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Preliminary investigations of Saanich Inlet, Vancouver Island, British Columbia, indicated that there was a stratification in the depth of occurrence, during daytime, of the euphausiid Euphausia pacifica and the amphipods Cyphocaris challengeri and Orchomenella pinguis. The presence of an oxycline and a gradient in the carbon dioxide concentration suggested that the stratification was associated with these environmental factors. A programme was conducted between July 1962 and June 1963 to determine whether the stratification was a persistent phenomenon and whether physical and chemical characteristics of the water were associated with the distribution of the organisms. Clarke-Bumpus plankton samplers were towed above, within, and below the oxycline on seven cruises. The survival of the species was measured above, within, and below the oxycline, for exposures of 1 to 12 hours for Euphausia pacifica and Cyphocaris challengeri and of 9 to 24 hours for Orchomenella pinguis, by lowering specimens in cylinders which were in communication with the environment. Laboratory experiments measured the oxygen consumption of the species when carbon dioxide produced by the organisms in experimental chambers accumulated and when it was absorbed. Stratification was a persistent phenomenon in which Euphausia pacifica occupied the upper position, Orchomenella pinguis the lower position and Cyphocaris challengeri an inter-mediate or upper position in the daytime aggregation of organisms. The position of the aggregation was not influenced by temperature or salinity, but was related to the concentration of oxygen, and carbon dioxide. The field experiments showed that Orchomenella pinguis could tolerate lower oxygen and higher carbon dioxide concentrations for much longer durations of exposure than could the other two species. The laboratory experiments indicated Orchomenella pinguis and Cyphocaris challengeri consumed less oxygen than Euphausia pacifica, but Cyphocaris challengeri was more susceptible to high concentrations of carbon dioxide than the other species. These facts offer partial explanations for the stratification of the species. / Science, Faculty of / Zoology, Department of / Graduate

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The areal hypolimnetic oxygen deficit model (AHOD) developed by Strom (1931) and Hutchinson (1938) was tested by examining the predictions which the model makes and by testing the assumptions which were made during the formulation of that model. The model was found to be incorrect. Rates of hypolimnetic oxygen depletion are strongly influenced by the morphometry and temperature of the hypolimnion. Lake morphometry influences at least two processes which affect oxygen concentrations. Significantly more oxygen is turbulently transferred into the hypolimnia of shallow lakes than deep lakes. However the maximum rates of vertical transport are always less than 15% of the observed rate of oxygen depletion. The morphometry of the hypolimnion exerts a much stronger influence upon the amount of respiration which occurs within the hypolimnetic water column. The amount of respiration measured in the water column increases as the thickness of the hypolimnetic water column increases. In oligotrophic lakes with shallow hypolimnia, less than 20% of the total amount of oxygen consumed in the hypolimnion is respired in the water column. In deep lakes more than 60% of the total amount of oxygen consumed is respired within the water column. Measured rates of water column respiration are strongly correlated with the temperature and amount of particulate organic matter present in the water column. / The rate of oxygen consumption within the hypolimnion is constant throughout the period of thermal stratification. Respiration does not depend upon the ambient concentration of oxygen present within the hypolimnion. Changes in oxygen concentration within any stratum of the hypolimnion of a lake can be predicted from a knowledge of the retention of phosphorus by the lake's sediments (Rp), the average temperature of the stratum during the period of thermal stratification (T), and the ratio of the volume of the stratum to the area of lake sediments horizontally contiguous to the stratum (V:SA). A simple statistical model developed from published estimates of rates of oxygen consumption (VOD mg/m('3)/day) predicts that / VOD = -6.6 + .0081T*Rp + 11.07T - 2.32T*Ln(V:SA). / The predictions of this equation agree very well with rates of oxygen depletion measured in 12 lakes which possess a diversity of physical and chemical characteristics. During the period of stratification, hypolimnetic oxygen concentrations can be estimated from the predicted rate of oxgyen depletion and an estimate of the initial oxygen concentration within the hypolimnion at the onset of stratification.

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The Upper Souris River was placed on the Environmental Protection Agencies (EPA) impaired waters list for low dissolved oxygen (DO). A Total Maximum Daily Load (TMDL) study was conducted to determine possible causes of DO depletion. From sampling and site visits it was determined nonpoint sources contributed the majority of organic loadings to the Upper Souris River. Through preliminary testing, it was determined that sediment oxygen demand (SOD) played a key role in depleting DO levels during winter months and required further investigation. River profile surveying, water quality sampling, and laboratory testing of SOD were carried out to determine parameters required for water quality modeling. SOD tests were conducted to determine impacts of sediment organic contents and temperature on SOD rate. Sediment oxygen demand rates ranged from 0.37 to 1.22 g O2/m2/d. The QUAL2K model was calibrated to simulate DO variations along the study reach under ice covered conditions.

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