Towards an upgrading of minimun flows: the ecological effects of summer low flows in a aregulated lowland river

In this study, we investigated the temporal evolution of the benthic macroinvertebrate community in an Italian regulated lowland river to clarify the ecological effects of summer low flows. Biomonitoring was carried out for three consecutive years, in a river site immediately below a large off-stream diversion, where minimum flows are released as an environmental protection measure. The three study years were characterized by different streamflow patterns, thus allowing us to compare the temporal trajectories of the community under different flow conditions. Moreover, the interruption of the low-flow periods due to overflow spilled by the upstream dam gave us the opportunity to assess the effects of experimental flow peaks. The analysis of standard macroinvertebrate community metrics showed that larger values of minimum flows favored the taxa belonging to the most sensitive insect orders (Ephemeroptera, Plecoptera and Trichoptera). Moreover, flow peaks interrupting prolonged low-flow periods acted as intermediate disturbance, enhancing community richness and diversity while decreasing density. These results can support the upgrading of current environmental-flow schemes.