Monjolinho River Research Articles

Occurrence and Environmental Risk Assessment of Contaminants of Emerging Concern in Brazilian Surface Waters.

We investigated the occurrence and the environmental risk of eight contaminants of emerging concern (CECs; acetaminophen, naproxen, diclofenac, methylparaben, 17β-estradiol, sulfathiazole, sulfadimethoxine, and sulfamethazine) in three Brazilian water bodies, namely, the Monjolinho River Basin (São Paulo State), the Mogi Guaçu River (São Paulo State), and the Itapecuru River (Maranhão State) in three sampling campaigns. The CECs were only quantified in surface water samples collected at the Monjolinho River Basin. Acetaminophen, naproxen, and methylparaben were detected in the range of <200 to 575.9 ng L-1, <200 to 224.7 ng L-1, and <200 to 303.6 ng L-1, respectively. The detection frequencies of the three measured compounds were between 33% and 67%. The highest concentrations of CECs were associated with intense urbanization and untreated sewage discharge. Furthermore, CEC concentrations were significantly correlated with total organic carbon, electrical conductivity, and dissolved oxygen levels, suggesting that domestic pollution from urban areas is an important source in the distribution of CECs in the Monjolinho River Basin. The environmental risk assessment indicated a high risk for acetaminophen (risk quotient [RQ] values between 2.1 and 5.8), a medium risk for naproxen (RQs between 0.6 and 0.7), and a low risk for methylparaben (RQs < 0.1) to the freshwater biota of the Monjolinho River Basin. Our findings show potential threats of CECs in Brazilian water bodies, especially in vulnerable areas, and reinforce the need for improvements in environmental regulations to include monitoring and control of these compounds in aquatic systems. Environ Toxicol Chem 2024;43:2199-2210. © 2024 SETAC.

Comparative Study of Water Quality Across Different Seasons in the Gregório River Watershed, São Paulo, Brazil

The goal of this study was to monitor the water quality in the Gregório river, São Carlos, São Paulo during the dry and rainy seasons using traditional methods such as physical and chemical analysis of the water and biological indicators. Six sampling points were monitored, ranging from the nearest location to the source of the river to its confluence with the Monjolinho river. Physical and chemical parameters of water (water surface temperature, dissolved oxygen, pH, and conductivity) were measured using a multiparameter probe. The distance between the points was determined according to the access to the site: from P1 to P2 (1328 m), from P2 to P3 (1278 m), from P3 to P4 (201 m), from P4 to P5 (820 m), and finally from P5 to P6 (1814 m). The biotic index used in conjunction with the environmental variables was the Biological Monitoring Working Party (BMWP), a qualitative index that utilizes benthic macroinvertebrates to classify water quality. Ceratopogonidae, Chironomidae, Chironomus, Enchytraeidae, Hirudinea, and Naididae were recorded at sites P1, P2, and P6 during both the dry and rainy seasons. This study, particularly at P6, it was observed that despite the higher concentration of dissolved oxygen compared to the other analyzed sites, which would indicate good water quality, the BMWP indicated that the location had a strongly polluted water quality, suggesting that environmental factors must be associated with biological indicators. It was concluded that the use of biological indicators along with environmental data provided a more reliable understanding of water quality.

Macroinvertebrates responses based on chemical and physical variables in urban streams

The Land uses and occupations around small watersheds generate negative impacts such as deterioration of water quality, environmental simplification, reduced availability of habitats for species, and loss of biodiversity. Benthic macroinvertebrates are an important aquatic community and are widely used in environmental monitoring actions in aquatic ecosystems, including urban streams, which are still little studied in Brazil. In our study, an urban headwater basin (Monjolinho River Basin) was studied on the benthic community structure, together with the physical and chemical variables of the water, as an environmental monitoring tool calculated by RHDEP, TSI, BMWP indexes and abundance-biomass curves. The results showed a gradient of environmental quality, where the best environments are a consequence of preserving the vegetation cover. These environments (Espraiado and Canchim) present groups sensitive to environmental degradation (Ephemeroptera, Plecoptera and Trichoptera), greater diversity and a better structure in the respective benthic macroinvertebrate assemblages. Among the streams sampled, one is very clean, four are moderately polluted, and one is severely polluted. Thus, considering that these streams’ waters are essential for public supply, actions to clean up and recover degraded environments are urgent and a priority.

Effects of Different Types of Zeolites on the Degradation Kinetics of Malathion Pesticide in Water

The study examined the effects of selected types of zeolites as an environmentally benign and friendly way to degrade, S-1, 2-bis (ethoxycarbonyl) ethyl O, O-dimethylphosphorodithioate (malathion), used as a model pesticide, from river water. The effect of the size of zeolite channels and dimensionality (such as 1D, 2D, and 3D), Si/Al ratio, and operating pH were studied to find a suitable type of zeolite and conditions to optimize the pesticide degradation. Mordenite (MOR (1D): Si/Al=6.83, and Si/Al=10.72), ferrierite (FER (2D): Si/Al=10.71), ZSM-5 (MFI (3D): Si/Al=6.83 and Si/Al=10.72) and USY (FAU (3D): Si/Al=2.77) zeolites were individually mixed with a water sample collected from Monjolinho River in São Carlos (SP), Brazil and the degradation trend studied. The results showed that all the zeolites accelerated the degradation of malathion. Nevertheless, lower zeolite Si/Al ratio and larger 3D channels or cavities had a positive influence on the degradation rate. The FAU zeolite presented the stronger degradation of the malathion with a half-life of 16.5 followed by ZSM-5 with 24.8, ferrierite with 29.7, and finally mordenite with 30.3 hours.

Isolation of Naegleria spp. from a Brazilian Water Source.

The genus Naegleria, of the free-living amoeba (FLA) group, has been investigated mainly due to its human health impact, resulting in deadly infections and their worldwide distribution on freshwater systems. Naegleria fowleri, colloquially known as the “brain-eating amoeba,” is the most studied Naegleria species because it causes primary amoebic meningoencephalitis (PAM) of high lethality. The assessment of FLA biodiversity is fundamental to evaluate the presence of pathogenic species and the possibility of human contamination. However, the knowledge of FLA distribution in Brazil is unknown, and to rectify this situation, we present research on identifying Naegleria spp. in the Monjolinho River as a model study. The river is a public Brazilian freshwater source that crosses the city of São Carlos, in São Paulo state, Brazil. Five distinct sampling sites were examined through limnological features, trophozoites culturing, and PCR against internal transcribed spacer (ITS) regions and 5.8S rRNA sequences. The results identified N. philippinensis, N. canariensisi, N. australiensis, N. gruberi, N. dobsoni sequences, as well as a Hartmannella sequence. The methodology delineated here represents the first Brazilian Naegleria spp. study on a freshwater system. Our results stress the urgency of a large scale evaluation of the presence of free-living amoebas in Brazil.

Chironomus sancticaroli (Diptera, Chironomidae) as a Sensitive Tropical Test Species in Laboratory Bioassays Evaluating Metals (Copper and Cadmium) and Field Testing.

Despite that chironomids are the most widely used benthic insect test species worldwide, little research has been conducted so far with tropical chironomid representatives. This study was designed to evaluate the indigenous midge Chironomus sancticaroli as a candidate test species for use in tropical toxicity assessments. To this end, laboratory water-only toxicity tests were conducted evaluating copper and cadmium. Obtained lethal concentration values were overall comparable or lower than those reported for other chironomids, including those most commonly used in temperate regions (C. riparius and C. dilutus). In addition, C. sancticaroli was deployed in situ in the Monjolinho River (São Paulo State, Brazil), and toxicity of sediment from this river was evaluated in the laboratory. Several field water and sediment quality parameters also were measured to enable correlating these with the effects observed in these toxicity tests. Field sediment toxicity to C. sancticaroli appeared to be related with sediment endosulfan concentrations, whereas effects noted in the in situ test were likely due to low pH values measured in river water. Chironomus sancticaroli appears to be a suitable candidate for inclusion as a test species in tropical toxicity evaluations in both the laboratory and the field.

Multivariate analyses of the effect of an urban wastewater treatment plant on spatial and temporal variation of water quality and nutrient distribution of a tropical mid-order river.

Freshwater resources are increasingly scarce due to human activities, and the understanding of water quality variations at different spatial and temporal scales is necessary for adequate management. Here, we analyze the hypotheses that (1) the presence of a wastewater treatment plant (WWTP) and (2) a polluted tributary that drains downstream from the WWTP change the spatial patterns of physicochemical variables (pH, turbidity, dissolved oxygen, and electrical conductivity) and nutrient concentrations (reactive soluble phosphorus, total phosphorus, nitrogen series, total nitrogen, and total dissolved carbon) along a mid-order river in SE Brazil and that these effects depend on rainfall regime. Six study sites were sampled along almost 4years to evaluate the impacts of human activities, including sites upstream (1-3) and downstream (5-6) from the WWTP. The impacts were observed presenting an increasing trend from the source (site 1) towards Água Quente stream (site 4, the polluted tributary), with signs of attenuation at site 5 (downstream from both WWTP and site 4) and the river mouth (site 6). Input of nutrients by rural and urban runoff was observed mainly at sites 2 and 3, respectively. At sites 4 and 5, the inputs of both untreated and treated wastewaters increased nutrient concentrations and changed physicochemical variables, with significant impacts to Monjolinho River. Seasonal variations in the measured values were also observed, in agreement with the pluviometric indexes of the region. Univariate analyses suggested no effect of the WWTP for most variables, with continued impacts at sites downstream, but non-parametric multivariate analysis indicated that these sites were recovering to chemical characteristics similar to upstream sites, apparently due to autodepuration. Therefore, multivariate methods that allow rigorous tests of multifactor hypotheses can greatly contribute to determine effects of both point and non-point sources in river systems, thus contributing to freshwater monitoring and management.

Urban Stream Vulnerability Toward PAHs and n-Alkanes and Their Source Identification

ABSTRACTMonjolinho River is an important water body located in the central urban region of São Paulo State in southeast Brazil. The present work reports a 4-year study related to spatio-temporal distribution and source identification of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in surface water and sediment samples of Monjolinho River. A total of 25 sampling campaigns for water, and 10 sampling campaigns for sediment collection, were performed from 2011 to 2014. In sediment samples, total PAHs were found in the range of 2.25 µg kg−1–26,253.87 µg kg−1, while n-alkane concentrations ranged from 0.01 to 165.64 µg kg−1. Total PAHs' concentration in surface water was in the range of 0.17–1,348.35 ng L−1, while n-alkanes were detected in the range of 6.17–316.15 µg L−1. Principal component analysis was used as a statistical tool for summarizing and interpreting a huge quantity of data. It was observed that concentrations of contaminants increased along the river course in urban zone. Distribution indexes were calculated to identify possible sources of carbon pool that pointed towards petrogenic, pyrogenic, and biogenic sources. The overall concentrations of PAHs and n-alkanes were low compared to many previous studies done elsewhere and were mostly below the threshold effects level except in very few occasional cases, while probable effect level was violated in 1 sample during 4 years. Although adverse impacts are unexpected due to overall low contaminant concentrations, unexpected industrial, and sewage discharges make it risky for safer use as a drinking water resource, especially in dry conditions.

Influence of environmental quality of the tributaries of the Monjolinho River on the relative condition factor (Kn) of the local ichthyofauna

The relative condition factors (Kn) of the fishes Astyanax paranae, Phalloceros harpagos and Poecilia reticulata were used as a means of assessing the influence of environmental conditions on the well-being of sub - populations of these species, with the eventual aim of using them as bioindicators of disturbance in tributary streams of the Monjolinho River, in São Carlos - SP. The power-law curve generated by the length-weight relationship indicated a positive allometric growth for the three species studied. Overall, the canonical correspondence analysis (CCA) positively correlated average Kn of A. paranae with well oxygenated and oligotrophic environments, typical of conserved areas or near the natural state. For the average value of Kn obtained for Phalloceros harpagosspecies, there was no significant difference between natural and disturbed areas. However, the CCA positively correlated the mean Kn of the speciesP. reticulata from similar environments with higher trophic level, suggesting that this species is indicative of disturbance.

A 3-year study on occurrence of emerging contaminants in an urban stream of São Paulo State of Southeast Brazil.

This manuscript reports a 3-year study on occurrence of pharmaceuticals, hormones, and triclosan in surface waters of a central urban region of São Paulo State of Southeast Brazil (the Monjolinho River in São Carlos). Water samples collected once at every 2months were pre-concentrated by solid-phase extraction (SPE) and analyzed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The most frequently detected compounds in higher concentrations were caffeine, paracetamol, and atenolol (maximum concentrations 129,585, 30,421, and 8199ngL(-1), respectively), while hormones estrone and 17-β-estradiol were the least detected, in levels up to 14.8ngL(-1). There was an increasing trend in concentrations of most of the compounds along the river course, especially downstream of the river where there is discharge of both wastewater treatment plant effluent and raw sewage from a particular region of São Carlos city. Concentrations of contaminants were higher during dry periods as a result of decline in the water levels. Decrease in concentrations near the river mouth occurred to different extents for each compound. It was high for caffeine and atenolol, but was very low for carbamazepine and diclofenac. The present study reports the first data about the occurrence of some major emerging contaminants in the Monjolinho River. Besides its regional significance, this work may assist in composing a dataset for water contamination diagnosis focusing on emerging contaminants, both in the Brazilian as well as in the Global studies related to aquatic ecosystems. Such datasets can be helpful for making future public policies on water quality, since these compounds are not yet legally regulated.

Biomarker responses as indication of contaminant effects in Oreochromis niloticus

The current study investigated oxidative stress parameters (enzymes activities, metallothionein content and lipid peroxidation) in freshwater fish, Oreochromis niloticus, tilapia exposure to Monjolinho River (in 4months of year: January, April, July and November). One critical site in Monjolinho River (site B) was assessed in comparison to a reference site (site A). Water pH and oxygen concentration was lower than that recommended by CONAMA (Brazilian National Environmental Committee), resolution 357/2005 for protection of aquatic communities, and ammonium and the metals Cu, Zn, Mn and Fe (on all months) concentrations were higher than the maximum concentration recommended. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were significantly decreased in liver and muscle in tilapia from Monjolinho River, throughout the year, in relation to reference except in gills that SOD activity increased. Glutathione S-transferase (GST) activity was significantly increased in liver of the tilapia from Monjolinho River in all sites, in relation to reference except in gills that GST activity increased in July and decreased in November, suggesting that GST activity could be induced to neutralize the pollutants toxicity. On the other hand, GST activity was significantly decreased in white muscle indicating a toxic effect of pollutants, resulting in a decreased ability of tilapia to perform defense reactions associated to GSTs. The decrease of catalase (CAT) activity in gills of the O. niloticus together with the increase of SOD activity, could explain the increased lipid peroxidation (LPO) level in this organ. Metallothionein levels in liver and gills were significantly high in all sites. Results indicate that the exposure to metals caused severe damage to tissues; despite the consensually assumed antioxidant induction as a sign of exposure to contaminants the effects seem in part to be mediated by suppression of antioxidant system with SOD, CAT and GPx as potential candidates for tissues toxicity biomarkers of pollutants.

Análise dos Desenvolvimentos Urbanos de Baixo Impacto e Convencional

This study shows the use of Conventional and LID methods in a microbasin, proving that through urban planning it is possible to create hydrologically functional landscapes, with a behavior similar to the natural one. The comparative analysis of the urban planning methods was performed in an urban microbasin on the Campus of the Federal University of Sao Carlos, in the Monjolinho River basin, in the municipality of Sao Carlos/SP. Hydrological, urbanistic and environmental aspects were evaluated to compare three scenarios: pre-development, existing conventional development and low impact development (LID). Parameters were selected to allow evaluating the proposed scenarios. The results show a landscaping and esthetic gain in the low impact development project, with the creation of 24% plant cover area, increase of areas rendered permeable by reducing 17% of the impervious areas (roads, parking lots and sidewalks) compared to conventional urbanization. As to the hydrological aspects, a reduction of 21% peak flow and 26.9% post-development volume are achieved compared to the conventional one, using LID techniques without the benefit of integrated maangement practices (IMPs). Using IMPs the infitration of rain water keeps the conditions as close as possible to natural conditions

Cadmium and lead toxicity on tropical freshwater periphyton communities under laboratory-based mesocosm experiments

Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l−1 Cd and 0.033 and 0.1 mg l−1 Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l−1) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l−1) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems.

Toxicity and sorption kinetics of dissolved cadmium and chromium III on tropical freshwater phytoperiphyton in laboratory mesocosm experiments

The objective of this study was to assess the interactive effects of Cd and Cr III on tropical phytoperiphyton community growth, metal sorption kinetics, as well as Cd and Cr mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural phytoperiphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into seven experimental systems containing clean glass substrates for phytoperiphyton colonization. The communities were exposed to mixtures of dissolved Cd and Cr concentrations of 0.01 and 0.1 mg.L −1 Cd and 0.05 and 0.2 mg.L −1 Cr. Phytoperiphyton chlorophyll a, ash-free dry mass, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg.L −1) affects phytoperiphyton growth while high concentration of Cr (0.2 mg.L −1) decreased the toxic effects of Cd on phytoperiphyton growth demonstrating the importance of studying metal mixtures in field studies. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum (Kützing) Czarnecki, and Nitzschia palea (Kützing) Smith and reduction of sensitive ones like Fragilaria capucina Desmazières, Navicula cryptocephala (Grunow) Cleve, Encyonema silesiacum (Bleisch) Mann, Eunotia bilunaris (Ehrenberg) Mills and Gomphonema parvulum (Kützing) Kützing), of phytoperiphyton communities with increasing Cd and Cr concentrations and exposure duration have been demonstrated in this study making phytoperiphyton communities appropriate monitors of metal mixtures in aquatic systems. Good Cd and Cr accumulation capacity by phytoperiphyton was demonstrated with total and intracellular metal content in phytoperiphyton reflecting the effects of dissolved concentrations of metal in the culture media and exposure duration. Increase in both Cd and Cr reduced sequestration of each other, with generally more Cd being sequestered compared to Cr. Field validation of the observed effects remains an interesting subject for further investigations.

Applicability of the Pampean Diatom Index (PDI) to streams around São Carlos-SP, Brazil

The objective of the current study was to assess the applicability of the Pampean Diatom Index (the PDI) to natural communities other than epipelic diatom communities as well as those growing on artificial substrates in Monjolinho River and its tributaries, São Carlos-SP, Brazil. Benthic diatoms and water quality sampling was done at 10 sites during summer base flow period (2008 and 2009). The PDI scores were calculated based on epilithic, epiphytic, epipsammic and epipelic diatom communities as well as those growing on bricks and glass substrates. Pearson correlation was used to determine the relationship between the PDI scores from different substrates sampled and measured physical and chemical water quality data. Two-way ANOVA was used to compare these correlation values among substrates. The PDI scores based on all the substrates showed significant correlations with physical and chemical variables. Insignificant differences in the PDI scores based on different natural substrates were recorded, with all substrates classifying the sites into to roughly the same categories. In the light of these results, the PDI can be applied to communities other than epipelic, and is applicable to the study area. The choice of substrate sampled may not affect accuracy of the PDI-based water quality assessment.

Genotoxicity and mutagenicity of water samples from the Monjolinho River (Brazil) after receiving untreated effluents

Cytotoxicity, genotoxicity and mutagenicity assays, using the Allium cepa test-system, were carried out in order to evaluate the effects of domestic and industrial effluents in the Monjolinho River in different seasons of the year. In the summer and intermediate seasons, chromosome aberration, micronuclei, cell death and inhibition of the mitotic index were observed in water samples collected at different sites. In the winter, either chromosome or cellular alterations were not observed. Through chemical analysis, we infer that the excessive metals such as Pb, Ni and Cu were mainly responsible for the effects observed in A. cepa cells. Limnologic analysis like electrical conductivity, dissolved oxygen and the presence of nitrogen and phosphated compounds showed that the river's contamination is due to organic matter discharge along its course. Moreover we note that this river had a higher self-depurative capacity at the end of its course, before its confluence with the Jacaré-Guaçu River.

Laboratory measurements of biomarkers and individual performances in Chironomus xanthus to evaluate pesticide contamination of sediments in a river of southeastern Brazil

This study aimed at evaluating biomarkers, individual and population responses in the native Chironomus xanthus to assess the toxicity of pesticide-contaminated sediments from the Monjolinho River (Southeast Brazil). We measured cholinesterase (ChE) and glutathione S-transferase activities (GST), as biomarkers and survival, individual growth and adult emergence, as individual performances. There was no response of the ChE activity and a tendency to decreased GST activity in contaminated sites, but this was generally not statistically significant. Therefore, there was no association of the biomarker responses with exposure to sediment containing pesticides. In contrast, ash free dry mass was significantly increased and male emergence was decreased in C. xanthus exposed to the same sediments. In conclusion, the selected biomarkers were not sensitive and specific enough to detect and anticipate effects of pesticide contamination at the levels measured in the study area. Nevertheless, individual performances alterations pointed to potential pollution problems and possible ecological consequences.

Benthic diatom community structure and habitat preferences along an urban pollution gradient in the Monjolinho River, São Carlos, SP, Brazil

Benthic diatom community structure and habitat preferences along an urban pollution gradient in the Monjolinho River, São Carlos, SP, Brazil

Analyses of the sediment toxicity of Monjolinho River, São Carlos, São Paulo State, Brazil, using survey, growth and gill morphology of two fish species (Danio rerio and Poecilia reticulata)

The objective of this work was to evaluate the toxicity of the sediments of the Monjolinho River (São Carlos - São Paulo/Brazil), through partial chronic toxicity bioassays with juveniles of D. rerio and P. reticulata. Histological analyses of the gills and biometric measurements were conducted to detect the possible deleterious effects that caused the death. In all points the sampled the alterations were found in the gills (hyperplasia, fusion of secondary lamellas and dilation of blood vessels), with the most intense lesions (second stage) occurring at the point two. The biometric analysis pointed to inadequate conditions for the growth of the test-organisms when exposed to the sediment samples. These results showed that the conditions of these environments were not suitable for the survival and growth of these fishes.

Oligochaeta (Annelida, Clitellata) in lotic environments in the state of São Paulo, Brazil

Despite the importance of Oligochaeta to the dynamics of aquatic ecosystems and to studies of the biology of pollution, there is currently a dearth of information on this group's ecology in Brazil. The aim of this study was to describe the Oligochaeta fauna in four watercourses - three urban and one rural - in the state of São Paulo: the Pinheirinho stream, the Água Branca stream, the Monjolinho River and the Gouveia stream, respectively. Sediment samples were taken with a Van Veen grab in two areas from each watercourse, during the summer and winter of 2001. In all collection areas, measurements of the pH, electrical conductivity, dissolved oxygen and turbidity of the water were made with a Horiba U-10 device. Principal component analysis showed that axes 1 and 2 explained 68.18% of the results' variability, with the first axis predominantly associated with the granulometric data and the second one with the limnological data. Cluster analysis indicated that area II of the Monjolinho River differed from the other collection sites. In the present study, the Oligochaeta group was represented by Tubificidae, Naididae, Alluroididae, Narapidae and Enchytraeidae. Among the three species of Tubificidae, Limnodrilus hoffmeisteri Claparede, 1862, was the most abundant and most frequent species. The results provided important information on the ecology and distribution of limnic Oligochaeta.