{"id":{"repo_id":"umn","oai_identifier":"oai:conservancy.umn.edu:11299/279264"},"canonical_url":"https://search.dev.ndltd.org/etd/umn/oai:conservancy.umn.edu:11299/279264","repository":{"repo_id":"umn","name":"University of Minnesota","base_url":"https://conservancy.umn.edu/server/oai/request"},"display":{"title":"Drivers And Dynamics Of Harmful Algal Blooms: Understanding Nitrogen Fixation And Bloom Composition In Minnesota Temperate Lakes","abstract":"Microbial communities play fundamental roles in structuring freshwater ecosystems by driving biogeochemical processes, regulating nutrient cycling, and maintaining ecosystem stability. Among these microbial communities, harmful algal blooms (HABs), dominated by cyanobacteria capable of producing toxins, have emerged as a growing environmental concern due to their impacts on water quality, ecosystem services, and human health. Historically, phosphorus has been considered the primary limiting nutrient controlling freshwater HABs, with management strategies largely focused on phosphorus reductions. However, this paradigm may partially reflect an underestimation of internal nitrogen contributions from biological nitrogen fixation, leading to an incomplete understanding of nitrogen dynamics in freshwater systems. Nitrogen fixation by cyanobacteria and heterotrophic bacteria can supplement nitrogen availability, supporting bloom development, persistence, and potentially toxicity. Likewise, diazotrophic microbes (capable of fixing nitrogen) may play a role in transitions in microbial community composition, particularly under nitrogen-limited conditions. Despite its potential importance, nitrogen fixation remains understudied and underrepresented in freshwater nutrient budgets and ecosystem models. This dissertation addresses these knowledge gaps by integrating traditional limnological monitoring techniques with molecular and biochemical approaches to examine the role of nitrogen fixation and microbial community structure in cyanobacterial blooms and in lake water columns in general. Sampling was conducted across six Minnesota lakes spanning a range of physical, chemical, and biological characteristics, capturing conditions during bloom events and in non-bloom periods. Nitrogen fixation rates were quantified using the acetylene reduction assay and analyzed in relation to environmental drivers through multilinear regression modeling. High throughput 16S rRNA gene sequencing characterized cyanobacterial and broader microbial communities across spatial and temporal gradients. In addition, a case study on Lake of the Woods (Minnesota, USA), a northern temperate lake with seasonal nitrogen-limited conditions, integrated nitrogen fixation measurements, molecular techniques, and toxin analyses to better understand nutrient dynamics, bloom community composition, and toxicity of HABs in this system. Together, this work aims to identify universal and lake-specific factors influencing HABs, improve predictions of bloom dynamics, and inform management strategies under changing climate and nutrient regimes.","abstract_html":"Microbial communities play fundamental roles in structuring freshwater ecosystems by driving biogeochemical processes, regulating nutrient cycling, and maintaining ecosystem stability. Among these microbial communities, harmful algal blooms (HABs), dominated by cyanobacteria capable of producing toxins, have emerged as a growing environmental concern due to their impacts on water quality, ecosystem services, and human health. Historically, phosphorus has been considered the primary limiting nutrient controlling freshwater HABs, with management strategies largely focused on phosphorus reductions. However, this paradigm may partially reflect an underestimation of internal nitrogen contributions from biological nitrogen fixation, leading to an incomplete understanding of nitrogen dynamics in freshwater systems. Nitrogen fixation by cyanobacteria and heterotrophic bacteria can supplement nitrogen availability, supporting bloom development, persistence, and potentially toxicity. Likewise, diazotrophic microbes (capable of fixing nitrogen) may play a role in transitions in microbial community composition, particularly under nitrogen-limited conditions. Despite its potential importance, nitrogen fixation remains understudied and underrepresented in freshwater nutrient budgets and ecosystem models. This dissertation addresses these knowledge gaps by integrating traditional limnological monitoring techniques with molecular and biochemical approaches to examine the role of nitrogen fixation and microbial community structure in cyanobacterial blooms and in lake water columns in general. Sampling was conducted across six Minnesota lakes spanning a range of physical, chemical, and biological characteristics, capturing conditions during bloom events and in non-bloom periods. Nitrogen fixation rates were quantified using the acetylene reduction assay and analyzed in relation to environmental drivers through multilinear regression modeling. High throughput 16S rRNA gene sequencing characterized cyanobacterial and broader microbial communities across spatial and temporal gradients. In addition, a case study on Lake of the Woods (Minnesota, USA), a northern temperate lake with seasonal nitrogen-limited conditions, integrated nitrogen fixation measurements, molecular techniques, and toxin analyses to better understand nutrient dynamics, bloom community composition, and toxicity of HABs in this system. Together, this work aims to identify universal and lake-specific factors influencing HABs, improve predictions of bloom dynamics, and inform management strategies under changing climate and nutrient regimes.","abstract_has_math":false,"creators":["Natwora, Kaela"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025","date_published":"2025","updated_at":"2026-07-24T05:20:05Z","subjects":[],"languages":["en"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/11299/279264","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Natwora, Kaela"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-03-18T14:26:01Z"]},{"key":"dc:date.issued","label":"Date","values":["2025"]},{"key":"dc:type","label":"Dc Type","values":["Thesis or Dissertation"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/11299/279264"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["University of Minnesota Ph.D. dissertation. 2025. Major: Water Resources Science. Advisor: Cody Sheik. 1 computer file (PDF); xii, 255 pages."]},{"key":"dc:description.abstract","label":"Abstract","values":["Microbial communities play fundamental roles in structuring freshwater ecosystems by driving biogeochemical processes, regulating nutrient cycling, and maintaining ecosystem stability. Among these microbial communities, harmful algal blooms (HABs), dominated by cyanobacteria capable of producing toxins, have emerged as a growing environmental concern due to their impacts on water quality, ecosystem services, and human health. Historically, phosphorus has been considered the primary limiting nutrient controlling freshwater HABs, with management strategies largely focused on phosphorus reductions. However, this paradigm may partially reflect an underestimation of internal nitrogen contributions from biological nitrogen fixation, leading to an incomplete understanding of nitrogen dynamics in freshwater systems. Nitrogen fixation by cyanobacteria and heterotrophic bacteria can supplement nitrogen availability, supporting bloom development, persistence, and potentially toxicity. Likewise, diazotrophic microbes (capable of fixing nitrogen) may play a role in transitions in microbial community composition, particularly under nitrogen-limited conditions. Despite its potential importance, nitrogen fixation remains understudied and underrepresented in freshwater nutrient budgets and ecosystem models. This dissertation addresses these knowledge gaps by integrating traditional limnological monitoring techniques with molecular and biochemical approaches to examine the role of nitrogen fixation and microbial community structure in cyanobacterial blooms and in lake water columns in general. Sampling was conducted across six Minnesota lakes spanning a range of physical, chemical, and biological characteristics, capturing conditions during bloom events and in non-bloom periods. Nitrogen fixation rates were quantified using the acetylene reduction assay and analyzed in relation to environmental drivers through multilinear regression modeling. High throughput 16S rRNA gene sequencing characterized cyanobacterial and broader microbial communities across spatial and temporal gradients. In addition, a case study on Lake of the Woods (Minnesota, USA), a northern temperate lake with seasonal nitrogen-limited conditions, integrated nitrogen fixation measurements, molecular techniques, and toxin analyses to better understand nutrient dynamics, bloom community composition, and toxicity of HABs in this system. Together, this work aims to identify universal and lake-specific factors influencing HABs, improve predictions of bloom dynamics, and inform management strategies under changing climate and nutrient regimes."]},{"key":"dc:title","label":"Title","values":["Drivers And Dynamics Of Harmful Algal Blooms: Understanding Nitrogen Fixation And Bloom Composition In Minnesota Temperate Lakes"]}]}],"canonical_facts":{"dc:creator":["Natwora, Kaela"],"dc:date.accessioned":["2026-03-18T14:26:01Z"],"dc:date.issued":["2025"],"dc:description":["University of Minnesota Ph.D. dissertation. 2025. Major: Water Resources Science. Advisor: Cody Sheik. 1 computer file (PDF); xii, 255 pages."],"dc:description.abstract":["Microbial communities play fundamental roles in structuring freshwater ecosystems by driving biogeochemical processes, regulating nutrient cycling, and maintaining ecosystem stability. Among these microbial communities, harmful algal blooms (HABs), dominated by cyanobacteria capable of producing toxins, have emerged as a growing environmental concern due to their impacts on water quality, ecosystem services, and human health. Historically, phosphorus has been considered the primary limiting nutrient controlling freshwater HABs, with management strategies largely focused on phosphorus reductions. However, this paradigm may partially reflect an underestimation of internal nitrogen contributions from biological nitrogen fixation, leading to an incomplete understanding of nitrogen dynamics in freshwater systems. Nitrogen fixation by cyanobacteria and heterotrophic bacteria can supplement nitrogen availability, supporting bloom development, persistence, and potentially toxicity. Likewise, diazotrophic microbes (capable of fixing nitrogen) may play a role in transitions in microbial community composition, particularly under nitrogen-limited conditions. Despite its potential importance, nitrogen fixation remains understudied and underrepresented in freshwater nutrient budgets and ecosystem models. This dissertation addresses these knowledge gaps by integrating traditional limnological monitoring techniques with molecular and biochemical approaches to examine the role of nitrogen fixation and microbial community structure in cyanobacterial blooms and in lake water columns in general. Sampling was conducted across six Minnesota lakes spanning a range of physical, chemical, and biological characteristics, capturing conditions during bloom events and in non-bloom periods. Nitrogen fixation rates were quantified using the acetylene reduction assay and analyzed in relation to environmental drivers through multilinear regression modeling. High throughput 16S rRNA gene sequencing characterized cyanobacterial and broader microbial communities across spatial and temporal gradients. In addition, a case study on Lake of the Woods (Minnesota, USA), a northern temperate lake with seasonal nitrogen-limited conditions, integrated nitrogen fixation measurements, molecular techniques, and toxin analyses to better understand nutrient dynamics, bloom community composition, and toxicity of HABs in this system. Together, this work aims to identify universal and lake-specific factors influencing HABs, improve predictions of bloom dynamics, and inform management strategies under changing climate and nutrient regimes."],"dc:identifier.uri":["https://hdl.handle.net/11299/279264"],"dc:language.iso":["en"],"dc:title":["Drivers And Dynamics Of Harmful Algal Blooms: Understanding Nitrogen Fixation And Bloom Composition In Minnesota Temperate Lakes"],"dc:type":["Thesis or Dissertation"]},"updated_at":"2026-07-24T05:20:05Z"}