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Browsing by Author "Wilkins, Michael, committee member"

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    Characterization of water quality pollution in mixed land use watersheds
    (Colorado State University. Libraries, 2020) Ludwig, Madeline, author; Arabi, Mazdak, advisor; De Long, Susan, committee member; Wilkins, Michael, committee member
    Anthropogenic sources of pollution often lead to degraded surface water quality in urban and agricultural streams. The Clean Water Act was developed to mitigate the negative effects of urbanization on water quality through the development of water quality targets and the Total Maximum Daily Load program. In this study, a probabilistic framework was developed to quantitatively assess how indicators of human influence impact vulnerability to E. coli impairment and nutrient concentrations in mixed land use watersheds across the state of Colorado. The models derived using this method can be used to predict instream pollutant concentrations and help regulatory agencies create sampling programs for at risk waterbodies. Specifically, the first part of this study explores vulnerability to E. coli impairment under varying levels of upstream anthropogenic influences and develops a probabilistic method for assessing E. coli pollution based on the regulatory monitoring program. In this study, vulnerability is defined as the probability that ambient instream pollutant concentrations exceed numeric water quality standards. The study objective was examined for 28 sites along the Cache la Poudre River and its tributaries including: Boxelder Creek, Fossil Creek, and Spring Creek in northern Colorado. Indicators of urban influence include land use, wastewater treatment plant discharge capacity, combined animal feeding operation capacity, and population. Multiple linear regressions analysis between anthropogenic indicators, E. coli concentrations and vulnerability provide significant (p < 0.05) and strong (R2 > 0.7) relationships. In general, land use predictor variables were able to accurately predict E. coli load, however the most important indicator of human influence differed between E. coli concentration response variables. Additionally, the second part of this study expands upon the multiple linear regression framework to develop regression models that can predict base level nutrient concentrations for stream segments in three regions of Colorado. Regression models were developed using data from 89 sampling locations upstream of wastewater treatment plants and 84 sampling locations downstream of wastewater treatment plants. An initial analysis of gaged sampling locations showed that flow was a significantly influenced instream nutrient concentrations. Area and slope of the contributing sub watershed were then analyzed in a regression analysis and were found to be a surrogate for streamflow. Strong (R2 > 0.7) and significant (p < 0.05) regression models for upstream and downstream locations were developed using area and slope, hydrologic, point, and non-point source predictor variables. The models showed that agricultural and urban activity significantly impacted instream baseline nutrient concentrations. The methodology developed in this study can be used to predict instream pollutant concentration and assist in the development of monitoring programs for at risk waterbodies.
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    Deciphering the biological determinants on methane cycling from Gulf Coast wetlands
    (Colorado State University. Libraries, 2024) de Melo Ferreira, Djennyfer Karolaine, author; Wrighton, Kelly C., advisor; von Fischer, Joseph, committee member; Melzer, Suellen, committee member; Wilkins, Michael, committee member
    In Chapter 1, I introduce the importance of coastal wetlands for ecosystem services, including carbon storage, physical barrier for natural disasters, and habitat for diverse fauna and flora. Sea level rise is one of the main environmental risks affecting coastal wetlands, because of their geographic position. The effects of saltwater intrusion into freshwater wetlands can change established environmental conditions and vegetation coverage, which affects the functionality of various ecosystem functions they provide. These changes can also affect the methane emissions from coastal wetlands, which are major sources of this potent greenhouse gas. In this chapter, I evaluate the current knowledge of microbial methane production and consumption, including aspects of the ecophysiological adaptation to salinity, and the changes in the microbial ecological interactions modulated by increased salinity from marine water intrusion. In Chapter 2, I conducted a study to characterize the microbial communities and geochemistry of soil and water compartments in three coastal wetlands following a salinity gradient from Barataria Bay, Louisiana. To investigate the methane cycling microbial communities and their distribution on a freshwater flotant, Jean Lafitte swamp, and saltwater marsh wetlands, I collected soil and water samples under different vegetation coverage from each wetland. I analyzed the 16S rRNA gene sequencing and paired this data within situ methane fluxes and porewater concentrations. I also analyzed the geochemistry of the soil samples including profiling the anions, cations, pH, and redox conditions of soil and water samples across wetlands. The analysis showed that the diversity of methane cycling microbial communities decreased with increased salinity. Although the distribution and relative abundance of methanogen functional types was not impacted, with hydrogenotrophic methanogens being the most abundant across all wetlands. Looking at the methanotroph abundance and taxonomy in soil and water samples, I observed that swamp and saltwater wetlands share more methanotroph members in the water column, while the soils had more site-specific similarities. My research findings contribute to the understanding of methane cycling microbial tolerance to saltwater and may be used in future works to create more robust methane prediction models. In Chapter 3, I summarize the key aspects of microbial methane cycling in coastal wetlands and offer future directions for pairing geochemical and microbial data, including using an 'omics' approach and expanding investigation to more wetlands. We discuss the valuable findings these tools can give, contributing to a more accurate prediction of the metabolisms behind the ecophysiology and ecology of methane fluxes in coastal wetlands, and how targeting specific genes and metabolism can better help climate model efforts. In the Appendix sections, I give an expanded characterization of the wetlands site description, hydrology, vegetation and topological heterogeneity. I observed that, although relatively close in geographical position, each wetland has a different salinity range, vegetation type and microtopography that can influence the distribution of microorganisms in the soil and water. Here, we also analyzed the redox potential, dissolved oxygen, pH and geochemical compounds (bromide, nitrate, ammonium, acetate, sodium, potassium, magnesium, sulfate, chloride, and iron (II)) of these wetlands. We found no correlation between geochemistry with depth, but noticed higher salt contents in the saltwater marshes, and shared geochemistry between the swamp and freshwater flotant wetlands, as expected. Conclusively, this thesis contributes to the understanding of microbial communities to natural fluxes of methane in coastal wetlands and their interaction with the geochemistry of these ecosystems.
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    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 member
    Wildfire 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.