Structure of the diatom community of the River Adige (North-Eastern Italy) along a hydrological gradient

Physical constrains such as water discharge, suspended solids and turbidity act as dominant factors in driving the planktonic diatom assemblages of the River Adige (North-Eastern Italy). Two sampling stations, characterised by different hydromorphological features (Cortina all’Adige and Boara Pisani, with torrential and more potamal characteristics, respectively) were sampled fortnightly following an integrated approach encompassing physical, chemical and biological measurements and aiming at identifying the dominant factors controlling the temporal development of the community. A morpho-functional approach was used to classify the diatom assemblages where Morpho-Functional Diatom Groups (MFDG) were defined for diatom genera, according to their morphology, habitat selection and modality of adhesion to river substrate. In the two sampling points, algal growth was never limited by nutrients or zooplankton. The irregular development of MFDG was determined by the stochastic hydrological events and changes in variables related to water discharge (suspended solids and light attenuation). Tychoplanktonic, benthic and drifted taxa (such as Diatoma spp., Encyonema spp., Navicula spp. and Nitzschia spp.) were dominant in the torrential station (Cortina all’Adige), while the contribution of euplanktonic unicellular centric taxa (such as Cyclotella spp., and Stephanodiscus spp.) was higher in the potamal station (Boara Pisani).