Preliminary evaluation of the algal periphyton biomass and community composition in the Isonzo River
(1) ARPA FVG (Regional Agency for Environmental Protection Friuli Venezia-Giulia), Via Cairoli 14, 33057 Palmanova (UD), Italy (2) Region FVG, Central management of Agri-food, Forestry and Fisheries Resources, Forest Station Villa Santina, Via Gortani 18, 33029 Villa Santina (UD), Italy
ARPA FVG, during the GREVISLIN project, carried out a preliminary study on the relationship between the hydrological regime and the abundance and composition of periphyton of the Isonzo river. In the present work an experimental approach has been applied to improve the general knowledge of the diatom community not only from a qualitative but also using a quantitative point of view. The purpose is to analyse the methods of colonization of the substrate of these organisms in a strongly hydromorphological impacted context through the use of the BenthoTorch, a portable fluorometer, purchased in the project, which allows to measure the chlorophyll-a concentration of diatoms, cyanobacteria and green algae directly in field. This instrument, placed on the surface of the pebble, emits light pulses at different wavelengths and records the fluorescence emitted by the accessory pigments of the 3 photosynthetic groups considered. Thanks to an algorithm, the fluorescence is converted into chlorophyll-a concentration returning the measure of primary production for each group. The measurements were collected between January and December 2020 in three sites along the Soča River (2 in Italy and 1 in Slovenia). At each site, biofilm measurements are been made at the moment of minimum outflow and in every sampling occasion 3 parallel transects have been defined (upper, medium and lower). In this preliminary study it is highlighted how the colonization limit of algal community, in the active riverbed, is particularly influenced by the management of the watercourse flow (hydropeaking). This result can be useful for "naturally" delineating the basic river flow rate, relating to the modified hydrological regime, suggesting some new insights into the choice of sampling sites for biological quality element monitoring used to define the ecological status, to sample in areas that are permanently submerged or affected by the alternation of lean, soft, dry.
Keywords: Periphyton, Isonzo river, hydromorphological impact, BenthoTorch, chlorophyll-a concentration
