RESUMEN
This research aimed at determining reference sites in southern Brazilian lotic systems, using the Water Quality Trophic Index (WQTI), based on epilithic diatom communities. Within the period of 2012 and 2016, 140 epilithic diatom samples from seven sampling sites within the spring area of the Andreas Stream Hydrographic Basin, Vera Cruz County, RS, Brazil, were analyzed quarterly. Similarly, from 2012 and 2014, water samples in these sampling sites were collected for determination of physicochemical and microbiological parameters, such as water temperature, pH, turbidity, dissolved oxygen, biochemical oxygen demand, nitrate, phosphate, total dissolved solids, and fecal coliforms. The results indicated the occurrence of two diatom samples groups with significant differences (p < 0.05). Group 1 (sampling sites P1, P4, and P5) was classified in the oligotrophic category with an average WQTI of 1.3 ± 0.2, while group 2 (sampling sites P2, P3, P6, and P7) was classified in the ß-mesotrophic category with an average value of 2.0 ± 0.4). Achnanthidium minutissimum and Platessa hustedtii the dominant species were classified as oligotrophic taxa. Thus, we proposed the upper limit of the first interval of the WQTI score scale, equal to 1.5, as a reference value to differentiate the limits between the "high" and "good" ecological status to determine "reference sites" for subtropical and temperate Brazilian aquatic systems. The physical, chemical, and microbiological water quality evaluation gives support to this proposal, as far as the results indicated a significant improvement in the water quality, classifying sampling sites P1, P4, and P5 as having good quality appropriate for multiple uses.
Asunto(s)
Diatomeas , Brasil , Monitoreo del Ambiente , Ríos , Calidad del AguaRESUMEN
This research aimed at developing the Trophic Water Quality Index (TWQI) for subtropical temperate Brazilian lotic systems based on a review of the indicative values of diatom species obtained using multivariate analysis techniques and considering the environmental gradient defined by a series of measured physical, chemical, and microbiological variables. Sampling was conducted from 2005 to 2009 in the Pardo River Hydrographic Basin, Rio Grande do Sul (RS), Brazil, and in the Andreas Stream Hydrographic Basin, RS, from 2012 to 2013. A total of 140 biological samples and 211 abiotic samples were collected. Data were analyzed by cluster analysis based on the Ward method and canonical correspondence analysis (CCA). The results indicated that total phosphate, turbidity, ammonia nitrogen, electrical conductivity, dissolved oxygen, and thermotolerant coliforms showed a significant correlation with the sample ordination made by CCA, in relation to a gradient of eutrophication. Eutrophication was operationally defined in a broad sense, including the problem of organic pollution and eutrophication of the water. The determination of the different tolerance degrees to eutrophication of the diatom taxa was used to assign trophic values of 1, 2.5, and 4 to species, corresponding to levels of low, medium, and high tolerance, respectively. By using the trophic values obtained for each diatom species, the TWQI constituted a new technological tool for environmental monitoring studies and showed a consistent, robust, and objective database for water quality assessment in subtropical temperate Brazilian lotic systems.