title: The influence of bedrock hydrogeology on catchment-scale nitrate fate and transport in fractured aquifers.
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 δ(15)N and δ(18)O. 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. Nitrate isotopic signatures in the groundwater of a freely draining catchment underlain by a karstified aquifer and a poorly draining aquifer with a low transmissivity aquifer.
authors.affiliation: Arup, 50 Ringsend Road, Dublin 4, Ireland; School of Planning, Architecture and Civil Engineering, Queen's University Belfast, UK.
authors.forename: Alison
authors.initials: A
authors.lastname: Orr
authors.affiliation: RPS, West Pier Business Campus, Dun Laoghaire, Co. Dublin, Ireland; School of Planning, Architecture and Civil Engineering, Queen's University Belfast, UK.
authors.forename: Janka
authors.initials: J
authors.lastname: Nitsche
authors.affiliation: School of Planning, Architecture and Civil Engineering, Queen's University Belfast, UK; Environmental Protection Agency, Richview, Clonskeagh Road, Dublin 14, Ireland.
authors.forename: Marie
authors.initials: M
authors.lastname: Archbold
authors.affiliation: Environmental Protection Agency, Richview, Clonskeagh Road, Dublin 14, Ireland; Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Ireland.
authors.forename: Jenny
authors.initials: J
authors.lastname: Deakin
authors.affiliation: School of Planning, Architecture and Civil Engineering, Queen's University Belfast, UK.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Ofterdinger
authors.affiliation: School of Planning, Architecture and Civil Engineering, Queen's University Belfast, UK.
authors.forename: Raymond
authors.initials: R
authors.lastname: Flynn
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis*; D062070:Hydrology; D007494:Ireland; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical
keywords: Denitrification; Groundwater; Nitrate isotopes; Nitrification