A New Method to Investigate Denitrification Dynamics During Simulated Floods in Soils

Abstract

Riparian ecosystems, through their anoxic properties driven by floods, play a crucial role in favouring denitrification. The absence of nitrous oxide (N₂O) reductase activity in the denitrification process provokes the emission of a potent greenhouse gas (GHG), N₂O, into the atmosphere. Our understanding of the contribution of denitrification to N₂O emissions is limited by the difficulties in capturing peak N₂O events and measuring dinitrogen gas (N₂), the final product of the process under soil flooding. In this study, we describe the GHG-Aquacosme, a new laboratory-based and ecosystem-relevant approach to simulate flood conditions and investigate GHG flux dynamics in intact riparian soil cores, focusing on N₂O. The system capabilities were tested on two different riparian soils with simultaneous monitoring of N₂O, carbon dioxide and porewater chemistry. We also used a simple mass balance approach to estimate the N₂ emissions. The GHG-Aquacosme proved efficient in the incubation of soil samples under atmospheric conditions, preserving the initial soil structure and heterogeneity and providing a high temporal resolution of N₂O emission dynamics upon flooding. This translated into heterogeneous outputs in terms of N₂O dynamics and denitrification-related parameters such as N₂O yield and nitrate removal efficiency. Finally, accounting for nitrogen (N) species diffusion within the system is recommended, and the setup can easily accommodate isotopic N tracer methodologies to investigate other N cycle pathways. Further research is encouraged to determine how the results from the GHG-Aquacosme application can be utilised in predictive models of N₂O emissions, particularly in relation to future scenarios and projections of riparian flooding.