Deducing the structure and origin of the Rocky Mountain Trench has proven to be a difficult problem in the past. To understand this feature more fully and to obtain information about the entire crustal section, an unreversed seismic refraction profile has been recorded in the southern Rocky Mountain Trench from 50°N to 53°N. Using blasts from two open pit coal mines, forty-four useful recordings were obtained over a distance of 540 km. Three components of short period ground motion were recorded by tape recording systems; the vertical component was also recorded by elements of the Mica array. Careful attention to amplitude scale factors results in the formation of a record section in which the energy pattern varies uniformly along the profile. A geometric ray theory interpretation involving Weichert-Herglotz integration of p-delta curves is used to obtain a velocity-depth structure. Approximate synthetic seismograms are then calculated using modified ray theory. Refractors with apparent P-wave velocities of 6.5 - 6.6 km/s and 8.22 ± 0.04 km/s are interpreted as the surface of the Precambrian basement and the Moho discontinuity, respectively. A velocity gradient is present in the lower crustal section. The depth to basement beneath the western Rocky Mountains at 50°30'N is calculated to be 6.5 ± 1 km. Near Radium, a significant anomaly in the seismic data is best interpreted as a northeasterly-trending normal fault with a downthrow of 5.6 ± 1 km to the northwest. The directions are inferred from gravity and magnetic trends in the region. Alternatively, the anomaly could represent a disappearance of the basement surface west of the east wall of the Trench. An anomalously thick crustal section is inferred from the data. A preferred model gives a depth of 51 ± 2 km southeast of Radium and 58 ± 2 km to the northwest. Study of a converted phase leads to the conclusion that there may be a discontinuity on the Moho surface beneath the Trench near 52°N. Analysis of arrivals shortly after the Pn phase is consistent with the interpretation of a low velocity zone, approximately 7 km thick, 8 km beneath the Moho. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Alpine tundra is notorious for its fragility and slow recovery following disturbance. Tourism is increasing in alpine areas, creating the need to improve our understanding of the impacts of recreation in these ecosystems. This study examined the impacts of hiking and off-highway vehicle use on the vascular flora of dry alpine meadows in the Canadian Rockies by comparing community data, including rare plant distributions, on recreational trails, on intact tundra meadows, and on sparsely vegetated gravel steps formed by frost disturbance. The trails were found to be different from both undisturbed and naturally disturbed tundra in terms of vascular plant cover, diversity, species composition and soil compaction. Rare plants do not seem to be adversely affected by recreational activities. Trampling leads to environmental conditions that will likely make regeneration of abandoned trails an extremely slow process, and it is advisable to limit the extent of trail networks in alpine areas. / Conservation Biology

Physical and chemical influences downstream of surface coal mines, including selenium (Se) release, water quality shifts, and habitat alterations can affect aquatic organisms. To evaluate these influences at the community level of organization, fish and macroinvertebrates were studied in mine-affected and reference streams. Se can be toxic to aquatic organisms and was measured in lotic food chains (water, biofilm, macroinvertebrates and juvenile salmonids). Invertebrate Se was significantly related to Se in juvenile fish muscle (westslope cutthroat, bull, rainbow and brook trout) and Se concentrations exceeded proposed individual-level reproductive effects thresholds in some rainbow and cutthroat trout. Community-level effects were only detected in rainbow trout where species specific biomass was negatively related to muscle Se concentration in stream reaches. Macroinvertebrate assemblages varied along a mineinfluence gradient defined by Se, alkalinity, substrate embeddedness and interstitial material size. Ephemeroptera were the most sensitive to mining effects and potential mechanisms influencing community composition included Se and ion toxicity and habitat degradation. This project highlights the need to study multiple organisms at different levels of ecological organization in order to understand and manage diverse mining impacts. / xi, 108 leaves : col. maps ; 29 cm

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