Characterization of the microbial diversity in the water fluxes of a wooded riparian strip set up for nitrogen removal

This research is part of a project aimed at verifying the potential of a specifically assessed wooded riparian zone in removing excess of combined nitrogen from the Zero river flow for the reduction of nutrient input into Venice Lagoon. Seasonal fluctuations of microbial populations in the water entering and leaving the wooded riparian strip were determined for at least two years. Combined approaches involving cultivation, microscopic approaches and DNA bases techniques were adopted to characterize both culturable and total microbial community. Seven major bacterial lineages, namely Firmicutes, Gammaproteobacteria,Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Flavobacteria, and Sphingobacteria were present in water samples as revealed by 16S rDNA sequence analysis of the culturable fraction of the bacterial population. Gammaproteobacteria were the most dominant both in spring and fall, although distinct bacterial communities were clearly detectable for the two seasons. However, while DGGE cluster analysis did not reveal significant differences between irrigation and drainage ditches, a significant alteration was detected by PCA based on 16S rDNA of the culturable fraction. Since the wooded riparian strip was vigorously working in terms of N removing by plant uptake and especially by microbial denitrification, as demonstrated by parallel studies performed on the same experimental site (Gumiero et al., 2011), it is reasonable to suppose that the culturable bacteria fraction is the one effectively carrying out the required task. In other words, the wooded riparian buffer zone specifically assessed for water remediation (nitrogen removal) is efficiently working as a result of the special conditions there produced to support the work of specific microbial populations. This is confirmed by the increase of metabolically active bacteria detected at the drainage ditches. Taken together, the overall results provide key indications for the management of a phytoremediation site