Spatio-temporal variations in physicochemical water quality and the impact of land use/land cover change In River Athi Basin, Kenya.

Abstract

The growing impacts of natural processes and human activities on water quality at global, regional, and local scales are raising concerns. The River Athi Basin natural gravitational flow toward lower elevations, ultimately reaching the Indian Ocean, facilitates waste disposal practices among the residence located along the river bank. This study sought to determine the Spatiotemporal Variations in Physicochemical Water Quality and the Impact of Land Use/Land Cover Change in the Mid Reaches of River Athi Basin, Kenya by; 1) examining the influence of land use/land cover change in river Athi Basin from 2015 to 2023. (2) Determining seasonal variation in the physicochemical water quality of the river Athi Basin. (3) Assessing the spatial variation in physicochemical water quality of the river Athi Basin. The study examined the influence of LULC changes from 2015 to 2023 using Landsat 8 imagery, GIS, remote sensing, and GPS technologies for data extraction, image processing, and LULC analysis. Pearson correlation analysis assessed spatial differences of land use land cover impacts on water quality across six sampling stations in the basin. Interview survey was used to supplement the water quality dataset. The studies applied multivariate analysis for spatial and temporal reduction of the multidimensional dataset and identification of pollution sources. Seasonal variations in the physico-chemical water quality of River Athi Basin was determined using eight physicochemical parameters (pH, EC, TDS, NO₃, K, PO₄, BOD, and COD) and two heavy metals (Cd and Cr). Data collection was carried out during two distinct seasonal periods: the short dry and rainy season (August-September for dry, November-December for rainy) in 2023, and the long dry and rainy season (January-February for dry, April-May for rainy) in 2024. An independent T-test was used to compare the mean levels of water quality parameters between dry and rainy seasons. The study assessed spatial variation in the physicochemical water quality of the river basin, covering six sampling stations. One way analysis of variance (ANOVA) compared the mean values of variables of the sampling stations. Multiple linear regression tested the influence of pH, EC, TDS, NO3, K, and PO4 on BOD and COD (oxidation parameters) and cadmium and chromium (heavy metals). The Pearson Product-Moment Correlation Coefficient (PPMCC) assessed the relationships between water physicochemical parameters and heavy metals in seasonal and spatial variations in water quality of the river basin. The findings on LULC analysis show notable shifts in land use from 2015 to 2023. Between these periods, the overall built-up increased to 0.29%, bare-lands declined by 7.06%. Farmlands, forests, and grasslands were elevated by 0.52%, 4.54%, and 2.77%, with decline in open waters by 1.24%. Spatial LULC difference with correlation analysis reveal higher amounts of EC, TDS, Cd, Cr, NO3, and PO4 influencing water quality. Interview survey revealed settlements, agriculture, and climate conditions as the main causes of degradation of water quality. Seasonal finding reveal significant fluctuations in pollution, with the dry season exhibiting higher pollution levels. February demonstrate proliferated temporal pollution, characterized by high concentrations of EC, TDS, BOD, and COD. Spatial finding demonstrated significantly higher pollution signatures in Athi River Town, Stony Athi, and NYS stations, while NYS contribute to higher levels of nutrients, organic pollutants, and heavy metals. In contrast, the control station and Kibwezi Bridge station demonstrates effective self-purification processes. Multivariate analysis revealed pollution sources over time and space in the River Basin. The stable pH levels over time and space was influenced by the buffering capacity. Multiple regression analysis indicates that physicochemical parameters, such as pH, EC, TDS, NO₃, K, and PO₄, explain 62% of BOD variation and 70% of COD variation, as well as 36% of both Cd and Cr variations. Pearson correlation analysis shows strong links between EC, TDS, BOD, and heavy metals (Cd, Cr), with significant associations among nutrients and other water quality indicators. Natural and anthropogenic activities are pivotal drivers of the water quality degradation of River Athi Basin over time and space. This study recommends that the National Environmental Management Authority (NEMA) and the National Environmental Policy (NEP) strengthen regulations on environmental management, water resource conservation, sustainable land use, public health protection, irrigation control, forest preservation, and aquatic ecosystem conservation in order to support global efforts toward achieving Sustainable Development Goals (SDGs).