Contrasting land uses affect Chironomidae communities in two Brazilian rivers

Abstract

We investigated whether the conversion of riparian land use from indigenous forest to pasture influences Chironomidae (midge) community composition in two Brazilian rivers. Our study was conducted in the main rivers (Sao Jose dos Dourados 6 th order, Aguapef 7 th order) of two large catchments in the State of Sao Paulo. Both are dominated by agricultural ecosystems but retain substantial patches of native riparian forest. Replicated artificial substrates (baskets filled with coarse clay gravel) were exposed at one forested reach and one pasture reach in each river. Each respective land use had to be present for at least 500m along both river banks above and alongside the study reach, and the riparian forest at the forested reaches had to be at least 50 m wide. Colonisation baskets were sampled after 44 days and all midge larvae sorted and identified to the lowest level possible (a total of 5,286 individuals belonging to 27 taxa). Land use affected midge communities, but not as expected. Densities of three dominant midge genera were significantly higher in pasture reaches than in forested reaches, possibly in response to moderate nutrient enrichment at the pasture reaches. Total midge density and taxon richness were similar across land uses. These results imply that land-use related changes in habitat conditions were not severe enough to represent a stressor (with negative effects) for the midge communities in the investigated large rivers, but rather acted as a subsidy, with mainly positive effects.