Diffuse pollution of urban rivers – case studies in Malawi and Swaziland
Diffuse pollution of two urban rivers has been presented in the light of two independent case studies executed during the rainy season of 2001. The first examines and evaluates the spatial river water quality variation (pH, EC, TC and TDS, BOD and COD) of Lilongwe River and tributaries, in its upper reaches, before it enters the capital city of Malawi – Lilongwe. The river is the major source of potable water supply of the city. Different types of land use patterns have been associated with the sampling locations chosen. Results show a considerable level of pollution with respect to TC only, associated mainly with informal settlements along the riverbanks and, possibly, with effluents from food industries. The second case study examines the spatial water quality variation (BOD5, ortho-P, nitrates, sulfates, ammonia, chlorides, DO, EC, pH, T, TSS, TC and FC) of Mbabane River and tributaries, which flows along the capital city of Swaziland – Mbabane. It collects the runoff and municipal effluents of the City, and provides water for direct domestic and agricultural use of the rural population, living downstream of the city. Results show that the major source of diffuse pollution is associated with municipal effluent discharges due to the malfunctioning of the treatment plant. The major parameters of concern are nutrients, organic and bacteriological pollution. However, 20 km downstream the city, the water quality improves due to additional discharges by tributaries mainly, and partial self-purification.