Using hydroacoustics and vertical gill nets, we evaluated the efficacy of hypolimnetic oxygenation as a lake management tool by quantifying summer vertical distributions of cisco (Coregonus artedi) in a treated and untreated basin of Amisk Lake, Alberta, during and after oxygenation (1988-1993) and in untreated Baptiste Lake, Alberta. In Baptiste Lake, the hypolimnion remained anoxic and cisco were restricted to epilimnetic waters. Oxygenation increased hypolimnetic dissolved oxygen (DO) concentrations in Amisk Lake, expanding habitat by up to 9 m. During oxygenation, hypolimnetic DO remained above concentrations avoided by cisco (<1.3 mg ·L-1) in the treated basin, but fell below this level by midsummer in the reference basin. Consequently, cisco were distributed up to 8 m deeper in the treated than in the reference basin. In August 1990, a metalimnetic oxygen minimum in the reference basin confined >70% of the cisco to the epilimnion, while >60% of the fish inhabited the metalimnion and hypolimnion in the treated basin. Although DO remained above avoidance concentrations throughout most of the treated basin, the highest densities of cisco occurred in water with mean ( ± SD) DO concentration and temperature of 3.1 ± 1.3 mg ·L-1 and 11.8 ± 2.1oC, respectively. Thus, the extent of habitat expansion for fish during oxygenation programs will also depend on the availability of suitable temperatures.
Continuous borehole optical televiewing reveals variable englacial debris concentrations at Khumbu Glacier, Nepal