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Item Impacts of forest mortality on streamflow in whitebark pine forests within the greater Yellowstone ecosystem(Montana State University - Bozeman, College of Letters & Science, 2024) Rautu, Teodora Stefana; Co-chairs, Graduate Committee: Brian V. Smithers and Danielle E. M. UlrichIncreasing forest mortality across the western U.S. raises concerns about its impact on streamflow. The hydrologic role of whitebark pine (Pinus albicaulis Engelm.) is of particular interest given its ongoing decline and prevalence at the upper treeline where precipitation is highest. Understanding the link between disturbed whitebark pine forests and streamflow is essential for better informing water resource management. In Chapter One, I investigated streamflow changes in two Wyoming whitebark pine watersheds: Upper Wind River (53% area affected by beetle outbreak) and Buffalo Fork (53% area affected by beetle outbreak and fire). Streamflow significantly increased post-beetle for Upper Wind River but did not significantly change post-disturbance for Buffalo Fork, attributed to the fire's limited spatial extent and post- beetle effects potentially occurring in the pre-disturbance period. In Chapter Two, I integrated Leaf Area Index into a hydrologic model to reflect changing canopy conditions and assessed water balance variables that drove the observed changes in streamflow in Chapter One. I found that an increase in annual precipitation primarily led to the increase in observed streamflow more so than forest mortality, and snowpack and snowmelt were consistent predictors of streamflow metrics. My findings suggest monitoring snow dynamics for accurate real-time and future streamflow forecasting. In Chapter Three, I used streamflow field data and the same hydrologic model to assess the impact of increasing tree mortality on streamflow within a whitebark pine- dominated watershed in Big Sky, Montana. After simulating mortality levels ranging from 0-90% for one year, tree mortality did not substantially impact streamflow until the 90% mortality level where annual flow and late summer flow substantially increased. Considering that mortality levels between 25-50% are more representative of whitebark pine mortality in one year, the lack of substantial impacts on snowpack and streamflow at the 25-50% mortality levels challenges the traditional assumption that whitebark pine mortality would lead to reduced snowpack and reduced late summer flow in open watersheds with 30% forest cover. Future studies should assess the multi-decade impacts of whitebark pine mortality on hydrologic processes and consider species differences in evapotranspiration as other subalpine species replace whitebark pine.Item Effectiveness of the nature-like fishway at Huntley Diversion Dam, Yellowstone River, Montana(Montana State University - Bozeman, College of Letters & Science, 2022) Anderson, Ian Richard; Chairperson, Graduate Committee: Alexander V. ZaleWe evaluated passage of a diverse fish assemblage through the nature-like fishway built around Huntley Diversion Dam, the uppermost of six low-head diversion dams on the Yellowstone River in Montana. Although nature-like fishways purportedly facilitate the passage of many species, relatively few have been evaluated, particularly on large rivers with unregulated discharge regimes. We examined seasonal and diel use of the Huntley fishway, quantified efficiencies and temporal metrics, and determined which factors influenced attraction and passage. We implanted > 3,500 fish of 14 species with passive integrated transponder tags, released most fish 250 m downstream of the fishway, and used stationary antennas to monitor movements of fish through the fishway in 2019 and 2020. Seasonal use of the fishway was generally associated with pre-spawning movements and occurred from April to August annually, and diel use reflected the known biology of each species. Attraction efficiencies were apparently low (usually < 50%), probably because of low motivation or the inability of fish to locate the entrance. Suckers released on opposite riverbanks downstream of the fishway were similarly successful at locating the entrance. Entrance efficiencies were usually > 90%. Both transit and passage efficiencies were usually > 60%, but fewer individuals (particularly among certain species) successfully passed than were able to transit to near the fishway exit. High river discharges were associated with decreased passage success and increased exit delays, probably because of problematic hydraulic conditions near the exit. Conditions throughout the rest of the fishway were appropriate, as most fish transited to near the exit in < 1 h regardless of discharge. Fourteen species passed upstream, demonstrating the functionality of nature-like fishways on large, unregulated rivers. However, the placement of such fishways must be thoughtfully considered to ensure that they remain effective over a wide range of environmental conditions.Item Ecosystem engineering at the streambed: how net-spinning caddisflies influence substrate flow dynamics(Montana State University - Bozeman, College of Letters & Science, 2020) MacDonald, Michael Joseph; Chairperson, Graduate Committee: Lindsey Albertson; Lindsey K. Albertson and Geoffrey C. Poole were co-authors of the article, 'Ecosystem engineering at the streambed: how net-spinning caddisflies influence substrate flow dynamics' submitted to the journal 'Ecohydrology' which is contained within this thesis.The streambed is an ecotone between surface waters and underlying hyporheic systems. Identifying the controls on advective flow through this ecotone is critical to understanding the movement of energy and matter in streams. Hydropsychids (net-spinning caddisflies) are aquatic macroinvertebrate ecosystem engineers that influence streambed cohesion, yet evidence of direct influence on hydrologic processes is lacking. Utilizing a novel downward flow permeameter, we demonstrate how net-spinning caddisfly colonization of the streambed interstitia at moderate but common densities (2,000 m^-2) can reduce the vertical hydraulic conductivity (KV) by up to 55% in coarse sand and gravels (median diameter = 12.91 mm). Sediment columns incubated in artificial stream water occupied by caddisflies showed greater reductions in KV relative to those without caddisflies. Additionally, organic matter content within sediment columns showed that occupation by caddisflies resulted in nearly two-fold increases in organic matter AFDM. Our research shows that the ubiquitous and numerous net-spinning caddisflies are likely to modulate the exchange of channel and hyporheic water by constructing nets in open pore spaces, increasing flow resistance, and decreasing flow velocities, as well as stimulating organic matter deposition with potential consequences for biofilm growth. These results suggest that caddisfly induced reductions to flow may influence transfer processes occurring at the streambed ecotone, altering biogeochemical processes in streams.Item Life history characteristics and the effects of climate on growth of Yellowstone cutthroat trout in headwater basins(Montana State University - Bozeman, College of Letters & Science, 2015) Uthe, Patrick Ryan; Chairperson, Graduate Committee: Alexander V. Zale; Robert Al-Chokhachy, Alexander Zale and Bradley Shepard were co-authors of the article, 'Life history characteristics and vital rates of Yellowstone cutthroat trout in two headwater basins' submitted to the journal 'Transactions of the American Fisheries Society' which is contained within this thesis.; Robert Al-Chokhachy, Bradley Shepard, Alexander Zale and Jeffrey L. Kershner were co-authors of the article, 'Effects of climate-driven stream factors on summer growth patterns of Yellowstone cutthroat trout' submitted to the journal 'Transactions of the American Fisheries Society' which is contained within this thesis.The Yellowstone Cutthroat Trout was historically distributed throughout the Upper Yellowstone and Upper Snake River drainages, but now occupies only 42% of its original range because of habitat degradation and introduced salmonid species. Many of the current strongholds are located on public land in mountainous watersheds with low human disturbance. However, knowledge of life history characteristics of headwater populations is limited. Moreover, streams throughout the Rocky Mountains have already exhibited symptoms of climate change through alterations in thermal and hydrologic regimes, but it is unknown how these changes will affect fish populations. To address these needs, we implemented a mark-recapture study on five populations of trout from Spread Creek, Wyoming, and Shields River, Montana, to estimate annual growth, survival rates, and movement patterns, and document the effects of discharge, temperature, and food availability on summer growth patterns. Survival rates were high compared to survival rates of other Cutthroat Trout subspecies and large trout generally had lower survival rates than small trout. Downstream movements out of streams by tagged trout were substantial. Annual growth rates varied among streams and size classes, but were relatively low compared to populations of Yellowstone Cutthroat Trout from large, low elevation streams. Trout grew more in length than weight in summer, suggesting an investment in structural growth rather than accumulation of reserve tissues. Temperature and discharge had strong effects on summer growth, but the effect of discharge was greater for growth in weight than in length, probably resulting from increased prey availability at high discharges. Temperature interacted with fish length such that small trout responded favorably to increased average daily temperatures near physiological optima and increased growing season length, whereas large trout responded negatively to warming temperatures. These estimates of key demographic parameters are useful in developing management and conservation strategies. Additionally, we documented that even under thermally suitable conditions, discharge can have significant effects on growth, making it important to consider multiple factors affected by climate change when devising climate adaptation strategies for coldwater fishes.