Autumnal and over-winter limnological conditions in Marquette, Corbett and Courtney Lakes in British Columbia were followed monthly from autumn, 1961, to spring, 1964, and some additional data were collected in winter, 1965. Indices of productivity for summer and winter conditions suggest that Courtney Lake is most productive, Marquette Lake least productive and Corbett Lake intermediate. Although over-winter mortality of fishes would be, expected to occur in Courtney Lake it has not been observed there whereas in Marquette and Corbett Lakes it frequently occurs. Marquette and Corbett Lakes were sharply stratified in summer because local topography provided protection from wind action whereas stratification in the more exposed Courtney Lake was ill-defined. Average wind velocities on Courtney Lake were 4.3 times greater and more unidirectional than those on Corbett Lake. Marquette Lake was subject to wind action similar to that of Corbett Lake. To test the hypothesis that winter limnological differences between Courtney and Corbett Lakes were due to insufficient autumnal circulation, Corbett Lake was experimentally circulated. Autumnal circulation in Courtney Lake was complete and resulted in over-winter survival of Salmo gairdneri and Richardsonius balteatus. Incomplete autumnal circulation and oxygenation in Corbett and Marquette Lakes resulted in over-winter mortality of Salmo gairdneri and Salvelinus fontinalis. In order to experimentally examine causes for the limnological differences between the lakes, Corbett Lake was artificially circulated. A compressed air "bubbler system" comprised of a submerged circles(circumference = 726 m) of plastic pipe and an air compressor was used to circulate Corbett Lake in the autumn of 1962 and 1963. The results of the experimental circulation of Corbett Lake compared to the limnological conditions in the "control" lakes, confirmed the original hypothesis. Below average snow fall in 1962-63 resulted indirectly in anomalous dissolved oxygen values (supersaturation). Consequently the expected over-winter mortalities of fishes in Marquette Lake did not occur whereas the expected winter mortalities did occur in 1961-62 and 1963-64. Winter light penetration and intensity in Corbett Lake was correlated with differences in snowfall between years. Light penetration and intensity differed considerably between lakes when snow and ice conditions were about equal (1965) because of differences in water quality. / Science, Faculty of / Zoology, Department of / Graduate

A comparative, limnological study of five, small, eutrophic lakes in the Interior of British Columbia was made over a period of two summers. Detailed morphometrical, physical, chemical and biological data are given. The effect of a rotenone base compound on the fauna of two of these lakes is shown both qualitatively and quantitatively by comparing them with the faunas in other lakes. A complete eradication of the fish in the lakes was obtained. Certain species of plankton and bottom organisms were killed by the poison but sufficient numbers survived to re-populate the lakes. The plankton populations did not revert to the previous level of abundance in the year following. The effect of the absence of coarse fish on certain shore organisms and Gladocera was indicated. / Science, Faculty of / Zoology, Department of / Graduate

Powell and Sakinaw Lakes are stably stratified ex-fjords, which became isolated from the Strait of Georgia approximately 11000 years ago by emerged sills due to postglacial isostatic rebound. Although both lakes contain highly sulphidic relict seawater (Powell 3.0 mM; Sakinaw 5.5 mM), they have distinct chemical differences, which may be due to Sakinaw receiving occasional inputs of seawater over the barely-emerged sill when strong onshore winds are coincident with spring tides. Powell Lake, now 50 m above sea level, has not received additional seawater since the sill originally emerged. Sakinaw has a very sharp chemocline located just below the oxic/anoxic interface, whereas in Powell, the interface is spread out over 200 m of the water column. Although both lakes have freshened, the ratios of major ion concentrations relative to chloride in the bottom saline waters are similar to those of present-day seawater. There are some differences, however, and these can be explained, in part, by the difference in molecular diffusivities for each of the ions. The bottom waters of Powell and Sakinaw Lakes are chemically similar to anoxic sediment porewaters. containing high concentrations of nutrients, DOC and alkalinity. Unlike Sakinaw, however, Powell Lake has very low concentrations of phosphate in its bottom waters, in spite of both lakes having similar particulate organic N:P ratios in their upper oxic waters. This may be attributable to more recent addition of sulphate to Sakinaw, allowing greater mineralization of phosphorus compared to the relatively oxidant-starved Powell Lake. High concentrations of reduced iron, hydrogen sulphide, and polysulphides result in formation of iron monosulphides and pyrite in the anoxic water columns of both lakes. The presence of these two minerals correlates well with their calculated saturation states. Pyrite precipitates directly with no monosulphide precursor at depths where sulphide concentrations are low; thus monosulphide phases are undersaturated. As sulphide levels increase with depth, iron monosulphides become saturated and are detected in the water column. Pyrite can then form via the slower reaction of elemental sulphur with monosulphide. The large separation of the oxic/anoxic interface and the chemocline in Sakinaw (∼10 m) and especially in Powell Lake (∼100 m) relative to that of sediment pore waters allows excellent resolution of these processes. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

In the summer of 1964 a study was carried out on the impounded Buttle and Lower Campbell Lakes located on Vancouver Island, British Columbia. An attempt was made to determine the effects of increased water level fluctuation on the limnology, particularly the bottom fauna, in areas with different substrate types. All data from two pre-impoundment studies were examined, and additional sampling carried out to provide a basis for comparison. In addition, several stations were chosen in each lake according to specific substrate types. These different bottom conditions were formed from the combined effects of erosion by water level fluctuation and wave action, over areas where different methods of pre-impoundment clearing of vegetation had been employed. The stations chosen were the shallow onshore areas which were exposed to the air during the winter months of minimum water level, the unexposed area immediately below the minimum drawdown level, and the pre-impoundment littoral zones in each study lake. A single pre-impoundment river channel station was located in Buttle Lake. In addition to bottom dredgings, funnel traps and nocturnal surface tows were used to sample the emerging insect fauna from each station. The total seasonal chironomid catch indicated significantly different total emergence between the several stations sampled. The pre-impoundment river station in Buttle Lake produced the highest total chironomid catch. Among the other stations the unexposed area immediately below the drawdown level was most productive. In Buttle Lake where the greatest seasonal fluctuation occurred and where the completely cleared littoral area was least protected from wave action, the total seasonal emergence over the exposed littoral area was very low. But in Lower Campbell Lake which received a much smaller seasonal water level fluctuation, total emergence was much higher over the exposed littoral. This area was cleared completely in this lake and the irregular shoreline afforded considerable protection from wind action. An inverted bathymetric distribution of the fauna was apparent with the greatest concentration occurring immediately below the drawdown limit in the unexposed littoral zone. The effects of water level changes were therefore considered the most important single factors influencing the bottom fauna distribution in each lake. / Science, Faculty of / Zoology, Department of / Graduate