Evaluation of water quality of an urban stream in southeastern Brazil using Chironomidae larvae (Insecta: Diptera)

Abstract

In order to estimate the water quality of São Pedro stream, through distribution and composition of Chironomidae larvae present in the sediment four sampling sites were selected. In each sampling site, three sediment samples were collected within a period of twelve months using the Petersen (0.0189 m²) and the van Veen (0.0518 m²) dredges. Samples were washed through a sieve with a 0.21 mm mesh and the collected organisms were sorted in transparent trays, with a light shine being reflected into the tray. The sites located in the greatest urban mesh showed high densities of the genus Chironomus and lower values for diversity, uniformity and taxa richness, in relation to sites located in a less urbanized area. A significant difference in density of Chironomidae larvae (p = 0.02; H = 5.89) was observed between the sites without domestic sewage effluents (site I) and those with the input of the effluents (sites II, III and IV). The Chironomidae larvae composition and the physical and chemical parameters were effective as indicators of the environmental alterations in São Pedro stream.

Chironomus; organic pollution; environmental alteration

ECOLOGY, BEHAVIOR AND BIONOMICS

Evaluation of water quality of an urban stream in southeastern Brazil using Chironomidae larvae (Insecta: Diptera)

Vívian Oliveira; Renato Martins; Roberto Alves

Programa de Pós-Graduação em Ciências Biológicas: Comportamento e Biologia Animal. Univ Federal de Juiz de Fora, Instituto de Ciências Biológicas, Bairro Martelos, 36036-900 Juiz de Fora, MG, Brasil; [e-mail], [e-mail], [e-mail]

ABSTRACT

In order to estimate the water quality of São Pedro stream, through distribution and composition of Chironomidae larvae present in the sediment four sampling sites were selected. In each sampling site, three sediment samples were collected within a period of twelve months using the Petersen (0.0189 m²) and the van Veen (0.0518 m²) dredges. Samples were washed through a sieve with a 0.21 mm mesh and the collected organisms were sorted in transparent trays, with a light shine being reflected into the tray. The sites located in the greatest urban mesh showed high densities of the genus Chironomus and lower values for diversity, uniformity and taxa richness, in relation to sites located in a less urbanized area. A significant difference in density of Chironomidae larvae (p = 0.02; H = 5.89) was observed between the sites without domestic sewage effluents (site I) and those with the input of the effluents (sites II, III and IV). The Chironomidae larvae composition and the physical and chemical parameters were effective as indicators of the environmental alterations in São Pedro stream.

Key words:Chironomus, organic pollution, environmental alteration

The organic pollution causes disruption of the aquatic habitat and modifies the benthic fauna distribution and composition (Callisto et al 2001). The community structure of benthic invertebrates has been used in the evaluation of water quality of aquatic environments in many regions (Janssens & Gerhardt 2003, Mccormick et al 2004, Helson et al 2006).

Chironomidae are frequently abundant among invertebrates in benthic substratum of rivers (Helson et al 2006, Aburaya & Callil 2007), streams (Roque et al 2003, Siqueira & Trivinho-Strixino 2005) and dams (Correia & Trivinho-Strixino 2005, Fusari & Fonseca-Gessner 2006, Moreno & Callisto 2006), being commonly found in high densities and taxa richness (Hirabayashi & Wotton 1998).

The worldwide distribution of Chironomidae, associated with the high diversity of species with different degrees of environmental tolerance, makes it an important group in the diagnosis and monitoring of aquatic environment (Armitage et al 1995). In Brazil, studies in the Rio Doce basin (Marques et al 1999), Velhas basin (Pompeu et al 2005) and Rio Ribeira (Trivinho-Strixino & Strixino 2005) showed that Chironomidae larvae are efficient in water quality evaluation.

The aim of this study was to assess the water quality of an urban stream in southeastern Brazil, by means of both the distribution and the composition of Chironomidae larvae in the sediment.

Material and Methods

São Pedro stream has 13.25 km of extension and it belongs to Rio Paraibuna basin, in the southwestern area of the municipality of Juiz de Fora, Minas Gerais state. Approximately 41.85% of the total drainage basin is situated in the urban area and there are several sites of input of domestic sewage effluents. The basin supplies São Pedro Dam which is responsible for nearly 9% of the city water supply (Latuf 2004).

Four sites along the stream were selected for sediment samples (sites I, II, III e IV) (Fig 1). Site I is located almost 2.5 km away from the urban area, without input of domestic sewage effluents and it has close vegetation along its edges, while site II is located at the beginning of the urban area, thus it is less influenced by these sewage effluents. Sites III and IV are located in the urban area, receiving large amounts of domestic effluents. Site IV is located just after a series of waterfalls.

From May of 2005 to April of 2006, sediment samples (three replicates per site) were obtained monthly, with Petersen (0.0189 m²) and van Veen (0.0518 m²) dredges and fixed using a 4% formalin solution. Samples were then washed in a sieve of 0.21 mm mesh size and the organisms were sorted in transparent trays, with a light shine being reflected into the tray, and conserved in 70ºGL ethanol solution. The identifications of Chironomidae genera were based on Epler (1992), Trivinho-Strixino & Strixino (1995) nd Wiederholm (1983). Fauna data of each sampling site in each month were analyzed as means of numeric density (individuals/m²).

pH (measured using portable pH meter), the level of dissolved oxygen (with spectrophotometry) and chlorophyll-a with a Turner fluorimeter were monthly measured in all sampling stations. Water sub-samples were filtered (black porous 0.2 m polycarbonate filters) and stained with acridine orange to determine heterotrophic bacteria density. The granulometric analysis of the sediment samples from April 2006 was conducted for each sampling site.

The Chironomidae structure and composition were analyzed by means of numeric density, taxa richness, Shannon's diversity index, Pielou's uniformity index, as well as the percentage of Chironomus larvae. These indices were used to evaluate the faunistic similarity among the sampling sites by means of cluster analysis (UPGMA with Euclidean distance). Analyses were performed using the PAST software (version 1.36).

In order to perform the analysis of the indicator value method (IndVal) (Dufrêne & Legendre 1997), we considered the groups formed by the similarity analysis. Taxa with an IndVal higher than 25% contribute to the habitat specificity and only these were considered as characteristic taxa. The significance of the indicator value of each species was tested using Monte Carlo statistics (1000 permutations). Analyses were performed using PCord 4.0.

One-way ANOVA was used to assess the existence of significant differences of chlorophyll-a concentration, pH, dissolved oxygen and bacterial density between the sampling stations. To assess the changes in taxa richness, Shannon's diversity index, Pielou's uniformity index, numeric density of Chironomidae, percentage and the numeric density of the genus Chironomus between the site without input of domestic sewage effluents and those located in the urban area, the Kruskal-Wallis test was applied. This non-parametric test was also used to verify the existence of significant differences in taxa richness among the three Chironomidae subfamilies found in each collection site. These tests were performed in the BioEstat 5.0.

Results

Granulometric analyses indicated that the sediment of São Pedro stream was predominantly sandy (Table 1). In sites I, III and IV predominated the medium-sized sand fraction and in site II the finer fractions (fine sand and silt-clay). Sites III and IV showed more contribution of coarse material (coarse sand and gravel) in relation to the other sites.

Values for chlorophyll-a concentration, pH and bacteria density increased in an upstream-downstream direction. The highest concentrations of dissolved oxygen were observed in sites I and IV (Table 2). One-way ANOVA detected significant differences between sampling stations to the variables chlorophyll-a concentration (P = 0.02; F = 3.62), pH (P < 0.01; F = 22.30) and dissolved oxygen (P < 0.01; F = 18.84).

The Chironomidae larvae that were collected in sediment samples belonged to the subfamilies Chironominae, Orthocladiinae and Tanypodinae. Larvae of Tanypodinae were restricted to site I, and they were represented by four genera. Three genera of Orthocladiinae were found, being Cricotopus the only genus present in all sampling sites. The subfamily Chironominae showed values significantly higher for taxa richness (P < 0.01; H = 193.73) in all sampled sites (Table 3). We observed significant difference in the numeric density of Chironomidae (P = 0.02; H = 5.89) between sites with (sites II, III e IV) and without (site I) the input of sewage effluents.

Those sites with the input of domestic sewage effluents (sites II, III and IV) showed values significantly lower of taxa richness (P < 0.01; H = 8.00), diversity (P < 0.01; H = 10.74) and uniformity indices (P < 0.01; H = 10.29) as compared to the organically unpolluted site (I) (Table 4). Sites II, III and IV showed values significantly higher of percentage (P < 0.01; H = 78.57) and the numeric density (P < 0.01; H = 79.62) of the genus Chironomus in relation to site I.

The cluster analysis (Cofenetic correlation = 0.99) indicated the occurrence of three groups (Fig 2): one formed by a site which is located in an area with no organic pollution from domestic sewage (site I); the second is formed by a site located in the beginning of the urban area (site II) and the third is formed by the site in the area with the largest urban concentration (sites III and IV).

In Table 5 IndVal analysis demonstrated that the genus Polypedilum was an indicator of the site without domestic pollution input (site I) and Chironomus an indicator of the sites in the area with the largest urban concentration (sites III and IV), consequently, with the highest sewage input.

Discussion

The high mean values for chlorophyll-a concentration, pH, and bacterial density registered in sites II, III and IV indicate that the water was receiving domestic effluents, once an increase in nutrients availability in the water accounts for an increase in those parameters (Leandrini et al 2002). The highest values of dissolved oxygen in site I may be attributed to the absence of domestic sewage input (Nonato et al 2007), while in site IV the high value of this variable is due to the presence of waterfalls (Latuf 2004).

Tanypodinae larvae were present only in site I. This subfamily is apparently intolerant to organic pollution, once it was not found in the sites with domestic effluents, as observed elsewhere (Marques et al 1999, Couceiro et al 2007).

The low percentage of Chironomus, the great values of the taxa richness, diversity and uniformity indices characterized site I as the one with the best water quality in comparison to the other sampling sites.

The decrease in Chironomidae diversity in sites II, III and IV is related to the dominance of the genus Chironomus, which is tolerant to organic and industrial pollutants (Gower & Buckland 1978, Davies & Hawkes 1981, Barbosa & Callisto 2000, Kleine & Trivinho-Strixino 2005, Azrina et al 2006), and is an effective biological indicator of stream pollution.

In Jurumirim Dams, São Paulo state, Brazil, the granulometric composition of the substrate was the main determinant of Chironomus density (Santos & Henry 2001). However, in São Pedro stream, this genus did not show any preference for substrate particle sizes, being found in all sites. The domestic sewage input observed in the present study in the sampling sites which are in the urban area may have contributed to the increase of Chironomus density in these sites. According to Sibley et al (1997), the numerical abundance of this genus is greatly influenced by food availability independently of the size of the substrate particles.

The cluster analysis indicated differences in the structure and composition of Chironomidae fauna among the three groups involved. The formation of the groups occurred mainly due to the numeric density of Chironomus that influenced the values of the diversity and uniformity indices. Based on these metrics it was possible to classify the site into the following groups: sites unpolluted by organics (site I), sites with moderate levels of organic pollution (site II) and sites with high levels of organic pollution (sites III e IV).

Polypedilum was considered an indicator of site I due to its high frequency and abundance. This genus is commonly found in different kinds of substrates (Amorim et al 2004, Pinder & Reiss 1983) and pollution levels (Epler 1992). This ecological plasticity makes difficult to identify which of the variables analyzed determined the genus as an indicator of site I. Chironomus was an indicator of sites III e IV, attesting its relationship with organically polluted aquatic environments.

In conclusion, our data indicate that Chironomidae larvae were suitable indicators in the evaluation of the water quality in the studied stream, therefore confirming the potential of this taxonomic group as indicators of organic pollution.

Acknowledgments

We would like to thank Fundação de Apoio à Pesquisa do Estado de Minas Gerais (FAPEMIG) for the financial support (CRA 1291/05) and the scholarship to Vívian Oliveira.

Received 06/I/09.

Accepted 29/V/09.

Edited by Kleber Del Claro - UFU

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Publication Dates

• Publication in this collection
  17 Jan 2011
• Date of issue
  Dec 2010

History

• Received
  06 Jan 2009
• Accepted
  06 Jan 2009