The study used a combination of landscape-scale synoptic surveys (catchment, reaches) and mesocosm surveys (experimental plots) to assess the impacts of conversion of natural valley-bottom wetlands to farming land on the water quality and retention of sediment and nutrients. The results showed that temperature, pH, electrical conductivity and dissolved oxygen concentration decreased, and total suspended solids (TSS) increased with storm water increase. Nitrogen (TN) and phosphorus (TP) accumulated in the catchment during the dry season and washed into the water courses during the early stages of the higher flows, with subsequent lower concentrations at the end of the rains due to dilution. Large proportions of the annual loads of TSS, TP and TN (93%, 60% and 67%, respectively) were transported during rainfall events that occurred in 115 days. Fishponds acted as temporal traps of TSS, TN and TP at the early stages of farming, and were a source of and TN and TP at the end of the farming period, in contrast to rice farming that generated sediments and nutrients early in the farming period and trapped them at the end of the farming season. Wetlands mostly acted as sinks but sometimes as a source of sediment and nutrients.
Table of Contents
1. General introduction
2. Effects of river discharge and land use and land cover (LULC) on water quality dynamics in Migina Catchment, Rwanda
3. Effects of agricultural land use on sediment and nutrient retention in valley-bottom wetlands of Migina catchment, southern Rwanda
4. Mesocosm studies on the effects of conversion of wetlands to rice and fish farming on water quality in valley bottoms of the Migina catchment, southern Rwanda
5. Mesocosm studies on the impacts of conversion of wetlands into fish and rice farming on sediment and nutrient loads to surface water
6. Effects of wetland conversion into farming on water quality, sediment and nutrient retention - synthesis, conclusions and recommendations
Abias Uwimana was born on 8 September 1975 at Kora, Gisenyi in Rwanda. After completing his primary and secondary education, he served as a primary school teacher at Kijote Primary School from 1999 to 2000. From 2000, he enrolled in the Bachelor's programme at the National University of Rwanda (NUR) and graduated in Chemistry in 2005. In 2007, he started his MSc studies in Water Resources and Environmental Management at NUR and graduated in 2008. In the same year, he started working at NUR as Assistant Lecturer and Laboratory Analyst for water quality. In 2009, he started his PhD studies at the IHE Delft Institute for Water Education in Delft, The Netherlands, conducting his PhD research activities while continuing his academic duties at the university, including teaching courses on environmental chemistry and management and water quality analysis, performing laboratory analyses, and supervision of BSc and Msc theses. As a laboratory analyst he took part in the Victoria Research (VICRES) project on assessment of water quality in the Akagera River since 2008-2009. In 2016, he received an international Travel Award to Corpus Christi, Texas, USA to present his work at the Annual Meeting of the Society of Wetland Scientists. Abias Uwimana is married and has three children.