Oldman Watershed Report June 2021 V 09 01 2024.pdf
Creators: name: Green, Kim
Publisher: name: figshare
Year: 2024
Subjects: classificationCode: 370901
subject: Geomorphology and earth surface processes
classificationCode: 370905
subject: Quaternary environments
classificationCode: 370704
subject: Surface water hydrology
classificationCode: 300703
subject: Forest ecosystems

description: The upper Oldman River provides critical habitat for two provincially and federally threatened native trout species and has experienced substantial disturbance due to logging and mining over the past 50 years. This study provides an in-depth investigation of the linkages between land cover changes and aquatic habitat; integrating geospatial analyses, field observations, fisheries data, and process-based modelling in order to identify and prioritize areas for restoration and protection. Several important findings have emerged regarding the current conditions of stream channels and the factors influencing distribution of Westslope Cutthroat Trout and Bull Trout in the upper Oldman River project area.Forest disturbance from past logging and mining activities concentrated in Racehorse Creek, Dutch Creek and headwaters of the Oldman River has been slow to recover leading to an increased frequency and magnitude of floods capable of disturbing the channels as well as minimal riparian retention along smaller headwater streams. Disproportionate downstream impacts across the study area stem from differences in elevation and aspect distribution of slopes, bedrock geology, and climate that influence the magnitude of streamflow and channel response to landcover change. Additionally, many stream channels throughout the upper Oldman River display extensive disturbance from the 1995 and 2013 flood events including eroded riparian areas and channel banks, changes in channel patterns, and removal of in-channel, habitat-forming woody debris.Bedrock geology, slope elevation and aspect distribution also appear to factor into the distribution of high value aquatic habitat, however, subwatersheds that consistently support higher numbers of Westslope Cutthroat Trout are different than those that consistently support higher numbers of Bull Trout. Westslope Cutthroat Trout are more widely distributed and appear to have a broader ecological niche, with smaller and warmer, south facing, low elevation streams supporting higher numbers of this species, including more juveniles. Bull Trout are less abundant, being limited in distribution by the presence of bedrock falls in the upper Oldman River. The highest numbers of Bull Trout are found in larger streams and the mainstem rivers and juvenile abundance being the greatest in streams with lower temperatures related to north facing headwaters.A prioritization framework highlights that high levels of forest harvest overlap high Westslope Cutthroat Trout abundances in the furthest upstream tributaries flowing south into the Oldman River as well as in North Racehorse Creek and mainstem Racehorse Creek. This has resulted in the habitat for this species being at greatest risk from changes to the flow and sediment regimes and riparian function in these subwatersheds. North Racehorse Creek and mainstem Racehorse Creek are also the primary subwatersheds where Bull Trout habitat is at risk from these same factors.The outcomes of this study illuminate landscape-scale linkages between watersheds characteristics and habitat values for aquatic species at risk in watersheds along the Eastern Slopes. Future recommended work includes additional statistical analyses of the patterns of native trout abundance and distribution, development of a stream temperature model, an investigation of woody debris dynamics and a synoptic survey of benthic macroinvertebrate density and distribution.