How hydromorphological constraints and regulated flows govern macroinvertebrate communities along an entire lowland river

Macroinvertebrates’ response to hydromorphological alterations and regulated flows along lowland rivers is still poorly known despite ecohydrology’s fundamental role in river science. Along the Oglio River (Northern Italy), several water abstractions and dams break it into segments with varying hydraulic and morphological properties. Three types of a priori different environments were identified (dammed, downstream and free flowing sections), and macroinvertebrate communities were sampled from each zone. This study aimed (i) to investigate patterns of macroinvertebrate communities along a regulated lowland river by testing the a priori zones; (ii) to find macroinvertebrate taxa that served as indicators of the various hydrological conditions and (iii) to verify hydromorphological control over ecological macroinvertebrate traits resulting in different trait values in each identified zone. Macroinvertebrate community was characterized in a total of 63 stations by means of two quantitative approaches, each exploring a surface of 0.5m2. The lowest richness values were found in dammed sites that tended toward lentic conditions. Ecnomidae (dammed zones), Limoniidae (downstream zones) and Heptageniidae (free flowing section) were identified as the best indicators of varying hydrological conditions. As suggested by the results of 4th Corner Method, environmental constraints define communities with different ecological traits. These results highlight hydromorphological control over macroinvertebrate community structure and reflect how regulated flows affect the Oglio River in terms of biodiversity, indicator taxa and ecological traits. The authors wish to stress the importance of considering the ecological effects of dams and impoundments on river systems in upstream areas as well as downstream.