Browsing by Subject "Denitrification"

Now showing 1 - 6 of 6
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    Agricultural Wetland Restoration: The Role of Sediment Removal, Hydroperiod and Time on Restoration Outcomes
    (2021-06) Winikoff, Sarah
    Restoring agricultural wetlands to remediate nutrient runoff, decrease flood risk, and improve wildlife habitat are areas of growing interest. One restoration strategy that may improve species diversity, enhance water retention, and decrease nutrient availability is the removal of accumulated eroded sediment from agricultural wetlands prior to restoration. In this work, we the measured physical and chemical characteristics of soils, characterized plant communities, and examined water column nutrient availability and denitrification potential in 54 restored agricultural wetlands in west central Minnesota. In half of the wetlands hydrologic function was restored by removing and plugging drainage tile and ditches, while hydrology was restored in the remaining basins following sediment removal (Excavation treatment), increasing basin depth by an average 30 cm. Excavation primarily influenced the plant community, by delaying the establishment of two invasive emergent macrophytes, hybrid cattail (Typha x glauca) and reed canary grass (Phalaris arundinacea), but the affect only lasted for 6 years. Contrary to expectations, soil properties, water column dissolved nutrients, and denitrification potential were all primarily influenced by hydroperiod – the number of consecutive days with standing water. Wetlands with longer hydroperiods had less bioavailable P in soils, lower dissolved N and P concentrations, and lower denitrification potential. We also found evidence that vegetation likely plays an important role in dissolved nutrient dynamics over time. Our results suggest that excavation may be an important tool in wetland restoration but its influence was lost as wetlands aged in the absence of invasive species management. Moreover, nitrogen and phosphorus dynamics were almost universally controlled by hydroperiod, with tradeoffs between nitrogen removal and phosphorus remineralization.
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    Denitrification in Agricultural Surface Waters: Quantifying the Effect of Environmental Parameters and Hydrologic Connectivity on Nitrate Uptake and Microbial Communities
    (2017-10) Tomasek, Abigail
    The development of synthetic fertilizer has led to increases in crop yields and allowed for global population growth over the past century. However, this increase in available nitrogen has greatly altered the global nitrogen cycle, including increased nitrate loading to surface water and groundwater in the Midwestern United States, with negative effects on human health and aquatic ecosystems. Therefore, there is a need for effective management strategies and an understanding of the mechanisms for nitrate transport and uptake. Denitrification, the microbiological reduction of nitrate to nitrogen gas, can be viewed as a net sink for reactive nitrogen in aquatic systems. Small areas, termed hot spots, and short time periods, termed hot moments, frequently account for a large portion of denitrification. This research focuses on identifying the environmental parameters and hydrologic regimes that promote denitrification, along with determining how parameters, denitrification rates, and microbiological communities are related at multiple temporal and spatial scales. At the finest scale, a recirculating laboratory flume was used to determine the effect of turbulence and organic carbon on denitrification rates and the microbial community. An outdoor experimental stream and flow-through basin in the Outdoor StreamLab at the St. Anthony Falls Laboratory (SAFL) were used to determine the effect of short-term inundation and periodic inundation on denitrification. At the largest scale, water and sediment samples were collected over two years from a field site in an agricultural watershed in Southern Minnesota. The objectives of this research were to: (1) determine how turbulence and organic carbon affect denitrification, (2) investigate how inundation and hydrologic connectivity leads to the formation of denitrification hot spots and hot moments, (3) quantify and correlate the driving environmental parameters of microbial denitrification and the differences in these relationships for in-channel and riparian locations in an agricultural watershed, (4) develop and evaluate functional relationships between environmental parameters and denitrification rates, and (5) identify how denitrifying gene abundances, denitrification rates, and environmental parameters are related across a hydrologic gradient from channels to riparian areas.
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    Effect Of Stream Channel Incision On The Depth To Groundwater In Riparian Corridors Across Southwestern Minnesota
    (2020-05) Pierce, Hilary
    Riparian buffers have the potential to remove nitrogen from shallow groundwater in the riparian corridor. Streams with a higher degree of incision may be less likely to have elevated groundwater tables, making them less effective at removing nitrogen from groundwater. By determining if there is a relationship between site characteristics and groundwater depth in the riparian corridor, riparian buffer planning can be guided to maximize efficiency. This study analyzes six sites on tributaries of the Minnesota River, characterizing them by their Rosgen stream channel type, degree of incision, soil type and dominant vegetation, and monitoring the depth to the shallow riparian groundwater table during several seasons. The monitored groundwater depth was used to confirm a water balance model of the depth to the water table at one of sites. This model was then used to predict the change to the depth of groundwater that would occur under more incised conditions.
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    Hydrology, Nutrient Removal, and Cost Effectiveness of Small, Edge-of-Field Tile Drainage Treatment Wetlands
    (2019-05) Gordon, Bradley
    Constructing treatment wetlands is a recommended practice for mediating nutrient pollution from non-point sources in the Mississippi River Basin. This research investigated the nitrogen and phosphorus removal effectiveness of a small, edge-of-field, constructed treatment wetland using field, laboratory, and modeling data. In the field, the wetland removed 67% (48-100%) of nitrate discharging from tile drainage but released soil legacy phosphorus from 2013 through 2016. Denitrification in the shallow groundwater and vegetation harvest were the greatest sinks for nitrogen and phosphorus, respectively. In the laboratory, three plant communities from the wetland (a wet prairie forb-dominant mix, a switchgrass and prairie cordgrass-dominant community, and a reed canary grass monoculture) were compared for nitrate removal. The wet prairie mix removed the most nitrate, and it had the lowest dissolved oxygen concentration and greatest ratio of denitrifying bacteria to total bacteria (nosZ:16S rRNA genes) – measured using a quantitative polymerase chain reaction (qPCR) – in its root zone. For the modeling component, the ACPF toolbox, the SWAT model, and a spreadsheet model were used to estimate the mass of nitrate-N removed from tile drainage if more edge-of-field wetlands were constructed in the Elm Creek HUC12 watershed. These smaller wetlands removed more nitrate-N per wetland area than larger wetlands (watersheds > 60 ha) but cost the same per mass removed if the small wetlands were designed to have a high saturated hydraulic conductivity. Results from this study suggest that edge-of-field wetlands can be more effective with a dual treatment of surface flow and shallow groundwater flow for nitrate removal and vegetation harvest for phosphorus removal. However, reed canary grass invasion could potentially decrease the nitrate removal effectiveness. If the wetland soils have a high conductivity, the smaller, edge-of-field designs could be as cost effective as large treatment wetlands but remove less land from agricultural production. This dissertation is composed of three individual chapters that will be published in peer reviewed scientific journals. The first chapter pertains to a field study that observed a small, edge-of-field tile drainage treatment wetland. This chapter will be submitted to Ecological Engineering. In the second chapter, the nitrate removal in three plant communities from the wetland was compared using mesocosms. Total bacteria and denitrifying bacterial populations in the root zones of these communities were also compared using qPCR. The work from this chapter was submitted to the Journal of Environmental Quality and is currently under review. The final chapter will be submitted to Agriculture, Ecosystems & Environment. This chapter compared the effectiveness of small, edge-of-field treatment wetlands with watersheds less than 60 ha to large treatment wetlands with watersheds greater than 60 ha. Multiple models were used to determine the best locations for each wetland in the Elm Creek watershed in southern Minnesota. Conclusions were drawn that small, edge-of-field wetlands are effective nutrient removal practices and can be improved with high saturated hydraulic conductivity, harvested vegetation, and diverse plant communities.
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    Impact of Biostimulation and Bioaugmentation on Microbial Communities in Woodchip Bioreactors
    (2021-12) Wang, Hao
    Woodchip bioreactors are used to remove nutrients from the subsurface drainage.However, the nitrogen removal performance and efficiency of woodchips are limited by low temperature and limited availability of liable carbon. Bioaugmentation (i.e., adding cold-adapted denitrifying microbes) and biostimulation (i.e., adding substrates to enhance the activities of indigenous microbial populations) are potential approaches to enhance nitrate removal of woodchip bioreactors at cold conditions, but their effectiveness is still unclear. My thesis research was done to clarify the effects of bioaugmentation and biostimulation on the microbial communities in woodchip bioreactors. I also examined how microbial community change influenced the overall nitrate removal. Previously isolated cold-adapted denitrifying bacteria Cellulomonas sp. strain WB94 and Microvirgula sp. strain BE2.4 were used in this study. These strains were obtained from woodchip bioreactors and were verified to reduce nitrate at cold temperatures. Based on the whole genome analysis, Microvirgula sp. strain BE2.4 has a complete set of denitrification genes, while Cellulomonas sp. strain WB94 has genes for cellulose degradation. These two strains were grown in the lab condition and inoculated back into the woodchip bioreactors located at Willmar, MN (i.e., bioaugmentation). In addition, acetate was added into the woodchip bioreactors as a liable carbon source to promote denitrification (i.e., biostimulation). Woodchip samples were taken before and after the bioaugmentation and biostimulation treatments to examine the changes in the abundance of inoculated strains and the impact of the two treatments on the microbial communities in woodchip bioreactors. Strain-specific TaqMan probe quantitative PCR assays were designed to quantify the abundance of inoculated strains. A high-throughput Nitrogen v Cycle Evaluation (NiCE) chip was also used to quantify various N cycle-related genes in many samples. Furthermore, microbial communities in the woodchip bioreactors were analyzed by sequencing the V4 region of the 16S rRNA gene on the Illumina MiSeq platform. TaqMan probe qPCR results showed that the abundance of inoculant Cellulomonas sp. strain WB94 increased in all the treatment and control bioreactors throughout the sampling period (p < 0.05), suggesting that genera Cellulomonas plays a key role in the cellulose degradation process inside aged woodchip bioreactors. The abundance of inoculant Microvirgula sp. strain BE2.4 tended to increase in the bioaugmentation bioreactors, although this increase was not statistically significant, most likely due to considerable variation between samples. 16S rRNA gene amplicon sequencing results showed that the treatments account for 4.07% of the difference in the microbial community between samples. NiCE chip results showed that the abundance of amoA, hao/hdh, and nosZ can be used to predict the nitrate removal rate of woodchip bioreactors. In addition, there was a positive relationship between the abundance of inoculant Microvirgula sp. strain BE2.4 and the abundance of denitrification gene norB and nosZ in the woodchip bioreactors. These results showed that bioaugmentation and biostimulation treatments could change the microbial communities in the woodchip bioreactors and increase the abundance of denitrifiers to optimize the denitrification efficiency of the bioreactors.
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    Measurement and modeling of denitrification in sand-bed streams of varying land use
    (2013-02) Guentzel, Kristopher Steven
    Processes that govern transport and transformation of aquatic nitrogen are of growing importance due to increases in anthropogenic nitrogen input from fertilizer application and fossil fuel combustion. Denitrification, the incremental reduction of soluble nitrate to gaseous end products, is the main pathway in which nitrogen is biologically removed from aquatic ecosystems. In this study denitrification is measured from sediment cores in five streams in central Minnesota, USA, using denitrification enzyme activity (DEA) assays as well as microbiological techniques including the amplification of nirS gene fragments through qPCR. Hydraulic and environmental variables are measured in the vicinity of the sediment cores to determine a possible mediating influence of fluid flow and chemical variables on denitrification activity. Denitrification rates measured using DEA analysis with amended nutrients ranged from 0.02-10.1 mg-N m-2 hr-1. Denitrification rates measured without amended nutrients were a factor of 5.35 less on average and ranged from 0.03-0.98 mg-N m-2 hr-1. The abundance of the denitrifier gene nirS was positively correlated with denitrification potential measurements (R2 = 0.79, P < 0.001) for most of the streams studied. NirS distribution in one of the sites, a field scale experimental stream called the Outdoor StreamLab, followed the spatial distribution of benthic organic matter closely along the sediment bed and through the sediment column. Predictive models to determine nitrate uptake via denitrification were derived from hydraulic, morphologic and water quality variables. The first used hydraulic data collected over three summers in the Outdoor StreamLab. A Gaussian-type function was fit to these data and was dependent on fluid flow and channel characteristics within the stream system. The second model was derived following dimensional analysis on data from the Outdoor StreamLab and four other natural streams of varying watershed and in-stream conditions. This predictive model integrated not only stream hydraulic data but also environmental, morphological and DEA measurements for nutrient-amended and unamended samples. The proposed model explained 75% and 60% of the variability in amended and unamended DEA rates, respectively. Results from this study verify that denitrification is ubiquitous across varying stream systems but is most dependent on the distribution of sediment organic matter and interstitial pore space as well as stream hydraulic characteristics.