Abstract:
Microbial communities, in particular bacterial assemblages, are key players in the provision of essential ecosystem services such as the mediation of biogeochemical cycles as well as the degradation of chemical pollutants. The responses of bacterial communities to changing environmental conditions are manifold but can include structural as well as functional alterations depending on the environmental stressors and toxic chemicals they are exposed to (e.g. pharmaceuticals, personal care products, pesticides, and industrial chemicals). In this study, environmental DNA (eDNA) was extracted from surface water samples collected from four small rivers in the Lake Victoria South Basin (Western Kenya) to : i) evaluate whether alpha- and beta-diversity change in dependency of land-use types, ii) identify the environmental variables that explain alterations in community structure, iii) qualitatively and quantitatively assess the consequences of antimicrobial stress on bacterial communities, and iv) evaluate bacterial functional changes related to the degradation of organic chemicals. Our findings suggest that bacterial community composition is a more sensitive indicator to reflect the impact of chemical pollution derived from different types of land-use compared to alpha diversity. Nutrients and stress from chemical pollution were the variables explaining the dissimilarities between bacterial communities in small, forested, urbanised and agricultural rivers. Furthermore, an assessment of potential ecological functions associated with the biodegradation of toxic chemicals unveiled a season-specific decline in bacterial degradation potential in all four rivers. Finally, our results indicate that bacterial communities in small streams in Kenya which run through areas characterised by a low degree of urbanization or subsistence agriculture, respectively, can have a similar potential impact on bacterial communities as rivers exposed to a high degree of urbanization, intensive agricultural activities, or mixed land-use in other areas around the world.