Browsing by Subject "Nitrate"

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Capturing Stormwater Nitrate and Phosphate with Sorptive Filter Media
(2017-07) Erickson, Andrew
Soluble phosphate and nitrate are more bioavailable than particulate forms. These nutrients result in eutrophication in both freshwater (typically phosphate-limited) and marine (typically nitrate-limited) systems. In addition, nitrate poses a public health risk at elevated concentrations in drinking water. This research shows that sand filters mixed with 5% iron filings captured, on average, 88% of the influent phosphate in laboratory experiments. Neither incorporation of iron filings into a sand filter nor capture of phosphate had a significant effect on the hydraulic conductivity. Pond-perimeter applications of iron enhanced sand filtration (IESF) with up to 10.7% iron by weight achieved between 29% and 91% phosphate reduction for five events within the first year of operation. After five years, however, a different pond perimeter IESF retained on average 26% of the influent phosphate over three rainy seasons. Retention was best for larger filtered volume events, but negative removal was observed for events with smaller filtered volume and low influent phosphate concentration. Non-routine maintenance improved the hydraulic performance of the pond perimeter IESF and, after a rinsing event, also improved phosphate retention rates to an average of 45%. An IESF was installed to treat agricultural tile drainage and found to reduce total phosphorus loads by 42% to 95% with a flow-weighted mean reduction of 66.3% ± 6.7% (a = 0.05) for 20 events in 2016. The phosphate load reduction varied from 9% to 87% with a flow-weighted mean reduction of 63.9% ± 7.7% (a = 0.05) for 31 events in 2015 and 2016. This research also shows that nitrate is captured abiotically by granular activated carbon (GAC) in laboratory experiments designed to mimic urban and agricultural stormwater runoff. The short contact time and inorganic characteristics of the influent synthetic stormwater suggest that the nitrate was captured by ion exchange, but (bi)carbonate may have competed with nitrate for capture by GAC. Abiotic capture of nitrate requires less stormwater storage volume and less residence time to remove nitrate compared to denitrification, and thus GAC could be used to design smaller treatment practices for nitrate removal.
Climate and Land Use Change Impacts on N-Loads in Iowa Rivers and Remediation of Tile Water with an Anion-Exchange Resin
(2017-12) Wolf, Kari
This research was conducted to (1) better understand the underlying reasons for a continuous increase in nitrate loads in the Gulf of Mexico, and (2) if an industrial anion resin can be used at a field scale to reduce N losses from tile-drained watersheds to the rivers. The first objective was accomplished through statistical analyses of climate and land use change impacts on streamflow, baseflow, flow weighted nitrate-N concentrations (FWNC) and nitrate-N-loads in three major rivers of Iowa. The rivers included the Des Moines River, the Iowa River, and the Raccoon River. The results from this analysis showed that natural log of annual streamflow, baseflow, and N-loads were primarily controlled by the precipitation in the corresponding watersheds. For streamflow and baseflow, this precipitation corresponded to the current years as well as previous year precipitation. Previous year precipitation reflected the lack or excess presence of stored water in the soil and its consequences in terms of increased or decreased overland flow, infiltration, and percolation processes. For N loads, the precipitation effect was limited to one-year precipitation for the Des Moines and the Iowa Rivers and two-year precipitation for the Raccoon River. There were individual years when streamflow, baseflow, and N loads were impacted by up to three previous years’ precipitation. Effect of land use change, in terms of increased soybean area, had no effect on annual streamflow, annual baseflow, annual flow-weighted N concentrations or annual N-loads in all three rivers. Additional regression analysis of FWNC and N-loads from 1987-2001 showed no effect of N fertilizer use as an explanatory variable for any of the three watersheds. Statistical analysis of the combined annual data from all three rivers showed that there was a unique relationship between the natural log of streamflow, the baseflow, and the N-yield (N-loads/watershed area) versus the precipitation. The precipitation effects were both in terms of current year precipitation and the previous year precipitation. The coefficient of determination (R2) of Ln(streamflow), Ln(baseflow) and Ln(N load) with precipitation for the combined data were 0.74, 0.70 and 0.54, respectively. Limited scatter in the N-yield data at a given annual precipitation level over three rivers suggested that variation in annual precipitation has much bigger impact on N losses than the differences in cultural or cropping practices between the three river watersheds over the study period. Considering that there has been a 10-15% increase in precipitation in the Upper Midwestern United States in recent years, the combined N Yield relationship with precipitation would suggest that the recent increases in N-loads or increased hypoxic area in the Gulf of Mexico are likely due to increased precipitation. Statistical analysis of N-loads over a shorter period of time (1987-2001) also showed that changes in fertilizer use had no effect on river N-loads. Regression analysis of monthly streamflow, baseflow, N-loads and FWNC concentration showed that natural log of streamflow, baseflow, and N-loads were generally linearly related to precipitation in a given month and a few prior months. In some cases earlier in the season, these variables were also related to previous year’s precipitation, an indication that some of the past water stored in the soil both above and below the drain tile is interacting with current months precipitation and affecting the streamflow and baseflow. In most cases, there was no effect of soybean area on natural log of monthly streamflow, baseflow, or N-loads. A field test on the use of anion exchange resin to remediate tile water for nitrate showed that nitrate adsorption by the resin is instantaneous. The efficiency of the resin to retain nitrate varied 7-46%. This efficiency generally decreased with time due to the presence of sulfate, bicarbonates, and organic anions in tile water, which competed with nitrate ions for adsorption to the resin. In some instances, nitrate concentration in the percolating water was higher than the tile water most likely due to the expulsion of adsorbed nitrate ions on the resin by sulfate ion in the tile water. The results also showed that potassium chloride (KCl) is an effective resin-regenerating agent and provides a means to recycle wastewater as KNO3 fertilizer back on land. Although the use of anion exchange resin is an attractive alternative to passive technologies like bioreactors, saturated buffers, control drainage, etc. for remediating nitrate in tile water, it also presents some challenges in its use under field conditions. These challenges include the fouling up of the resin by sediment, sulfate, bicarbonate, and organic anions in tile water; costs associated with buying of resin and regenerating salt (KCl versus NaCl); need for a large volume of clean water for cleaning of resin; and the difficulty of treating large volume of tile water in-situ. However, the feasibility study shows that small-scale units similar to home water softener can be developed for individual homes in rural area where groundwater may be high in NO3-N concentration and NO3-N remediation is needed.
Constructed wetland used to treat nitrate pollution generated from agricultural tile drainage waters in Southern Minnesota
(2014-09) Ross, Nikol Bailey
Nitrate molecules are highly soluble in water and are bioavailable to plants. These properties are why excess nitrates in water are one of the main causes of hypoxia in the northern Gulf of Mexico. Over 90% of these nitrates originate from non-point sources such as agricultural fields. In fields with tile drainage systems nitrates have a swift passageway from field to surface waters. This study focuses on one Midwestern farm field located in southern Minnesota, along Elm Creek, a Blue Earth tributary. Tile drainage water from this field discharges into Elm Creek at a concentration averaging 23.0 mg/L NO3 as NO3-N. During the spring of 2013 a three celled treatment wetland was constructed adjacent to Elm Creek. The tile drainage system was re-routed to discharge into the constructed wetland. In the 2013 field season water volumes were monitored continuously and water samples were taken from the inlet, the wetland cells, and the outlet on a periodic basis. During the season the volume of tile drainage water that reached Elm Creek as surface water was reduced by 82%. The concentration of NO3-N in the water was not significantly reduced. However, the total load of NO3-N that reached Elm Creek as surface water was reduced by 262 to 332 pounds (14.4-18.2 lbs./acre). Most of the water that did not reach Elm Creek infiltrated into the subsurface soils and still contained NO3-N. Using the MPCA's (2013) estimates of groundwater denitrification for agroecoregions, a 45% reduction rate was applied at this location. When the 45% reduction rate is applied to the subsurface load it is estimated that 113.0 to 134 lbs. (6.21-7.36 lbs./acre) of NO3-N were removed from the infiltrated water. Thus a total of 124 to 172 lbs. (6.81-9.45 lbs./acre) of NO3-N were removed from the entire wetland system which accounts for 37.1-43.3% of the NO3-N.A concurrent laboratory experiment was set up in 2013 to test the effectiveness of different soils and vegetation at removing nitrate loads. Wetland mesocosm experiments were set up with soil collected from the field site and the design vegetation used in the field cells. Three vegetated mesocosm tanks were planted in Coland soils with Switchgrass (Panicum virgatum), Fringed Sedge (Carex crinita) and a tank with an equal mix of Dark Green Bulrush (Scirpus atrovirens), Panicum virgatum, and Carex crinita. The results showed that the mixed vegetation regime and the Panicum virgatum had significantly greater nitrate removal than the control (Coland bare soil). The mixed vegetation mesocosm had the highest amount of nitrate removal after 10 days at 34.9%. There was no significant difference in the nitrate removal rates in the soils tested.
Corn production and environmental implications under varying nitrogen and management practices
(2013-12) Maharjan, Bijesh
Economic and environmental issues combined have increased the need for better understanding of the fate of nitrogen (N) applied to crop production systems. The objectives of this dissertation were to evaluate the effects of different N sources including conventional urea (CU), polymer-coated urea (PCU), stabilized urea with chemical inhibitors (IU), and anhydrous ammonia (AA) on N losses and yield. Besides N sources, their interaction with placement (deep- versus shallow-banded; broadcast/incorporation versus subsurface banding), tillage management (conventional tillage versus no tillage) and irrigation management (irrigated versus rain fed) were also studied. In the first experiment, split-applied CU increased yield and N uptake compared with preplant applied PCU or IU and decreased nitrate (NO3-) leaching compared with PCU in a sandy loam soil. Direct soil-to-atmosphere nitrous oxide (N2O) emissions were significantly less with IU or split-U than with PCU and there was a trend for greater emissions with split-U than with IU (P =0.08). Irrigation significantly increased NO3- leaching during the growing season, but had no effect on direct N2O emissions in the same experiment. Indirect emissions due to NO3- leaching were estimated to be 79-117% of direct emissions using the default value of EF5, thus signifying the potential importance of indirect emissions in evaluating management effects on N2O emissions. In the second experiment, no-till significantly increased N2O emissions in fertilized treatments in a dry year and decreased crop yield in the control treatment in a silt loam soil. There were no significant differences in N2O emissions, grain yield or NO3- leaching potential with AA placement depth. In the third experiment, mid-row banding (MRB) significantly increased N2O emissions compared to broadcast/incorporation (BI) for PCU and CU in silt loam soils. Nitrous oxide emissions were correlated to a greater extent with soil nitrite (NO2-) intensity than with nitrate (NO3-) intensity; N intensity being a measure of integrated N concentrations over time. Compared to BI, MRB reduced NH3 volatilization loss and the CU treatment had greater NH3 loss than PCU or IU had. All these experiments highlighted the significant roles that N and other management practices can play in mitigating N losses.
The Digestive Tract Microbiome and Cardiometabolic Disease: Exploring Nitric Oxide and Lipopolysaccharide Synthesis as Mechanistic Intermediates
(2023) Bohn, Bruno
Introduction: The role of the digestive tract microbiomes on cardiometabolic health is becoming ever clearer. However, mechanistic remain largely unexplored and methods exploring metabolic outputs are lacking. This dissertation explores a novel approach to quantify the microbiome's lipopolysaccharides (LPS) and nitric oxide (NO) producing potential, two molecules with known health effects. We investigated the association between functional metrics and cardiometabolic health among healthy individuals and heart failure (HF) patients.Methods: Cross-sectional data from adults free of cardiometabolic disease (ORIGINS) and with HF (HFM) were used. Blood pressure was measured and biomarkers or inflammation and/or endotoxemia quantified from blood serum. Oral (saliva) and/or gut microbiomes were characterized with 16S rRNA (HFM/ORIGINS) and/or metagenomic sequencing (ORIGINS). Pathway- and gene-level functional profiles were operationalized as metrics of LPS- and NO-producing potentials. Metrics were compared across sequencing approaches (ORIGINS). For each cohort, multivariable linear regression was used to explore associations between: i) blood pressure and NO-producing potential; ii) inflammation and NO-producing potential; iii) inflammation and LPS-producing potential; and iv) endotoxemia and LPS-producing potential (HFM). Results: In ORIGINS, 253 and 170 participants had 16S and metagenomic data, respectively. A modest positive association was observed between functional metrics, with more features detected through 16S methods. Metagenomic and 16S-derived NO-reducing potential metrics were linked to lower inflammation and blood pressure, respectively. No meaningful associations were observed for LPS-producing potential. In HFM, saliva and gut 16S sequencing data was available for 146 and 128 participants, respectively. No correlations were observed between gut and oral microbiomes. No meaningful associations were observed between NO-producing potential and blood pressure. Gut LPS-producing potential, but not oral, was associated with endotoxemia. Inflammation was not meaningfully linked to either functional feature. Conclusions: A novel approach to utilized microbiome functional profile metrics was explored. Findings were mixed, but highlighted the potential use of these approaches in population-based studied of the human microbiome and cardiometabolic health.
Four Cover Crops Dual-Cropped With Soybean: Agronomics, Income, And Nutrient Uptake Across Minnesota
(2018-02) Ott, Matthew
Many agricultural watersheds in Minnesota have toxic levels of phosphorus and nitrogen, much of which originates in agricultural fields that are fallowed from October through May. Autumn-sown winter cover crops can be used to retain these nutrients. Soil NO3-N levels and and quantities of N sequestered by winter rye (Secale cereale), Tillage Radish® (Raphanus sativus), and the oilseed crops, winter camelina (Camelina sativa), and pennycress (Thlaspi arvense) were evaluated in a relayed cover crop/soybean production system at three sites spanning the north-south climatic gradient of Minnesota. Tillage Radish® sequestered the most N in autumn, but winter-killed and had high soil NO3-N levels in spring. Winter rye was terminated chemically by early May at each site, whereas the oilseed crops were allowed to grow into June to full maturity and their seeds were harvested. In autumn through early May, winter camelina and pennycress sequestered about 25% less N than winter rye. However, they often sequestered ≥ 2.5 times more N than winter rye when compared at maximum seasonal biomass (up to 130 kg N ha-1), with some of this N coming from spring fertilizer application. The relative amount of applied N captured by oilseeds, defined here as applied N sequestration efficiency, was 95% and 68% for winter camelina and pennycress, respectively. Winter camelina yields ranged from 600 to 1100 kg ha-1, while pennycress yields ranged from 900 kg ha-1 to 1550 kg ha-1. When combined with yields of relay-cropped soybean, net income for relay-crop systems was generally equivalent to mono-cropped soybean.
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.
Improving Maize Production and Ground-Water Quality through Nitrogen Management in Minnesota’s Irrigated Coarse-Textured Soils
(2016-03) Struffert, Anne
Elevated groundwater nitrate (NO3-N) concentrations in irrigated sandy soils under corn (Zea mays L.) production in the Midwest is of increasing concern, and has prompted the need to identify new or enhanced nitrogen (N) management practices in these areas. The objective of this study was to evaluate agricultural technologies that may improve N management for profitable corn production and mitigate negative effects of NO3-N in groundwater. From 2011 to 2014 corn was grown at two sites in Minnesota on sandy soils, Dakota County, MN with a continuous corn (CC) rotation and Pope County, MN with a CC, corn after soybeans (CSB), and soybean after corn (SbC) rotations. Twelve treatments were applied including urea broadcast at rates of 0, 45, 90, 135, 180, 225, 270, and 315 kg N ha-1 as a split application, half at pre-plant and half at the V4 development stage, pre-plant Super U at 180 kg N ha-1, and pre-plant ESN at 180 and 225 kg N ha-1. Canopy sensing with SPAD, GreenSeeker, and Crop Circle was done at V8 and V12 and NO3-N basal stalk measurements at R6 development stage. Soil water NO3-N samples were collected weekly throughout the growing season below the rooting zone using suction lysimeters. The mean Maximum Return to N (MRTN) was 231 kg ha-1 and produced a mean-yield increase above the unfertilized check of 6.5 Mg ha-1. Canopy sensors and plant measurements provided limited utility and generally under-predicted N needs. Nitrogen use efficiency and yields were increased with split-applied urea compared to all other pre-plant sources at 180 kg N ha-1, but no reduction in NO3-N leaching occurred. Season-long NO3-N concentrations ranged from 10 to 46 mg L-1 and overall annual loss was 27 to 41 kg NO3-N ha-1. Reducing N rate below the MRTN substantially reduced yield without reducing NO3-N leaching losses.
Investigation of soil and plant characteristics across a continuum of non-native earthworm invasion in hardwood forests, Tettegouche State Park, MN USA
(2013-06) Bennett, Zachary David
Invasive earthworms cause profound changes in forest floor thickness, soil structure and chemistry, and plant community composition within cold temperate hardwood forests. However, few studies have examined these effects across a continuum of earthworm invasion and in conjunction with canopy disturbance. The research objectives of this thesis were to determine the changes of earthworm invasion on the upper soil horizon's thickness, gravimetric water content, potential horizon field capacity, and available nitrogen and phosphorus; and plant communities in hardwood forest sites within Tettegouche State Park, MN USA. All sites were uneven-aged, unmanaged northern hardwood forests of an approximate age of 225 years. The canopies were dominated by sugar maple and had experienced substantial canopy disturbance (9.7 - 20.5% opening) during an ice storm in spring 2009. Earthworms were sampled in the fall of 2010-2011. Each of the four sites were invaded by differing earthworm assemblages ranging from minimally invaded (1 species and average biomass of 0.1729 AFDgrams/m2) to heavily invaded (5 species and average biomass of 14.12 AFDgrams/m2). In the upper soil horizons O horizon thickness decreased and A horizon thickness increased with increasing earthworm richness and biomass. Mineral soil gravimetric water content was measured biweekly (May-August 2011) but did not differ among sites. Total potential horizon field capacity, including the O horizon, determined that 53-59% of the available water in a 12 cm deep core at field capacity is held in the O horizon. Availability of NO3 was significantly higher in the heavily invaded site compared to all other sites. Plant communities were assessed in the summer of 2009-2011, nonmetric multidimensional scaling was used to analyze the relationship of herbaceous plant species richness and percent cover to environmental variables and that species richness and diversity indices were positively correlated with O horizon thickness and negatively correlated with earthworm richness and biomass. The main conclusions of this study are that 1) moderate canopy disturbance had no affect on soil characteristics, or earthworms and plant communities; 2) earthworm assemblages (richness and biomass) were strongly correlated with changes in forest floor thickness, moisture holding capacity, nitrogen availability and plant community composition in these sugar maple forests, and 3) traditional exclusion of the O horizon when measuring water holding capacity in forest soils should be reconsidered given the large proportion of potential water holding capacity it provides, and is lost when a site is heavily invaded by earthworms. The implications of the loss of the O horizon and the associated loss of water holding capacity on ecosystem functions and biotic communities of hardwood forest systems need to be more fully explored.
Karst Hydrogeologic Investigation of Trout Brook, Dakota County, Minnesota
(2013-02) Groten, Joel T.; Alexander, E. Calvin
Trout Brook in the Miesville Ravine County Park of Dakota County is the trout stream with the highest nitrate concentration in the karst region of southeastern Minnesota. Water quality data from 1985 and 1995 (Spong, 1995) and from 2001, 2002, 2006 and 2010 by the Dakota County Soil and Water Conservation District (SWCD) (2010) document an increasing level of nitrate in Trout Brook. A karst hydrogeologic investigation was designed to measure nitrate levels at sampling points along the stream and to increase our understanding of the source and movement of nitrates throughout the length of Trout Brook. Eighteen springs and seeps have been located in the Main Branch and tributaries of Trout Brook. A previously unreported flowing section and stream sieve, Weber Sieve, were found above what had been thought to be the head of perennial flow in the East Branch of Trout Brook. Two new sinkholes developed after the 14-15 June 2012 flood in a field northeast of the East Branch of Trout Brook. This investigation included regular monitoring of major anions in the streams and springs, synoptic stream flow measurements, a dye trace of a sinking stream in the Trout Brook drainage, and continuous temperature monitoring at two springs. The initial assumption was that the majority of the baseflow of Trout Brook was from discrete springs. However, synoptic baseflow and nitrate measurements show that only 30-40 percent of the total flow in Trout Brook is from discrete springs, and the rest appears to be from distributed groundwater discharge directly into the stream. Both the discrete springs and the distributed recharge occur along reaches of Trout Brook that drain the significant high transmissivity zone near the bottom of the regionally important Shakopee aquifer. Dye traces have confirmed flow-paths from Weber Sieve to LeDuc and Bridgestone Springs and have begun to define springsheds for these head water springs. The temperatures of two springs were monitored for 7.5 months. The observed small, seasonal temperature fluctuations at the springs seem to be due to the air temperature while storms that result in flooding and surface runoff cause larger, short-term temperature fluctuations. Nitrate concentrations and chloride/bromide ratios decreased systematically from the upstream springs to the downstream springs. The nitrate concentrations have been increasing at four springs from 1985 to 2012 and at two surface sampling points from 2001 to 2012. The nitrate concentration of another surface sampling point increased from 2001 to 2006 but decreased from 2006 to 2012. Snowmelt and rainfall runoff was sampled on 2 March 2012 and showed no detectable nitrate in the runoff from a watershed with no row-crop agriculture, but elevated nitrate was detected in an adjacent watershed with row-crop agriculture. All of these trends illustrate the dominance of agricultural sources of nitrate in Trout Brook.
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.
Metagenomic Survey Of Denitrifying Woodchip Bioreactors: Carbon And Nitrogen Cycling Under Varying Temperature And Flow Regimes
(2020-02) Pauleon, Aaron
The denitrifying woodchip bioreactor (WCBR) is a promising edge of field technology used as a biofilter of nitrate pollutants. These reactors have diminishing performance under low temperature and high flow conditions. In this study the taxonomic, nitrogen metabolism, and glycoside hydrolase profiles of meso-scale biochar-amended denitrifying woodchip bioreactors (WCBRs) are assessed and compared through shotgun metagenomic sequencing with reads aligned to protein coding sequences. Four treatment conditions: 14.5oC+12Hr hydraulic residence time (HRT), 14.5oC+4Hr, 6oC+12Hr, and 6oC+4Hr were analyzed in triplicate for the effects of temperature and flow rate (HRT) on the removal of nitrate from synthetic agricultural runoff water. The experimental design offered greater flow and temperature controls than field scale reactors while offering greater size and realism than most lab-scale reactors. Temperature and flow conditions had significant impacts in every category of analysis. The warm (14.5oC) and slow (12Hr HRT) WCBRs removed the greatest percentage of nitrate (75% of 30mg/L influent), were the most microbially abundant, and the most diverse. These reactors also had greatest average metagenomic potential for plant matter degrading enzymes. The taxonomic and functional analyses indicate bacterial dominance among extracted DNA, although ascomycete fungi were present across all treatments (0.7%-5.2%). By estimates, most bacteria across WCBRs were atypical denitrifiers (>50%) while a minority were typical denitrifiers (<12%). Large portions (78%) of the core nitrogen metabolism were attributed to the creation or assimilation of ammonia with nitrogen fixation appearing unexpectedly enriched (26%). Comparisons to bacteria-dominant midwestern corn soil reveal relatively high fungi representation, low archaea representation, and lower microbial diversity in the WCBR samples. The overall metagenomic commitments to nitrogen cycling and glycoside hydrolases were higher in the WCBRs befitting a concentrated nitrate and polysaccharide environment. The findings of this study highlight the otherwise unreported taxonomic and metabolic patterns of WCBRs, revealing topics for future study and potential avenues for further engineering to inform and enhance the use of denitrifying woodchip bioreactors moving forward.
Modeling Flow and Nitrate Losses for Small Watersheds in Southeastern Minnesota
(2021-07) Greve, Mark
Watershed planners and decision makers need tools to determine which best management practices (BMPs) are most effective at reducing nitrate pollution in the Root River Basin of southeastern Minnesota. The Root River Field to Stream Partnership is monitoring three subwatersheds of the Root River (Headwaters, Crystal Creek, and Bridge Creek) for flow and nutrient flux. Additionally, an individual agricultural field in each subwatershed is also being monitored. The Soil and Water Assessment Tool (SWAT) used data from these monitored sites to attempt to create calibrated hydrology and nitrate flux models. Inputs for modeling were obtained using publicly available sources for land cover, soils, elevation, and weather data. Model calibration for hydrology and nitrate flux was done via the trial and error method. Accurate hydrology models were produced for both the Headwaters and Crystal Creek subwatersheds, but a good nitrate model was produced only for the Headwaters due to several complications from underlying karst features in the Crystal and Bridge Creek subwatersheds that were difficult to account for using the SWAT model. Accurate SWAT models could not be developed for Bridge Creek and the field sites. The Headwaters model was then run using ten combinations of BMP scenarios to determine their effectiveness at reducing nitrate losses. Reducing nitrogen fertilizer application rates to economical rates and splitting applications of nitrogen resulted in a fourteen and sixteen percent decrease in nitrate losses, respectively. Applying nitrogen only in the spring and placing filter strips on steeply sloping agricultural land reduced nitrate flux by six percent each.
The nitrate deposits of rock crevices in the Upper Mississippi Valley
(2013-08) Brick, Gregory Arthur
Prompted by French fur-trader Pierre-Charles Le Sueur's 1700 report of caves containing saltpeter (potassium nitrate) along the Minnesota shore of Lake Pepin, this study located what are thought to be the original caves and revealed a hitherto unsuspected widespread district of cave nitrate deposits in the Upper Mississippi Valley (UMV). Of the 103 caves sampled from nine geologic formations, 67% had elevated nitrate concentrations (>50 ppm NO3) in their sediments relative to surrounding surface soils (<10 ppm NO3). These nitrate concentrations, up to 3.5 percent dry weight of sediment (35,000 ppm), are comparable to the concentrations found at Mammoth and Dixon caves, Kentucky, an historical nineteenth-century saltpeter mining locality, which range from 0.01 to 4 percent. But the Hill (1981) seeping groundwater model, which satisfactorily accounts for the nitrate deposits of the historic saltpeter caves of the southeastern United States, does not apply in the UMV. Through the application of geochemical and isotopic analysis to soil solutions it was concluded that the source of the nitrate was organic matter such as guano, scats, urine, carcasses, and plant materials, and that the nitrate accumulated because the cave roof protected the soluble nitrate ion from leaching and by blocking out sunlight, prevented plants from growing and thus extracting this nutrient. Le Sueur's claim of finding saltpeter (more likely, a saltpeter precursor, such as calcium nitrate) in Minnesota caves, for making gunpowder in the wilderness, is thus credible.
Nitrate dynamics in an agricultural watershed, Minnesota, U.S.A.
(2018-05) McLellan, Katherine
Nitrate is a common agricultural pollutant with severe ecological consequences. The Cottonwood River Watershed is an intensively managed agricultural setting within the Mississippi River Basin, which exports nitrate that contributes to the hypoxic zone in the Gulf of Mexico. Understanding nitrate sources, pathways, and processes within the Cottonwood River Watershed sheds light on the larger issue of nitrate loading to the Gulf. This study utilizes an end-member mixing analysis (EMMA) approach to identify water and nitrate sources to the Cottonwood River; performs a nitrate mass balance to find magnitudes of in-stream nitrate transformation over a range of discharges and dates; and assesses long-term concentration-discharge relationships in the watershed to elucidate nitrate processes. The three main sources of water that contribute to the Cottonwood River at Lamberton (approximately halfway up the watershed) are tile drainage, shallow groundwater, and Quaternary aquifer groundwater. In-stream nitrate removal is found to be highest at low discharge levels, which occur late in the crop growing season. Concentration-discharge relationships from long-term datasets confirm this finding, and demonstrate that intra-annual variation in nitrate concentrations has decreased during the period of record. Nitrate removal within the stream channel is attributed to biogeochemical processes such as denitrification and dissimilatory nitrate reduction to ammonium, which disproportionately decrease in-stream nitrate concentrations at low discharges. Given the low in-stream nitrate removal at high discharges, management of nitrate in agricultural watersheds should strive to decrease peak discharges.
Nitrate Leaching Mitigation with Kura Clover and Rye Covers for Corn and Soybean in Irrigated Sands
(2021-10) Wayment, Jessica
In addition to best nitrogen (N) management practices, integration of cover crops, such as winter rye (Secale cerale L.) and kura clover (Trifolium ambiguum), into annual row crops may be an effective mitigation strategy to reduce nitrate (NO3-- N) leaching from irrigated sandy soils. This study was conducted in the Central Sands region of Minnesota from 2016-2020. The objectives were to evaluate, at variable N rates, rye and kura’s ability to reduce NO3-- N leaching and determine the impacts of the covers on soil N availability, corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] N uptake, and grain yield in continuous corn (CC), corn-soybean (CSb) and soybean-corn (SbC) cropping systems. From 2017-2020, kura reduced NO3-- N leaching by 69% (42 kg NO3-- N ha-1) compared to no cover crop but inter-crop competition resulted in reduction of 26% (2.3 Mg ha-1) in corn and 21% (0.8 Mg ha-1) in soybean grain yield. While inter-crop competition was successfully reduced with chemical suppression of kura, this also reduced the NO3-- N leaching benefit of kura. Inconsistent establishment and growth of rye resulted in variable results across years. Overall, however, rye had little effect on corn yield and reduced NO3-- N leaching compared to no cover by 11% (7 kg NO3-- N ha-1) in CC and 26% (19 kg NO3-- N ha-1) in CSb. In SbC, rye reduced yields 5% (0.2 Mg ha-1) and increased leaching by 25% (15 kg NO3-- N ha-1). Regardless of cropping system or cover crop variables, applying N above optimum rates provides no agronomic benefit and increases risk of NO3-- N leaching. Restricting N applications below optimum rates provides little or no NO3-- N leaching benefits and reduced grain yield. While best N management practices combined with cover crops can meet the need for grain production and minimize NO3-- N leaching in certain situations, minimizing inter-crop competition, and ensuring adequate annual rye establishment and N availability will prove essential to wide adoption of these alternative management systems.
Nitrate removal in biochar amended, electrically stimulated up-flow wetlands
(2022-05) Runnoe, Emma
Human disruption of the natural nitrogen cycle has major environmental repercussions. Increased in nitrate concentrations in surface water, due to increased fertilization of agricultural farmland and subsequent run-off, can lead to saltwater ecosystem eutrophication and hypoxia, as seen seasonally in the Gulf of Mexico. A major source of nitrate contamination in Minnesota is the result of fertilizer application increasing the nitrate concentration in snow melt run-off. As the Mississippi River eventually feeds into the Gulf of Mexico, finding efficient, cost-effective treatment technologies for agricultural run-off is essential. An emerging treatment strategy of interest is the implementation of constructed wetlands, which aim to recreate the natural chemical, microbial, and physiological processes of a natural wetland. Constructed wetlands are low maintenance and are low-cost, but nutrient removal is highly dependent on temperature and flow rate. Therefore, with increased runoff during the spring, nitrate removal efficiencies in constructed wetlands decrease. To improve the constructed wetland’s nitrate removal efficiency, electrical stimulation could be applied to enhance autotrophic denitrification through the addition of an electron donor source. Here, synthetic agricultural runoff was fed to two biochar-amended, bench-scale, up-flow constructed wetland reactors to test the nitrate removal efficiency of a control system and a system with alternating between applied and no applied current. The reactors were amended with biochar, a highly porous, electroactive substrate, to enhance electron transfer efficiency and provide ample surface area for biofilm growth. The experiments were conducted twice, and effluent nitrate concentrations were monitored using segmented flow analysis. The total carbon concentration and pH were monitored throughout experimentation. Denitrifier copy numbers were measured upon experimental completion. The control systems exhibited variability, both showing low nitrate removal in experiment one and nitrate elution in experiment two. The applied current resulted in a pH change in the effluent which deteriorated the electrode and inhibited microbial growth. Without buffer, the electrically stimulated system showed low denitrification efficiencies, with high variability in performance. It is hypothesized that biochar adsorption influenced nitrate removal because reapplying current resulted in nitrate elution from the reactor. The denitrifier gene copies of DNA extracted from all experiments were low, but their presence signified the possibility of biological denitrification. Overall, low nitrate removal rates were measured throughout experimentation, but the data confirms that hydrolysis of water was occurring, which could act as an electron donor for autotrophic denitrification in the presence of a more abundant microbial community. Also, nitrate removal was achieved in both systems without a carbon source. Optimization of current density and electrode material is necessary for a complete understanding of nitrate removal mechanics, but this data reveals the practical limitations of upscaling bioelectrochemical systems in this manner.
One-carbon metabolism and breast cancer
(2013-02) Inoue-Choi, Maki
Breast cancer is the most common cancer among women in the United States. Nutrients in one-carbon metabolism (OCM) have been examined as potential modifiable risk factors because of OCM’s important role in DNA methylation and DNA synthesis. However, biologic mechanisms between OCM and carcinogenesis are still not clarified. The first manuscript tested the hypothesis that OCM nutrient status and genetic variation in methionine adenosyltransferases (MAT1A, MAT2A and MAT2B) are associated with plasma S-adenosylmethionine (SAM) levels in a cross-sectional analysis among healthy Singapore Chinese adults. Choline and methionine were strongly and positively associated with plasma SAM levels (ptrend<0.0001), and folate and betaine were positively associated with plasma SAM only in men (ptrend=0.02). The association between MAT1A rs2993763 and plasma SAM was modified by gender and plasma methionine levels. In the same study population, the second manuscript cross-sectionally tested the hypothesis that plasma SAM levels alone or in combination with genetic variation in DNA methyltransferases (DNMT1, DNMT3A and DNMT3B) are associated with global DNA methylation measured at long interspersed nucleotide element-1 (LINE-1). The LINE-1 methylation index was positively associated with plasma SAM levels (p≤0.01), with a plateau at approximately 78% and 77% methylation in men and women, respectively. Among men, there were statistically significant positive or negative associations between DNMT1 rs2114724 or DNMT3A rs758127 genotype and the LINE 1 methylation index, respectively (ptrend<0.01). The SAM-LINE-1 methylation association was modulated by DNMT1 rs2114724 genotype in men only. In a prospective cohort study, the third manuscript attempted to replicate increased breast cancer risk related to higher dietary nitrate intake only among those with low folate intake, which was previously reported by a case-control study. Opposite my hypothesis, among women with total folate intake 400 μg/day or above, breast cancer risk was statistically significantly higher among women in the highest quintile of nitrate intake from public water (HR=1.40, 95%CI=1.05-1.87) and private well users (HR=1.38, 95%CI=1.05-1.82) than those with the lowest nitrate intake from public water. The projects described in this dissertation contribute evidence describing how OCM may be related to cancer risk, and are a step in pursuit of my long-term goal to enhance our understanding of cancer etiology through OCM.
Radish and other brassica cover crop effects on nitrogen availability and weed management
(2013-09) Gieske, Miriam Frances
Use of radish (Raphanus sativus L.) and other brassica species as cover crops has increased in the US Midwest in recent years, as farmers seek new ways to reduce nitrogen losses and manage weeds. Brassicas can take up large amounts of nitrogen quickly, but their effects on nitrogen available to subsequent crop are mixed. Fall-seeded radish cover crops suppress fall weed growth. Little is known about the ability of spring-seeded radish to suppress weeds. The first objective of this research was to determine the effects of radish seeding date (mid-August [Date 1], late August [Date 2], mid-September [Date 3], late September [Date 4]), accession, and seeding rate (4.1 to 22.4 kg ha-1) on canopy cover, biomass, and nitrogen accumulation of a fall-seeded radish cover crop. To accomplish this objective, two-year field experiments were established at St. Paul and Lamberton, MN in 2010 and 2011. The effect of seeding date was larger and more consistent than the effects of accession and seeding rate. At St. Paul, radish cover was ≥ 79% for all rates and accessions at seeding dates 1-3, but ≤ 59% at Date 4. Delaying seeding decreased radish biomass by 143 kg ha-1 day-1. Total nitrogen accumulation averaged 96-225 kg ha-1 at Date 1 and 57-132 kg ha-1 at Date 3. At Lamberton, severe drought resulted in poor radish growth at Dates 2-4. In Minnesota, radish cover crops should be planted by mid-September at 5 kg ha-1.The second objective of this research was to determine the effect of fall-seeded brassica cover crops on nitrogen availability in the subsequent growing season. Two-year field experiments were established at St. Paul, Rosemount, and Lamberton, MN in 2010 and 2011. Brassica cover crops accumulated large amounts of nitrogen, up to 151 kg ha-1. In 2010-2011, a wet year, they had little effect on nitrogen availability in the subsequent growing season, but in 2011-2012, a dry year, they reduced nitrogen availability. Brassica cover crops have the potential to reduce nitrogen leaching, but their failure to increase later nitrogen availability suggests that nitrogen taken up by the cover crops is not available when the subsequent crop needs it.The third objective of this research was to determine the effect of fall- and spring-seeded radish cover crops on the density, cover, and biomass of weeds in organically-managed corn. Again, two-year field experiments were established at Rosemount and Lamberton, MN. Spring-seeded radish does not appear feasible as a cover crop in Minnesota. Shoot biomass of spring-seeded radish averaged 385 kg ha-1, compared to 3057 kg ha-1 for fall-seeded radish in the same fields. Effects of radish cover crops on weed density, cover, and biomass were inconsistent. The effect of fall-seeded radish ranged from a 44% decrease in August weed cover to an 88% increase in June weed density in the reduced tillage treatment relative to plots without fall-seeded radish. The effect of spring-seeded radish ranged from a 46% decrease in June weed density to a 94% increase in August non-crop biomass. Radish cover crops are unlikely to improve management of summer annual weeds in organic systems over the short term.
Water and well-being: Advances in measuring the value of water quality to people
(2013-12) Keeler, Bonnie L.
Water quality is declining in many parts of the world due to land-use change, pollution, and other stressors. In addition to the ecological impacts of these changes, water quality also affects the provision of multiple ecosystem goods and services including human health, recreation, and livelihoods. Investments designed to protect or restore water quality can be expensive and decision-makers must weigh the costs of new regulations against the public benefits provided by clean water. In order to make informed decisions regarding the management of our land and water resources, we need information on the ways that changes in water quality affect human well-being and the economic value of those changes. In Chapter One I address this gap by introducing a comprehensive framework for the valuation of water quality-related ecosystem services. In Chapter Two I apply this framework to an investigation of land-use change and consequences to groundwater quality and find that grassland conversion to agriculture is likely to result in significant costs to private well owners. In Chapter Three I use geo-tagged social media to assess visitation patterns to recreational lakes and find that lake users visit clear lakes more frequently and travel further to lakes with greater water quality. Using interdisciplinary approaches that are both generalizable and scalable, my work highlights the real costs associated with changes in water quality and in doing so addresses an important information gap needed to support environmental decision-making.

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