Water, Air, & Soil Pollution: Focus

, Volume 4, Issue 6, pp 97-105

First online:

A conceptual model of spatially heterogeneous nitrogen leaching from a welsh moorland catchment

  • C. D. EvansAffiliated withCentre for Ecology and Hydrology Email author 
  • , B. ReynoldsAffiliated withCentre for Ecology and Hydrology
  • , C. J. CurtisAffiliated withECRC, University College London
  • , H. D. CrookAffiliated withCentre for Ecology and HydrologyDepartment of Geography, School of Human and Environmental Sciences, University of Reading
  • , D. NorrisAffiliated withCentre for Ecology and Hydrology
  • , S. A. BrittainAffiliated withCentre for Ecology and Hydrology

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Soil- and stream-water data from the Plynlimon research area, mid-Wales, have been used to develop a conceptual model of spatial variations in nitrogen (N) leaching within moorland catchments. Extensive peats, in both hilltop and valley locations, are considered near-complete sinks for inorganic N, but leach the most dissolved organic nitrogen (DON). Peaty mineral soils on hillslopes also retain inorganic N within upper organic horizons, but a proportion percolates into mineral horizons as nitrate (NO 3 ), either through incomplete immobilisation in the organic layer, or in water bypassing the organic soil matrix via macropores. This NO 3 reaches the stream where mineral soilwaters discharge (via matrix throughflow or pipeflow) directly to the drainage network, or via small N-enriched flush wetlands. NO 3 in hillslope waters discharging into larger valley wetlands will be removed before reaching the stream. A concept of catchment ‘nitrate leaching zones’ is proposed, whereby most stream NO 3 derives from localised areas of mineral soil hillslope draining directly to the stream; the extent of these zones within a catchment may thus determine its overall susceptibility to elevated surface water NO 3 concentrations.


hillslope hydrology immobilisation nitrate leaching zones nitrogen saturation