Surface Water Quality Response to Land Use Land Cover Change in an Urbanizing Catchment: A Case of Upper Chongwe River Catchment, Zambia

摘要

The Upper Chongwe River Catchment has recently been overexploited for water resources with increased complaints by various water users about the deteriorating quality of surface water within the sub-catchment. This study was motivated by the need to investigate and understand the response of surface water quality to land use land cover (LULC) change due to urbanization. Water samples, collected at 9 sampling sites from 2006 to 2017, were analyzed for water quality using the weighted arithmetic water quality index and trend using the Mann-Kendall statistics. LULC change is detected and analyzed in ERDAS Imagine 2014 and ArcGIS 10.4 using 2006 Landsat 5 TM and 2017 Landsat 8 OLI imageries. The relationship between LULC change and water quality was performed with multiple regression analysis and Pearson correlation. The results reveal that Built-up area, Grassland and surface water increased by 5.48%, 13.34% and 0.03% respectively while Agricultural land and Forest Land decreased by −13.41% and −5.42% respectively. The water quality index ranged from 43.04 to 110.40 in 2006 and from 170 to 430 in 2017 indicating a deterioration in the quality of surface water from good to unsuitable for drinking at all the sampled sites. Built-up/bare lands exhibited a significant positive correlation with EC (R2 = 0.61, p ≤ 0.05), turbidity (R2 = 0.69, p ≤ 0.05), TDS (R2 = 0.61, p ≤ 0.05), Cl (R2 = 0.62, p ≤ 0.05) and a significant negative correlation with NH₄ (R2 = style="white-space:nowrap;">−0.729, p ≤ 0.05). Agriculture exhibited a significant positive correlation with turbidity (R2 = 0.71, p ≤ 0.01) and Fe (R2 = 0.75, p ≤ 0.01. Forest cover correlated negatively with most of the water quality parameters apart from Fe, DO, NO₃ but was not statistically significant. Grassland had a significant negative correlation with temperature (R2 = style="white-space:nowrap;">−0.68, p ≤ 0.05). Clearly, urbanization has made a disproportionately strong contribution to the deterioration of surface water quality indicating that intensive anthropogenic activities exacerbate water quality degradation. These results provide essential information for land use planners and water managers towards sustainable and equitable management of limited water resources.