title: Consequences of varied soil hydraulic and meteorological complexity on unsaturated zone time lag estimates.
abstract: The true efficacy of a programme of agricultural mitigation measures within a catchment to improve water quality can be determined only after a certain hydrologic time lag period (subsequent to implementation) has elapsed. As the biophysical response to policy is not synchronous, accurate estimates of total time lag (unsaturated and saturated) become critical to manage the expectations of policy makers. The estimation of the vertical unsaturated zone component of time lag is vital as it indicates early trends (initial breakthrough), bulk (centre of mass) and total (Exit) travel times. Typically, estimation of time lag through the unsaturated zone is poor, due to the lack of site specific soil physical data, or by assuming saturated conditions. Numerical models (e.g. Hydrus 1D) enable estimates of time lag with varied levels of input data. The current study examines the consequences of varied soil hydraulic and meteorological complexity on unsaturated zone time lag estimates using simulated and actual soil profiles. Results indicated that: greater temporal resolution (from daily to hourly) of meteorological data was more critical as the saturated hydraulic conductivity of the soil decreased; high clay content soils failed to converge reflecting prevalence of lateral component as a contaminant pathway; elucidation of soil hydraulic properties was influenced by the complexity of soil physical data employed (textural menu, ROSETTA, full and partial soil water characteristic curves), which consequently affected time lag ranges; as the importance of the unsaturated zone increases with respect to total travel times the requirements for high complexity/resolution input data become greater. The methodology presented herein demonstrates that decisions made regarding input data and landscape position will have consequences for the estimated range of vertical travel times. Insufficiencies or inaccuracies regarding such input data can therefore mislead policy makers regarding the achievability of water quality targets.
authors.affiliation: Crops, Environment and Land Use Program, Teagasc, Johnstown Castle, Co. Wexford, Ireland; Civil Engineering, National University of Ireland, Galway, Co. Galway, Ireland. Electronic address: sara.vero@teagasc.ie.
authors.forename: S E
authors.initials: SE
authors.lastname: Vero
authors.affiliation: Sustainable Land and Soils, Department for Environment, Food and Rural Affairs, London, United Kingdom.
authors.forename: T G
authors.initials: TG
authors.lastname: Ibrahim
authors.affiliation: Crops, Environment and Land Use Program, Teagasc, Johnstown Castle, Co. Wexford, Ireland.
authors.forename: R E
authors.initials: RE
authors.lastname: Creamer
authors.affiliation: Teagasc Research Operations Group, Statistics and Applied Physics Department, Ashtown, Dublin 15, Ireland.
authors.forename: J
authors.initials: J
authors.lastname: Grant
authors.affiliation: Civil Engineering, National University of Ireland, Galway, Co. Galway, Ireland.
authors.forename: M G
authors.initials: MG
authors.lastname: Healy
authors.affiliation: Earth and Ocean Sciences, National University of Ireland, Galway, Co. Galway, Ireland.
authors.forename: T
authors.initials: T
authors.lastname: Henry
authors.affiliation: Crops, Environment and Land Use Program, Teagasc, Johnstown Castle, Co. Wexford, Ireland; School of Geosciences, University of the Witwatersrand, Private bag 3, PO Box Wits 2050, Johannesburg, South Africa.
authors.forename: G
authors.initials: G
authors.lastname: Kramers
authors.affiliation: Crops, Environment and Land Use Program, Teagasc, Johnstown Castle, Co. Wexford, Ireland.
authors.forename: K G
authors.initials: KG
authors.lastname: Richards
authors.affiliation: Crops, Environment and Land Use Program, Teagasc, Johnstown Castle, Co. Wexford, Ireland.
authors.forename: O
authors.initials: O
authors.lastname: Fenton
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring / Q000379:methods*; D052918:Environmental Restoration and Remediation; D062070:Hydrology; D008685:Meteorological Concepts; D008962:Models, Theoretical; D012987:Soil / Q000737:chemistry*; D013997:Time Factors; D014872:Water Movements; D060753:Water Quality
chemical_list: D012987:Soil
keywords: Hydrus; Time lag; Unsaturated; Water quality