Assessing the ecological condition of streams in a southeastern Brazilian basin using a probabilistic monitoring design Juliana Jiménez-Valencia & Philip R. Kaufmann & Ana Sattamini & Riccardo Mugnai & Darcilio Fernandes Baptista Received: 30 June 2013 /Accepted: 18 March 2014 /Published online: 15 May 2014 # Springer International Publishing Switzerland 2014 Abstract Prompt assessment and management actions are required if we are to reduce the current rapid loss of habitat and biodiversity worldwide. Statistically valid quantification of the biota and habitat condition in water bodies are prerequisites for rigorous assessment of aquatic biodiversity and habitat. We assessed the eco- logical condition of streams in a southeastern Brazilian basin. We quantified the percentage of stream length in good, fair, and poor ecological condition according to benthic macroinvertebrate assemblage. We assessed the risk of finding degraded ecological condition associated with degraded aquatic riparian physical habitat condi- tion, watershed condition, and water quality. We de- scribe field sampling and implementation issues en- countered in our survey and discuss design options to remedy them. Survey sample sites were selected using a spatially balanced, stratified random design, which en- abled us to put confidence bounds on the ecological condition estimates derived from the stream survey. The benthic condition index indicated that 62 % of stream length in the basin was in poor ecological con- dition, and 13 % of stream length was in fair condition. The risk of finding degraded biological condition when the riparian vegetation and forests in upstream catch- ments were degraded was 2.5 and 4 times higher, com- pared to streams rated as good for the same stressors. We demonstrated that the GRTS statistical sampling method can be used routinely in Brazilian rain forests and other South American regions with similar conditions. This survey establishes an initial baseline for monitoring the condition and trends of streams in the region. Keywords Ecological assessment . Streams . Probabilistic monitoring design . Multimetric index . Relative risk Introduction Estimating the ecological condition of aquatic ecosys- tems is a conservation priority for South America’ s very diverse ecosystems such as the Brazilian Atlantic Forest (Mast et al. 1997) because anthropogenic pressures have left few unaffected ecosystems (Begon et al. 2006). Scientific inferences about the condition of wide- spread freshwater ecosystems are more robust when sampling designs are able to aid the assessment of broad concerns (Stevens and Olsen 2000). National and state water quality surveys have shown that appropriate bio- logical indicators and spatially balanced statistical sam- pling designs that employ randomized site selection are Environ Monit Assess (2014) 186:4685–4695 DOI 10.1007/s10661-014-3730-9 J. Jiménez-Valencia (*) : D. F. Baptista Programa de Pós-Graduação em Ecologia, Instituto de Biologia, UFRJ, Ilha do Fundão, Rio de Janeiro CEP 21941-590, Brazil e-mail: jjvingamb@gmail.com J. Jiménez-Valencia : A. Sattamini : R. Mugnai : D. F. Baptista Laboratório de Avaliação e Promoção da Saúde Ambiental—IOC/FIOCRUZ, Rio de Janeiro CEP 21040-360, Brazil P. R. Kaufmann U.S. Environmental Protection Agency, 200 Southwest 35th Street, Corvallis, OR 97333, USA