Effect of land use/cover on water quality of River Rwizi, Mbarara municipality, Uganda

Abstract

Understanding the effect of land use/cover on water quality is helpful for effective water quality management. In this study, spatial and temporal variations of water quality of River Rwizi, Mbarara municipality, Uganda were assessed using analysis of Variance (ANOVA), Principal component analysis (PCA), Redundancy analysis (RDA) in a GIS environment. Water samples from eight sites were analyzed for physical-chemical and microbial parameters seasonally. Statistical analysis revealed that in the rainy season, TSS (114.8) mg/l, Turbidity (102.09) NTU, BOD (30.9) mg/l, TN (20.6), TP (17.2), NO3-N (16.8), O-PO4 (3.2) mg/l, Faecal coliform (363) /100ml and Faecal streptococci (319) /100ml displayed higher values. In the dry season, DO (10.5) mg/l displayed higher values. Six different land uses/cover existed in this area with Grassland (27.4%), Forests (22.2%) and cultivation (22%) as the dominant ones. In the dry season, built up areas positively correlated with pH (0.532), faecal coliforms (0.438), Escherichia Coli (0.422), Nitrates (0.402); and negatively correlated to Hardness (-0.444). In the rainy season built up areas positively correlated to BOD (0.429), DO (0.426) and negatively to Temperature (-0.435). Cultivation correlated positively to TN (0.449) and negatively to Turbidity (-0.489) in the dry season. Forests negatively correlated to TDS (-0.486) in the dry season; and negatively correlated to phosphates (-0.626) and turbidity (-0.472) in the rainy season. Wetlands only correlated to faecal streptococci (0.414) in the rainy season. These results revealed that water pollution in river Rwizi resulted primarily from Built up areas therefore they should be critical areas of river restoration or management. Also Forests in Rwizi catchment should be preserved as they help in water filtration.