Regionalisation is key to establishing reference conditions for neotropical savanna streams

Abstract

Areas with minimal anthropogenic influences are frequently used as reference sites and represent the best ecological state available in a region. Streams in such conditions are necessary for evaluating the conservation status of aquatic ecosystems of a region and to monitor them, taking natural environmental variability into consideration. Therefore, the aim of the present study was to analyse whether hydrological units are reliable regional units for aggregating reference sites. To this end, reference sites were studied in three different landscape units of the same hydrological unit. The study tested the hypothesis that water quality, physical habitat structure and the composition and structure of macroinvertebrate assemblages will be more similar for sites in the same landscape unit than for sites located in different landscape units in the same hydrological unit. The study showed that taxonomic richness and composition of the macroinvertebrate assemblages were negatively affected by site slope and positively affected by the presence of leaf packs on the streambed. The three landscape units supported significantly different macroinvertebrate assemblages and indicator taxa. Therefore, a hydrological unit does not constitute a homogeneous entity in terms of environmental variables and biological composition if it incorporates high landscape heterogeneity. These results should improve and facilitate the selection of reference sites for biomonitoring programs and for managing tropical headwater streams.