title: Nitrogen in river basins: sources, retention in the surface waters and peatlands, and fluxes to estuaries in Finland.
abstract: Nitrogen export from diffuse and point sources and its retention in the major river basins of Finland is quantified and discussed. The estimated total export from river-basins in Finland was 119,000 tonnes N a(-1) for the period 1993 to 1998 based on N export from different land use types defined in a GIS-based assessment model, incorporated with estimates of N inputs from atmospheric deposition and point sources. Agriculture contributes 38% of the total export, varying in the range 35-85% in the south-western basins and 0-25% in the northern basins. This estimate of N export from agriculture was based on regional N balances together with data from small agricultural research catchments. Forestry contributes on average 9%, with increasing dominance towards eastern and northern parts of the country: from 2% to 15% in the southern-mid-western Finland basins to 10-30% in the large northern basins. 'Background' N export from forests on both mineral and organic soils contributes 27% on average; in the northern basins it may contribute from 40% up to 90% of the total load. The estimate was calculated based on practically all data available from 42 small, experimental catchments in Finland. Of the total N input to Finnish river-systems, 0% to 68% was retained in surface waters and/or peatlands, with a mean retention of 22%. The highest retention of N (36-61%) was observed in the basins with the highest lake percentages. The lowest retention (0-10%) of N was in the coastal basins with practically no lakes. In the national N mass balance, 38,000 tonnes N a(-1) (32%) was estimated as lake retention and 4,000 tonnes N a(-1) (3%) as retention in peatlands. On the basis of mass balances and sensitivity analysis, retention was in most cases estimated to be in the range of 7.5-12.5 kg ha(-1)a(-1) in lakes and 0-1.5 kg ha(-1)a(-1) in peatlands. The model results were tested using the split-sample technique and uncertainty estimates for different data sources are provided and discussed.
authors.affiliation: Finnish Environment Institute, SYKE, P.O.Box 140, FIN-00251 Helsinki, Finland. Ahti.Lepisto@ymparisto.fi
authors.forename: Ahti
authors.initials: A
authors.lastname: Lepistö
authors.forename: Kirsti
authors.initials: K
authors.lastname: Granlund
authors.forename: Pirkko
authors.initials: P
authors.lastname: Kortelainen
authors.forename: Antti
authors.initials: A
authors.lastname: Räike
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring; D005387:Finland; D016468:Forestry; D005843:Geography; D008962:Models, Theoretical; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D009930:Organic Chemicals / Q000032:analysis / Q000378:metabolism; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism; D045483:Rivers / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D014873:Water Pollutants / Q000032:analysis*; D014881:Water Supply
chemical_list: D009930:Organic Chemicals; D012989:Soil Pollutants; D014873:Water Pollutants; D010758:Phosphorus; D009584:Nitrogen