Assessment of macroinvertebrates communities responses across regulated and non regulated sites

Abstract

One of the direct consequences of flow regulation is the alteration of flow and stream temperature conditions, but studies describing and quantifying the response of biotic elements to changes in both variables have been sparsely done. This study analyzes macroinvertebrate community responses to flow regulation, through the study of discharge and stream temperature variability across two regulated rivers (Esla and Porma Rivers) and one non regulated river (Curueño River), all of them located in the Upper Esla basin (Duero Basin).Two sampling reaches were selected in each river located at the same latitudinal range. Discharge variability was measured in all rivers. Stream temperature records were collected from each reach sampling site at 2 hour intervals using HOBO temperature loggers between summer 2013 to summer 2016. Macroinvertebrates were collected in autumn and summer and individuals were subsequently identified to genus level, except for Diptera which was identified to sub-family level and Oligochaeta which was identified as such. We quantified macroinvertebrate community abundances, functional traits and some community indices: Richness, Shannon diversity and EPT (abundance of Ephemeroptera, Plecoptera and Trichoptera families). Macroinvertebrate functional traits were processed from Tachet et al. (2003) database. Similarity percentages (SIMPER) analysis were implemented to find the most sensitive taxa and traits, together with analysis of similarities (ANOSIM and PERMANOVA) to quantitatively explore the relation between regulated and non-regulated sites. Preliminary results show a higher dissimilarity in macroinvertebrate communities between regulated and non regulated sites in summer, while there is no regime effect on autumn samples. This could be explained by the higher discharge and the lower stream temperature found in regulated rivers during summer, as a consequence of the dam regulation purposes. Regulated rivers showed a higher richenness and Shannon diversity. Some taxa as Micrasema, Gammarus, Glossiphonia or Pisidium were only found in regulated reaches. The Porma river showed the highest regulation intensity and contained the most rich and diverse macrobenthos. Our results show that flow regulation effects on macrobenthos are site-specific and in some cases may imply the improvement of their flow and temperature conditions along the summer months.