Environmental & Conservation Sciences Doctoral Work

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Browsing Environmental & Conservation Sciences Doctoral Work by browse.metadata.department "Environmental and Conservation Sciences"

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    An Agent-Based Model for the Water Allocation and Management of Hydraulic Fracturing
    (North Dakota State University, 2022) Lin, Tong
    An agent-based model (ABM) is developed to simulate the impacts on streamflow and groundwater levels by the dramatic increase of hydraulic fracturing (HF) water use. To develop the agent-based model, institution theory is used to model the regulation policies, while evolutionary programming allows agents to select appropriate strategies when applying for potential water use permits. Cognitive maps endow agents’ ability and willingness to compete for more water sales. All agents have their influence boundaries that restrict their competitive behavior toward their neighbors but not to non-neighboring agents. The decision-making process is constructed and parameterized with both quantitative and qualitative information. By linking institution theory, evolutionary programming, and cognitive maps, our approach is a new exploration of modeling the dynamics of coupled human-natural systems (CHNS) to address the high complexity of the decision-making process involved in the CHNS. The ABM is calibrated with HF water-use data, and the calibration results show that it is reliable in simulating water depot number, depot locations, and depot water uses. The SWAT (Soil and Water Assessment Tool) model of the Little Muddy River basin and the MODFLOW of the Fox Hill-Hell Creek regional aquifer are coupled with the ABM to simulate the changes in streamflow and groundwater level, respectively, under different scenarios such as HF water demand, climate, and regulatory policies. The integrated modeling framework of ABM, SWAT, and MODFLOW can be used to support making scientifically sound policies in water allocation and management for hydraulic fracturing.
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    Anthropogenic stressors on freshwater wetlands: a microbial perspective
    (North Dakota State University, 2024) Cornish, Christine
    Benthic microbial communities play fundamental roles in wetland ecosystems including nutrient and energy cycling, and the degradation and assimilation of pollutants. Because of these crucial roles, along with their short-life cycles and high diversity, microorganisms can also play an important role as indicators of environmental change, which is particularly relevant in the current climate of increasing anthropogenic stressors, including factors such as emerging pollutants and climate change. Consequently, understanding the responses of microbes to environmental change is critical. To assess the effects of anthropogenic stressors on microbial communities in wetland ecosystems, I examined the response of sediment microorganisms from North Dakota wetlands in both microcosm and field-scale studies. First, I used 16S rRNA gene sequencing to analyze wetland microbial community responses to glyphosate treatments using an experimental microcosm approach. I found no significant differences in microbial communities among concentrations or treatments compared to controls, suggesting microorganisms in this region may have evolved glyphosate tolerance. Second, also taking an experimental approach, I measured methane, carbon dioxide, and nitrous oxide flux and porewater concentrations in microcosms to analyze net microbial production and consumption of greenhouse gases following glyphosate and/or 2,4-D treatment. I found high glyphosate concentrations significantly increased carbon dioxide emissions potentially due to increased microbial activity from the use of glyphosate as a substrate, or due to increased respiration as a stress response. Lastly, I used 16S rRNA gene sequencing to compare microbial communities in natural and restored wetlands across the North Dakota Prairie Pothole Region to assess the effects of a physical stressor, hydrologic restoration. I found no significant differences in microbial communities across wetlands, which may be due to the lack of direct sediment disturbance from restoration, or due to the ability of microorganisms to rapidly recover, thus showing no assemblage differences 25 years after restoration. Overall, I demonstrated that integrating microbial ecology with ecotoxicology and restoration ecology can be a beneficial and applicable research approach to understanding the impact of anthropogenic-induced environmental change on wetlands and show that the use of microbial metrics and mechanisms can provide valuable insight on pertinent issues of global concern.
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    Freshwater Cyanotoxin Mixtures in Recurring Cyanobacterial Blooms in Voyageurs National Park
    (North Dakota State University, 2021) Christensen, Victoria
    Algal and cyanobacterial blooms can foul water systems, inhibit recreation, and produce cyanotoxins, which can be toxic to humans, domestic animals, and wildlife. Blooms that recur yearly present a special challenge, in that chronic effects of most cyanotoxins are unknown. To better understand cyanotoxin timing, possible environmental triggers, and inter-relations among taxa and toxins in bloom communities, recurring cyanobacterial blooms were investigated at three recreational sites in Kabetogama Lake in Voyageurs National Park from 2016-2019. Results indicated that peak neurotoxin concentrations occurred before peak microcystin concentrations and that toxin-forming cyanobacteria were present before visible blooms, which is a serious human health concern. Two cyanotoxin mixture models (MIX) and two microcystin (MC) models were developed using near-real-time environmental variables and additional comprehensive variables based on laboratory analyses. Comprehensive models explained more variability than the environmental models and neither MIX model was a better fit than the MC models. However, the MIX models produced no false negatives, indicating that all observations above human-health regulatory guidelines were simulated by the MIX models. The results show that a model based on a cyanotoxin mixture is more protective of human health than a model based on microcystin alone. In 2019, 7 of 19 toxins were detected in various mixtures. The potential toxin producing cyanobacteria, Microcystis, was significantly correlated with microcystin-YR, while Pseudanabaena sp. and Synechococcus sp. were negatively correlated to several toxins. Jaccard and Sorenson indices indicated strong same-day similarities among the three bloom communities. Nitrogen-fixing cyanobacteria were present at every site, and when combined with internal loading of phosphorus, might explain similarities among sites, and why seasonal differences, even in samples from the same site, were stronger. Information from this dissertation adds to the body of work on recurring blooms and under-studied toxins and toxin mixtures, providing a better understanding of future research options for freshwater cyanotoxins in and outside of Voyageurs National Park.
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    Investigation of Organic Nitrogen Activity in Biological Processes of Water Resource Recovery Facilities
    (North Dakota State University, 2021) Bhardwaj, Ruchi Joshi
    The decrease in effluent inorganic nitrogen concentration in water resource recovery facilities (WRRFs) has been effectively achieved by including or finetuning the biological nutrient removal process. However, soluble organic nitrogen (sON) remains relatively unchanged, resulting in no reduction in the proportion of sON in effluent nitrogen. Therefore, for some WRRFs subjected to stringent nitrogen discharge limits, the removal of sON is crucial. Furthermore, the interest in sON is growing due to its impact on eutrophication, close relationship with the membrane fouling in wastewater treatment and the formation of nitrogenous disinfection byproducts in drinking water treatment. The overall aim of this research work was to determine the limits and capabilities pertaining to the removal and production of organic N in two different biological wastewater treatment processes, activated sludge process and moving bed biofilm reactors (MBBRs). Three research tasks were performed. In the first task, the effect of sludge retention time (SRT) on the production of organic nitrogen fractions (particulate, colloidal and soluble) and the biodegradability of produced sON in an activated sludge process was investigated. SRT influenced each fraction (particulate, colloidal and soluble) of organic nitrogen along with the biodegradability of effluent sON. The second task investigated sON activity in batch reactors mimicking nitrifying MBBRs. Although net production of sON was observed, both production and ammonification coexisted in the reactors which regulated the sON concentration. Organic carbon bioavailability and/or ammonia concentration were found to influence the production and ammonification of sON. The task also identified the variation in the bacterial activity in the biofilm during nitrification when exposed to different C/N ratios in the influent. The third task examined sON activity under heterotrophic and nitrifying sludge to identify how one sludge type is better than the other in removing sON under a simple aerobic reactor. Higher degradation of sON was identified in the presence of heterotrophic sludge than nitrifying sludge. Results from this dissertation research provide a better understanding of sON activity for two different biological wastewater treatment processes, which is critical for optimizing the removal of sON in WRRFs.
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    Three-dimensional Structures of Flows in a River Bend: Open Surface and Ice-covered Condition
    (North Dakota State University, 2024) Koyuncu, Berkay
    The existence of river ice has a significant role in flow characteristics during the winter and spring seasons. From the onset of freeze-up until the ice cover melts, river ice alters the flow structures, resulting in severe consequences such as ice jams, ice dams, and flash floods in spring. Nonetheless, the hydraulic and hydrologic mechanisms of river ice remain largely unknown due to difficulties of the field scale studies in severe winter seasons. In this work, the impacts of the ice cover on the vertical and cross-sectional velocity profile, secondary flow patterns, and shear velocity are investigated using analytical methods and fieldwork observations as well as the state-of-the-art computational fluid dynamics (large-eddy simulation) model. Results show the presence of river ice alters the secondary flow patterns and may induce double circulation in the thalweg area of natural cross-sections or near vertical channel walls of artificial channels/flumes. Results also indicate that the lateral distribution of the shear velocity is differentiated from the open surface condition as the high shear velocity can be observed near the inner and outer banks in ice-covered conditions. In this work, a numerical method is also developed to estimate the depth-averaged velocity profile based on the cross-section geometry. Model results demonstrate that the numerical method can accurately capture the velocity profile in irregular cross-sections based on fieldwork observations. This method helps to minimize the fieldwork efforts during the winter seasons. The future work will focus on the combined impact of the ice cover and the channel curvature (river bend) on the three-dimensional flow structures under different scenarios including the transitional stage. This work provides insights into the transient dynamics of flows during the freeze-up and breakup periods.