Inter-annual and habitat variation of the mayfly assemblage in grassland and pine afforested headwater streams (Cordoba, Central Argentina)

Mayflies are widely used as indicators of stream conditions since their presence and abundance are closely associated with changes in environmental characteristics. We aim to analyze the richness and abundance patterns of mayflies in headwater streams of the Ctalamochita river basin in central Argentina, where some sub-basins have been fully afforested with exotic pines. We sampled 3 grassland streams and 3 pine afforested streams in 2008, 2012, 2014, and 2015. We took Surber samples in riffles and in 2012 we also sampled 2 additional habitats: pools and macrophyte patches. We found ten mayfly genera. Americabaetis and Leptohyphes were the most frequent and abundant and Cloeodes and Tricorythodes were rare, with a relative frequency < 3%. Richness and abundance were higher in grassland streams (ANOVA, p < 0.05), but the abundance pattern of different mayfly genera varied. In 2012 mayfly abundance was higher in pools and macrophytes in the afforested streams (ANOVA, p < 0.05), but it was similar among habitats in grassland streams. Different species dominated different habitats and stream types, and some shared the same habitat. In riffles and pools, the dominant genera was similar for afforested and grassland streams, while in macrophyte the dominance varied according to the riparian vegetation. Distribution patterns are influenced by microhabitat characteristics, which may be conditioned by changes in riparian land uses.