Indirect N2O emissions from shallow groundwater in an agricultural catchment (Seine Basin, France)

Abstract

Production and accumulation of nitrous oxide (N2O), a major greenhouse gas, in shallow groundwater might contribute to indirect N2O emissions to the atmosphere (e. g., when groundwater flows into a stream or a river). The Intergovernmental Panel on Climate Change (IPCC) has attributed an emission factor (EF5g) for N2O, associated with nitrate leaching in groundwater and drainage ditches-0. 0025 (corresponding to 0. 25% of N leached which is emitted as N2O)-although this is the subject of considerable uncertainty. We investigated and quantified the transport and fate of nitrate (NO3-) and dissolved nitrous oxide from crop fields to groundwater and surface water over a 2-year period (monitoring from April 2008 to April 2010) in a transect from a plateau to the river with three piezometers. In groundwater, nitrate concentrations ranged from 1. 0 to 22. 7 mg NO3--N l-1 (from 2. 8 to 37. 5 mg NO3--N l-1 in the river) and dissolved N2O from 0. 2 to 101. 0 μg N2O-N l-1 (and from 0. 2 to 2. 9 μg N2O-N l-1 in the river). From these measurements, we estimated an emission factor of EF5g = 0. 0026 (similar to the value currently used by the IPCC) and an annual indirect N2O flux from groundwater of 0. 035 kg N2O-N ha-1 year-1, i. e., 1. 8% of the previously measured direct N2O flux from agricultural soils. © 2011 Springer Science+Business Media B.V.