Fine Sediment Contributions to Cyanobacterial Growth: Potential Threats to Drinking Water Reservoirs

Abstract

In the drinking water industry, the transport and release of nutrients such as phosphorus (P) to the water column is largely overlooked in reservoir management. Phosphorus is considered the key limiting nutrient for algal and cyanobacterial growth, although micronutrients and other macronutrients like nitrogen (N) are also important in cyanobacterial growth and toxin production. Thus, an understanding of P and N dynamics in freshwater systems is essential for effective, holistic reservoir management to ensure both source water availability and quality. The importance of understanding P and N form and mobility is further underscored by their association with natural and anthropogenic landscape disturbances. These disturbances can lead to increases in erosion, sediment transport, and nutrient bioavailability. Consequently, this thesis examined the bioavailability of P from fine sediments, and their role in cyanobacterial proliferation in two phases. Phase 1 evaluated geochemical composition, particulate P fractionation, and phosphorus mobility from fine sediments collected from two watersheds: the Elbow River watershed and the Crowsnest watershed. In the Elbow River Watershed, the Elbow River flows into the Glenmore Reservoir. Drum Creek was impacted by the 2003 Lost Creek wildfire and is located in the Crowsnest watershed. Sediment characterization revealed that bioavailable P is highest in Drum Creek, Glenmore Reservoir, and Elbow River, respectively. Batch experiments indicated that fine sediment in the Glenmore Reservoir is a source of bioavailable P to the water column. Phase 2 investigated the role of sediment-associated nutrients to cyanobacterial proliferation. A method for microcosm experiments using amended natural waters and sediments was developed and implemented. Results indicated that potential toxin-forming M. aeruginosa proliferation can be enhanced by fine sediment, compared to samples with no sediment. Unexpectedly, microcosms with Glenmore Reservoir sediment had significantly higher cell densities than those treated with Drum Creek sediment, and N concentrations did not have any significant effects. The laboratory benchtop studies conducted herein demonstrate proof-of-concept that sediment-associated nutrients can lead to increases of cyanobacterial proliferation. This type of experiment and its results can be an insightful tool to bridge gaps between understanding M. aeruginosa proliferation from a laboratory to natural settings.