Diatomee nei corsi d’acqua mediterranei: prelevo dove devo?

Mediterranean watercourses are characterized with a marked seasonality, with fl oods in spring and autumn and dry periods in summer.As a consequence, hydromorphological changes, like creation of microhabitats, are responsible of impacts on biological populations. In order to detect the effects in the short and medium term, this work provided frequent sampling campaigns during 2014. In this paper, the results of the fi rst sampling campaign (April 2014) are analysed, with the aim of assessing the diversifi cation of diatomic communities between microhabitats and determining differences in the primary production of diatoms. We selected ten study streams, in which we identified two sampling stations: one upstream station, not subject to extreme seasonal variations in fl ow, and one downstream station,characterized with intermittence of water regime. In each station we collected 6 samples of diatoms: the fi rst one according to the standard protocol, while 5 samples were collected from differentiated microhabitats. The community data were analysed with the NMDS. The results showed signifi cant differences between rivers, and between upstream and downstream sites. In particular, communities of microhabitat were found signifi cantly different within the same sampling station between microhabitats and the standard sample, which is not representative of all microhabitats. It is therefore important to carry out sampling activities in differentiated microhabitats to obtain the best representation of the community. We fi nally examined the potential impacts on diatomic indices (IPS, TI) and on primary production.