Theses and Dissertations

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Open Access
A climatological study of snow covered areas in the western United States
(Colorado State University. Libraries, 2012) Moore, Cara, author; Kampf, Stephanie K., advisor; Fassnacht, Steven R., committee member; Sibold, Jason S., committee member
Snow accumulation and timing of melt affect the availability of water resources for the Western United States. Climate warming can significantly impact the hydrology of this region by decreasing the amount of precipitation falling as snow and altering the timing of snowmelt and associated runoff. Therefore, it is essential to characterize how regional climatology affects snow accumulation and ablation and to identify areas that may be especially sensitive to climate warming. This can help resource managers plan appropriately for hydrologic changes. This study utilizes 11-year average (2000 - 2010) MODIS Snow Cover Area (SCA) and Land Surface Temperature (LST) data and annual PRISM precipitation to determine how elevation, slope orientation, latitude, and continentality influence regional characteristics of SCA and LST for early April, early May, early June, and early July in four focus regions: the Colorado Rockies, the Sierra Nevada, the Washington Cascades, and the Montana Rockies. Then, using monthly averages of the 11-year MODIS SCA for January to June, we examine the spatiotemporal evolution of the snowpack and LST throughout the Western U.S. We use threshold values of January to July 11-year average SCA to determine the duration of snow persistence and delineate zones of intermittent, transitional, persistent and seasonal snow. Within the transitional and persistent snow zones, we use 11-year average LST data for January-February-March (LSTJFM) to categorize five different snow sensitivity zones. Areas with the highest winter average land surface temperatures are assumed to be most sensitive to climate warming, whereas areas with the lowest land surface temperature are assumed to be least sensitive. Results show that snow cover tends to increase with increasing elevation, and the elevation of snow cover is lower in higher latitudes, maritime environments, and most western slopes. Land surface temperature tends to decrease with increasing elevation, increasing latitude, and tends to be colder on most western slope sites. The largest divergence between eastern and western slope SCA and LST characteristics is observed in the Sierra Nevada, while little divergence is observed in the Colorado Rockies. Snow cover in the Western U.S. is observed predominantly along two main axes: from north to south along the Cascades and the Sierra Nevada, and from northwest to southeast along the axis of the Rocky Mountain Cordillera. The snow line is lowest in the Washington Cascades and highest in the Colorado Rockies; between these two areas a northwest/southeast elevation gradient is observed. The warmest snow zones (warmest JFMLST) are at lower elevations of the Cascades/Sierra Nevada and in the southwest, whereas coolest snow zones (coldest JFMLST) are in the interior northern Rockies, mid to higher elevations of the Cascades, and the higher elevations of the Colorado Rockies and the Sierra Nevada. The warmest snow zones are likely to be most sensitive to climate warming, as these locations are vulnerable to shifting toward intermittent winter snow cover.
Open Access
Acid mine drainage impacts in the Upper Arkansas River Basin: a study of water quality, treatment efficiency, and predicted longevity
(Colorado State University. Libraries, 2019) Moore, Megan, author; Covino, Tim, advisor; Ross, Matthew, committee member; Wilkins, Mike, committee member; Rhoades, Charles, committee member
Mining activity in the Sugarloaf and Leadville mining districts of Leadville, Colorado has impaired water quality in the Upper Arkansas River Basin. Tributary and main channel waters are often out of compliance with state water quality standards, and stream flora and fauna as well as human use of these waterways is threatened by acid mine drainage. This study aims to describe the impact historical mining activity has had on the waters of the Upper Arkansas River Basin by characterizing water quality, analyzing metal removal efficiency from both active and passive treatment sites in the area, and estimating the time it will take for drainage from mining tunnels to naturally comply with state water quality standards. A comparison of instream dissolved concentrations of cadmium, copper, iron, lead, manganese, and zinc to state water quality standards shows waters of the Upper Arkansas River Basin are often out of compliance with chronic and/or acute standards. This is seen more frequently upstream from treatment sites and higher up in the tributary system than at tributary mouths or in the main channel of the Arkansas River. An examination of metal removal from the Leadville Mine Drainage Tunnel and Yak Tunnel water treatment plants along East Fork and California Gulch shows dissolved metal reduction between 33 and 100 percent compared with 0 to 84 percent at the passive Dinero Wetland Complex along Lake Fork. Finally, an analysis of projected longevity highlights the importance of clean-up plans for future mining projects with estimated impaired water quality continuing upwards of 2000 years at Yak Tunnel.
Open Access
Alpine wind speed and blowing snow trend identification and analysis
(Colorado State University. Libraries, 2012) Fuller, Jamie D., author; Laituri, Melinda, advisor; Cooley, Daniel, committee member; Doesken, Nolan, committee member; Elder, Kevin, committee member
The substantial quantity of climate change related analyses has resulted in increased research efforts concerning temporal wind speed trends. A change in wind speeds over time could have a widespread effect on snow transport and distribution in alpine regions. Since alpine meteorological stations are sparsely distributed, the intentions of this research were to explore North American Regional Reanalysis (NARR) to assess long-term trends of atmospheric conditions affecting snow transport with greater spatial coverage. NARR is a consistent, continuous and long-term dataset spanning the extent of North America at a spatial resolution of 32 km2 grids. NARR data were compared to two alpine sites (Niwot Ridge, Colorado and Glacier Lakes Ecological Experiments Station, Wyoming) from1989 to 2009. Multiple analyses were conducted to evaluate dataset agreement and temporal trends of alpine climatic conditions at the annual, seasonal and daily scales. The correlation of temperature, precipitation and wind speed between NARR and alpine in situ datasets showed temperature data as correlated, but wind and precipitation lacked agreement. NARR wind speed data were systematically lower when compared to observational data for both locations, but the frequency of wind events was captured. Thus, to more accurately assess blowing snow dynamics using NARR additional methods would be needed to relate the lower wind speed values to the extent of blowing snow. Trend analyses of wind speed datasets for each temporal scale (annual, seasonal and daily) showed slight trends, minimal significance and trends were not significantly different between NARR and in situ data. The statistical similarities were observed for trends with opposite signatures and slopes and a result of weak trends. Additional blowing snow analyses were conducted using temperature, wind speed and precipitation to estimate probable blowing snow events. The low agreement between NARR and observational data for wind speed and precipitation parameters prohibited the use of NARR to assess blowing snow processes and expand spatial and temporal coverage.
Open Access
Are wild and scenic rivers really "free-flowing"?
(Colorado State University. Libraries, 2021) Willi, Kathryn Rosalie, author; Kampf, Stephanie K., advisor; Ross, Matt R. V., advisor; Badia, Lynn, committee member
This study quantified the "free-flowing" character of wild and scenic river watersheds by first developing linear regression models to predict the "natural condition" of a river's magnitude, timing, frequency, and variability of flows. We compared these estimates of "natural" flow to the observed values for stream gages within wild and scenic river watersheds and found that nearly half (45.1%) had at least one altered flow metric. This was significantly lower (p < 0.05) than the fraction of altered gages outside wild and scenic river watersheds, and supported our other conclusion that wild and scenic rivers are associated with protected areas. On the other hand, wild and scenic river watersheds had a significantly higher (p < 0.05) fraction of gages with dam storage densities ≥ 100 megaliters·km-2 than gages outside wild and scenic river watersheds. Because the Wild and Scenic Rivers Act was designed as a complement to dam development, many wild and scenic rivers are designated in direct response to the threat of dam construction, or to counterbalance special rivers that have already been dammed. We posit that this biases wild and scenic river designations towards locations where dam development is common. Our study's findings expose a paradox in how a wild and scenic river designation can fully "protect and enhance" a river's free-flowing character. True protection of these special resources does not stop at designation, and requires additional support from managing agencies and stewardship groups to make improvements to their watersheds.
Open Access
Assessing flow alteration and channel enlargement due to dam management at Hog Park Creek, Wyoming
(Colorado State University. Libraries, 2016) Carleton, Tyler J., author; Fassnacht, Steven R., advisor; Butters, Gregory, committee member; Stednick, John D., committee member
As part of a complex water exchange agreement, Little Snake River water is piped through the Continental Divide and released into Hog Park Creek to replace over-appropriated North Platte River piped to Cheyenne, Wyoming. The Little Snake River water, in addition to native flows, has used Hog Park Creek as a conduit since the 1960s. As a result, Hog Park Creek has continued to enlarge. This study assesses flow alterations and channel enlargement at Hog Park Creek due to dam management. To assess flow alterations at Hog Park Creek without a pre-dam daily flow record, the Precipitation-Runoff Modeling System (PRMS) simulated natural flows from 1995 to 2015. A regionalization technique transferred calibrated parameters to Hog Park Creek model parameterization from Encampment River model parameterization. Along with the simulated natural flows, reference flows were used to compare to the post-dam flow record. All comparisons indicate the greatest flow alterations were winter and spring monthly flows and low flows. The April median flows and 7-day low flows more than tripled. To a lesser degree of deviation, significant flow alterations included peak flow alterations such as greater magnitude, longer duration, increased frequency, earlier peak flow timing, and faster fall rates. In addition, flow alterations due to climate were assessed. The climate trends reflect warmer-wetter climate change with a shift to earlier peak flows. However, these flow alterations are minor compared to those by dam management. The climate projections compared historic (1980-1999) and future (2040-2059) PRMS simulated natural flows using warmer-wetter and -drier scenarios. Both scenarios project more frequent, flashier peak flows. The warmer-wetter scenario also projects a shift to earlier peak flows. This projected shift of peak flows to mid-May is earlier than the current artificial peak flows in late-May and the natural peak flows in early June. Channel enlargement measured at Hog Park Creek is consistent with qualitative channel response for increased flows and sediment loads less than sediment transport capacity. Stream surveys from 2006 and 2015 measured irregular channel widening and bed degradation. The riffle cross-sections (XSs) measured little change while pool XSs at the maximum point of scour measured extensive widening (+ 3.6 m). Ecologic implications of continued channel enlargement were evaluated by modeling changes in water surface elevations using the Hydrologic Engineering Center River Analysis System (HEC RAS). Between 2006 and 2015, modeling indicated a decrease in water surface elevation by 3 cm per decade and a decrease in flood inundation area of 70 m2 per 1 m of stream length per decade. Additionally, the hydraulic modeling results support the theory that alluvial channel form is most influenced by bankfull flow, which in this case is the 1.5-year flood. Based on this agreement, modeling indicated channel enlargement began near a pre-dam bankfull flow of 3.8 m3 s-1 (135 ft3 s-1) and has since increased to 5.5 m3 s-1 (195 ft3 s-1) in 2015. A possible trajectory of channel enlargement is to a bankfull flow of 5.8 m3 s-1 (205 ft3 s-1), which is based on the 1.5-year flood since dam enlargement in the 1980s. However, without a stable flow regime, a stable channel form is not possible. Thus, to improve aquatic and riparian habitat, a stable flow regime and channel form will be necessary. For this reason, recommendations for a modified flow regime based on the findings of this study are developed and can be used as guidance for adaptive management.
Open Access
Biogeochemical implications of beaver-mediated fluvial complexity in river-floodplain meadows
(Colorado State University. Libraries, 2018) Weiss, Tristan N. M., author; Covino, Tim, advisor; Wohl, Ellen, committee member; Rhoades, Charles, committee member; Falkowski, Michael, committee member
Mountain river networks alternate between narrow, transport dominated segments and low gradient wide valley segments that can be important locations for the retention and processing of carbon and nutrients. In North America, beaver (Castor canadensis) engage in dam building that enables the establishment of complex river-floodplain meadows (hereafter "meadows"), characterized by wide riparian corridors, multi-thread channels, and high levels of river-floodplain connectivity. However, in many river-floodplain systems, human land-use and the removal of beaver has led to fluvial simplification characterized by reductions in riparian vegetation and channel incision. We examined differences in hydrology and biogeochemistry among four meadows of varying beaver activity and associated fluvial complexity within Rocky Mountain National Park, USA. We quantified water and dissolved organic carbon (DOC) flux, measured fluorescent dissolved organic matter (DOM) character, and monitored ecosystem metabolism. At complex meadow segments, we observed increased stability across space and through time in patterns of water flux and DOC concentration, export, and character. While DOC dynamics were stable at complex meadow segments, in simplified meadow segments we observed increases in DOC concentration and export, and shifts toward more terrestrially sourced, aromatic, and humic DOM. These results suggest that complex river-floodplain systems facilitate stability in stream flows and maintain water quality with respect to DOC concentration, flux, and form. Conversely, the loss of fluvial complexity in simplified meadow segments can lead to lost hydrologic and biogeochemical stability and make the valley segments more sensitive to future perturbations. Because wide-complex meadow segments can act as key locations of hydrologic retention in mountain stream networks, understanding how fluvial simplification alters water and DOC dynamics may be important for developing targeted restoration strategies for altered mountain headwater systems.
Open Access
Building on sustainable development goal indicator 11.3.1. for improved utility and guidance
(Colorado State University. Libraries, 2023) Cardenas-Ritzert, Orion, author; Vogeler, Jody, advisor; McHale, Melissa, committee member; Leisz, Stephen, committee member
The increased production of broad-coverage spatial datasets and investigation of these datasets by spatial analysis techniques allows for consistent examinations of urbanization patterns across the globe. Spatial data and analyses have proven valuable for sustainable urban development initiatives, including Sustainable Development Goal (SDG) 11 under the United Nation's 2030 Agenda for Sustainable Development. SDG Indicator 11.3.1 is a geospatially measured indicator implemented under SDG 11 for monitoring rates of urban expansion and population growth in a specific area over a period of time. Current methodological approaches and data inputs may hinder the application of SDG Indicator 11.3.1 at certain scales and extents. The overarching goal of this research is to build on the utility of SDG Indicator 11.3.1 by enhancing an existing urban delineation method for automated function, examining urban change at the urban agglomeration level across broad extents, highlighting hotspots of SDG Indicator 11.3.1, and evaluating the impacts of the spatial resolution of data inputs on SDG Indicator 11.3.1 and related outputs. In Chapter 1, we advanced an existing urban delineation method for the automatic identification of individual urban agglomerations across broad extents. We accomplished this by integrating various open-source datasets and tools with spatial analysis techniques. We used this methodology to examine SDG Indicator 11.3.1 and additional urban change metrics for urban agglomerations in Ethiopia, Nigeria, and South Africa over the 2016 to 2020 period. In Chapter 2, we applied our delineation methodology and examined the influence of spatial resolution of land use data on urban delineation, urban change metrics, and urban related land use change in Ethiopia over the 2016 to 2020 period. The results of Chapter 1 revealed trends of urban change and highlighted hotspots of SDG Indicator 11.3.1 at multiple levels across the three African countries. Chapter 2 revealed the implications of using varied spatial resolutions of land use maps when delineating urban areas, assessing SDG Indicator 11.3.1 and other urban change metrics, and examining urbanization-driven land use change.
Open Access
Comparison of digital terrain and field-based channel derivation methods in a subalpine catchment, Front Range, Colorado
(Colorado State University. Libraries, 2012) Hastings, Blaine, author; Kampf, Stephanie, advisor; Laituri, Melinda, committee member; Niemann, Jeffrey, committee member
Understanding the reliability of digitally derived channel networks for mountainous headwater catchments is important to many water resource and land-use management applications. Digital elevation models (DEMs) have become an essential tool for an increasing array of mountain runoff analyses. The purpose of this study is to investigate the influence of digitally-derived topographic variables on channel network formation for a high-elevation glaciated watershed. To accomplish this, our objectives were to (1) test how differences in gridded DEM resolution affect spatially distributed topographic parameters of local slope (tan β), specific contributing area (αs), and topographic wetness index (TWI) derived from both eight and infinite directional flow algorithms, (2) map the actual stream channel network at Loch Vale and examine the influence of surface variables on channel initiation, and (3) evaluate the performance of common methods for deriving channel networks from gridded topographic data by comparing to the observed network. We found that coarser DEM resolution leads to a loss of detail in spatial patterns of topographic parameters and an increase in the calculated mean values of ln(αs) and TWI. Grid cell sizes above 1m result in a substantial shift in the overall cumulative frequency distributions of ln(αs) and TWI towards higher values. A field survey at Loch Vale revealed a complex and disjointed channel network, with 242 channelized points and 30 channel heads. We found no predictable relationships between channel head locations and geomorphic process domains. Analysis of variance (ANOVA) showed no statistically significant difference in mean ln(αs) and TWI for channel head locations grouped by elevation, aspect, slope, formation process or upslope land cover type. For most DEM resolutions and flow partitioning algorithms, deriving channel networks with spatially constant flow accumulation and TWI thresholds provides poor network representation. The publicly available National Hydrography Dataset (NHD) layer oversimplifies the channel network by neglecting almost all first and second order channels. Many of the DEM-derived channel networks that use spatially constant flow accumulation and TWI thresholds also do not reproduce the locations of low order channels in the observed channel network well. Assumptions of topographic control on channel initiation are not shown to be valid at Loch Vale, likely due to their inability to capture subsurface processes and geologic features important to channel formation. However, if using these topographically dependent threshold methods to delineate channel networks, we suggest the use of field-based survey data to identify appropriate thresholds. With appropriate thresholds, both 1m and 10m DEMs can produce channel networks with similar drainage densities to the observed network, even if locations of low order channels are not predicted accurately. Performance degrades for 30m DEMs, so we suggest that DEMs with resolutions coarser than 10m should be avoided for channel network delineation.
Open Access
Conservative solute transport processes and associated transient storage mechanisms: a comparison of streams with contrasting channel morphologies, land use, and land cover
(Colorado State University. Libraries, 2021) Emanuelson, Karin, author; Covino, Timothy, advisor; Ross, Matthew R. V., committee member; Morrison, Ryan R., committee member
Land use within a watershed impacts stream channel morphology and hydrology and therefore in-stream solute transport processes. In this study, I selected two stream sites with contrasting channel morphology, land use and land cover: Como Creek, CO, a relatively undisturbed, high-gradient, forested stream with a gravel bed and complex channel morphology and Clear Creek, IA, an incised, low-gradient stream with low-permeability substrate draining an agricultural landscape. At these sites, I performed conservative stream tracer experiments to address the following questions: 1) How does solute transport vary between streams with differing morphologies and watershed land use?, and 2) How does solute transport at each stream site change as a function of discharge? I analyzed in-stream tracer time series data and compared results quantifying solute attenuation in surface and subsurface transient storage zones. I found significant differences in solute transport metrics between sites and significant trends in these metrics with varying discharge conditions at the forested site but not at the agricultural site. In the relatively undisturbed, forested stream there was a broad range of transport mechanisms and evidence of substantial exchange with both surface and hyporheic transient storage. In this forested site, changing discharge conditions activated or deactivated different solute transport mechanisms and greatly impacted advective travel time. Conversely, in a simplified, agricultural stream there was a narrow range of solute transport behavior across flows and predominantly surface transient storage at all measured discharge conditions. These results demonstrate how channel simplification resulting from land use change inhibits available solute transport mechanisms across varying discharge conditions.
Open Access
Effect of mountain pine beetle kill on streamflow generation mechanisms
(Colorado State University. Libraries, 2016) Wehner, Christine Elisabeth, author; Stednick, John D., advisor; Fassnacht, Steven R., committee member; Niemann, Jeffrey, committee member
The mountain pine beetle (Dendroctonus ponderosae) is an endemic species to Colorado, but a recent epidemic resulted in the mortality of millions of acres of lodgepole pine forest in Colorado since 2002. This study examined the effect of the mountain pine beetle kill on streamflow generation mechanisms using different tracer methods. Eleven nested watersheds with varying level of beetle-killed forest area (47.1% to 97.4%) were chosen for study. Groundwater, surface water, and precipitation samples were taken and analyzed for stable isotope composition (2H and 18O), specific conductivity, and chloride concentrations. Four methods were employed to partition sources of streamflow, or streamflow generation mechanisms (SGM), in beetle-killed watersheds. Stable isotopes (2H and 18O) were used to determine mean fractional contribution of each source (groundwater, rain, and snow) to streamflow. Rain and snow contribution were negatively correlated with beetle-killed forest area (p=0.08 and p=0.35 respectively). Groundwater was positively correlated with increasing beetle-killed forest area (p=0.23). Specific conductivity and chloride were each used in a 2-component (groundwater and precipitation) hydrograph separation. Using specific conductivity, beetle kill was negatively correlated with average groundwater contribution (ρ = -0.13), but the result was not significant (p = 0.71). Using chloride, the results were correlated (ρ=0.19), but not significant (p = 0.58). Specific conductivity and chloride measurements were then coupled in a 3-component (groundwater, rain, and snow) end member mixing analysis (EMMA). Beetle-killed forest area and fractional groundwater contribution were positively correlated (ρ=0.26), but not significant (p = 0.43). Watershed characteristics were examined to determine potential metrics of groundwater contribution. Mean watershed elevation displayed a significant negative correlation with mean groundwater contribution (p = 0.08).
Open Access
Effects of conjunctive use on streamflow at the Tamarack State Wildlife Area, northeastern Colorado
(Colorado State University. Libraries, 2012) Donnelly, Erin, author; Stednick, John, advisor; Ronayne, Michael, committee member; Sale, Thomas, committee member; Kampf, Stephanie, committee member
The Tamarack Recharge Project in northeastern Colorado is intended to augment the streamflow of the South Platte River by 10,000 acre-feet between April and September to increase aquatic habitat for four federally threatened or endangered bird and fish species in Nebraska. The project goal is to retime surface water flows by pumping unappropriated alluvial groundwater into a recharge pond where it infiltrates and returns to the river at critical low flow periods. Retimed surface water flow will help maintain critical habitat for native aquatic species by increasing streamflow without harming water rights holders. To evaluate the effects of this managed groundwater recharge on streamflow in the South Platte River, the hydrologic environment was characterized and quantified through streamflow monitoring, water table elevation mapping, and a groundwater tracer study. Stream discharge measurements were taken at 4 cross sections on the South Platte River. Two cross sections were considered upgradient of the recharge pond and two were downgradient of the recharge pond. The mean flow of the upstream cross sections was 2.64 cubic meters per second (cms) compared to 2.66 cms at the downstream cross sections, which was not a significant difference. A fluorescein tracer study was used to estimate groundwater travel times and hydraulic conductivity. Based on the arrival time of the breakthrough curve at different piezometers, the mean hydraulic conductivity was estimated to be 331 m/d. Using this value, the estimated return time to the South Platte River at 4 cross sections ranged from 92 to 534 days. Measurements of discharge and water table elevations suggesting that Tamarack Project did not produce a measureable increase in streamflow in the South Platte River during the target period are not indicative of project functionality. The annual volume of water pumped into the recharge pond was less than 1% of the annual yield of the South Platte River. While the volume of return flows did not produce measureable results in the river, data from the tracer study and in-stream vertical hydraulic gradient data indicate a gaining stream condition during the fall and a losing stream during the winter and early spring. Potential source(s) of groundwater discharging to the stream include the recharge pond and irrigation return flows and warrant further study.
Open Access
Effects of early snowmelt on plant phenophase timing and duration across an elevation gradient
(Colorado State University. Libraries, 2021) Wilmer, Chelsea, author; Kampf, Stephanie, advisor; Steltzer, Heidi, advisor; Hufbauer, Ruth, committee member
Plant phenology is an important indicator of the effects of climate change, yet the relative importance of both the drivers of plant phenology and the importance of individual phenophases in how plants respond to climate change is not well understood. Here we assess the impact of early snowmelt, a critical climate perturbation in mountain regions, on the timing and duration of individual plant phenophases across an elevation gradient in Crested Butte, Colorado. We observed a sequence of plant phenophases, new leaves, full leaf expansion, first open flower, and full leaf color change at five sites at distinct elevations (2774 m, 2957 m, 3167 m, 3475 m, 3597 m) across three mountain life zones (montane, subalpine, and alpine) in 2017 and 2018. In the spring of 2018, we used solar radiation absorbing fabric to accelerate the timing of snowmelt and observed the differences in timing for early snowmelt plots relative to control plots. The two study years had different snowmelt timing with 2018 being much earlier than 2017, so we analyzed the data to evaluate the effect of year using unmanipulated plots only, and also, separately the snowmelt manipulation, on phenophase start dates and durations. Phenophase timing was advanced at nearly all sites in 2018 and was not clearly linked to shifts in duration, which were variable. The snowmelt manipulation did not shift the timing of phenophases at the lowest elevation in our elevation gradient and the effect of the experiment on the timing of phenophases decreased as elevation increased. Even though snowmelt was significantly accelerated in the manipulation plots in 2018 at the lowest elevation the timing of phenophases were not advanced. This may indicate a threshold beyond which early snowmelt no longer advanced leaf emergence. Earlier snowmelt in mountain regions can shift the timing and duration of plant growth, though not consistently, which will have consequences on how plants affect the movement of water and retention of nutrients and metals in mountain watersheds.
Open Access
Effects of flow modification and forest disturbance on streamflow across Colorado
(Colorado State University. Libraries, 2020) Eurich, Abigail M., author; Kampf, Stephanie K., advisor; Bhaskar, Aditi, committee member; Evangilista, Paul, committee member
Human activities alter streamflow around the world. In Colorado, flow modifications, land use change, and forest disturbances all modify streamflow, but the relative magnitudes of these effects are not well-quantified. This study examined how streamflow quantity across Colorado has been affected by three classes of change: (1) flow modifications from reservoirs and diversions, (2) urbanization, and (3) forest disturbance. The goal of this work was to identify the magnitude of streamflow alterations from these different types of stressors to understand the sensitivity of the state's streams to future changes, both natural and anthropogenic. A total of 215 watersheds were used to analyze effects of flow modifications and urbanization, and 71 of these watersheds were analyzed for effects of forest disturbance. Flow modifications and land use change have altered 85% of the gaged streams in this study. Of the stressors studied, the largest effects are from transbasin diversions, which reduce flow by an average of 20% in watersheds with diversions out of the watershed and increase flow by an average of 221% in watersheds with diversions importing water from another basin. Across all types of watersheds, the gaged streams in the Plains and Southwest regions of the state are most altered, and those in the Rio Grande are the least altered. The lower elevation areas are experiencing the largest percent changes relative to their natural flow regime (average water imports = 38 mm, 875%); the reduction in flow from high elevation watersheds is large in magnitude as well, but it equates to a smaller percent of the expected flow (average water exports = -71 mm, -18%). Forest disturbance may increase or decrease streamflow depending on the characteristics of the watershed and the disturbance, but the magnitude of the impact remains within the natural variability of streamflow in similar watersheds. A significant change in streamflow was observed in 25% of watersheds affected by disturbance, mainly with increases in flow following beetle mortality and severe wildfire. Streamflow decreased following smaller wildfires and in watersheds with South- and West-facing dominant aspects. Overall, anthropogenic modifications to streamflow via diversions that move water between watersheds have the largest effect on mean annual streamflow, whereas streamflow changes from forest disturbance mostly remain within the range of natural variability.
Open Access
Effects of mountain pine beetle caused tree mortality on streamflow and streamflow generation mechanisms in Colorado
(Colorado State University. Libraries, 2014) Maggart, Ariann Lenore, author; Stednick, John D., advisor; Fassnacht, Steven, committee member; Ronayne, Michael, committee member
The mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB), an endemic beetle in Colorado forests, saw dramatic population growth in the 1990's. As a result of this epidemic, the mountain pine beetle killed large tracts of forest as it spread. To evaluate the effects of MPB caused tree mortality on streamflow and streamflow generation mechanisms multiple investigative approaches were taken. In north-central Colorado, 21 watersheds representing minimally to highly affected watershed areas were chosen. Physical watershed characteristics were determined through a geographic information system. Long-term streamflow records for each watershed were assessed for data stationarity and change-points in peak flow, date of peak flow and annual water yield. Peak streamflow, date of peak streamflow and annual water yield all had stationarity. Since data were stationary, change-point analyses were not conducted. Streamflow, groundwater and precipitation samples were collected and analyzed for stable isotope concentrations. Isotopes of 2H and 18O partition source water contributions to streamflow from precipitation as snow or rain and groundwater (as a surrogate for groundwater). Annual δ2H and δ18O isotopic signatures for streamflow and streamflow source waters, as snow, groundwater and rain, were determined and used to partition source water contributions to streamflow for each watershed. In general, during the 2012 water year, source water contributions to streamflow were as follows: snow 60%, groundwater 20% and rain 20%. The correlations between snow, groundwater and rain contributions to streamflow and MPB killed area were not statistically significant at α ≤ 0.05 (psnow = 0.582, pgroundwater = 0.543 and p;rain = 0.897). While Colorado has suffered extensive forest kill since the onset of the MPB epidemic, the results of this study suggest that MPB killed watershed area has little to no effect on peak streamflow, date of peak streamflow, annual water yield or streamflow generation mechanisms.
Open Access
Effects of post-fire mulch applications on hillslope-scale erosion
(Colorado State University. Libraries, 2023) Geller, Jordyn, author; Kampf, Stephanie, advisor; Barnard, David, advisor; Nelson, Peter, committee member
Wildfires are increasing in frequency and intensity, greatly altering the landscape and increasing risk of erosion. Mulching is a common restoration technique used after wildfire to enhance protective ground cover and reduce erosion, yet most studies are conducted at the plot-scale. This study applies an experimental approach to evaluate the impact of mulch treatments at the hillslope-scale using varying mulch levels. Similar adjacent hillslopes were chosen to minimize variability in landscape features. The objectives of this research are to 1) examine the effectiveness of post-fire mulching in reducing erosion at the hillslope-scale, and 2) identify landscape features and precipitation factors contributing to the occurrence and magnitude of sediment yield. Sediment fences were installed in convergent swales and planar hillslopes to quantify sediment yields before and after aerial wood mulch application. Rain gauges were installed to compute rainfall amount (mm), duration (hr), and maximum intensities (mm/hr) by storm event. Field observations, coupled with game camera footage, were utilized to evaluate whether each storm produced sediment in the fences. Surface cover surveys were conducted to assess cover changes over the season. Collectively these data were used to 1) identify rainfall intensity thresholds for erosion, 2) examine controls on sediment generation occurrence with a binomial distribution mixed-effects model, 3) examine controls on the magnitude of sediment yield using a gamma distribution mixed-effect model, and 4) assess relative importance of variables relating to sediment yield using random forest models. Threshold rainfall intensities for generating erosion at the study sites were 32-38 mm/hr for MI5, 11-18 mm/hr for MI15, 7-13 mm/hr for MI30, and 5-8 mm/hr for MI60. Across all models of erosion occurrence and magnitude of sediment yield, maximum rainfall intensity and total precipitation were primary drivers of erosion. There was no evidence of a mulch treatment effect on sediment occurrence or magnitude, likely resulting from insufficient initial mulch cover and a high-intensity storm that removed much of the mulch shortly after it was dropped on the hillslopes. Contributing area, slope mean, and slope length showed no influence on sediment yield, likely due to limited variation in these variables between hillslopes. These results highlight the importance of mulch cover that will stay in place under extreme rainfall. Future hillslope-scale studies should consider dropping mulch during a time period that is unlikely to have high intensity rainfall and explore mulch materials and application methods that will better ensure adequate initial cover for reducing hillslope-scale erosion.
Open Access
Effects of snow persistence on soil water nitrogen across an elevation gradient
(Colorado State University. Libraries, 2019) Anenberg, Alyssa Nicole, author; Kampf, Stephanie, advisor; Baron, Jill, advisor; Borch, Thomas, committee member
In the western United States, the timing and magnitude of snowmelt is an important control on soil water and nutrient availability. Warming trends can alter the timing of snowmelt, directly impacting snow cover and soil freeze-thaw cycles, as well as available water for downstream use. While prior research relating snow to soil water nitrogen has focused on areas with persistent winter snow, the snow and soil water dynamics in lower elevation areas with intermittent snowpack are not as well documented. The broad goal of this study is to understand how the duration of snow persistence affects soil moisture and soil water nitrogen concentrations. The specific objectives are to address (1) how the duration of snow persistence affects soil moisture across an elevation gradient, from areas where the snowpack ranges from shallow and intermittent to deep and persistent throughout the winter and (2) how this gradient in snowpack affects soil water nitrogen. Three study sites that span a 1500m elevation gradient were established in the Colorado Front Range to monitor snow, soil moisture, and soil water nitrogen. The highest elevation site, Michigan River, is located in the persistent snow zone; the middle elevation site, Dry Creek, is in the transitional snow zone; and the lowest elevation site, Mill Creek, lies in the intermittent snow zone. Each site was equipped with soil moisture probes at 5 and 20cm depth, soil temperature probes, snow depth poles monitored by time-lapse cameras, and ion exchange resin probes. The Mill Creek research site also contained nine snow manipulation chambers and twenty-seven tension lysimeters to sample soil water nitrogen. Snow cover persisted for longer periods of time as elevation increased and soil temperatures decreased. Lower elevation sites were consistently warmer and drier than the higher elevation site. At the highest elevation site, soil moisture increased after a large pulse of snowmelt in the late spring, while the lower elevations experienced multiple smaller pulses of soil moisture following individual snow events. In the snow manipulation chambers, plots with increased snow depth experienced increased soil moisture, however plots with decreased snow depth did not always produce the lowest soil moisture. Additionally, soil moisture in the control snow plots and in plots with increased snow depth consistently increased throughout the melt season, whereas plots with decreased snow depth briefly increased after each snowmelt event then declined to pre-event levels. NO₃– and NH₄+ were correlated with soil moisture, and large increases in soil moisture were associated with a flushing signal of NO₃–. This suggests that soil water nitrogen is regulated by the amount of soil water available, and that nitrogen can be impacted when changes in snow alter soil moisture timing and magnitude.
Open Access
Ethiopian socio-hydrology: geographies of development and change in the water tower of Africa
(Colorado State University. Libraries, 2017) Chignell, Stephen M., author; Laituri, Melinda J., advisor; Evangelista, Paul H., committee member; Leisz, Stephen J., committee member
Water access, sanitation, and security remain key foci of international aid and development initiatives. However, the increasing interconnectedness of hydrologic and social systems can cause such initiatives to have unexpected and cascading effects across geographic scales. This presents new challenges for meeting ever-growing demand, as distant and complex socioeconomic and environmental relationships, or "telecouplings," may significantly influence the outcomes and sustainability of development projects. Predicting future water scenarios thus requires both integrative and basic research into the structure and function of socio-hydrological systems. I explored these emerging concepts in Ethiopia, which is the source of water for much of the Horn of Africa and receives over half of its annual budget from foreign development aid. I analyzed the geography of water in Ethiopia from two perspectives. First, I used examples from the literature to identify water development initiatives in rural and urban settings and at local and national scales. I then situated these initiatives within the telecoupling framework to reveal underlying socio-hydrological relationships. My results indicate that water development is linking Ethiopia's hydrology with geographically distant communities and markets and creating new and often unexpected flows of people, material, and capital. This is resulting in cross-scale feedbacks among urbanization, geopolitics, and the food-energy-water nexus in Ethiopia. Second, I conducted basic research into alpine wetland dynamics in the Bale Mountains, which provide the only perennial source of water to highland communities and 12 million downstream water users in East Africa. I found that wetlands more than double in extent between dry and wet seasons, and that just 4% of the alpine zone is saturated year-round. I found evidence of a hydrological continuum based on geologic and glacial legacies, which suggests that geology is a principal control on alpine wetland hydrology in Bale. I used this to develop a typology of wetland function, which provides a baseline for future research into climate change impacts and surface-groundwater connectivity.
Open Access
Evaluating and correcting sensor change artifacts in the SNOTEL temperature records, southern Rocky Mountains, Colorado
(Colorado State University. Libraries, 2017) Ma, Chenchen, author; Fassnacht, Steven, advisor; Kampf, Stephanie, advisor; Wei, Yu, committee member
In many high elevation mountain regions, documented warming rates have been greater than the global surface average. These warming rates directly affect the snowpack, runoff, ecosystems, agriculture and species that rely on a high elevation snowpack. Temperature records from the snow telemetry (SNOTEL) network across the Southern Rocky Mountains in the western United States have high warming rates, which may have been affected by systematic inhomogeneities in the temperature data caused by sensor changes. This study evaluates the maximum, average, and minimum temperature trends from 68 long-term SNOTEL stations across Colorado for the period from the 1980s through 2015 using the non-parametric Mann-Kendall/Theil-Sen's analyses before and after the temperature records were corrected for the sensor-caused inhomogeneities. Three homogenization methods were tested using a simple temperature index snow accumulation and melt model. Results show that the significant warming trends found in the original datasets, especially in minimum temperature (average increase of 1.2 °C per decade), decreased (to an average of 0.5 °C per decade) after homogenization. Step-like shifts in temperature datasets were observed in SNOTEL temperature records at the time of temperature sensor change, which created a discontinuity in the temperature dataset. The temperature-index snow model simulated snow water equivalent (SWE) well (more than 93% of the calibrated stations within the "good" and "very good" performance category for all three statistical-evaluation periods based on the Nash-Sutcliffe coefficient of efficiency, NSCE) using the new temperature sensor dataset. However, these models did not perform as well when using the original (pre-sensor change) and homogenized temperatures, with 23% of stations for the original temperature data and 44-69% of stations for two homogenized temperature datasets within the "good" and "very good"temperature data, but they did not fully correct for the effects of sensor change on the temperature records. The NSCE and bias statistics from SWE modeling using the original and homogenized datasets suggest that the homogenization methods evaluated in this study are applicable for many of the SNOTEL stations in Colorado but not all, and need to be applied with caution. Potential users of temperature products from the SNOTEL network should also be very careful when choosing time periods for future climate change research and assessments. More long-term climate monitoring stations should be installed in high elevation mountain regions to document and investigate elevation-dependent warming.
Open Access
Evaluating post-fire woody mulch effects on soil and stream nitrogen
(Colorado State University. Libraries, 2024) Richardson, Mikaela, author; Kampf, Stephanie, advisor; Rhoades, Chuck, advisor; Ross, Matt, committee member; Wilkins, Mike, committee member
Severe wildfires often increase nitrogen (N) loss from burned watersheds, impacting downstream water quality, water treatability, and aquatic habitat. Woody mulch is commonly applied to mitigate soil erosion and enhance revegetation post-fire, but it also provides a source of labile carbon (C) that may stimulate microbial immobilization and limit N release from soils. The objective of our study was to evaluate whether mulch application influenced turnover and loss of soil C and N in laboratory leaching trials and hillslope field settings, and then compared post-fire C and N in streams draining mulched and unmulched catchments. In the laboratory, we quantified C and N inputs and leaching outputs from mulched and unmulched soil columns. Within the Cameron Peak fire burn scar in northern Colorado, we compared soil N availability and potential leaching losses between mulched and unmulched hillslope plots. We also measured C, N, and other chemical constituents in streams draining three mulched and three unmulched catchments. In the laboratory leaching studies, mulch added high concentrations of dissolved organic carbon (> 500 mg L-1) and decreased nitrate leaching from soil columns by 27% during repeated simulated rainfall events. In hillslope plots, mulching also reduced soil nitrate, with greater impacts following spring snowmelt when N losses from soils to streams was highest. However, the effect of mulching was not measurable at the catchment scale due to low application rates and mulch extent, paired with high topographic and geomorphic variability amongst the catchments. Our findings show that C inputs from woody mulch can influence soil N retention in burned watersheds when applied at a minimum rate of 5 Mg ha-1; however practical constraints on aerial application may make it challenging to apply enough mulch for any downstream response to be detectable. Coupled with physical erosion protection, the biogeochemical impacts of mulching may facilitate soil and vegetation recovery following severe wildfire and reduce post-fire N losses to streams if sufficiently applied. Therefore, further post-fire rehabilitation efforts should optimize mulch operations by prioritizing sensitive watersheds and treating them with adequate mulch.
Open Access
Evaluating the spatial variability of snowpack properties across a northern Colorado basin
(Colorado State University. Libraries, 2012) Sexstone, Graham Andrew, author; Fassnacht, Steven, advisor; Laituri, Melinda, committee member; Sibold, Jason, committee member
Knowledge of seasonal mountain snowpack distribution and estimates of its snow water equivalent (SWE) can provide insight for water resources forecasting and earth system process understanding, thus, it is important to improve our ability to describe the spatial variability of SWE at the basin scale. The objectives of this thesis are to: (1) develop a reliable method of estimating SWE from snow depth for the Cache la Poudre basin, and (2) characterize the spatial variability of SWE at the basin scale within the Cache la Poudre basin. A combination of field and Natural Resource Conservation Service (NRCS) operational-based snow measurements were used in this study. Historic (1936 - 2010) snow course data were obtained for the study area to evaluate snow density. A multiple linear regression model (based on the historical snow course data) for estimating snow density across the study area was developed to estimate SWE directly from snow depth measurements. To investigate the spatial variability and observable patterns of SWE at the basin scale, snow surveys were completed on or about April 1, 2011 and 2012 and combined with NRCS operational measurements. Bivariate relations and multiple linear regression models were developed to understand the relation of SWE with physiographic variables derived using a geographic information system (GIS). SWE was interpolated across the Cache la Poudre basin on a pixel by pixel basis using the model equations and masked to observe SCA (from an 8-day MODIS product). The independent variables of snow depth, day of year, elevation, and UTM Easting were used in the model to estimate snow density. Calculation of SWE directly from snow depth measurement using the snow density model has strong statistical performance and model verification suggests the model is transferable to independent data within the bounds of the original dataset. This pathway of estimating SWE directly from snow depth measurement is useful when evaluating snowpack properties at the basin scale, where many time consuming measurements of SWE are often not feasible. Bivariate relations of SWE and snow depth measurements (from WY 2011 and WY 2012) with physiographic variables show that elevation and location (UTM Easting and UTM Northing) are most strongly correlated with SWE and snow depth. Multiple linear regression models developed for WY 2011 and WY 2012 include elevation and location as independent variables and also include others (e.g., eastness, slope, solar radiation, curvature, canopy density) depending on the model dataset. The final interpolated SWE surfaces, masked to observed SCA, generally show similar patterns across space despite differences in the 2011 and 2012 snow years and differing estimation of SWE magnitude between the combined dataset of field-based and operational-based measurements (modelO+F) and the dataset of operational-based measurements only (modelO). Within each of the model surfaces, interpolated volume of SWE was greatest within Elevation Zone 5 (3,043 - 3,405 m). The percentage of the total interpolated SWE volume for each model was distributed similarly among elevation zones.