Affiliation: | 1 Department of Biology, York University, Toronto, Canada M3J IP3 2 National Water Research Institute, Box 5050, Burlington, Ontario, Canada L7R 4A6 |
Abstract: | Two large circular enclosures, each containing approx. 550 m3 of water, 14 m deep, and open to the mud-water interface, were used to monitor the effects of hypolimnetic aeration. One enclosure was held as a control, the other aerated every 3 or 4 days for a period long enough (usually < 2 h) to maintain hypolimnetic O2 levels at > 4 mg 1−1. Nutrient additions (10 g of 90% H3 PO4 and 250 g NaNO3 per week) to each enclosure were controlled from the commencement of the experiment (17 June 1980) until its completion (2 November 1981). Temperatures in both enclosures were identical. Hypolimnetic O2 levels in the control fell to zero during both summers, but remained at > 4 mg 1−1 in the aerated enclosure. Free N2 concentrations in the hypolimnion of the aerated enclosure was higher than in the control. Concentrations of H2S in the control hypolimnion increased to > 5 mg 1−1 and concentrations of CH4 increased to > 18 mg 1−1. Both remained at or near zero in the aerated enclosure. Tests of aerator efficiency suggested that the full air-lift design that was employed had an average O2 exchange efficiency of 42% which is higher than the values reported for most other designs. |