Abias Uwimana

PhD fellow

Biography

Abias UWIMANA graduated from the MSc Programme in Water Resources and Environmental Management, in University of Rwanda in 2008. His MSc topic was the characterization and management of water treatment sludge.

Since 2008 to 2015, he has been working as a laboratory analyst for water quality and Assistant Lecturer at the University of Rwanda and was appointed Lecturer in 2016.
 

Topic

Rehabilitation of Sediment and Nutrient Retention Functions in Wetland s of Migina Catchment, Rwanda

Research Summary

This research assesses the effects of conversion of natural wetlands to agricultural farms on the water quality and retention of sediments, nitrogen and phosphorus.  Migina catchment in Rwanda was selected as a study model because the land there is very steep and exposed to high human pressure. To achieve the study objectives several approaches were used involving a combination of landscape-scale synoptic surveys (catchment, reaches and experimental plots) of land use and land cover (agricultural farms, fishponds/dam, forest/wetlands), landscape features (slope, area, length, population density), rainfall, water discharge and water quality parameters (nitrogen, phosphorus, suspended solids , dissolved oxygen, conductivity, pH and temperature). Results have shown that EC, temperature, DO and pH decreased with increasing discharge. TSS related positively to discharge, increasing 2-8 times during high flow periods. TN and TP followed a mechanism of buildup in the dry season, washout in early periods of high flows and dilution at the late stages of rainy periods. Seasonally, there was a strong relationship between net yield and discharge, with 93%, 60% and 67% of the annual TSS, TP and TN yields, respectively, transported during 115 days with rain. Fishponds acted as temporal traps of sediments and nitrogen and phosphorus at early farming stages, and a source of and nitrogen and phosphorus at the end of farming, in contrary to rice farming that generated sediments and nutrients at early farming period and trap them at the end of farming. Biomass nutrient uptake was higher in rice farms (45%) and wetlands (36%), in contrast to fishponds (0.61%) where most of nitrogen and phosphorus accumulated in the pond sediments (>90%). Despite fertilizer input in rice farms (10 times higher than in fishponds) and the absence fertilizer input in wetlands, nutrient soil storage decreased (by 4.7 and 1.4% for nitrogen and phosphorus respectively) in rice farms, but increased (by 3.3% and 4.4% of nitrogen and phosphorus respectively) in fishponds and (by 3.8% and 1% of nitrogen and phosphorus respectively) in wetlands. It is very important to consider the efficient recycling of water, sediments and nutrients through rotational rice crops in fishpond sediments. Wetlands could also be integrated with rice and fish farming and act as sediment and nutrient buffer systems in the critical periods of faming (rice farm ploughing and weeding, and pond drainage).

Publications

Uwimana, A., Nhapi, I., Wali, U.G., Hoko, Z., Kashaigili, J., (2010). Sludge characterization at Kadahokwa water treatment plant. Water Science and Technology : Water Supply - WSTWS 10.5, 847-858.

Uwimana, A., van Dam, A., Gettel, G. et al. (2017) Effects of River Discharge and Land Use and Land Cover (LULC) on Water Quality Dynamics in Migina Catchment, Rwanda, Environmental Management 60: 496-512pp. https://doi.org/10.1007/s00267-017-0891-7.

Uwimana, A., van Dam, A., Gettel, G. et al. (2018) Effects of Agricultural Land Use on Sediment and Nutrient Retention in Valley Bottom Wetlands of Migina Catchment, Southern Rwanda, 219: 103-114 pp. https://doi.org/10.1016/j.jenvman.2018.04.094

Uwimana, A., van Dam, A., Irvine, K., 2018. Effects of conversion of wetlands to rice and fish farming on water quality in valley bottoms of the Migina catchment, southern Rwanda.  Ecological Engineering , Volume 125, 15 December 2018, Pages 76-86. https://doi.org/10.1016/j.ecoleng.2018.10.019

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