Geospatial Analysis for Heavy Metals and Water Quality Assessment in Bugesera Agricultural Wetlands of Rwanda

Abstract

Agricultural wetlands are crucial ecosystems for provision of food, water purification, soil retention, nutrients cycling, to name few. However, they are more exposed to heavy metals deposition generating ecological concerns. Therefore, spatially explicit study for water quality and heavy metals’ contents in wetlands to reveal metal contamination sources are key steps for sustainable utilization of water resources in irrigated wetlands. Water samples were collected from surface water alongside the Gashora river. Three sampling sites (Karugenge, Karumuna and Muzi) were selected as the show high occurrence of flooding in wetland. A Global Positioning System (GPS) was used to obtain positional data where surface water samples were collected. A point (vector) database was developed for the attributes of soil, water, and associated parameters. The Photometric, calcination, titration and atomic adsorption spectrometer machines were used to detect the heavy metals. The application of GIS analysis through interpolation using Kriging was used to generate the predictive maps. Principal Components Analysis techniques was used to correlate water quality parameters for similarities and dissimilarities through cluster analysis. All statistical analyses were performed using STATA 13.0 and ArcGIS 10.5 was used to generate prediction maps. The study findings on water quality analysis shows that the ranges of heavy metals were Ca, Mg, Na, K, Cu, Zn, Mn, Pb, Cd and Cr concentration were 3.9–23; 10–22; 2–11; 10.6 –20.6; -7– 210; 0.63– 0.81; 110–160; 0.37–12; 0.15– 0.78; and 0.23–4.4ppm while for water quality analysis, the ranges for pH, EC, TDS, TH, SAR, MAR, KR and SSP concentration were 7–7.8; 190–300; 130–200; 55 –150; 26– 110; 47– 73; 8.2–72 and 35–60 respectively. The greatest heavy metals show maximum values compared to Rwanda national and international permissible limits for irrigation. Thus, there is a need of water treatment to reduce the harmfulness effect to plant and human being.