Microbial and hydrological influences on nitrate isotopic composition in an agricultural lowland catchment

Wexler, Sarah K.; Hiscock, Kevin M.; Dennis, Paul F.

doi:10.1016/j.jhydrol.2012.08.018

Cited by 26 publications

(11 citation statements)

References 36 publications

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“…respectively, but in accordance with ratio between 1.0 to 2.0 defined by Kendall et al, (2008). Nevertheless, a ratio of δ 15 N/δ 18 O is in the same range (1.4 to 2.5) as Wexler et al (2012), where denitrification was found to occur in a more complex scenario.…”

Section: Redox Zonationsupporting

confidence: 74%

The role of ecotones in the dehalogenation of chloroethenes in alluvial fan aquifers

Herrero

Puigserver

Nijenhuis

et al. 2021

Environ Sci Pollut Res

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The presence of ecotones in transition zones between geological strata (e.g. layers of gravel and sand interbedded with layers of silt in distal alluvial fan deposits) in aquifers plays a significant role in regulating the flux of matter and energy between compartments.Ecotones are characterised by steep physicochemical and biological gradients and considerable biological diversity. However, the link between organic pollutants and degradation potential in ecotones has scarcely been studied. The aim of this study is to relate the presence of ecotones with the dehalogenation of chloroethenes. A field site was selected where chloroethene contamination occurs in a granular aquifer with geological heterogeneities. The site is monitored by multilevel and conventional wells.Groundwater samples were analysed by chemical, isotopic and molecular techniques.The main results were as follows: 1) two ecotones were characterised in the source area, one in the upper part of the aquifer and the second in the transition zone to the bottom aquitard, where the aged pool is located; 2) the ecotone located in the transition zone to the bottom aquitard has greater microbial diversity, due to higher geological heterogeneities; 3) both ecotones show the reductive dehalogenation of perchloroethylene and trichloroethylene; and 4) these ecotones are the main zones of the reductive dehalogenation of the pollutants, given the more reductive conditions at the centre of the plume. These findings suggest that ecotones are responsible for natural attenuation, where oxic conditions prevailed at the aquifer and bioremediation strategies could be applied more effectively in these zones to promote complete reductive dehalogenation.

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Section: Redox Zonationsupporting

confidence: 74%

The role of ecotones in the dehalogenation of chloroethenes in alluvial fan aquifers

Herrero

Puigserver

Nijenhuis

et al. 2021

Environ Sci Pollut Res

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“…Conversely, in regions of confined groundwater and smaller BFI (0.40–0.70), lower permeability glacial deposits reduce infiltration rates and allow low oxygen conditions to develop where denitrification and/or nitrifer denitrification can occur before the infiltrating water recharges groundwater. This process partially protects groundwater from NO 3 – leaching and results in lower NO 3 – and N 2 O concentrations at these sites . Although regions of unconfined mudstone are not protected by overlying glacial deposits, the lower permeability of the mudstone relative to the chalk results in similar opportunities for denitrification and/or nitrifier denitrification, thus resulting in lower NO 3 – concentrations, reduced rates of soil-to-river N 2 O transfer and lower EF 5r values.…”

Section: Resultsmentioning

confidence: 99%

Hydrogeological Controls on Regional-Scale Indirect Nitrous Oxide Emission Factors for Rivers

Cooper

Wexler

Adams

et al. 2017

Environ. Sci. Technol.

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Indirect nitrous oxide (NO) emissions from rivers are currently derived using poorly constrained default IPCC emission factors (EF) which yield unreliable flux estimates. Here, we demonstrate how hydrogeological conditions can be used to develop more refined regional-scale EF estimates required for compiling accurate national greenhouse gas inventories. Focusing on three UK river catchments with contrasting bedrock and superficial geologies, NO and nitrate (NO) concentrations were analyzed in 651 river water samples collected from 2011 to 2013. Unconfined Cretaceous Chalk bedrock regions yielded the highest median NO-N concentration (3.0 μg L), EF (0.00036), and NO-N flux (10.8 kg ha a). Conversely, regions of bedrock confined by glacial deposits yielded significantly lower median NO-N concentration (0.8 μg L), EF (0.00016), and NO-N flux (2.6 kg ha a), regardless of bedrock type. Bedrock permeability is an important control in regions where groundwater is unconfined, with a high NO yield from high permeability chalk contrasting with significantly lower median NO-N concentration (0.7 μg L), EF (0.00020), and NO-N flux (2.0 kg ha a) on lower permeability unconfined Jurassic mudstone. The evidence presented here demonstrates EF can be differentiated by hydrogeological conditions and thus provide a valuable proxy for generating improved regional-scale NO emission estimates.

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“…At the Massachusetts Military Reservation (MMR), chemical and isotopic evidence indicated that nitrification occurred near the contact between the plume and the oxic overlying groundwater, whereas it did not occur in the anoxic zone (Böhlke et al 2006). Wexler et al (2012) found that nitrification occurred in surface after mixing of shallow groundwater and flow from surface drainage based on isotope composition of nitrate. In groundwater underlying the Civic Center area of Malibu, CA, isotope of nitrate associated with nitrogen concentrations indicated that nitrification also occurred in the saturated zone after mixing of treated sewage discharges and native groundwater (Izbicki, 2014).…”

Section: Nitrificationmentioning

confidence: 99%

A stable isotope approach and its application for identifying nitrate source and transformation process in water

Kang

Sun

2015

Environ Sci Pollut Res

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Nitrate contamination of water is a worldwide environmental problem. Recent studies have demonstrated that the nitrogen (N) and oxygen (O) isotopes of nitrate (NO3(-)) can be used to trace nitrogen dynamics including identifying nitrate sources and nitrogen transformation processes. This paper analyzes the current state of identifying nitrate sources and nitrogen transformation processes using N and O isotopes of nitrate. With regard to nitrate sources, δ(15)N-NO3(-) and δ(18)O-NO3(-) values typically vary between sources, allowing the sources to be isotopically fingerprinted. δ(15)N-NO3(-) is often effective at tracing NO(-)3 sources from areas with different land use. δ(18)O-NO3(-) is more useful to identify NO3(-) from atmospheric sources. Isotopic data can be combined with statistical mixing models to quantify the relative contributions of NO3(-) from multiple delineated sources. With regard to N transformation processes, N and O isotopes of nitrate can be used to decipher the degree of nitrogen transformation by such processes as nitrification, assimilation, and denitrification. In some cases, however, isotopic fractionation may alter the isotopic fingerprint associated with the delineated NO3(-) source(s). This problem may be addressed by combining the N and O isotopic data with other types of, including the concentration of selected conservative elements, e.g., chloride (Cl(-)), boron isotope (δ(11)B), and sulfur isotope (δ(35)S) data. Future studies should focus on improving stable isotope mixing models and furthering our understanding of isotopic fractionation by conducting laboratory and field experiments in different environments.

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Microbial and hydrological influences on nitrate isotopic composition in an agricultural lowland catchment

Cited by 26 publications

References 36 publications

The role of ecotones in the dehalogenation of chloroethenes in alluvial fan aquifers

The role of ecotones in the dehalogenation of chloroethenes in alluvial fan aquifers

Hydrogeological Controls on Regional-Scale Indirect Nitrous Oxide Emission Factors for Rivers

A stable isotope approach and its application for identifying nitrate source and transformation process in water

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