Evaluation of the effect of wetland conversion on quantitative soil properties and water quality in namutumba district, Uganda

Abstract

There are many land use changes happening in Uganda whose impacts have not yet been well studied. This study determined the land use changes that occurred in Namutumba districts between 1988 and 2018 and determined the effect of wetland conversion on soil properties and water quality. Landsat images of resolution of 30 m were downloaded from landsat.org for a period of 30 years; 1988, 1998, 2008 and 2018. Image classification was done using Maximum Likelihood Classification and percentage change in areas under different land uses were determined for years; 1988-1998, 1998-2008 and 2008-2018. Representative soil samples and water samples were collected from cultivated wetlands and uncultivated wetlands in the different water systems of Naiyede, Mpologoma, Naigomba and Namakoko in Namutumba district. The soil and water samples were assessed for pH, organic matter (OM), nitrogen (N), phosphorous (P), potassium (K), boron (B), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), iron (Fe), sodium (Na), manganese (Mn), cadmium (Cd), lead (Pb), colour, total hardness (TH), total dissolved solids (TDS), total suspended solid (TSS), turbidity, nitrates (NO3-), total solids (TS), pH, alkalinity, conductivity (Co), chromium (Cr), phosphates (PO43-), chloride (Cl), Cd and sulphates (SO42-). Results of land use change indicated a reduction in areas under open water, wetlands, woodland and bush lands and increase in built up areas and wetlands. Cultivation of wetlands significantly (p<0.05) increased the amounts of P, Na and Cd. However, there were significantly (p<0.05) lower average amounts of quantitative soil properties; pH, OM, N and Cu in cultivated wetlands as compared to the uncultivated. Cultivation of wetlands significantly (p<0,05) increased water quality parameters; TDS, TSS, conductivity, Na, Ca, Cl, SO42-, PO43- and TH. On the other hand, water quality parameters; pH, Co, alkalinity, Mg, Cr, Fe, Cd and NO3- were not significantly (p>0.05) affected by cultivation. It can be concluded that most of the fragile ecosystems in Namutumba District is being converted into built up areas and farmlands and it is negatively affecting some of the soil and water quality parameters. These results are crucial in informing policy makers in designing by-laws and policies for protecting fragile ecosystems such as wetlands from degradation.