Nitrate and Nitrous Oxide Dynamics Under Urine Application in an Alluvial Gravel Vadose Zone

Abstract

Understanding nitrogen (N) processes within the vadose zone is important to es mate N losses to groundwater systems. A fi eld trial was undertaken to examine the dynamics of nitrate (NO 3 ) and nitrous oxide (N 2 O) in an alluvial gravel vadose zone underlain by shallow groundwater. Synthe c urine (980 kg N ha −1 ) with a bromide (400 kg Br ha −1 ) tracer was applied to the surface of a 10-by 20-m plot, and changes in subsurface NO 3 , Br, and N 2 O concentra ons were compared with those from an adjacent plot, with just the Br tracer applied. Soil solu on and air were monitored at mul ple depths (from 0.2 to 5 m) over an 18-mo period. Transport of solu on was rapid in the gravel material with some Br transported to 3-m depth immediately a er the urine applica on. N 2 O was produced within the soil a er urine applica on. NO 3 to Br ra os indicated denitrifi ca on in the soil above the gravels, but none within the alluvial gravel vadose zone. In the "-urine" plot N 2 O concentra ons increased with depth, with upward fl uxes above the water table to the soil, sugges ng N 2 O produc on near the water table. A diff erent pa ern was observed in the "+urine" plot where N 2 O was produced both at the soil zone above the gravels and near the water table leading to both upward and downward N 2 O fl uxes. Overall N 2 O fl uxes in the soil zone were greater than at the water table.Abbrevia ons: DNR, denitrifi ca on and nitrate ammonifi ca on; ECD, electron capture detector; TDR, me-domain refl ectometry.

Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection

“…These factors reduce the potential for transformation processes and plant uptake to occur (Liao et al, 2012). Moreover, various studies conducted under similar conditions (soil types and agriculture land use) to in the current study presented insignificant nitrogen transformation processes and doubt the ability to attenuate nitrate within the deeper vadose zone (Green et al, 2008;Burow et al, 2010;Gautam and Iqbal, 2010;Dann et al, 2013;Zhang et al, 2014;Turkeltaub et al, 2015b). However, other studies sug- gested contrasting conclusions.…”

Real-time monitoring of nitrate transport in deep vadose zone under a crop field – implications for groundwater protection

“…Nitrate fate in the subsurface has been investigated by various approaches, such as (i) isotopic signature analysis in groundwater systems (Oren et al, 2004;Wassenaar et al, 2006;Showers et al, 2008;Baram et al, 2013), (ii) cropmanagement strategies, which combine crop production and nitrate leaching to the subsurface (Hanson et al, 2006;Doltra and Muñoz, 2010;Beggs et al, 2011), and (iii) studies based on data from the deep vadose zone (Dann et al, 2010;Nolan et al, 2010;Botros et al, 2012;Kurtzman et al, 2013;Dahan et al, 2014;Turkeltaub et al, 2015b). Nevertheless, estimates based on data obtained from excavated soil profiles and pore-water sampling during a short period of time represent a snapshot in time of the sediment's chemical state rather than dynamic temporal variations.…”

Variability of unsaturated Bromide fluxes as measured through a layered volcanic vadose zone in New Zealand

“…Suction cup samplers, typically made of ceramic or stainless steel materials, have been deployed on a more routine basis for sampling pore water at multiple depths through the vadose zone (e.g. Dahan et al ., ; Dann et al ., , ). Initially, suction cup samplers were only capable of subsampling pore water on an intermittent basis.…”