UBC Theses and Dissertations
Mitigating impacts of temperature-oxygen squeeze in a mesotrophic-eutrophic lake : Wood Lake, BC, Canada Young, Christopher J.
Warm surface waters and hypoxic hypolimnion during summer stratification in eutrophic lakes, known as a temperature-oxygen squeeze, can limit available habitat for aquatic species. This study of Wood Lake, a calcareous eutrophic lake situated in the semi-arid Okanagan Valley of BC, Canada, was motivated by a decline in kokanee return spawners following a severe temperature-oxygen squeeze in 2011. Field data collected in 2015/2016, combined with DYRESM, a one-dimensional physical simulation model, was employed to investigate the factors influencing the thermal aspect of the temperature-oxygen squeeze. A relatively early and weak spring freshet in 2015 was followed by severely restricted inflows due to upstream diversions and coincident with relatively warm regional air temperatures from May through July. These factors triggered a marling event in Wood Lake and also resulted in the early onset of high epilimnetic temperatures and hypoxic hypolimnion (>20°C and <2 mg/L by mid June 2015). However, a cooler August and September, compared to 2011, alleviated the temperature-oxygen squeeze in 2015 by allowing the surface layer to cool. Simulations of the lake’s thermal response to meteorological perturbations on weekly and seasonal time scales consistently showed the thermal component of the Wood Lake temperature-oxygen squeeze is sensitive to the degree and timing of changes in air temperature; elevated August and September air temperatures, combined with high retention time due to limited inflow, restricts Kokanee fish habitat by increasing surface layer temperature during September when hypolimnetic oxygen is most diminished. While the marling event reduced water clarity, it did not significantly influence the lake’s thermal structure. DYRESM was employed to evaluate the effect of several proposed management scenarios involving the alteration of inflows and outflows with the goal of reducing September surface layer temperature of Wood Lake. It was shown that returning Wood Lake’s volumetric fluxes to pre-industrial rates by supplementing inflow from one of two adjacent lakes has the potential to reduce the thermal component of the seasonal temperature-oxygen squeeze.
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