Assessment of nitrogen retention in the Seine river basin by different approaches

Transcription

1 Assessment of nitrogen in the Seine river basin by different approaches Grizzetti B. 1, Passy P. 1, Billen G. 1, Garnier J. 1, Bouraoui F. 2 1 CNRS/University Pierre et Marie Curie, Paris, France 2 European Commission, JointResearchCentre, Ispra, Italy SWAT Conference, July 2013, Toulouse, France

2 Objective Assess the nitrogen in the Seine river basin (~ km 2, France) by three models : GREEN, RiverStralher and SWAT Reflect on nitrogen in the river basin and its modelling representation Nitrogen definition Modelling approaches: GREEN RiverStralher SWAT Nitrogen in the Seine river basin

3 Nitrogen cascade Quantify nitrogen fluxes? Processes WATER (Sutton et al. 2011; Galloway et al. 2003; 2008)

4 Nitrogen River basin Nitrogen : permanent or temporary removal of nitrogen in the river basin Aquatic continuum from land to ocean (Billen et al. 1991) Soils groundwaters riparian zones, floodplains Rivers estuaries

5 diffuse Nitrogen in the aquatic continuum Soil Riparian zone point Aquifer River Hyporheic zone

6 Model GREEN Grizzetti et al. (2008; 2013) diffuse point Basin River Conceptual statistical regression model Sub-catchments ~170 km2 Annual nitrogen load Application at the European scale

7 Model RiverStralher Billen and Garnier (2000) Nitrogen leaching Riparian point Aquifer River Physically based model of stream processes plus conceptual model of nitrogen diffuse emissions from soils River axes (1km resolution), sub-basins (stream segments lumped by Stralher order) Daily nitrogen concentration Application in river basins

8 Model SWAT diffuse Crop uptake Soil Aquifer wetlands River Arnold et al. (1998) point Physically based model of water and nutrient processes in the river basin Sub-basins and Hydrological Response Unit (HRUs) Daily water flow and nitrogen concentration Application in river basins

9 jan feb mar apr may jun jul aug sep oct nov dec Temperature ( C) Area of study Seine river basin Altitude: m Seine river basin (Pose) ~65000 km 2 Geology: limestone, clays & chalk Soils: fertile agricultural soils Land use: 53% arable land 26% forest 13% grassland 7% urban 1% water (Station 610, Period ) Precipitation (mm) Temperature ( C) Population density: 215 inh/km 2 0 0

10 Predicted TotN Load (tonn) Results GREEN Seine river basin (Pose): 351 sub-basins Grizzetti et al. (2013) Nitrogen The model GREEN was calibrated against monitored 10 data for years for total N and total P (sub-catchment average area ~170 km 2 ) 1 E= Measured TotN Load (tonn)

11 Results RiverStralher Passy et al. (2013) Observed Modelled Spatial discretisation: 5 main river axes 21 sub-basins ~3000 stream segments

12 Results SWAT 45 sub-basins 373 HRUs

13 Water flow (m3/s) Results SWAT - water flow Water flow - Seine Pose Validation E=0.59 Observed Modelled Calibration E=

14 Water flow (m3/s) Water flow (m3/s) Results SWAT - water flow Water flow - Marne (at Gournay-sur-Marne) E=0.51 Observed Modelled E= Water flow - Yonne (at Courlon-sur-Yonne) E=0.68 Observed Modelled E=

15 NO3 (mgn/l) PO4 (mgp/l) Results SWAT - water quality NO3 - Seine Pose Modelled Observed PO4 - Seine Pose Modelled Observed Calibration E=

16 NO3 load (tonn/month) Results SWAT- water quality NO3 Load - Seine Pose Observed Modelled E= Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05

17 Comparison modelling approaches diffuse Basin GREEN RiverStrahler SWAT point River Load Diffuse emissions Aquifer Riparian point River Load diffuse Plant uptake Soil Aquifer Wetlands point River Load Conceptual model Sub-catchments ~170 km 2 Annual nitrogen load Conceptual & physicallybased model 5 axes, 21 sub-basins 10 days nitrogen concentration Physically-based model HRUs (373) Daily water and nitrogen flow

18 Nitrogen budget diffuse point 93 6 Basin GREEN RiverStrahler SWAT River 5 Load 14 (kgn/ha) Diffuse emissions 16 point 8 28 River 12 3 Riparian Load 21 (kgn/ha) diffuse Crop uptake Soil Aquifer Wetlands 18 point River Load Annual values for the period: (kgn/ha)

19 ton N/yr Nitrogen river Nitrogen GREEN River Ret SWAT River Ret RS River Ret RS Riparian Ret Annual average flow (m3/s) (secondary axis) 0 0

20 Concluding thoughts To better manage nitrogen we need to improve our understanding of the processes and our capacity of quantifying the fluxes Comparing modelling approaches understanding of processes and uncertainty of estimates Models GREEN, RiverStralher, SWAT Processes riparian areas, aquifer, delay of nitrogen pollution accumulated in aquifers

21 Thank you SWAT Conference, July 2013, Toulouse, France