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 mussel s. The test system is a short (2.3 km) phytoplankton-rich section of the Se neca River, N.Y., which is believed to represent an upper bound of the impa ct of this exotic invader on oxygen resources because of the unusually high population densities and limited turbulent mixing that prevail. Model cali bration is supported by comprehensive measurements of DO, which resolve diu rnal and seasonal patterns, and various forcing conditions over a four-mont h period. Wide temporal variations in the areal consumption rate of DO by z ebra mussels [zebra mussel oxygen demand (ZOD), g . m(-2) . day(-1)] were d etermined 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 asso ciated with organically enriched deposits. The model performs well in simul ating 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 st udy section; it was entirely responsible for the substantial observed DO de pletion, 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 su ccessful in simulating the persistence of DO depletion 15 km downstream. Th e model is expected to have management utility for this and other phytoplan kton-rich rivers that have been, or will be, invaded by zebra mussels.