Browsing by Author "Rhoades, Charles, committee member"
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Item 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 memberMining 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.Item Open Access Amendment effects on soil physical properties and restoration of decommissioned forest roads(Colorado State University. Libraries, 2017) Berlejung, John Michael, author; Fonte, Steven, advisor; Rhoades, Charles, committee member; Paschke, Mark, committee memberUnsealed forest roads, including logging roads and unauthorized roads created by hunters, miners, and recreational users, generate significant harmful effects to local ecosystems and waterways. Rapid restoration of these roads is necessary to prevent erosion, downstream implications for water quality, and a variety of other deleterious ecosystem impacts. Soil amendments, including mulches, composts, and other materials, offer promise to improve soil health, restore soil structure, and support revegetation of these sites. I tested the viability of three locally-sourced soil amendments wood straw mulch, Biosol fertilizer, and biochar alone and in paired combinations to restore soil physical properties important for improved hydrologic function and plant growth. I found that amendment combinations of biochar + mulch and biochar + Biosol significantly reduced soil bulk density when compared to unamended controls. Other factors (aggregate stability, infiltration, sediment production) suggested potential for improvement relative to unamended control plots, but no significant differences between treatments were observed due to high variability within and between sites. Regression analyses revealed that soil physical properties, particularly wet aggregate stability, was significantly correlated with key soil erosion parameters such as infiltration and runoff, suggesting aggregate stability could provide a useful measure of soil restoration success.Item 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 memberMountain 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.Item Open Access Carbon and nitrogen eroded from burned forests in the western U.S.(Colorado State University. Libraries, 2013) Pierson, Derek, author; Binkley, Daniel, advisor; Rhoades, Charles, committee member; Kelly, Eugene, committee memberPost-wildfire landscapes and downstream aquatic resources are influenced by carbon (C) and nitrogen (N) losses from soil erosion. As opposed to soil erosion, rarely measured losses of sediment C and N may account for a substantial portion of fire impacts. We measured erosion of C and N following eight wildfires for four to six years in the western U.S and compared losses from untreated, burned hillslopes and small catchments with those from adjacent areas that received erosion mitigation treatments. Losses of C, N and sediment were greatest the first two years and declined in subsequent years. Cumulative losses from untreated, burned areas were 16 - 4,700 kg C/ha and 0.7 - 185 kg N/ha over the study period. Across wildfire locations, median sediment C and N concentrations ranged from 0.011 - 0.036 g N/kg and 0.23 - 0.98 g C/kg. Post-fire erosion control treatments reduced C, N and sediment losses by 65-75% compared to untreated areas and generally increased the concentrations of C and N in eroded material. The total C and N lost in post-fire erosion was < 20% of the estimated amount lost from organic and mineral soil layers during combustion and < 5% of the estimated amount remaining in mineral soils after combustion. In general, the N lost with soil erosion is unlikely to impair the productivity of recovering forests, but the eroded N may have consequences on downstream water quality and aquatic habitat.Item Open Access Fire, fungi, flora, and flow: post-fire fungal community assemblages, vegetation establishment, and soil hydrophobicity in forests of the southern Rocky Mountains(Colorado State University. Libraries, 2023) McNorvell, Michael A., author; Stevens-Rumann, Camille, advisor; Rhoades, Charles, committee member; Remke, Michael, committee member; Wilkins, Michael, committee memberWildfire is an important ecological driver of ecosystem dynamics in the southern Rocky Mountains at multiple landscape scales, guiding establishment of forest biota both aboveground and below. Size, frequency, and severity of wildfires in coniferous forests across the western United States is increasing at an unprecedented rate. Despite wildfire's significant but disparate influences on forest soils, post-fire research has often focused on aboveground vegetation in isolation from study of belowground soil characteristics and the fire ecology of soil biota. Fungi are vital to forest ecosystems for their functional roles, however, the effects of wildfire on forest-specific fungal communities and how those communities subsequently influence post-fire vegetation communities and soil environments has not been extensively researched in the region over the past several decades. This is a prominent knowledge gap, especially as fungi are highly variable across functional groups, space, and time even in unburned systems. Thus, to build on our understanding of contemporary fire ecology in forested ecosystems of the Southern Rockies, we investigate three wildfires that burned in the state of Colorado during the 2020 fire season and address three research objectives: 1) Examine the influence of forest type and fire severity on post-fire fungal community composition across soil depth and temporal gradients; 2) Determine the effects of post-fire fungal community diversity on forest understory plant diversity and abundance; and 3) Explore relationships between fungal assemblages and observed soil hydrophobicity in burned forested environments. We found that though fire severity and soil depth were the primary influences on quantified fungal diversity, the composition of fungal community assemblages was most heavily influenced by forest type: forests developed fungal communities compositionally unique to one another just two years after fire. Diversity of fungi showed significant influence on aboveground plant diversity and abundance, especially mutualistic fungi (ecto- and arbuscular mycorrhizae) and their respective plant hosts. Finally, significant relationships between fungal diversity and soil hydrophobicity were observed mediated by forest type, fire severity, soil depth, and year post-fire, though these patterns were difficult to surmise and the influence of other important variables may be at play. By more fully understanding how soil fungi interact with aboveground vegetation establishment and belowground soil conditions after wildfire, this research may help inform managers of pathways to better achieve desired post-fire outcomes by leveraging fungal relationships in soil remediation, site preparation, and conservation of post-fire forest ecosystems.Item Open Access Forest soil C and N responses to salvage logging and belowground C inputs in bark beetle infested stands(Colorado State University. Libraries, 2020) Avera, Bethany N., author; Cotrufo, M. Francesca, advisor; Rhoades, Charles, committee member; Rocca, Monique, committee member; van Diepen, Linda, committee memberManaging forest ecosystems in this era of global change requires a fundamental understanding of forest soil properties and processes. Forest disturbance events are projected to increase in severity and frequency, requiring a better understanding of how post-disturbance management will impact ecological processes such as soil nutrient dynamics and stocks of soil carbon (C). The research in this dissertation focused on areas of widespread mortality in lodgepole pine (Pinus contorta var. latifolia) in northern Colorado due to the most recent outbreak of the endemic mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins). The goal of this research was to examine soil nitrogen (N) stocks, plant N uptake, and changes in forest soil C stocks in soil organic matter (SOM) due to tree mortality and subsequent salvage logging and from different belowground C inputs. To achieve this aim, I compared the three most prevalent management options: 1) uncut beetle-infested lodgepole pine stands and clear-cut salvage logged areas with either 2) post-harvest residue retention or 3) post-harvest residue removal. To determine the impacts of MPB-infestation and salvage logging on ecosystem N stocks and plant N uptake, I implemented an experimental field study by adding 15N-labeled ammonium sulfate to research plots centered over lodgepole pine seedlings. Measuring N stocks and 15N recovery in soil and vegetation pools over two growing seasons highlighted the coupled nature of forest C and N cycling between plant and soil forest ecosystem compartments. The majority of the 15N label was recovered in the soil and was not impacted by the management treatments. In contrast, the N uptake by lodgepole pine seedlings was driven primarily by the amount of C fixation and the patterns of C fixation, in turn, related to other environmental factors modulated by the management treatment, such as available light. An observational field study sought to quantify changes in forest soil C stocks in the bulk soil and SOM fractions and detect any changes in C chemistry as a result of management that may impact C persistence. In the dry, high elevation forests studied, soil C increased with salvage logging likely due to mixing of surface residues and O horizon C into the mineral soil during logging. The distribution of C stocks among the mineral soil fractions and the chemistry of those fractions indicated that root C accumulation in the particulate organic matter (POM, >53 μm) is an important mechanism of soil C accumulation in these forest soils. A mechanistic laboratory incubation evaluated the efficiency of mineral-associated organic matter (MAOM, <53 μm) formation from root and hyphal necromass inputs with different C chemistries. This study showed that rye root necromass with more labile and less structural C than pine roots, was processed most in the 38-day incubation and contributed much more efficiently to the formation of MAOM than did the pine roots. Despite less processing, the arbuscular and ectomycorrhizal fungal necromass both contributed as efficiently as rye roots to MAOM formation. These results indicate that both C chemistry and C/N ratio exert controls on residue processing and MAOM formation. Together, this dissertation work showed that salvage logging stimulated the growth of lodgepole pine seedlings, resulting in increased storage of both C and N in the plant biomass above- and belowground. As this pine root biomass turns over, the root necromass will contribute C to the POM fraction, the largest pool of soil C in this system. The net increase of forest soil C with salvage logging found in this study is notable as it suggests that the MPB-infested lodgepole pine forests of Colorado can be salvage logged with a low risk of significant soil C loss. Additionally, the highest recovery of the N label was in the soil, thus the high soil N recovery with higher soil C supports SOM is a sink of N reducing N losses. Finally, pine seedling colonization by ectomycorrhizal fungi may further aid with nutrient retention and the efficient formation of MAOM during regeneration.Item Open Access Implementing organic amendments to enhance maize yield, soil moisture, and microbial nutrient cycling in temperate agriculture(Colorado State University. Libraries, 2018) Foster, Erika J., author; Cotrufo, M. Francesca, advisor; Comas, Louise, committee member; Rhoades, Charles, committee member; Wallenstein, Matthew D., committee memberTo sustain agricultural production into the future, management should enhance natural biogeochemical cycling within the soil. Strategies to increase yield while reducing chemical fertilizer inputs and irrigation require robust research and development before widespread implementation. Current innovations in crop production use amendments such as manure and biochar charcoal to increase soil organic matter and improve soil structure, water, and nutrient content. Organic amendments also provide substrate and habitat for soil microorganisms that can play a key role cycling nutrients, improving nutrient availability for crops. Additional plant growth promoting bacteria can be incorporated into the soil as inocula to enhance soil nutrient cycling through mechanisms like phosphorus solubilization. Since microbial inoculation is highly effective under drought conditions, this technique pairs well in agricultural systems using limited irrigation to save water, particularly in semi-arid regions where climate change and population growth exacerbate water scarcity. The research in this dissertation examines synergistic techniques to reduce irrigation inputs, while building soil organic matter, and promoting natural microbial function to increase crop available nutrients. The research was conducted on conventional irrigated maize systems at the Agricultural Research Development and Education Center north of Fort Collins, CO. The first field experiment tested a temporally limited irrigation strategy with high application rates of organic amendments (30 Mg ha-1) to increase soil moisture, N and P retention, and enhance soil microbial activity. The experiment used biochar created from bio-energy production. The control plots contained 1.49% total soil carbon, and biochar addition increased total carbon to 2.67%. The biochar also had variable impacts on microbial extracellular enzyme activities, causing a 40% reduction in β-1,4-glucosidase and phosphatase activities, with repercussions for hydrolysis of soil P and cellulose. However, the biochar amendment did not enhance yield. This field experiment also found that the limited irrigation technique reduced water inputs by 30% while maintaining yield. The second experiment of the dissertation determined the mechanism behind the decrease in extracellular enzymatic activities after biochar addition. Through a combination of a Bradford protein assay and a fluorometric assay of potential enzymatic activities, the pine wood biochar adsorbed and reduced both β-glucosidase and acid phosphatase activities by 75-100% relative to a control soil. Though highly variable, depending upon pH, the main factor influencing activity levels was the solid phase. The high temperature biochar had a large surface area within micropores. The substrate can diffuse into the micropores, where it is inaccessible to large enzymes; there is lower catalysis of those substrates, which indicates potentially lower nutrient release in the soil. Finally, to examine the agronomic efficacy of biochar, a second maize field trial was developed also implementing full and limited irrigation. This experiment incorporated an engineered coconut hull biochar, characterized by a neutralized pH, removed toxins from the surface, and homogenized pores. The biochar was banded directly onto the seed row at a low application rate (0.8 Mg ha-1). Additionally, a surface applied plant growth promoting P solubilizing bacterial inoculum was tested alone, and in combination with biochar. To determine the efficacy of these amendments to improve soil nutrient availability and maize yields, the soil nutrient supply, crop nutrient concentration and accumulation, and soil bacterial community composition were measured. The bacterial community data was analyzed using a cutting-edge technique based on Exact Sequence Variants to analyze single nucleotide differences, enhancing comparability with future studies. In this experiment the biochar increased soil available K and S which correlated to crop uptake, shifted the early season microbial community, and increased by 20% over the control (+1.95 Mg ha-1). The inoculum and combination treatments did not impact yield, but in these plots we observed the presence of bacterial families that were added in the original inoculum. Overall this work emphasized the efficacy of precision management strategies with biochar application to enhance yield. This dissertation work underlines the importance of contentiously selecting specific amendment type, application rate and method to achieve either agronomic or environmental benefits. Continued research with synergistic approaches will help to develop best practices within the region to manage agroecosystems for improved resilience.Item Open Access Lodgepole pine regeneration after mountain pine beetle and wildfire: a case study in the High Park Fire, CO(Colorado State University. Libraries, 2016) Wright, Micah, author; Rocca, Monique, advisor; Rhoades, Charles, committee member; Hoffman, Chad, committee memberThe 2012 High Park Fire burned over 35,000 hectares, including 5,000 hectares of lodgepole pine (Pinus contorta) forest that had recently been attacked by mountain pine beetle (MPB, Dendroctonus ponderosae). This sequence of events provided an excellent opportunity to investigate the effects of combined disturbance on lodgepole pine regeneration trajectories. I examined the influence of MPB mortality, high canopy fire severity, site characteristics, and post fire mulching treatments on lodgepole pine recovery at both landscape (∼hectare) and fine (∼cm) spatial scales. At the landscape scale, lodgepole pine seedling densities varied from 240 to 470,000 stems/ha. Seedling densities decreased as MPB mortality and high canopy fire severity increased. At the fine scale, lodgepole pine seedling establishment was positively related to local cone abundance and negatively related to high canopy fire severity. Topographic variables such as aspect and elevation did not have a strong influence on seedling density or establishment at either scale, nor did competition from recovering vegetation have an influence at the fine scale where it was considered. In areas with high canopy fire severity, post-fire straw mulching treatments were positively related to seedling establishment, indicating that mulching treatments may have additional benefits beyond erosion control. My research demonstrates that combinations of pre-fire mountain pine beetle mortality and high canopy fire severity can affect lodgepole pine regeneration, and may drive heterogeneity in the post-fire landscape.Item Open Access Subalpine forest ecosystem responses to long-term nitrogen loading at Loch Vale Watershed, Colorado, USA(Colorado State University. Libraries, 2020) Weinmann, Tim, author; Boot, Claudia, advisor; Baron, Jill, advisor; Rhoades, Charles, committee member; Covino, Tim, committee memberThis thesis presents the results of a long-term N fertilization experiment in the Loch Vale watershed of Rocky Mountain National Park and presents a conceptual model hypothesizing environmental controls on ecosystem responses to N fertilization. The experiment consisted of annual 25 kg N ha-1 application of NH4NO3 fertilizer to three 30 x 30 m subalpine forest plots from 1996 to 2017. Soil, plant, and lysimeter samples were collected over the course of the experiment to address three research goals. First, determine whether increased N input leads simply to increased N output, or whether observable ecosystem effects result. Second, describe changes in the ecosystem responses over time and determine the controls that govern those changes. Third, identify results of the experiment that may generalize to other coniferous forests around the world. The results show that N fertilization causes ecosystem effects in Loch Vale which vary over time and space due to the influence of hypothesized controlling factors such as soil moisture, pH, and plant uptake of N. The results of the Loch Vale experiment suggest that impacts of excess N on boreal forests may include increased plant growth where soil moisture is adequate, but when coupled with drought may lead to increased rates of nitrification, N mineralization, NO3- leaching, and soil acidification.