Analysis of Nutrient Dynamics in Roxo Catchment Using Remote Sensing Data and Numerical Modeling Imesh Chanaka Bihawala Vithanage March, 2009 Analysis of Nutrient Dynamics in Roxo Catchment Using Remote Sensing Data and Numerical Modeling by Imesh Chanaka Bihawala Vithanage Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree of Master of Science in Geo-information Science and Earth Observation. Specialisation: Integrated Watershed Modeling and Management. Thesis Assessment Board Professor Dr. Z. Bob Su, Chairman, WREM Department, ITC Dr. Ir. D.C.M. Augustijn, External Examiner, WEM Department, UT Dr. Ir C.M.M. Chris Mannaerts, First Supervisor, WREM Department, ITC Dr. B.H.P. Maathuis, Second Supervisor, WREM Department, ITC M. Yevenes, Advisor, WREM Department, ITC INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION ENSCHEDE, THE NETHERLANDS Analysis of Nutrient Dynamics in Roxo Catchment Using Remote Sensing data and Numerical Modeling Disclaimer This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Analysis of Nutrient Dynamics in Roxo Catchment Using Remote Sensing data and Numerical Modeling Abstract The water quality in catchments is influenced by the complex combinations of land use, point sources combined with weather and other natural and human influences. Agricultural non point source pollution is usually considered a major cause of water quality deterioration in larger agricultural catchments. Farmers usually tend to use more fertiliser with the intention of making more harvest without considering the optimum doses, and their effects on the environment. Excess nutrients leached through the watershed and are collected on the downstream water bodies, making them eutrophic, being excessive algae and/or plant growth due to an abundance of nutrients. The excess growth of algae and phytoplankton has various deleterious effects of the water storage and distribution systems like clogging of filters, reduction of dissolved oxygen (DO), unpleasant taste and odour. Some algae species (e.g., blue green algae) may be toxic to fish, animals (like birds) and even humans (Chapra, 1997). In addition ammonia (NH3), nitrates (NO3) and nitrites (NO2) can be harmful when present in excessive amounts in water. In this study, our aim was to research the hydrological and environmental processes associated with Nitrogen (N) and Phosphorous (P) compounds and their dynamics in the hydrological system of the Roxo catchment. A model is developed that simulates the catchment flow hydraulics and the water quality in the catchment and Roxo reservoir. A special effort was put in place to model the effects of the Beja city waste water treatment plant (WWTP) as a test case for the model. This WWTP is an identified nutrient point source in the upper catchment. The hydrological, physical and biochemical water quality processes have been developed using Duflow Modeling Studio (DMS) including its Rainfall Runoff component model (RAM), based on linear reservoir theory. RAM elements (runoff areas) permit simulation of runoff hydrograph at the detailed sub-catchment level and permit to simulate distributed nutrient source (N, P) apportionment of agricultural areas to streams. Because no direct stream flow gauging station was present existing in the upper Roxo, a reservoir water balance technique was used to estimate daily catchment stream flow to the reservoir. An extensive data set was available for this purpose. The hydrological model calibration and validation was based on this, was judged satisfactory. During summer periods, some small negative inflows were computed. These small estimation errors were considered due the precision in the level measurements, as well as uncertainties in some water abstraction values (extra unregistered withdrawals) or losses (evaporation, groundwater) from the reservoir especially during summer periods. The flow calibration of DMS was finally performed using cumulative decadal inflow values. Besides running of the DMS model using interpolations from daily rain gauge data, we have run the model with remote sensing derived rainfall data (i.e. the Meteosat Multi-sensor Precipitation Estimate or MSG-MPE). We used a density of 18 data extraction points to represent catchment rainfall inputs. A simulation period starting from Jan 2007 to May 2008 with daily time steps was used for the purpose, and was a function of the availability of the MSG satellite rainfall data products. The study showed that the MSG daily rainfall data is not properly correlated with the daily gauge precipitation records. However when compared with the entire period, the cumulative result showed good agreement with the i aggregated gauge station total rainfalls. The hydrologic responses produced using MPE showed that there are discrepancies with runoff hydrographs and this can be explained by the occasional high magnitude rainfalls recorded in the MPE that are significantly different from the gauge records. After calibration and validation of the flow model, and comparison of the rainfall runoff response using ground gauged rainfall and satellite precipitation inputs, nutrient export from the agriculture areas, and the impact of a point source (i.e., the WWTP) was simulated. These first results were interpreted and compared to observed stream and reservoir water quality data. Although, initial water quality modeling results are encouraging, and confirmed we were able to simulate the magnitudes and local spatial and temporal variations of the nutrient processes, much more model and parameter uncertainties need to be eliminated before the water quality model can be judge as appropriate for the upper Roxo catchment and the reservoir system. This can be obtained through further study and research. ii Analysis of Nutrient Dynamics in Roxo Catchment Using Remote Sensing data and Numerical Modeling Acknowledgements First and the foremost I am grateful to my employer National Water Supply and Drainage Board, Sri Lanka for allowing me to take this valued long-term fellowship to pursue with Master of Science Degree. At the same time I am thankful to ITC for offering me this esteemed MSc degree programme and also providing me with a scholarship for financing all expenses during 18 months period. I express my heartiest appreciation to my 1st supervisor Dr Ir. C.M.M Mannaerts for the support and guidance extended to me during this whole research period. The encouragement and the critical reviews had immensely helped in shaping up the thesis to the due expectations. Further, during the field campaign at Portugal, Chris’s assistance was enormous as he had not limit himself just a supervisor’s task but guided us at all possible occasions to get the maximum out of field visit. I would also acknowledge the Dr B.H.P Maathuis, my 2nd supervisor. He often supported me at critical junctures when struggling with technical issues. At the same time I am grateful to Drs J.B de Smeth for providing space at the laboratory and supplying ancillary logistics for performing water sample analysis and the supervision over performing water quality testing in due manner. I would also like to remember the Technical Director I. Oliveira and his staff of COTR, Engineer Alexandre Leal of EMAS, The Director ABROXO and Engineer R. Nobre from IPB (Beja) for the corporation extended to us in providing essential information for the success of this research study. I am also thankful to Mariella, Murat and colleagues Fransiska, Prescilla and Daphne, who were with me during the field campaign and for working as a team in attending the objectives. Moreover they made the field campaign more enjoyable. I would also like to acknowledge the lecturers of the WREM programme, whom made me equipped with proper tools and techniques to proceed with the research work. It is also essential to thank ITC library in providing essential information and resources, when I made a simple request to them. I also wish to thank all my friends in the WREM 2008 for giving suggestions, thoughtful reviews during this research phase. Last but not least, I would like to express my sincere gratitude to my family, Niroshini, Iresh and Harshi for the moral support and love they have showed me during this long duration I was away from them. Especially the tolerance they have showed during this tough time made this task possible for me and to concentrate more on my studies. Finally I wish thank my parents for supporting me in all possible ways and looking after my family with utmost care during this 18 months period. iii Table of contents 1. Introduction.................................................................................................................................1 1.1. Background......................................................................................................................1 1.2. Research problem.............................................................................................................2 1.3. Objectives ........................................................................................................................3 1.4. Research questions ...........................................................................................................3