The influence of bedrock hydrogeology on catchment-scale nitrate fate and transport in fractured aquifers

Alison Orr, Janka Nitsche, Marie Archbold, Jenny Deakin, Ulrich Ofterdinger, Raymond Flynn

    Research output: Contribution to journalArticle

    2 Citations (Scopus)
    238 Downloads (Pure)

    Abstract

    Characterising catchment scale biogeochemical processes controlling nitrate fate in groundwater constitutes a fundamental consideration when applying programmes of measures to reduce risks posed by diffuse agricultural pollutants to water quality. Combining hydrochemical analyses with nitrate isotopic data and physical hydrogeological measurements permitted characterisation of biogeochemical processes influencing nitrogen fate and transport in the groundwater in two fractured bedrock aquifers with contrasting hydrogeology but comparable nutrient loads. Hydrochemical and isotopic analyses of groundwater samples collected from moderately fractured, diffusely karstified limestone indicated nitrification controlled dissolved nitrogen fate and delivery to aquatic receptors. By contrast nitrate concentrations in groundwater were considerably lower in a low transmissivity highly lithified sandstone and pyrite-bearing shale unit with patchy subsoil cover. Geophysical and hydrochemical investigations showed shallower intervals contained hydraulically active fractures where denitrification was reflected through lower nitrogen levels and an isotopic enrichment ratio of 1.7 between δ15N and δ18O. Study findings highlight the influence of bedrock hydrogeological conditions on aqueous nitrogen mobility. Investigation results demonstrate that bedrock conditions need to be considered when implementing catchment management plans to reduce the impact of agricultural practices on the quality of groundwater and baseflow in receiving rivers.
    Original languageEnglish
    Pages (from-to)1040-1052
    Number of pages13
    JournalScience of the Total Environment
    Volume569-570
    Early online date16 Jul 2016
    DOIs
    Publication statusPublished - 01 Nov 2016

    Keywords

    • Groundwater Nitrate isotopes Nitrification Denitrification

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