An assessment of the impacts of land use change on water quality and discharge – a case study of Chongwe catchment

Goodson Masheka; Chewe Mwila; Mweene Himwiinga– Mufiti; Muumbe Lweendo

Goodson Masheka Mulungushi University, Department of Engineering
Chewe Mwila 1Mulungushi University, Department of Engineering
Mweene Himwiinga– Mufiti 1Mulungushi University, Department of Engineering
Muumbe Lweendo

Keywords: Discharge, water quality, land use/land cover (LULC), geographical information system (GIS), remote sensing (RS)

Abstract

The impact of Land Use and Land Cover (LULC) changes on water quality and discharge is critical for regional water security. In this study, the effects of LULC changes on water quality and discharge in Zambia’s Chongwe River were evaluated. Spatio-temporal changes in LULC from 1980 to 2021 were analyzed at 10-year intervals, correlating LULC changes with river water quality. To determine trends in water quality, the study employed the Mann-Kendall (MK) test for statistical assessment. Time-series Landsat images were analyzed through supervised classification, allowing quantification of LULC changes over time. Five main LULC classes were identified based on spectral reflectance signatures, focusing on Agriculture, Forest, Built-up, and Grasslands. Significant shifts in land use patterns were observed between 1980 and 2021. Built-up and agricultural lands expanded, while forest and grassland areas declined. From 1980 to 1990, agricultural land increased from 0.91% to 1.08%, built-up land from 0.87% to 1.10%, and grasslands from 64.93% to 68.62%. In contrast, forest lands decreased from 32.96% to 29.03% and water bodies from 0.34% to 0.19%. Between 2000 and 2021, agricultural land rose from 5.63% to 11.01%, and built-up land from 1.32% to 4.65%, while forest land decreased from 31.01% to 24.12%, grasslands from 61.90% to 60.17%, and water bodies from 0.14% to 0.05%. The MK test results for water quality parameters such as pH, EC, TDS, Na, Cl, and Mg showed an increasing trend, while temperature, Fe, K, and SO4²⁻ decreased over the catchment at the four sampling stations. These trends are primarily attributed to expanded built-up areas and agricultural land, leading to increased impervious surfaces and enhanced surface runoff from cultivated lands, which transports chemical fertilizers to the river. Furthermore, dry season discharge levels were found to be significantly affected by water abstraction for irrigation and domestic use.

The study concluded that LULC changes significantly correlate with water quality. Specifically, agricultural land showed a negative correlation with discharge in the dry season, while built-up areas exhibited a positive correlation.