Taste and Odor Event Dynamics of a Midwestern Freshwater Reservoir

Abstract

Eagle Creek Reservoir (ECR), located in the Midwestern U.S., is a freshwater limnic system plagued by seasonal Harmful Algal Blooms (HABs) which generate water-fouling Geosmin (GSM) and 2-Methylisoborneol (MIB) Taste and Odor (T&O) compounds. Past investigations of T&O event dynamics have identified Actinomycetes as responsible for MIB production and several genera of cyanobacteria for GSM production. During 2018, a temporally and spatially expansive sampling regimen of the reservoir was carried out and a battery of biological, chemical, physical, and hyperspectral experiments performed. The resulting data was analyzed using time series, cross-correlation, lag time, and multivariate analyses as well as machine learning algorithms to pick apart and interrogate any relationships between HABs, T&O events, and environmental parameters. The results show that local weather and watershed conditions exert significant control over the state of the reservoir and the behavior of the algal community. GSM and MIB peaked during early May under well-mixed, cold, and nutrient-rich water column conditions, then declined under summer thermal stratification before making a small resurgence during late season mixing. Bloom die-off and decay was effectively ruled out as a mechanism controlling T&O concentrations, and no links were found between T&O concentrations and algal biomass. Strong evidence was found that GSM/MIB concentrations were a response by bloom microbes to changing nutrient conditions within the reservoir, and it was determined that nutrient fluxes from the watershed 30-40 days prior to peak T&O concentrations are likely instrumental in the development of the slow- ix growing microbes characteristic of the reservoir. Attempts were made to assess spatial and temporal variability but no significant spatial differences were identified; differences between sampling sites were far smaller than differences between different sampling dates. The findings here add to the growing body of literature showing T&O and HAB dynamics are more closely linked to the relative abundance and speciation of nutrients than other parameters. Additionally, these findings carry important implications for the management of ECR and other similar freshwater reservoirs while highlighting the importance of reducing watershed eutrophication.