Georgia Southern University
Organic matter (OM) release from anaerobic sediments during summer months results in water quality deterioration in eutrophic reservoirs. The Occoquan Reservoir is a part of indirect potable water reuse system in northern Virginia, was used as a study site. After the onset thermal stratification and subsequent hypolimnetic oxygen depletion, OM in the water column increases. Lab-scaled experiment were performed to replicate this scenario and to characterize the released OM using fluorescence excitation emission matrices and Parallel Factor Analysis (PARAFAC). Results revealed that under aerobic conditions, sediment OM release was very low (TOC < 5 mg/L). Conversely, during anaerobic and reduced environment, TOC increased up to 16 mg/L as OM released from sediments. Maintaining anoxic conditions by keeping a nitrate concentration greater than 2 mg-N/L above the sediment water interface (SWI) decreased OM release to some extent. Characterization results revealed that under aerobic conditions, the OM present in the water column was mainly high molecular weight humic-like material, commonly found in natural water. However, three types of OM were observed from anaerobic sediments: high molecular weighted humic-like material, fulvic-like material, and protein-like substances. Protein-like substances were found in reduced environments and coincided with high concentrations of phosphate and nitrogen, suggesting increased phytoplankton productivity. The relative percentage of humic-like material was higher in the aerobic environments, while the protein percentage was high during the anaerobic conditions due to increased biosynthesis. Overall, results showed that maintaining an oxidized level prevented the breakdown of higher molecular weight OM into low molecular weight OM, which have potentiality to lead eutrophication. Finally, preventing the release of sediment OM can decrease the potentiality of formatting carcinogenic disinfection byproducts in water supply sources.