Benthic macroinvertebrate assemblages detect the consequences of a sewage spill: a case study of a South American environmental challenge

Benthic macroinvertebrate assemblages are used to assess anthropogenic stressors and pressures globally—although considerable spatial and temporal variability in those assemblages occur naturally and in their sampling. We evaluated the effects of an untreated domestic sewage spill on the spatial–temporal occurrence, structure and dynamics of benthic macroinvertebrate assemblages, through use of occupancy probability and time series modelling. Our study produced three key results: (1) Site colonization, extirpation, and occupancy probabilities of resistant and sensitive assemblages were not influenced by the predictor variables measured before and after the spill nor between sites. (2) Over time, site occupancy for the proportion of sensitive taxa increased while the proportion of resistant taxa decreased. (3) Artificial substrates reduced natural variability more than Surber sampling of natural substrates, but macroinvertebrate family richness differed over time regardless of sampling device. We conclude that rigorous monitoring and data analyses of benthic bioindicators can be a cost-effective approach for assessing the biotic effects of sewage discharges on neotropical urban streams.