Physical constraints on riverine diatoms: A case study from adige river (North-Eastern Italy)

Physical constrains on riverine diatoms: a case study from Adige River (North-Eastern Italy)

 Centis Barbara, Tolotti Monica & Salmaso Nico
IASMA Research Center, Edmund Mach Foundation - Agricultural Institute of San Michele all’Adige. Via Mach, 1, 38010 S. Michele all’Adige (Trento) Italy.
E-mail of corresponding author: barbara.centis@iasma.it

 

 Physical constraints, such as water discharge, turbulence and turbidity, are known to effect biological communities of watercourses, along with chemical and biotic forcing factors. Aim of this work is to study how the physical environment influences the pelagic diatom populations of Adige River (NE Italy), which is characterised by peculiar morphology and hydrology. Five stations distributed along the hydrological gradient of the river has been sampled forthnightly during one hydrological year (March 2007- February 2008). Diatom assemblages were studied considering Morpho-Functional Diatom Groups (MFDG), defined on diatom genera according to their morphology and adhesion to river substrate. The data collected indicate a high impact of physical factors on both species selection and proportion of MFDG, thus resulting in a higher percentage of centric diatoms (Cyclotella, Stephanodiscus and Melosira spp.) in the downstream stations, where higher water levels and more pelagic conditions allow fast growing r-selected opportunist or process-constrained ruderal (C and CR strategists) species. Conversely, torrential conditions in the northern stations, consisting in lower water levels and higher water velocities, expose the river bed to a stronger erosion, so that the planktonic diatom community in this site mainly included drifted, tychoplanktonic pennate taxa (Diatoma, Encyonema, Navicula and Nitzschia spp).