• N leaching to groundwater from dairy production involving grazing over the winter on a clay-loam soil

      Necpalova, Magdalena; Fenton, Owen; Casey, Imelda A.; Humphreys, James; Department of Agriculture, Food and the Marine, Ireland; RSF07-511 (Elsevier B. V., 15/08/2012)
      This study investigated concentrations of various N species in shallow groundwater (< 2.2 m below ground level) and N losses from dairy production involving grazing over the winter period on a clay loam soil with a high natural attenuation capacity in southern Ireland (52˚51’N, 08˚21’W) over a two year period. A dense network of shallow groundwater piezometers was installed to determine groundwater flow direction and N spatial and temporal variation. Estimated vertical travel times through the unsaturated zone (<0.5 yr, time lag) allowed the correlation of management with groundwater N within a short space of time. There was a two way interaction of the system and sampling date (P < 0.05) on concentrations of DON, oxidised N and NO3--N. In contrast, concentrations of NH4+-N and NO2--N were unaffected by the dairy system. Grazing over the winter had no effect on N losses to groundwater. Mean concentrations of DON, NH4+-N, NO2--N and NO3--N were 2.16, 0.35, 0.01 and 0.37 mg L-1 respectively. Soil attenuation processes such as denitrification and DNRA resulted in increased NH4+-N levels. For this reason, DON and NH4+-N represented the highest proportion of N losses from the site. Some of the spatial and temporal variation of N concentrations was explained by correlations with selected chemical and hydro-topographical parameters (NO3--N/Cl- ratio, distance of the sampling point from the closest receptor, watertable depth, depth of sampling piezometer, DOC concentration). A high explanatory power of NO3--N/Cl- ratio and the distance of the sampling point from the closest receptor indicated the influence of point sources and groundwater-surface water interactions.
    • Time lag: a methodology for the estimation of vertical and horizontal travel and flushing timescales to nitrate threshold concentrations in Irish aquifers

      Fenton, Owen; Schulte, Rogier P.; Jordan, Philip; Lalor, Stanley T. J.; Richards, Karl G.; Department of Environment, Heritage and Local Government; RPS Group Ltd (Elsevier Science Ltd., 02/04/2011)
      The Water Framework Directive (WFD) in Europe aims, inter alia, to achieve at least “good” water quality status by 2015 by mitigating the causes of pollution. However, with the implementation of programmes of measures in 2012, many catchments may not achieve good water quality status within this timeframe due to the time lag of nutrient transport from source to receptor via hydrological and hydrogeological pathways. An appraisal of catchment time lag issues offers a more realistic scientifically based timescale for expected water quality improvements in response to mitigation measures implemented under the WFD. A simplified methodology for the calculation of nitrate time lag in a variety of Irish hydrogeological scenarios is presented, based on unsaturated vertical and aquifer flushing times required to reach environmental quality standards. Horizontal travel time is estimated for first occurrence of nutrients in a surface water body. The results show that achievement of good water quality status in the Republic of Ireland for some waterbodies may be too optimistic within the current timeframe of 2015 targets but improvements are predicted within subsequent 6 and 12 year cycles.