na represa. A represa de Ponte Nova é um reservatório monomíctico, quente, com temperatura variando entre 16.9ºC e 29.0 ºC e hipolímnion anóxico ( 8 metros de profundidade) em janeiro. A comunidade bentônica foi composta por 36 taxa, sendo Chironomidae o grupo com maior riqueza, com 21 taxa. Chaoboridae (Chaoborus) foi o táxon dominante, representando cerca de 70% do bentos total, e a maior densidade da fauna bentônica, 851 ind.m -2, foi registrada em julho. Batimetricamente, as maiores densidades foram usualmente registradas nas áreas mais profundas da represa ( 8 metros) devido à maior abundância de Chaoborus. Chironomidae e Oligochaeta ocorreram em baixa densidade e habitaram preferencialmente as regiões mais rasas. Por outro lado, os valores dos índices de diversidade (Shannon-Wiener e de Margalef) diminuíram com o aumento da profundidade. A regressão múltipla Stepwise apontou como variáveis significativas, a profundidade (b = -0.39, p para Chaoborus; b = , p para quironomídeos; b = , p para oligoquetos); a temperatura (b = , p = para Chaoborus; b= , p para oligoquetos), fração fina do sedimento (b = 0.218, p = para oligoquetos), as concentrações de matéria orgânica (b = , p Acta Limnol. Bras., 19(4): , 0.001 para Chaoborus; b = , p para oligoquetos) e oxigênio dissolvido (b = 0.156, p para Chaoborus; b = , p = para quironomídeos) como os principais predictores na distribuição dos organismos bentônicos. A represa de Ponte Nova possui uma comunidade de invertebrados bentônicos diversificada; com alta riqueza de táxons e baixas densidades populacionais. Palavras-chave: Bentos, composição de macroinvertebrados, distribuição por profundidade, Chironomidae, represa tropical. Introduction The number of reservoirs has increased all over the world (Tundisi, 1993), and in Brazil this scenario is not different. Much limnological information about these ecosystems has been accumulated for decades and, although there is less information on the structure of benthic communities in Brazilian reservoirs (Pamplin et al., 2006), the number of studies on this community has increased (Santos, 1995; Soriano, 1997; Corbi & Trivinho-Strixino, 2002; Moretto et al., 2003, and others) in the last years. In most lentic freshwaters, the benthic community is mainly composed of chironomids larvae and oligochaetes, but other groups, less rich and abundant, can also be present. Those organisms are crucial to the aquatic ecosystems, since they play a role in the energy transfer and nutrient cycling (Covich, 1999). Many abiotic and biotic factors (e.g., substrate type, food availability, oxygen concentration, and predation) have been pointed out as significant to the abundance and distribution of these organisms (Bechara, 1996; Jónasson 1996). Many authors, such as Petridis & Sinis (1993, 1995), Giovanni et al. (1996), and Baudo et al. (2001), have demonstrated that depth is a key factor in the distribution of benthos in lentic ecosystems. Limnological studies (e g., Goldman & Horne, 1983, Wetzel, 1993, Esteves, 1998) have identified three different zones (littoral, sublittoral and profundal) in which benthic organisms can live and which are frequently defined by a gradient of physical and morphological features, such as habitat complexity, light penetration, macrophytes occurrence, among others. Comparatively, littoral zones are more diverse than the profundal ones; however, the latter have recently aroused the interest of many researchers (Esteves, 1998). The aim of the current study was to investigate the structure (composition and abundance) of the benthic fauna in the Ponte Nova Reservoir by analyzing the temporal and bathymetric distribution patterns as well as the factors contributing to these patterns. Material and Methods Study Area Ponte Nova Reservoir (23 o 33 S and 45 o 50 W) is located in the upper basin of the Tietê River, in the southern region of São Paulo state (Fig. 1). Its construction was completed in 1972 and was aimed at controlling water level and, sometimes, supplying the metropolitan area of São Paulo city with water. The reservoir covers an area of about 28 km 2 and has a mean volume of 296x10 6 m 3. Maximum and mean depths are 18.5 and 10.5 meters, respectively (Takino & Maier, 1981). Mean outflow is 9.9 m 3.s -1 and the residence time is around 346 days. Drainage area is 320 km 2 and the main tributaries are Tietê River and Claro River. Ponte Nova Reservoir is the unique reservoir before the metropolitan region of São Paulo city. Its surroundings are characterized by pasture and agricultural areas, and remnants of Atlantic forest. The climate in the region is classified as mesothermal, with rainy summers and dry winters (Cwb type in Köppen classification), and the average temperature of 17.5 o C. Peaks of precipitation are observed between December and March, ranging from mm to mm, and the mean annual rainfall is about mm (SIGRH, 2002). Sampling and laboratorial analyses Samplings were carried out in January, April, July and November of A total of 90 sites were established in the reservoir. At each sampling site, one sample was collected using a Van Veen grab (area: 378 cm 2 ), totalizing 360 samples during the study. Material was sieved through a 210 mm mesh net and fixed in 10% formalin. 440 PAMPLIN, P.A.Z. & ROCHA, O. Temporal and bathymetric distribution of benthic macroinvertebrate... At the laboratory, the organisms were hand-sorted, and then identified and counted. Identification (at genus or species level) of invertebrates was performed under optic microscope and stereomicroscope, using manuals and identification keys (Brinkhurst & Marchese, 1991; Trivinho- Strixino & Strixino, 1995; Epler, 2001). Chironomids larvae and oligochaetes were mounted in semi-permanent slides with Hoyer solution to evidence important morphological features. Density, relative abundance and occurrence frequency were estimated as structure parameters of macroinvertebrates community. Shannon-Wiener diversity and Margalef richness indexes were calculated according to Margurran (2003). Abiotic variables (ph, conductivity, dissolved oxygen and temperature) were measured in a site near the reservoir bottom by using a multiprobe HORIBA U-10 model. The profiles of these variables were determined between 8:00 to 9:00 a.m. in a central site, as indicated in Fig. 1. In April, dissolved oxygen concentration was not measured due to technical troubles with the multiprobe sensor apparatus. Organic matter (peroxide digestion method) in sediment and the granulometric composition (Suguio, 1973) were determined in samples obtained with a core sampler (area: 33.2 cm 2 ). Figure 1: Map of Ponte Nova Reservoir and sampling stations. The arrow indicate the station where profiles of ph, conductivity, temperature and dissolved oxygen concentration were measured. Acta Limnol. Bras., 19(4): , Data analysis One-way ANOVA test was used to determine differences between the seasonal samplings for the macroinvertebrates and environmental data. A Stepwise Multiple Regression (forward method) was performed in order to identify the main variables controlling benthic distribution. Detrended Correspondence Analysis ordination (DCA) was used to evidence the importance of depth on benthos distribution. Taxa with relative abundance superior to 1% were considered in this last method. To minimize discrepancy values, only macroinvertebrate data were previously Ln(x+1) transformation.. All statistical analyses were performed using Statistica (StatSoft 2001) and Instat (GraphPad Instat 2000). Results Environmental variables Tab. I summarizes the range, mean and standard deviations of some limnological variables of sediment of the Ponte Nova Reservoir. Only temperature, dissolved oxygen, ph and conductivity were significantly different (p ) among the sampling periods. The ph near the bottom ranged from 5.07 to 7.83, and the conductivity varied between 22 ms.cm -1 and 50 ms.cm -1, with major values registered in November. As regards the oxygen concentrations, the smallest mean value was recorded in January, due to the anoxia in some parts of the reservoir. In the last two samplings, this condition was not documented and the mean oxygen concentration was around 11.0 mg.l -1. Sediment of the Ponte Nova Reservoir was enough heterogeneous in relation to granulometric composition, with high values of sand (up to 97.52%) in some areas, and of clay (up to 85.08%) in others (Tab. I). Percentage of organic matter in the sediment ranged from 0.43% to 28.85% in the whole period (ANOVA F = 0.577; p = 0.630). Table I: Maximum, minimum and mean± S.D. (standard deviation) values of limnological variables measured at the surface of Ponte Nova Reservoir in 2001 and results of ANOVA. ANOVA Variables January April July November F p ph ( ) ( ) ( ) ( ) Conductivity (ms.cm -1 ) ( ) ( ) ( ) ( ) Dissolved oxygen (mg.l -1 ) ( ) ( ) ( ) Temperature ( o C) ( ) ( ) ( ) ( ) Organic Matter (%) ( ) ( ) ( ) ( ) Sand (%) ( ) ( ) ( ) ( ) Clay (%) ( ) ( ) ( ) ( ) Silt (%) ( ) ( ) ( ) ( ) PAMPLIN, P.A.Z. & ROCHA, O. Temporal and bathymetric distribution of benthic macroinvertebrate... Thermal structure in the Ponte Nova Reservoir was well established with an evident stratification in January, when temperature decreased progressively, around 5.5 o C, from 7.5 meters to near the bottom; while in the others periods, a nearly complete isotherm was present (Fig. 2). As regards the dissolved oxygen, water column was well oxygenated with concentrations around 8.44 mg.l -1 ; except in January, when an anoxic hypolimnetic layer was defined in depths over 10.5 meters. Values of ph were more discrepant in January and April, when they ranged roughly 1.60, while in other two samplings, the difference was not more than In January, ph showed patterns similar to temperature and dissolved oxygen, with values varying between 6.62 and 7.04 above 9.5 meters and from 5.55 to 5.82 in depths lower than 11.5 meters (Fig. 2). For electrical conductivity, concentrations in the water column were the same in July and November, while in January and April an increase near to the bottom was observed. Figure 2: Vertical variation of temperature, dissolved oxygen, ph and conductivity in Ponte Nov Reservoir. Gray areas indicate the bottom of the reservoir. Acta Limnol. Bras., 19(4): , Composition and distribution of benthos A total of 8,934 specimens belonging to 36 taxa were collected in the Ponte Nova Reservoir (Tab. II). Chironomidae was the richest group, with 21 taxa, followed by Oligochaeta, with 10 species. Odonata, Trichoptera, Chaoboridae and Ceratopogonidae (both families of Diptera) were also present, each one represented by a taxon. In the reservoir, most taxa were rare, with relative abundance lesser than 1% and occurrence in up to 2.0% of the total samples collected. On the other hand, Chaoborus (Lichtenstein, 1800) was the most important taxon, comprising 59.1% of all organisms collected and being present in 69.1% of the samples collected. Chironomidae and Oligochaeta comprised approximately 32.7% and 7.7% of the total abundance, respectively. Among the chironomids, Polypedilum (Kieffer, 1912) was prevalent, with 7.9% of abundance and occurring in 37.3% of the total samples, followed by Caladomyia (Kieffer, 1921), with 5.2% and 34.0%, respectively. About oligochaetes, Branchiura sowerbyi (Beddard, 1892) was the dominant species, both in the relative abundance (4.1%) and in the frequency of occurrence (40.4%). Mean densities of the four periods were significantly different (ANOVA: F = 3.213; p = ), mainly due to Chaoboridae and Chironomidae densities (ANOVA: F = ; p for Chaoboridae and F = ; p for Chironomidae). The highest mean density was registered in July, 851 Table II: Taxonomic composition and relative abundance of benthic collected in Ponte Nova Reservoir in Taxons Number of organisms January April July November Occurrence Relative (%) out of Abundance 360 (%) samples OLIGOCHAETA Alluroididae Brinkhurstia americanus (Brinkhurst, 1964) Naididae Allonais lairdi (Naidu, 1965) Dero (Dero) multibranchiata (Steiren, 1892) Pristina americana (Cernosvitov, 1937) Slavinia evelinae (Marcus, 1942) Opistocystidae Opistocysta funiculus (Cordeiro, 1948) Tubificidae Bothrioneurum americanum (Stolc,1886) Branchiura sowerbyi (Beddard, 1892) Limnodrilus hoffmeisteri (Claperede, 1892) Limnodrilus udekemianus (Claperede, 1892) HIRUDINEA Glossiphonidae PAMPLIN, P.A.Z. & ROCHA, O. Temporal and bathymetric distribution of benthic macroinvertebrate... Table II: Cont. Taxons DIPTERA (Chironomidae) Tanypodinae Number of organisms January April July November Relative Abundan ce (%) Occurrence (%) out of 360 samples Ablabesmyia (Johannsen, 1905) Coelotanypus (Kieffer, 1913) Djalmabatista (Fittkau, 1968) Labrundinia (Fittkau, 1962) Procladius (Skuse, 1889) Chironominae Axarus (Roback, 1980) Caladomyia Chironomus (Meigen, 1803) Cladopelma (Kieffer, 1921) Cryptochironomus (Kieffer, 1918) Dicrotendipes (Kieffer, 1913) Fissimentum dessicatum (Cranston & Nolte, 1996) Fissimentum sp2 (Roback, 1966) Goeldichironomus (Fittkau, 1965) Harnischia (Kieffer, 1921) Nilothauma (Kieffer, 1921) Polypedilum (Kieffer, 1912) Polypedilum (Asheum) (Sublette & Sublette, 1983) Saetheria (Jackson, 1977) Zavreliella (v. d. Wulp, 1874) Caladomyia (Kieffer, 1921) Tanytarsus (Kieffer, 1920) OTHERS DIPTERANS Chaoborus (Lichtenstein, 1800) Bezzia (Kieffer, 1899) ODONATA Phyllocycla (Calvert,1948) TRICHOPTERA Cyrnellus (Banks,1913) Total Richness (S) ind.m -2 ; while in the other samplings, densities were very similar, ranging from 562 ind.m -2 to 601 ind.m -2 (Fig. 3). Chaoboridae was the main component of benthic community in first two samplings, with about 77% of the total in each period; while the relative abundance of Chironomidae was around 16%. In the samplings conducted in July and November, a decrease in the relative abundance of Chaoboridae (around 45%) and a correspondent increase in the relative abundance of Chironomidae (up to 50%) were observed. In the Ponte Nova Reservoir, oligochaetes had low relative abundance, ranging from 5% in April to 12% in November. Acta Limnol. Bras., 19(4): , Other invertebrates accounted up to 0.7% of total benthos in July and November (Fig. 3). Fig. 4 shows the mean values of Shannon-Wiener and Margalef indexes in the Ponte Nova Reservoir. ANOVA test pointed out a significant difference between the periods (F = ; p and F = 8.651; p for Shannon-Wiener and Margalef indexes, respectively). In the first two samplings, lower values were registered for both indexes (around 0.68 for Shannon- Wiener and 0.88 for Margalef index); while in July and November, the values were 1.05 and 1.31, respectively. Figure 3: Mean density of total benthos and relative abundance of the main invertebrate groups in Ponte Nova Reservoir in Vertical bars in the density refer to the confidence interval (a = 0.05). Figure 4: Values of Shannon-Wiever and Margalef diversity indexes for the samplings periods at Ponte Nova Reservoir in PAMPLIN, P.A.Z. & ROCHA, O. Temporal and bathymetric distribution of benthic macroinvertebrate... Considering the depth distribution in the Ponte Nova Reservoir, densities were usually higher in the deepest areas (Fig. 5). I n J a n u a r y, d e n s i t i e s a r o u n d i n d. m-2 were found up to 6 meters, followed by a progressive increase until 14 meters, where a d e n s i t y o f i n d. m -2 w a s r e g i s t e r e d ( i n d. m-2, 95% confidence intervals), and up to that depth mean density d e c l i n e d a r o u n d i n d. m -2. D e n s i t i e s i n A p r i l v a r i e d b e t w e e n i n d. m -2 ( ind.m -2, 95% confidence intervals) and 441 i n d. m-2 ( i n d. m -2, 9 5 % c o n f i d e n c e intervals) until 8 meters of depth, and in the superior depth density improved to 1084 ind.m -2 (mean density: 910 ind.m -2 ). In July, peaks of high densities were observed in depth above 4 meters with mean density e q u a l i n d. m -2. D u r i n g N o v e m b e r, t h e highest densities occurred between 8 and 12 meters depth, with mean density of 1297 ind.m -2. Inversely, both Shannon-Wiener and Margalef diversity indexes decreased in the highest depth (especially after 6 meters), as shown in Fig. 6. F i g u r e 5 : D e p t h v a r i a t i o n o f t o t a l d e n s i t y o f b e n t h o s i n P o n t e N o v a R e s e r v o i r i n Ve r t i c a l b a r s i n density refer to the confidence interval (a = 0.05). Figure 6: Depth variation of Shannon-Wiever and Margalef diversity indexes s in Ponte Nova Reservoir in Vertical bars in density refer to the confidence interval (a = 0.05). Acta Limnol. Bras., 19(4): , High densities in deeper areas (over 8 meters) were due to the presence of Chaoboridae, which preferentially inhabited these areas with relative abundance usually above 70% (Fig. 7). In April, Chaoboridae and Chironomidae had similar abundance ranging between 39% and 49% until 4 met
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