A stable isotope and hydrochemical approach to examining denitrification along a shallow groundwater - surface water continuum in an agriculturally-impacted catchment

Garrard, Nicholas (2019) A stable isotope and hydrochemical approach to examining denitrification along a shallow groundwater - surface water continuum in an agriculturally-impacted catchment. Doctoral thesis, University of East Anglia.

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Abstract

The global population is steadily increasing and subsequently, so is food production. Over the past century, the global pool of reactive nitrogen has doubled. Whilst improving crop production, this has detrimental effects on human and environmental health. Therefore, it is important to understand the consequential forcing of the nitrogen cycle and the natural attenuation processes within, namely denitrification.
The main aim of this research was to determine the spatial distribution and significance of denitrification in an agriculturally-impacted catchment in Norfolk, UK. The stable isotopes of nitrate (15NNO3 and 18ONO3) were measured alongside hydrochemical characteristics of field drains (representing the soil zone), stream water, benthic sediment pore water, boreholes and the hyporheic zone (HZ) (beneath and to the sides of the stream bed). The HZ was sampled from a series of nested in-stream piezometers along a 1.6 km reach. A mass balance approach was then used to assess the magnitude of denitrification within the study catchment.
The results show evidence for denitrification within the soil zone, demonstrated by dual fractionation of nitrate isotopes and negative correlation between nitrate concentration and δ15NNO3 and δ18ONO3 values. Soil type influenced denitrification, showing a positive correlation between percentage clay and δ15NNO3 and δ18ONO3values. Tillage regime was also suggested to influence denitrification. In-stream denitrification was also detected, though there was no associated reduction in dissolved nitrate concentration with nitrate isotope enrichment. Tentative isotopic evidence for benthic pore water denitrification is also presented. There was no isotopic evidence for HZ denitrification, suggesting that management approaches should not focus on this zone. Mass balance calculations indicate catchment-wide denitrification rate of 0.023 – 0.044 kg N ha d-1, equating to 27 – 42% of nitrogen in soil leachate.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Jackie Webb
Date Deposited: 01 Mar 2019 11:55
Last Modified: 01 Mar 2019 12:00
URI: https://ueaeprints.uea.ac.uk/id/eprint/70065
DOI:

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