The Castelhano Stream
Hydrographic Basin, located in the city of Venancio Aires, RS, Brazil, shows an
area of 675.3
km2, highlighting the Castelhano Stream as their main water course.
The stream is the main responsiblity for the local water supply; however, there are no published studies in
the literature regarding their water quality. In this context, the present
research aimed to assess the water quality of Castelhano Stream in terms of
organic pollution and eutrophication, applying the Biological Water Quality
Index (BWQI), which uses epilithic diatoms communities as bioindicators. Biological
samples were collected at three sampling stations along the stream in the
months of September, November and December 2012. The results showed 81
identified species, distributed in 30 genera. The water pollution levels
detected ranged from “strong” (66.7%) and “very strong” (33.3%), with differences in species
composition between sampling stations. The sampling station S1 in the upper
reaches was characterized by the presence of indicative species of acidophilus
and lentic environments with large amounts of organic matter. The sampling
stations S2 and S3, in the intermediate and lower reaches, respectively, showed
a substitution of species in the community, with the presence of highly
tolerant taxa to organic pollution and eutrophication. The high pollution
levels detected along the basin are related to the nutrients and high organic
load originating from livestock, domestic and industrial waste, as well as
excess fertilizers and agricultural inputs used in farming. The results
demonstrate the necessity to implement mitigation measures to contain the
processes of organic pollution and eutrophication detected due to the dangers
offered to public health and the environment.