The Prevalence of Bacteria-Sediment Associations and Their Effect on Sediment Settling Velocities in Aquatic Environments of Agricultural Saskatchewan and Alpine British Columbia
Bacteria-sediment associations (BSA) are the natural interactions between bacteria and sediment particles that influence both bacterial survival rates and properties of sediment particles. A newly developed method for quantifying BSA was applied to an agricultural watershed in southeastern Saskatchewan and an alpine watershed in the southern Coast Mountains of British Columbia. Both watersheds exhibited spatial and temporal trends of BSA. Impacts corresponding to land use and anthropogenic activity are also present. Development of a novel method for determining BSA allowed for samples taken from remote areas to be assessed. Membranes with 8 μm pore diameter separated planktonic organisms from sediment-associated organisms. The use of acridine orange fluorochrome and a fluorescence microscope allowed for all organisms to be viewed. Samples from the Pipestone Creek watershed in southeast Saskatchewan confirmed the presence of BSA within in-field runoff, and in Pipestone Creek. The percentage of bacteria associated with sediment range from 2% at in-field locations to a maximum of 70% in Pipestone Creek with samples from the creek having significantly higher BSA values than those from in-field locations. Results from the Pipestone Creek watershed show that winter bale grazing (WBG) of cattle, when compared to fall manure spreading (FMS) and a control of no manure spreading, leads to a larger export of total bacteria during spring snowmelt. The application of WBG also leads to an increase in sediment export and a decrease in mean particle diameter. In the Lillooet River watershed, BSA were also noted to be present at all sample locations with the percentage of bacteria associated with sediment ranging from 1% - 40% depending on time of day and location within the watershed. Decreased BSA was measured at locations associated with planktonic bacteria influx via intensive agricultural runoff and wastewater treatment. Laboratory experiments using a laser backscatter device reveal an increase in sediment settling velocity associated with increased bacteria concentrations. Particle-size distributions of the sediment vary with an increase in some size classes and a decrease in others. The changes in particle sizes and settling velocities are consistent with the process of flocculation occurring within the 23-hour sample duration. The results from this study provide insight into the impacts of BSA in contrasting environments through the application of a novel BSA quantification method. Furthermore, the documentation of the impact of BSA on the settling velocity of sediments provides a more holistic understanding of varved sediments and therefore better informs process-inference, leading to more holistic paleoenvironmental reconstructions.
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Faculty of Graduate Studies and Research, University of Regina