Modeling Combined Effects of Forestry, Agriculture and Deposition on Nitrogen Export in a Northern River Basin in Finland

Abstract The development of the spatial N export and retention model N_EXRET for large river basins is presented, utilizing remote-sensing-based land use and forest classification. Export coefficients describing the contribution from agriculture, forestry and peat harvesting were estimated based on empirical studies. Representativeness of forest treatment coefficients have been evaluated by use of data from a small, well-documented test catchment. Simulation results from the application of the model to the Oulujoki river basin (22 840 km2) are discussed. Model estimated N fluxes were compared with measured N fluxes in separate points of the river basin. Based on source apportionment, agriculture contributes 17% of the total export, varying between 8% in the uppermost subbasin and 38% in the lowermost subbasin close to the sea. Forestry contributes almost as much, 16%, with less pronounced variation (11–24%) between the different sub-basins. In the separate subbasins, 7–37% of the incoming gross N export was retained. Based on mass balances and sensitivity analyses, retention was estimated to be in the range of 5–10 kg ha−1yr−1 in lakes and 0–1 kg ha−1yr−1 in peatlands. The model results were validated by testing to data from the 3 closely situated river basins. However, further testing is needed in river basins where land use and deposition patterns differ clearly from these northern basins.

[1]  R. Andersson,et al.  Leaching of nitrogen from a forest catchment at söder»sen in southern Sweden , 1991 .

[2]  W. Boynton,et al.  The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean , 1996 .

[3]  Erik Jeppesen,et al.  Modelling of seasonal variation in nitrogen retention and in-lake concentration: A four-year mass balance study in 16 shallow Danish lakes , 1996 .

[4]  M. Jansson,et al.  Sedimentation and mineralisation of organic carbon, nitrogen and phosphorous in a large humic lake, northern Sweden , 1997 .

[5]  Penny J Johnes,et al.  Evaluation and management of the impact of land use change on the nitrogen and phosphorus load delivered to surface waters: the export coefficient modelling approach , 1996 .

[6]  Gene E. Likens,et al.  Technical Report: Human Alteration of the Global Nitrogen Cycle: Sources and Consequences , 1997 .

[7]  Ari Nissinen,et al.  Effects of nitrogen deposition on tree growth and soil nutrients in boreal Scots pine stands , 1998 .

[8]  N. Nikolaidis,et al.  MODELING OF NONPOINT SOURCE POLLUTION OF NITROGEN AT THE WATERSHED SCALE 1 , 1998 .

[9]  Rebecca J. Lunn,et al.  DEVELOPMENT AND APPLICATION OF A NITROGEN MODELLING SYSTEM FOR LARGE CATCHMENTS , 1996 .

[10]  F. Wulff,et al.  LONG-TERM, SEASONAL AND SPATIAL VARIATIONS OF NITROGEN, PHOSPHORUS AND SILICATE IN THE BALTIC - AN OVERVIEW , 1988 .

[11]  Achim Drebs,et al.  Suomen vesitase 1961-1990 valuma-alueittain , 1995 .

[12]  H. Grip.  Water chemistry and runoff in forest streams at Kloten , 1982 .

[13]  Erkki Tomppo,et al.  Kunnittaiset metsävaratiedot 1990–94 , 1970 .

[14]  A. Bleeker,et al.  Nitrogen and Phosphorus Fluxes from Finnish Agricultural Areas to the Baltic Sea , 1995 .

[15]  G. Likens,et al.  Technical Report: Human Alteration of the Global Nitrogen Cycle: Sources and Consequences , 1997 .

[16]  G. Billen,et al.  N, P and Si retention along the aquatic continuum from land to ocean , 1991 .

[17]  P. Dillon,et al.  Retention and Resuspension of Phosphorus, Nitrogen, and Iron in a Central Ontario Lake , 1990 .

[18]  Jari Varjo.  Change detection and controlling forest information using multi-temporal Landsat TM imagery. , 1997 .

[19]  P. Huttunen,et al.  Long-term effects of forestry managements on water quality and loading in brooks , 1999 .

[20]  B. Arheimer,et al.  Influence of catchment characteristics, forestry activities and deposition on nitrogen export from small forested catchments , 1995 .

[21]  D. Schindler,et al.  Ecological effects of acid deposition upon peatlands: a neglected field in «acid-rain» research , 1984 .

[22]  B. Arheimer.  Riverine nitrogen : Analysis and modelling under Nordic conditions , 1999 .

[23]  Kenneth H. Reckhow,et al.  An Examination of Land Use - Nutrient Export Relationships , 1982 .

[24]  H. Behrendt.  A comparison of different methods of source apportionment of nutrients to river basins , 1999 .

[25]  Maja Brandt,et al.  Modelling nitrogen transport and retention in the catchments of southern Sweden , 1998 .

[26]  S. Syri,et al.  Application of nitrogen transfer matrices for integrated assessment , 1998 .