INSTITUT FÜR HYDROLOGIE ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG I.BR. Sebastian Wrede Distributed Solute Transport Modelling in the Fyrisån Catchment in Sweden Diplomarbeit unter Leitung von Prof. Dr. Ch. Leibundgut Freiburg i. Br., März 2005 INSTITUT FÜR HYDROLOGIE ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG I.BR. Sebastian Wrede Distributed Solute Transport Modelling in the Fyrisån Catchment in Sweden Referent: Prof. Dr. Ch. Leibundgut Koreferent: Dr. J. Lange Diplomarbeit unter Leitung von Prof. Dr. Ch. Leibundgut Freiburg i. Br., März 2005 How could drops of water know themselves to be a river? Yet the river flows on Antoine de Saint-Exupéry Acknowledgements First of all, I would like to thank my supervisors Dr. Jan Seibert and Prof. Dr. Stefan Uhlenbrook. They were always patient to answer my various questions and supported my work in numerous ways. The motivation and scientific advice given by Prof. Dr. Uhlenbrook during my time at the University in Freiburg and my visit in Delft encouraged me throughout the scientific work of this thesis. Dr. Seibert provided continuous support and constructive comments during my time at Stockholm University. My thanks go as well to my referent Prof. Dr. Christian Leibundgut and my coreferent Dr. Jens Lange for giving me the opportunity to write this thesis in close cooperation with the University of Stockholm. Finally I would like to thank several persons for their contribution to this thesis: Steve Lyon, Thomas Grabs, Ingo Heidbüchel, Helen Dahlke, Jennie Tjernell, Linda Gren, Anne Wildfang, Christoph, Claire and Bernhard Wrede for supporting me in different ways throughout my diploma time. Your help was really appreciated. Funding for residence in Sweden was partly provided by the German Academic Exchange Service (DAAD) and is gratefully acknowledged. Sebastian Wrede Contents I Contents Contents..................................................................................................................................... I List of figures ......................................................................................................................... IV List of tables ........................................................................................................................... VI Notations................................................................................................................................VII Abstract .................................................................................................................................. XI Zusammenfassung .............................................................................................................. XIII 1. Introduction ......................................................................................................................1 1.1. Objectives ...................................................................................................................3 1.2. Procedure....................................................................................................................4 2. Background.......................................................................................................................5 2.1. Nitrogen sources and transformation..........................................................................5 2.1.1. Nitrogen leakage from the terrestrial system......................................................5 2.1.2. Nitrogen sources and retention in the aquatic system ........................................8 2.1.3. Link to catchment characteristics .....................................................................10 2.2. Models for nitrogen transport simulations................................................................10 3. The Fyrisån catchment...................................................................................................14 3.1. Morphology, topography and land use.....................................................................14 3.2. Climate .....................................................................................................................16 3.3. Hydrology.................................................................................................................17 3.4. Chemistry .................................................................................................................18 4. Model development ........................................................................................................19 4.1. Software framework .................................................................................................19 4.1.1. PCRaster ...........................................................................................................19 4.1.2. PEST.................................................................................................................19 4.2. Hydrological model ..................................................................................................20 4.2.1. Basic model concept.........................................................................................20 4.2.2. Regionalisation of climatic input variables ......................................................22 4.2.3. Snow accumulation and melt............................................................................22 4.2.4. Urban runoff.....................................................................................................24 4.2.5. Soil moisture accounting ..................................................................................24 4.2.6. Runoff generation.............................................................................................27 4.2.7. Sub-grid variability...........................................................................................32 4.2.8. Channel routing and lakes ................................................................................34 4.2.9. Water management...........................................................................................35 4.2.10. Run-time performance enhancements of the model.........................................35 4.2.11. Verification.......................................................................................................36 4.2.12. Parameterisation ...............................................................................................36 4.2.13. Evaluation model and objective functions .......................................................38 4.3. Solute transport model..............................................................................................38 4.3.1. Basic model concept.........................................................................................38 4.3.2. Modelling nitrogen transport............................................................................40 4.3.3. Modelling terrestrial leakage............................................................................41 4.3.4. Modelling retention..........................................................................................42 II Contents 4.3.5. Verification ...................................................................................................... 44 4.3.6. Parameterisation............................................................................................... 45 5. Data base......................................................................................................................... 46 5.1. Spatial data............................................................................................................... 48 5.1.1. Digital elevation model.................................................................................... 48 5.1.2. River network and local drainage network ...................................................... 48 5.1.3. Land use........................................................................................................... 49 5.2. Meteorological and hydrological data...................................................................... 49 5.3. Chemistry data......................................................................................................... 51 5.3.1. Non-point source emissions............................................................................. 51 5.3.2. Point source emissions..................................................................................... 53 5.3.3. Water chemistry monitoring network .............................................................. 54 5.4. The Fyrisån data base............................................................................................... 54 6. Synoptic sampling campaign ........................................................................................ 56 6.1. Basic concept........................................................................................................... 56 6.2. Experimental details................................................................................................. 57 6.2.1. Rational for the location of sample sites.......................................................... 57 6.2.2. Sampling .......................................................................................................... 59 6.2.3. Laboratory analysis.......................................................................................... 60 6.2.4. Calculation of runoff and loads........................................................................ 60 6.2.5. Sourcesheds and land use