Recovery of groundwater N2O at the soil surface and its contribution to total N2O emissions

Abstract

Production and accumulation of the major greenhouse gas nitrous oxide (N 2 O) in surface groundwater might contribute to N 2 O emissions to the atmosphere. We report on a 15 N tracer study conducted in the Fuhrberger Feld aquifer in northern Germany. A K 15 NO 3 tracer solution (60 atom%) was applied to the surface groundwater on an 8 m 2 measuring plot using 45 injection points in order to stimulate production of 15 N 2 O by denitrification and to detect its contribution to emissions at the soil surface. Samples from the surface groundwater, from the unsaturated zone and at the soil surface were collected in regular intervals over a 72-days period. Total N 2 O fluxes at the soil surface were low and in a range between -7.6 and 29. , indicating that indirect N 2 O emissions from the surface groundwater of the Fuhrberger Feld aquifer occurring via upward diffusion are hardly significant. Due to these observations we concluded that N 2 O dynamics at the soilatmosphere interface is predominantly governed by topsoil parameters. However, highest 15 N enrichments of N 2 O throughout the profile were obtained in the course of a rapid drawdown of the groundwater table.We assume that such fluctuations may enhance diffusive N 2 O fluxes from the surface groundwater to the atmosphere for a short time.

Nitrous oxide fluxes and dissolved N gases (N2 and N2O) within riparian zones along the agriculturally impacted San Joaquin River

“…The contribution of groundwater N 2 O to surface fluxes is dependent on multiple environmental factors such as soil moisture and texture that influence the production and consumption of N 2 O as it diffuses upwards through the vadose zone (von der Weymann et al 2009). N 2 O fluxes from IR positions were inversely related to groundwater depth in shallow wells (r = -0.49, P \ 0.001, Figure S1; Table 2).…”

“…McPhillips et al (2015) found that longer residence time of groundwater flow increased denitrification rates while promoting lower N 2 O:N 2 ratios. Some studies have concluded that N 2 O fluxes from groundwater are not an appreciable contribution to the atmosphere (Clough et al 1999;Weymann et al 2009). During diffusion through the saturated zone, N 2 O may be further reduced to N 2 , reducing the potential for N 2 O emissions from groundwater to the atmosphere.…”

Balancing watershed nitrogen budgets: accounting for biogenic gases in streams

“…Weymann et al (2009) demonstrated that groundwater N 2 O contributes negligibly to the flux of N 2 O to the atmosphere from surface soils. Similarly, we found that groundwater delivery of N 2 O makes up a small portion of total biogenic N 2 O emissions (15 % on average) from strongly gaining agricultural streams where groundwater would be expected to be an important source compared to other aquatic systems.…”

Kinetics of N<sub>2</sub>O production and reduction in a nitrate-contaminated aquifer inferred from laboratory incubation experiments

“…Since N 2 O concentrations in the unsaturated zone above the groundwater table are low, i.e. similar to ambient N 2 O concentrations (von der Weymann et al, 2009), we want to emphasize that the described N 2 O accumulation is a result of the in situ production in the groundwater. In contrast, the unsaturated zone was identified as an N 2 O source for British limestone aquifers (Mühlherr and Hiscock, 1998).…”