Microbial Remobilisation on Riverbed Sediment Disturbance in Experimental Flumes and a Human-Impacted River: Implication for Water Resource Management and Public Health in Developing Sub-Saharan African Countries

Resuspension of sediment-borne microorganisms (including pathogens) into the water column could increase the health risk for those using river water for different purposes. In the present work, we (1) investigated the effect of sediment disturbance on microbial resuspension from riverbed sediments in laboratory flow-chambers and in the Apies River, Gauteng, South Africa; and (2) estimated flow conditions for sediment-borne microorganism entrainment/resuspension in the river. For mechanical disturbance, the top 2 cm of the sediment in flow-chambers was manually stirred. Simulating sudden discharge into the river, water (3 L) was poured within 30 s into the chambers at a 45° angle to the chamber width. In the field, sediment was disturbed by raking the riverbed and by cows crossing in the river. Water samples before and after sediment disturbance were analysed for Escherichia coli. Sediment disturbance caused an increase in water E. coli counts by up to 7.9-35.8 times original values. Using Shields criterion, river-flow of 0.15-0.69 m³/s could cause bed particle entrainment; while ~1.57-7.23 m³/s would cause resuspension. Thus, sediment disturbance in the Apies River would resuspend E. coli (and pathogens), with possible negative health implications for communities using such water. Therefore, monitoring surface water bodies should include microbial sediment quality.