Executive Summary
Stream temperature governs aquatic ecosystem function. Although there has been extensive research on the effects of land use on thermal regimes in lotic systems, little is known about the effect of forestry road crossings on stream temperature. Understanding these effects is important for managing watersheds along the eastern slopes of Alberta, where numerous streams are designated as critical for native trout. This study applied a spatial comparison – downstream (SCD) design to evaluate the effect of forestry road crossings on stream temperature in the headwaters of the Oldman River watershed.
Field work took place during the summer of 2024 and covered a range of stream sizes across the upper Oldman and Crowsnest watersheds. The SCD design used loggers positioned upstream and downstream of forestry road crossings, with five loggers per site. The upstream reference loggers suggested streams sampled warm by less than 0.4° C in the absence of riparian disturbance (i.e. crossings). Where crossings were present, the largest effect was observed in maximum daily stream temperature. A key finding of this work is that the effects of road crossings on stream temperature were spatially variable with smaller catchment (<10 km2) and stream sizes (< 3 m wide) being the most responsive.
Thermal changes observed here do not fall outside the range of tolerances for westslope trout or bull trout. Additionally, small streams like those responding to road crossings are suggested to have lower probability of native trout presence. However, these streams could still support populations by providing food and other resources. It is also possible that these streams provide important rearing or refuge habitats for young fish. These types of questions and the implications of changes in thermal conditions in response to road crossings will be explored in future work.
Citation
Moore, R.D., MacDonald, R.J., Spannier., S., Wicharuk, N., and Kissinger, B. Effects of Forest Road Stream Crossings on Stream Temperature – Results of a Field Study in the Upper Oldman River Watershed. Prepared for fRI Research. 2025. 74 pp.
