Characteristics and Origins of Metalimnetic Dissolved Oxygen Minima in a Eutrophic Reservoir

• Published in: Lake and reservoir management 1998-09, Vol.14 (2-3), p.332-343
• Main Authors: Effler, Steven W., Gelda, Rakesh K., Perkins, MaryGail, Matthews, David A., Owens, Emmet M., Stepczuk, Carol, Bader, Andrew P.
• Format: Article
• Language: English
• Subjects: dissolved oxygen; mass balance; metalimnetic minimum; metalimnion; negative heterograde curve; reservoir operation
• ISSN: 1040-2381; 2151-5530
• DOI: 10.1080/07438149809354341

The occurrence and characteristics of metalimnetic dissolved oxygen (DO) minima are documented, the origins of the phenomena are evaluated, and the contribution of DO consumption in this layer to overall consumption below the epilimnion is resolved, for Cannonsville Reservoir, NY. The analysis utilizes detailed vertical profiles of temperature and DO collected in the lacustrine zone of the reservoir over the 1988-1997 interval, profiles of scalar irradiance and fluorescence measured in 1995, calculations of vertical profiles of phytoplankton production and respiration of DO for selected conditions, and mass balance analyses for DO in the metalimnion and hypolimnion of the reservoir over the 10-year record. The metalimnetic minimum is shown to be a recurring phenomenon in the reservoir, that was conspicuously manifested in late summer in each of the 10 years. The position of the minimum below the water surface has been rather uniform in mid-summer but other features, including the extent of DO depletion, have varied greatly. Respiration of relatively high concentrations of phytoplankton biomass within the metalimnion, located below the compensation depth, contributed to the development of the observed minima. The high phytoplankton concentrations of the metalimnion probably are associated with slowed descent rather than interflow(s). On average, ~ 70% of the DO consumption exerted below the epilimnion over the 1988-1997 interval occurred in the metalimnion. The average DO consumption rate in this layer, normalized for layer volume, was 80 mg·m −3 ·d −1 . It was necessary to accommodate the important effects of export and exchanges between layers (entrainment flows) associated with reservoir operations in the mass balance framework used to estimate consumption rate(s).