title: Analysis of the hydrology and flow of nitrogen in 17 Danish catchments.
abstract: In the search for tools for evaluating the effects of national action plans combating diffuse nutrient pollution causing eutrophication of surface waters, a study of the nitrogen (N) flow in 17 Danish agricultural catchments was carried out. Data on N input and N harvest for the agricultural year of 1993/1994 was obtained from questionnaire surveys facilitating the set up of N balances. Net export of N from the catchments measured at the outlet was obtained from time-series of stream water chemistry and discharge from 1993-1997. N leaching from the root zone of each field was calculated using an empirical model. A physically based lumped rainfall-runoff model was used for separating the hydrograph time-series into three runoff components: baseflow, interflow and overland flow. Large regional variations in net N input were found ranging from 62 kg N ha(-1) yr(-1) in the loamy eastern part of the country dominated by cereal production to 137 kg N ha(-1) yr(-1) in the western part characterised by less fertile sandy soils and dominated by animal husbandry. N leaching from the root zone showed a corresponding variation with regional averages ranging from 34.5 kg N ha(-1) yr(-1) to 90.9 kg N ha(-1) yr(-1). No similar regional pattern could however be found regarding net N export, and no relationship could be established between net N export and root zone N leaching. This finding was ascribed to a varying and in some catchments very high (>80%) N retention during subsurface transport to the stream. The hydrological modelling revealed that loamy catchments had a high proportion of quick flow (overland flow + interflow), whereas baseflow dominated the sandy catchments. Further, a highly significant relationship between N retention and proportion of quick flow was found emphasising the importance of understanding the hydrological pathways. This should be taken into consideration when evaluating the N loading of surface waters resulting from a given agricultural practice and the effects of possible changes in this practice.
authors.affiliation: National Environmental Research Institute, Department of Streams and Riparian Areas, Silkeborg, Denmark.
authors.forename: H E
authors.initials: HE
authors.lastname: Andersen
authors.forename: M L
authors.initials: ML
authors.lastname: Pedersen
authors.forename: O
authors.initials: O
authors.lastname: Jørgensen
authors.forename: B
authors.initials: B
authors.lastname: Kronvang
mesh_terms: D003718:Denmark; D004784:Environmental Monitoring; D005068:Eutrophication; D008962:Models, Theoretical; D009584:Nitrogen / Q000032:analysis*; D012822:Silicon Dioxide; D012987:Soil; D012989:Soil Pollutants; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D014873:Water Pollutants; D012822:Silicon Dioxide; D009584:Nitrogen