Total suspended solids loading of stormwater from different land use areas in an urban watershed

Abstract

Purpose. Land use within a watershed affects surface water quality by creating a process by which diffuse pollutants such as suspended solids, trace metals, and nutrients enter rivers and streams. The purpose of this study is to assess pollution-load for Total Suspended Solids (TSS) and some trace metals in runoff samples collected during storm events in selected sub-catchment locations representing different land use areas in an urban watershed; and to determine the effects of land-use on the content of pollutants in stormwater using Event Mean Concentration (EMC).
 Results. There were high EMC and Site Mean Concentrations (SMC) of TSS in stormwater in the six land-use zones examined, with values ranging from 154.0 mg L−1 to 1464.0 mg L−1; and 216.5 mg L−1 to 1153.4 mg L−1 for EMC and SMC respectively. The total content of suspended solids was significantly high, above the acceptable threshold of 100.0 mg L−1 stipulated by the WHO. The researchers also found a statistically significant variation in TSS loading of stormwater from the commercial land-use areas compared with the other land-use zones. A strong correlation was also observed between the volume of stormwater discharged and the TSS load. However, the concentrations of trace metals in stormwater were low across the land use zones. The commercial districts of the studied cities were found to be major sources of suspended solids in stormwater, and pollution of the urban watersheds leading to the deterioration of the rivers.
 Scientific novelty. This study attempted to qauntify TSS load in stormwater and determine the contributions of the diffferent urban land-use areas to pollution yield.. It contributes to scientific efforts to directly quantify surface water pollution from nonpoint sources, since little attention has been paid to diffuse pollution, especially in sub-Saharan Africa; and provides baseline data for assessing urban stormwater in low-income countries.
 Practical value. This study offers guidelines for city authorities to develop land use policies to control surface water pollution and urban waste. The findings may also serve as emperical basis for greater advocacy by civil society organizations for the proper management and control of urban rivers and streams for public health benefits.