Özet:

Diatom community structure and morphotype classification were studied and periphyton biomass, course particulate organic matter (CPOM), hydrogeomorphological parameters, and nutrient concentrations were measured at 4 stations downstream of the Cecita dam (Mucone River) and at 3 control sites located on different tributaries of the Mucone River in May, August, and November 2005. The lowest values of current velocities and the highest amounts of sand deposition and CPOM accumulation were detected at the stations closest to the dam. Downstream, the confluence with the first permanent tributary (Cerreto River) of the Mucone showed a "rhythral" morphology, similar to that of the control sites. Multivariate analysis showed that the community was constantly segregated into 2 groups: G1 (stations upstream of the Cerreto inflow), dominated by early colonizers, adapted to both high and low current velocity and tolerating burial and light deficiencies; and G2 (all other stations), where the prevailing taxa were species typical of stable environments with high values of flow and abundance of coarse substrates. Genus-based morphotype classification failed to detect any differences between the 2 groups. Biomass levels were higher at station G2 than G1, while accumulation of CPOM downstream of the reservoir promoted fine particulate organic matter production and a switch from autotroph to heterotroph dominated biofilms.

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