Modelling Transport of Nitrogen Compounds in Geita Wetland along Mtakuja River

Ezrael J. Masawe, Richard Kimwaga, Fredrick Mwanuzi


The impacts of excessive nitrogen loading to streams in a watershed occur in the receiving waters such as rivers at the outlet of the watershed. To quantify the impacts of land use and management practices on the nitrogen loading at the watershed outlet, simulation models are needed that can both predict the nitrogen loading at the edge of individual fields and predict the fate of nitrogen as it moves through the river network to the watershed outlet. This paper presents the results of a model analysis for describing the processes governing transformations and transport of nitrogen compounds (NO3-N and NH4-N) through Mtakuja River in the Geita wetland. The model was made in Soil and Water Assessment Tool (SWAT), a watershed model developed to assess the impact of land management practices on water, sediment and agricultural chemical yields with varying soils, land use and management conditions. Two monitoring stations namely MTSP1 and MTSP2 were established along Mtakuja River. A set of SWAT model inputs representative of the water conditions was collected from the established monitoring stations. The model was calibrated and validated for the prediction of flow and nitrogen compounds (NO3-N and NH4-N) transport, against a set of measured mean monthly monitoring data. Sensitive model parameters were adjusted within their feasible ranges during calibration to minimize model prediction errors. At the gauging station MTSP2, the calibration results showed that the model predicted mean monthly flow within 18% of the measured mean monthly flow with the r2 coefficient and Nash-Sutcliffe (NSE) were 0.84 and 0.82, respectively. At the water quality monitoring station MTSP2, the calibration results showed the model predicted nitrogen compounds (NO3-N and NH4-N) loadings within 21% and 23% of their respective measured mean monthly loadings. The mean monthly comparisons of r 2 values for nitrogen compounds ranged from 0.77 to 0.81 while the Nash-Sutcliffe Efficiency (NSE) values were between 0.72 and 0.73. The model results and field measurements demonstrated that about 70% of the annual nitrogen compounds loadings which would otherwise reach Lake Victoria are retained in the wetland. The Mtakuja river model can therefore be used for prediction of nitrogen compounds (NO3-N and NH4-N) transformation processes in the Geita wetland.


Keywords: Ammonia-nitrogen, Geita wetland, Mtakuja River, Nitrate-nitrogen, Soil and Water Assessment Tool (SWAT).

Full Text:



American Public Health Association (APHA), American Water Works

Association (AWWA), and Water Environment Federation (WEF) (2012). Standards Methods for Examination of Water and

Wastewater, 22nd ed., Washington, DC

Bosch D.D., Sheridian J.M., Batten H.L. and Arnold J.G. (2005). Evaluation of the SWAT model on a Coastal Plain Agricultural Watershed. Trans. ASAE, 47(5): 1493-1506.

Brown, L.C. and Barnwell Jr. T.O. (1987). The enhanced water quality models QUAL2E and QUAL2E-UNCAS documentation and user manual. EPA document EPA/600/3-87/007. USEPA, Athens, GA.

Cannel M.G.R. (1982). World Forest Biomass and Primary Production

Data. Natural Environmental Research Council, Institute of terrestrial

Ecology, Penicuick, Midlothian, Scotland Academic Press.

De Pauw E. (1984). Soils, Physiography and Agro-Ecological Zones of

Tanzania. Crop Monitoring and Early Warning Systems Project, FAO.

GCPS/URT/047/NET, Ministry of Agriculture, Dar es Salaam.

Dijkshoorn J.A. (2003). SOTER database for Southern Africa (SOTERSAF) – Technical Report. Wageningen, International Soil Reference and Information Centre.

DI Luzio M., Srinivasan R. and Arnold J.G. (1997). An Integrated User Interface for SWAT using ArcView and AVENUE. St. Joseph, MI,

American Society of Agricultural Engineers paper No. 97-2235

DI Luzio M., Srinivasan R. and Arnold J.G. (2002). ArcView Interface for SWAT2000 User’s Guide. Backland Research and Extension Center, Temple, Texas BRC Report 02-07. Texas Water Resources Institute, College Station, Texas. TWRI Report TR-193.

Gassman W.P., Reyes M.R., Green C.H. and Arnold J.G. (2005). SWAT peerreviewed literature: A review, Proceedings of the 3rd International SWAT conference, Zurich, Switzerland.

Jayakrishnan R., Srinivasan R., Santhi C. and Arnold J.G. (2005). Advances in the Application of the SWAT model for water resources management. Hydrol. Process. 19, 749762 (2005). Published online in Wiley InterScience. Available online at

Kayima J.K. and Mayo A.W. (2018). Characteristics of macrophytes in the Lubigi Wetland in Uganda. International Journal of Biodiversity

and Conservation, 10(10): 394-406, DOI: 10.5897/IJBC2018.1206.

Kayima J.K., Mayo A.W. and Norbert J. (2018). 'Ecological characteristics and morphological features of the Lubigi Wetland in Uganda. Environment and Ecology Research, 6(4): 218-228, DOI: 10.13189/eer.2018.060402.

Mac M.J., Opler P.A., Puckett Haecker C.E. and Doran P.D. (2010). Status and trends of the nation’s biological resources, 2 vol., US Department of the Interior, US Geological Survey, Reston, Va., 1998. Available online at Accessed on 24th June.

Nash J.E. and Sutcliffe J.V. (1970). River flow forecasting through conceptual models, Part1, A discussion of principles, Journal of Hydrology, 10: 282-290.

Neitsch S.L., Arnold J.G., Kiniry J.R. and Williams J.R. (2001). Soil and Water Assessment Tool Theoretical Documentation Version 2000: Draft – April 2001. US Department of Agriculture – Agriculture Research Service, Temple, Texas.

Ndomba P.M., Mtalo F.W. and Killingtveit A. (2005). The Suitability of SWAT model in sediment yield modelling for ungauged catchments: A case study of Simiyu river basin catchments, Tanzania. Proceedings of the 3rd International SWAT conference,

Zurich, Switzerland.

Wang Q.G., Dai W.N., Zhao X.H., Ding F., Li S.B. and Zhao Y. (2009).

Numerical model of thermal discharge from Laibin power plant based on Mike 21, Research of Environmental Sciences, 22(3): 332–336.

Sharpley, A.N. and Williams, eds., (1990). EPIC-Erosion Productivity Impact Calculator, model documentation. U.S. Department of Agriculture, Agricultural Research Service, Tech.Bul.1768.

Prasad S.N., Ramchandra T.V., Ahalya N., Sengupta T., Kumar A., Tiwari A.K., Vijayan V.S. and Vijayan L. (2002). Conservation of wetlands of India- a review, International Society for Tropical Ecology, 43(1): 173-186.

Van Griensven A., Francos A. and Bauwens W. (2002). Sensitivity

analysis and auto-calibration of an integral dynamic model for river water quality, Wat. Scie. Technol., 45(5):



  • There are currently no refbacks.