AWWA JAW56618

The Horseshoe-Bartlett water supply reservoir system on the Verde River in Arizona was studied to determine the impact of hydrologic variability on dissolved organic carbon (DOC) export from the watershed and DOC production within the reservoir system. High DOC concentrations occurred during spring snowmelt and late summer monsoon rains. The majority (~90%) of DOC loading (kilograms per month) from the Verde River watershed occurred in the spring. Bacterial consumption and algal production of DOC changed the chemical characteristics of DOC in the reservoir. DOC loading was reduced by 21 to 38%, and haloacetic acid precursor loading was reduced by 30 to 45% as water passed through the Horseshoe- Bartlett reservoir system in 1998-99. Depending on annual hydrologic patterns and reservoir operation, the Horseshoe-Bartlett reservoir system can either produce or consume DOC. Includes 34 references, tables, figures.