Environmental Management DOI 10.1007/s00267-017-0891-7 Effects of River Discharge and Land Use and Land Cover (LULC) on Water Quality Dynamics in Migina Catchment, Rwanda Abias Uwimana 1,2,3 ● Anne van Dam 1 ● Gretchen Gettel 1 ● Bonfils Bigirimana 2 ● Kenneth Irvine 1,3 Received: 27 September 2016 / Accepted: 5 May 2017 © Springer Science+Business Media New York 2017 Abstract Agricultural intensification may accelerate the loss of wetlands, increasing the concentrations of nutrients and sediments in downstream water bodies. The objective of this study was to assess the effects of land use and land cover and river discharge on water quality in the Migina catchment, southern Rwanda. Rainfall, discharge and water quality (total nitrogen, total phosphorus, total suspended solids, dissolved oxygen, conductivity, pH, and temperature) were measured in different periods from May 2009 to June 2013. In 2011, measurements were done at the outlets of 3 sub-catchments (Munyazi, Mukura and Akagera). Between May 2012 and May 2013 the measurements were done in 16 reaches of Munyazi dominated by rice, vegetables, grass/ forest or ponds/reservoirs. Water quality was also measured during two rainfall events. Results showed seasonal trends in water quality associated with high water flows and farming activities. Across all sites, the total suspended solids related positively to discharge, increasing 2–8 times during high flow periods. Conductivity, temperature, dissolved oxygen, and pH decreased with increasing discharge, while total nitrogen and total phosphorus did not show a clear pattern. The total suspended solids concentrations were consistently higher downstream of reaches dominated by rice and vegetable farming. For total nitrogen and total phosphorus results were mixed, but suggesting higher concentration of total nitrogen and total phosphorus during the dry and early rainy (and farming) season, and then wash out during the rainy season, with subsequent dilution at the end of the rains. Rice and vegetable farming generate the transport of sedi- ment as opposed to ponds/reservoir and grass/forest. Keywords Agriculture ● Discharge ● Land use ● Nutrients ● Water quality ● Wetlands Introduction Pollution by nutrients is recognized as the most widespread cause of water quality degradation (UN WWAP 2009), with runoff from agriculture a major source of nutrient and sediment pollution (USEPA 2005). In sub-Saharan Africa, agricultural intensification is critical to increase food security and economic development. Intensification occurs both by increasing the area of land under cultivation, and through an increase of fertilizer inputs and irrigation. Despite international recognition of the importance of wetlands and national policies for their protection, contra- dictory policies and practice lead to the conversion of wetlands to farmland throughout eastern, western, and southern Africa. Wetland conversion also occurs infor- mally, with wetlands used in the dry season for production of sugarcane, groundnut, vegetables, and fruits, as well as for grazing livestock (McCartney et al. 2010; Schuyt 2005; Wood et al. 2013). Loss of wetlands, often involving increases in fertilizer and irrigation, enhances risks of increased erosion and nutrient export (Verhoeven et al. 2006). Despite these pressures, there are very few field * Abias Uwimana abias.uwimana@gmail.com 1 Department of Water Science and Engineering, IHE Delft Institute for Water Education, P.O. Box 3015, Delft, DA 2601, The Netherlands 2 University of Rwanda, College of Science and Technology, P.O. Box 3900, Kigali, Rwanda 3 Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, Wageningen, AA 6700, The Netherlands