publications | Mary Foltz

2024

The ratio of denitrification end-products were influenced by soil pH and clay content across different texture classes in Oklahoma soils

Shaima Khalifah, and Mary E. Foltz

Frontiers in Soil Science, 2024

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Nitrous oxide (N₂O) is a potent greenhouse gas that contributes to stratospheric ozone depletion and global climate change. Soil denitrification has two potential end-products, N₂O and dinitrogen (N₂), and the ratio of these end-products (N₂O:(N₂O+N₂) or the N₂O ratio) is controlled by various factors. This study aims to quantify the influence of soil pH on the ratio of denitrification end-products in Oklahoma soils with different soil textures. Six natural grassland soils encompassing three distinct soil textures were incubated in the laboratory under natural and modified pH with an overall tested pH ranging from 2 to 10. Denitrification end-products were measured in the laboratory using the acetylene inhibition technique and further estimated using a process-based biogeochemical model. Both the laboratory and model results showed that soil pH and texture influenced the ratio of the denitrification end-products. Generally, as soil pH increased the N₂O ratio decreased, although both lab and model results indicated that this relationship was not linear. Soil texture may have an indirect effect on the N₂O ratio, as two soils of the same texture could have different N₂O ratios. However, clay percentage of the soil did show a linear positive correlation with the N₂O ratio, suggesting components of soil texture may be more influential than others. Overall, soil pH was a controlling factor in the ratio of denitrification end-products and the newly observed nonlinear relationship warrants further study, particularly when considering its effects in different soil textures.

2023

Field soil properties and experimental nutrient additions drive the nitrous oxide ratio in laboratory denitrification experiments: a systematic review

Mary E. Foltz, Agustín Alesso, and Julie L. Zilles

Frontiers in Soil Science, 2023

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Nitrous oxide (N₂O), which contributes to global climate change and stratospheric ozone destruction, can be produced during denitrification. Although the N₂O ratio, a measure of denitrification completion, is influenced by various properties, studies have largely been limited to site- or treatment-specific conclusions. The primary objective of this study was to identify important factors driving N₂O ratios and their relationships in soils by systematically reviewing and quantitatively evaluating results from published laboratory denitrification studies. A database with 60 studies (657 observations) was compiled, including studies meeting the minimum criteria: (i) laboratory experiments on soils, (ii) nutrient (carbon and/or nitrogen) addition, and (iii) N₂O and dinitrogen gas measurements. Of these, 14 studies (100 observations) had sufficient data for inclusion in the meta-analysis to assess the effect of added nutrients on the N₂O ratio. Furthermore, we modeled the effect of moderators on treatment effect by fitting a meta-regression model with both quantitative and categorical variables. Close review of studies in the database identified soil pH, carbon addition, and nitrogen addition as important variables for the N₂O ratio, but trends varied across studies. Correlation analysis of all studies clarified that soil pH was significantly correlated with the N₂O ratio, where soils with higher pH had lower N₂O ratios. The meta-analysis further revealed that nutrient addition had an overall significant, positive treatment effect (0.30 ± 0.03, P<.0001), indicating that experimentally adding nutrients increased the N₂O ratio. The model was most significantly improved when soil texture was used as a moderator. The significance of soil texture for the N₂O ratio was a major finding of this study, especially since the assays were usually conducted with soil slurries. Overall, this study highlights the importance of field soil properties (i.e., pH, texture) and laboratory conditions (i.e., nutrient addition) in driving the N₂O ratio and N₂O production from denitrification in soils.
Life cycle greenhouse gas emissions for irrigated corn production in the U.S. great plains

Raana Koushki, Sumit Sharma, Jason Warren, and 1 more author

Environmental Challenges, 2023

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Agricultural management practices improve crop yields to satisfy food demand of the growing population. However, these activities can have negative consequences, including the release of greenhouse gas (GHG) emissions that contribute to global climate change. To mitigate this global environmental problem, the management practices that contribute the most to system GHG emissions should be identified and targeted to mitigate emissions. Accordingly, we estimated the cradle-to-product GHG emissions of irrigated corn production under various farmer-selected scenarios at an experimental testing field in the semi-arid U.S. Great Plains. We applied a carbon footprint approach to quantify life cycle GHG emissions associated with pre-field (e.g., energy production, fertilizer production) and in-field (e.g., groundwater pumping, fertilizer application) activities within fourteen scenarios in the 2020 Oklahoma Testing Ag Performance Solutions (TAPS) sprinkler corn competition. We determined that 63% of the total GHG emission from corn production was associated with in-field activities and that agricultural soil emissions were the overall driving factor. Soil biochemical processes within agricultural soils were expected to contribute an average of 89 ± 18 g CO2-eq kg−1 corn of the total 271 ± 46 g CO2-eq kg−1 corn estimated from these systems. On-site natural gas combustion for agricultural groundwater pumping, pre-field fertilizer production, and pre-field energy production for groundwater pumping were the next most influential parameters on total GHG emissions. Diesel fuel, seed, and herbicide production had insignificant contributions to total GHG emissions from corn production. The model was most sensitive to the modeled GHG emissions from agricultural soil, which had significant uncertainty in the emission factor. Therefore, future efforts should target field measurements to better predict the contribution of direct soil emissions to total GHG emissions, particularly under different managements. In addition, identifying the optimal application rate of irrigation water and fertilizer will help to decrease GHG emissions from groundwater irrigated crops.
Wetland Removal Mechanisms for Emerging Contaminants

Land, Jan 2023

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In recent decades, previously unobserved trace compounds have become more widely detected in wastewater treatment effluents and freshwater ecosystems. Emanating from various sources and presenting potential human health and ecological risks at much lesser concentrations than traditional contaminants, detection of “emerging contaminants” has increased with improvements in analytical techniques. The behavior of emerging contaminants in wetlands is a topic of increasing interest, as natural wetlands are known to transform and sequester pollutants and constructed or treatment wetlands are widely utilized to address elevated concentrations of constituents of concern. Both natural and constructed wetlands are complex biogeochemical systems with interrelated abiotic and biotic mechanisms leading to the removal of emerging contaminants. A literature review was performed to assess the current state of knowledge of various wetland mechanisms involved in removing these contaminants from surface waters and effluents. The primary mechanisms discussed in the literature are sorption, photodegradation, microbial biodegradation and phytoremediation. The most influential mechanisms are dependent on the properties of the contaminants and wetland systems studied. Common trends exist for different constructed wetland designs to leverage various mechanisms based on hydrology, substrate and vegetation plantings. Much remains to be understood about the various processes occurring in wetlands as they relate to emerging contaminant removal. Improving the understanding of the potential role of wetland mechanisms can help manage this environmental challenge more effectively.

2021

Influence of rye cover cropping on denitrification potential and year-round field N₂O emissions

Mary E. Foltz, Angela D. Kent, Sotiria Koloutsou-Vakakis, and 1 more author

Science of The Total Environment, Apr 2021

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Cover cropping is beneﬁcial for reducing soil erosion and nutrient losses, but there are conﬂicting reports on how cover cropping affects emissions of nitrous oxide (N2O), a potent greenhouse gas. In this study, we measured N2O ﬂuxes over a full year in Illinois corn plots with and without rye cover crop. We compared these year-round measurements to N2O emissions predicted by the Intergovernmental Panel on Climate Change (IPCC) Tier 1 equation and the Denitriﬁcation-Decomposition (DNDC) model. In addition, we measured potential denitriﬁcation and N2O production rates. The ﬁeld measurements showed typical N2O peaks shortly after fertilizer application, as well as a signiﬁcant late-winter peak. Cover cropping signiﬁcantly reduced all peak N2O ﬂuxes, with decreases ranging from 39 to 95%. Neither model was able to accurately predict annual N2O ﬂuxes or the decrease in N2O emissions from cover-cropped ﬁelds. In contrast to ﬁeld measurements, lab assays found that cover cropping signiﬁcantly increased potential denitriﬁcation by 90–127% and potential N2O production by 54–106%. The rye cover-cropped plots had lower soil nitrate and higher soil carbon. When limiting nitrate and excess carbon were provided in lab assays, the proportion of N2O resulting from denitriﬁcation decreased. These results suggest that the discrepancy between the observed decrease in ﬁeld N2O emissions and the increase in denitriﬁcation potential may be due to the difference in available nutrients between the ﬁeld and laboratory measurements. Overall, these results suggest the importance of late-winter peaks in N2O emissions and the potential of rye cover cropping to reduce N2O emissions from agricultural ﬁelds.
Can online summer camps work? Evidence from adapting a high school hands-on water quality module for online delivery

Mary Foltz, and Sotiria Koloutsou-Vakakis

In 2021 Illinois-Indiana Regional Conference Proceedings, Apr 2021

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There is evidence that participation in summer engineering camps facilitates students’ understanding of the work engineers do, which can influence their decisions toward selecting engineering majors in college and engineering career paths [1]. The Environmental Engineering and Sustainability summer camp for high school students has been offered at the University of Illinois at Urbana-Champaign since 2012, under the summer camp outreach umbrella of the Grainger College of Engineering [2]. The week-long camp includes hands-on activities aimed to introduce students to engineering design, scientific inquiry, sustainability, and how engineers contribute to protecting human health and the environment. In summer 2020, due to the pandemic, the camp was reformatted from in-person to virtual. The virtual platform enabled the camp to reach more students, especially those with limited resources to attend an in-person camp. Therefore, we believe it is worth reflecting on the benefits and challenges of this reformatted summer camp and suggest ways online student experience can be improved in the future.
Biological nitrate removal with emerald ash borer-killed ash and high-tannin oak woodchips

Niranga M. Wickramarathne, Laura E. Christianson, Mary E. Foltz, and 3 more authors

Frontiers in Environmental Science, Mar 2021

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Two common tree species, ash ( Fraxinus sp.) and oak ( Quercus sp.), could provide readily available media for denitrifying bioreactors that use wood-based carbon for biological nitrate treatment. However, it is not known if the wood from Emerald Ash Borer-killed (EAB-killed) ash trees is an effective carbon source for nitrate removal compared to other wood species or if the high-tannin nature of oak inhibits denitrification potential. This lab-scale study showed that EAB-killed ash woodchips did not significantly differ in nitrate removal or denitrification potential compared to a commercially available blend of hardwood chips. However, neither treatment performed as well as oak woodchips in these metrics. Use of high-tannin oak in bioreactors is currently restricted by a federal standard in the United States. Ash woodchips beneficially exhibited the lowest nitrous oxide production potential, and their dissolved phosphorus leaching fell within the range of other woodchip types. Emerald ash borer-killed ash wood could be an effective source for denitrifying bioreactors located within affected regions and oak woodchips merit additional investigation for the application of denitrifying bioreactors.
Nitrate Removal and Woodchip Properties across a Paired Denitrifying Bioreactor Treating Centralized Agricultural Ditch Flows

Bryan Maxwell, Laura Christianson, Richard A. C. Cooke, and 4 more authors

Water, Dec 2021

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Treatment of nitrate loads by denitrifying bioreactors in centralized drainage ditches that receive subsurface tile drainage may offer a more effective alternative to end-of-pipe bioreactors. A paired denitrifying bioreactor design, consisting of an in-ditch bioreactor (18.3 × 2.1 × 0.2 m) treating ditch base ﬂow and a diversion bioreactor (4.6 × 9.1 × 0.9 m) designed to treat high-ﬂow events, was designed and constructed in an agricultural watershed (3.2 km2 drainage area) in Illinois, USA. Flow and water chemistry were monitored for three years and the woodchip and bioreactor-associated soil were analyzed for denitriﬁcation potential and chemical properties after 25 months. The inditch bioreactor did not signiﬁcantly reduce nitrate concentrations in the ditch, likely due to low hydraulic connectivity with stream water and sedimentation. The diversion bioreactor signiﬁcantly reduced nitrate concentrations (58% average reduction) but treated only ~2% of annual ditch ﬂow. Denitriﬁcation potential was signiﬁcantly higher in the in-ditch bioreactor woodchips versus the diversion bioreactor after 25 months (2950 ± 580 vs. 620 ± 310 ng N g−1 dry media h−1). The passive ﬂow design was simple to construct and did not restrict ﬂow in the drainage ditch but resulted in low hydraulic exchange, limiting nitrate removal.

2019

Prediction of N₂O emissions under different field management practices and climate conditions

Mary E. Foltz, Julie L. Zilles, and Sotiria Koloutsou-Vakakis

Science of The Total Environment, Jan 2019

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Due to the contributions of nitrous oxide (N2O) to global climate change and stratospheric ozone destruction, it is important to understand how climate and agricultural management affect N2O emissions. Although the processbased Denitriﬁcation Decomposition (DNDC) model is often used for quantifying emissions of N2O, the accuracy of these predictions remains in question, and it is not clear which input variables, environmental or ﬁeld management, have the greatest effect on model performance. In this study, DNDC was evaluated for prediction of N2O ﬂuxes from two climatically-different corn-ﬁeld sites in the United States (a Colorado irrigated ﬁeld and a Minnesota rainfed ﬁeld). Besides climate, these sites offer the additional advantage that measurements are available for multiple ﬁeld management practices, including fertilizer application, tillage, and crop rotation. This evaluation found that DNDC did not consistently, correctly predict daily-scale N2O ﬂuxes. Cumulative growing season N2O ﬂuxes were signiﬁcantly under-predicted in Colorado and were both under- and over-predicted in Minnesota. Model calibration of four soil input parameters did not signiﬁcantly improve N2O emission predictions at either site or time scale. Modeled and measured N2O ﬂuxes and model error were all strongly correlated with precipitation. Over-predictions of N2O ﬂuxes were associated with heavy precipitation and high modeled denitriﬁcation. Based on our results, model improvements to decrease model error for corn cropping systems in temperate climate zones should focus on better accounting for the effects of precipitation on denitriﬁcation. Despite discrepancies in daily and cumulative growing season N2O ﬂuxes, DNDC correctly identiﬁed the only ﬁeld management (fertilizer application rate) that signiﬁcantly inﬂuenced the measured N2O ﬂuxes.