CNR-IRSA activities related to INHABIT

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Denitrification measurements

In the last decade several studies related to biogeochemical processes regulating nutrients availability in the riparian ecotones have highlighted the key role of denitrification in reducing nitrate contribution to surface and ground-waters. Through the sequential reduction of nitrate, operated by facultative anaerobic bacteria, it is produced gas-form N2 resulting in an effective loss of N from the water.
Analytical methodology has been - and still is - one of the main restrictions in the study of denitrification. There are several reasons making the quantification of this process difficult to assess: i) the measurement of the product of denitrification is problematic since N2 constitutes 80% of the terrestrial atmosphere and, on the other hand, the measurement of the disappearance of the substrate can be not satisfactory since nitrate has different origins and pathways of transformation; ii) the frequent use of radioactive tracers, in the case of nitrogen, is not convenient; iii) denitrification is characterized by large spatial and temporal variability, being among the most dynamic biochemical processes with various environmental regulators (oxygen, nitrate, carbon).
As part of several projects, aimed at testing the role of riparian strips in the removal of nitrate, acetylene method (Yoshinari & Knowles, 1976) was used to measure denitrification potential in soil samples collected on the ground surface (5-10 cm) in the vicinity of piezometers. The presence of acetylene blocks the denitrification process at the state of nitrous oxide, whose amount is subsequently quantified by gas chromatography. The soil samples are incubated in the absence of oxygen, with surface or underground  water collected during sampling and / or with solutions of nitrogen nitrate at variable concentrations.
Figure shows an example of results obtained by incubating samples of soils collected in the riparian zone of Cameri (NO). Performance of bacterial denitrification is evaluated as a function of different availability of nitrate nitrogen. Different performed tests showed as the increase of the availability of nitrate nitrogen (NO3-N) also increases the N2O production.
Production curves obtained for the different samples, show, after a first phase of rapid growth, a slower plateau trending phase, typical of biological reactions.