Microbial diversity and denitrification in a wooded riparian strip

This study 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. General objectives of this project were to increase knowledge on the processes which allow the riparian strips to act as a buffer and to identify the most appropriate management strategies in order to maximize the efficiency of these systems in supporting the microbial activities involved in the process. For this purpose, specific objectives were pursued to determine seasonal fluctuations of the microbial populations in the soil/water of the wooded riparian strip. The bacterial communities were determined by combined approaches involving cultivation, microscopic approaches and DNA bases techniques to characterize both colturable and total microbial community inside and outside the riparian strip. ARDRA and DGGE analyses of soil, collected at different depths, showed a clear decrease of the microbial diversity in deeper horizons as compared to the medium depth and surface ones. A comparison between this soil and that collected from an undisturbed zone external to the riparian strip, indicated that this effect can be also observed in the external area, although higher microbial diversity was always present in the internal soil. DGGE cluster analysis and PCA of both genetic and chemical properties of water samples, indicated that the bacterial populations present at the drainage ditches are rich in denitrifiers as a result of a mixing of bacterial communities carried by the Zero river flux and those already present in the soil of the riparian strip. Taken together, the overall results confirm what it was demonstrated by other chemical-physical analysis: the wooded riparian buffer zone assessed for water remediation (nitrogen removal from the river) is effectively working as a result of the special conditions there produced to support the work of specific microbial populations. The microbiological analysis here accomplished can also contribute to understand the bacterial population dynamic of an agricultural soil when transformed in a wooded strip and to provide key indications for the management of a phytoremediation site.