River Dissolved Oxygen Model with Zebra Mussel Oxygen Demand (ZOD)

The development, calibration, and application of a dynamic two-dimensional mass balance model for dissolved oxygen (DO) for rivers are documented for the first time accommodating the oxygen demand associated with zebra mussels. The test system is a short (2.3 km) phytoplankton-rich section of the Seneca River, N.Y., which is believed to represent an upper bound of the impact of this exotic invader on oxygen resources because of the unusually high population densities and limited turbulent mixing that prevail. Model calibration is supported by comprehensive measurements of DO, which resolve diurnal and seasonal patterns, and various forcing conditions over a four-month period. Wide temporal variations in the areal consumption rate of DO by zebra mussels zebra mussel oxygen demand (ZOD), g?m?2?day?1] were determined through model calibration. These determinations are supported by closure with earlier estimates based on simple DO budget calculations, and with laboratory biomass-specific oxygen consumption rates published in the scientific literature. Values of ZOD at times (e.g., >50 g?m?2?day?1) were an order of magnitude greater than the sediment oxygen demand associated with organically enriched deposits. The model performs well in simulating important features of the complex patterns of DO observed, including (1) DO depletion across the study section; (2) vertical DO stratification; and (3) diurnal changes. ZOD was the dominant sink for DO over the river study section; it was entirely responsible for the substantial observed DO depletion, and it was the major cause of the DO stratification during periods of low flow. A preliminary extension of the model is demonstrated to be successful in simulating the persistence of DO depletion 15 km downstream. The model is expected to have management utility for this and other phytoplankton-rich rivers that have been, or will be, invaded by zebra mussels.