Temporal patterns of stream biofilm in a mountain catchment: one-year monthly samplings across streams of the Orobic Alps (Northern Italy)

Periphyton is the dominant primary producer in mountain streams and sustains the higher trophic levels. While certain periphyton groups, particularly diatoms, have received extensive study, the comprehensive characterization of the entire community has been largely neglected. This study aims to investigate the temporal pattern of biofilm in mountain streams characterized by different water thermal regimes. A one-year quantitative campaign, involving monthly samplings, was conducted in five subalpine streams in Northern Italy’s Orobic Alps to collect epilithic biofilm from a wide surface area. The total biomass was quantified and the periphyton was analyzed both for composition (diatoms, green algae, cyanobacteria, and red algae) and for pigments. Disturbance, water temperature, physico-chemical conditions, nutrients, substrate diversity, and light availability were assessed concurrently with biofilm samplings. Results show sharp biofilm variations over months. In all sites, the disturbance was the primary factor reducing biomass and pigment content. Annually, all sites experienced similar turnover in periphyton composition mainly associated with light and water temperature. Overall, the study indicates that frequent quantitative investigations of biofilm help understand intra-annual variations and identify key drivers. Such information is useful to understand the ecosystem processes and the food web dynamics.