Environmental effects and urban impacts on aquatic macroinvertebrates in a stream of central Brazilian Cerrado

The urban effects on macroinvertebrate trophic structure were evaluated in a stream located in central Brazilian Cerrado. Samplings were evaluated from May/2004 to March/2005 in the upper, middle and lower sections. Characterization of ecological conditions and habitat diversity indicated headwater as “natural” site, up and downstream the urban region were “altered” ones, and the sites located nearest to urban area were considered “impacted”. A well oxygenated and transparent water, acid pH, low electrical conductivity (<0.22 µS/cm), and low nutrients concentrations (<0.03 mg/L PO ₄ ⁻² , <0.05 mg/L N–NH₄ and <3.0 mg/L N–NO ₃ ⁻² ) was registered for headwater area. Stretches located near the urban region had higher electrical conductivity (48–100 µS/cm), higher ammonium (7.16 mg/L), and poor oxygenated water. The trophic organization was different along the stream and related to environmental preservation degree. Shredders occurred only in the headwater (Phylloicus sp., Trichoptera). Predators were dominant in upstream sites of the urban area (>90 % of biomass). In the sites located near the urban area, an alternative predominance was observed between gathering collectors and predators, with the gathering collectors dominance in the area impacted by city sewage inflow (>90 %). There was a progressive participation of scrapers in stretches located downstream of the city. Biomass was dominated by predators (>50 % in six sites) encompassing larger organisms (>20 mm), and gathering collectors were density dominants (from 53 to 99 %). Predators were the most dominant functional feeding group (22 taxa), followed by scrapers (eight), gathering collectors (seven) and filtering collectors (five). The results state that the Sobradinho stream is under different degrees of environmental impacts with lower preservation levels of its natural conditions, even in areas close to its headwater.