Spatial and temporal dynamics of coliform contamination within Yamoussoukro lake waters in Côte d’Ivoire: impact on the safety of surrounding vegetable cropping

There is a lack of information on the seasonal and spatial variations of bacterial pollution and the drivers of these variations within and around the Yamoussoukro lakes. In order to explain the dynamic of bacterial pollution of these lakes and assess the health risks associated with the contamination of surrounding vegetable crops, Escherichia coli and thermotolerant coliforms were used as indicators of pollution. Sampling was conducted from the lakes and surrounding vegetables such as carrots, lettuce and cabbage. In total 31 water points during 4 dry seasons and 4 rainy seasons, for the years 2015-2016 and 2016-2017 were sampled according to the Canadian sampling method. Water bacterial loads were high (710 CFU/mL and 791.8 CFU/mL) during the rainy seasons while the ones on the vegetables were high during the dry seasons (84.6 CFU/mL and 105.8 CFU/mL). The spatial location of the lakes from upstream to downstream and the rainy seasons strongly contributed to the evolution of bacterial loads from one lake to another. Moreover, it was shown that the dissolved organic carbon and the turbidity positively impacted the evolution of the bacterial loads throughout the two years. Overall no matter what season, the lake waters were not suitable for vegetable irrigation.