Progress 08/01/07 to 07/31/12
Outputs
OUTPUTS: We have further explored the strong coupling of the nitrogen cycle with soil iron and carbon. Addition of nitrate to soil under iron(III)-reducing conditions led to a reoxidation of iron(II) coupled to nitrate reduction. This past year, activities have included conducting laboratory and field experiments to investigate the contribution of chemical and biological iron(II) oxidation by nitrite and nitrate to the overall process of nitrate-dependent, iron(II) oxidation. This has involved mentoring one M.S. student and one Ph.D. student. Additional activities have included the incorporation of these results in one undergraduate soil science course and one graduate level soil chemistry course. The results derived from these activities have also been disseminated via three presentations at the annual Soil Science Society of America Meetings in San Antonio, TX. One of these presentations was an invited talk at a symposium attended by approximately fifty people, including university and industry scientists. One Ph.D. graduate student, one M.S. graduate student, and three undergraduate research assistants have contributed to the project. PARTICIPANTS: Individuals who participated in this project were Chris Matocha, Martin Vandiviere, Prakash Dhakal, Stephanie Pyzola, Morgan Barnes, Jon Bott, and Louis Chailloux. Chris Matocha served as the project director (PD) overseeing the collection of data to address objectives pertaining to the project and the training of graduate and undergraduate students. As research technician in the PDs lab, Martin Vandiviere maintained the instrumentation used in the collection of data. Prakash Dhakal was a Ph.D. student assessing the role of iron(II) minerals and surface Fe(II) complexes in the reduction of nitrate and nitrite. Stephanie Pyzola was supported by this project and addressed the contribution of native iron(II) and manganese(II) oxidation to nitrate reduction in whole soil studies. Morgan Barnes and Jon Bott were both undergraduate research assistants who contributed to the collection of data. Louis Chailloux was an exchange student from France who collected data on a well-drained soil, showing that nitrate-dependent iron(II) oxidation can occur in oxic soil types. Interdisciplinary collaborations were forged between soil microbiology (Mark Coyne), chemistry (Ann Frances Miller), and engineering (Frank Huggins) to help answer questions relevant to this project. The latter collaboration was added after the initiation of the project. In addition, there have been collaborative arrangements with Ravi Kukkadapu at the Department of Energy's Environmental Molecular Science Lab in Richland, WA. This project has lended itself to the training of two graduate students and three undergraduate students. TARGET AUDIENCES: This science-based knowledge has been introduced into the undergraduate soil science course taught every spring semester by Chris Matocha. This course has an enrollment of approximately eighty students. The material is presented to illustrate how coupled processes involving nitrogen-iron and nitrogen-manganese represent an underappreciated aspect of the nitrogen cycle and how this impacts management. The results generated from this project have also been incorporated into the section on the nitrogen cycle taught in the graduate-level soil chemistry. This course has an enrollment that ranges from eight to fifteen graduate students. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The contribution of Fe(II) oxidation to nitrate reduction was 40% in the Sadler soil under anoxic conditions. Nitrous oxide was identified as a transient product of nitrate reduction and the remainder was converted to dinitrogen. These results are significant because historically, soil organic carbon is thought of as the sole electron donor in nitrate reduction. In this soil, soil organic carbon was in a three-fold excess over soil iron and yet it did not override the influence of soil iron(II). Acetate was the predominant water-soluble organic carbon species which emerged during the anoxic incubation. At early times (5 min- 6 h), iron(II) decreased with concomitant nitrate reduction and there was little change in acetate concentrations. At longer reaction times (24 h-72 h), acetate concentrations decreased drastically with a steady oxidation of iron(II) in the acid-extractable fraction as nitrate was reduced. Fourier transform infrared analysis of the clay fraction seems to indicate that phyllosilicate iron(III) might be the source of the iron utilized during nitrate reduction. Another interesting discovery is that manganese(II) was also oxidized during nitrate reduction, accounting for 25% of the nitrate reduced. This is surprising because total manganese was 20-fold less than total iron and 68-fold less than total soil organic carbon, yet, it accounts for one-quarter of the nitrate reduced. Some of this fundamental information has been published in two journal articles and there are two others in preparation. It is plausible that chemical and biological iron(II) oxidation coupled to nitrate reduction operate simultaneously at early time periods, whereas biological pathways may predominate at longer times. Another interesting finding is that nitrate-dependent iron(II) oxidation also occurred in a well-drained soil, indicating that this process could be occurring on a broader scale. As our experiments were intended to simulate fertilizer nitrate addition, these results have important implications for farmers, land managers, and the general public. We hope these findings will aid in the timing and efficiency of fertilizer N applications and that one cannot consider soil organic carbon alone when estimating losses from denitrification. Better utilization of N fertilizer will benefit both farmers and the general public because water resources will be protected from elevated nitrate levels and nitrous oxide release to the atmosphere can be better predicted and minimized. Furthermore, the Sadler silt loam is an agriculturally important soil in western Kentucky. The drainage from this area ends up in the Mississippi river basin, which feeds into the Gulf of Mexico. The results from this study will lead to future grant proposals where we will identify soil properties which will allow one to predict nitrate-dependent iron(II) and manganese(II) oxidation.
Publications
- Dhakal, P., Matocha, C.J., Huggins, F.E., and Vandiviere, M. 2013. Nitrite Reduction by Magnetite. Environmental Science and Technology, (Accepted Pending Revision).
- Matocha, C.J., Dhakal,P., Pyzola, S.M. 2012. The Role of Abiotic and Coupled Biotic/Abiotic Mineral Controlled Redox Processes in Nitrate Reduction. Advances in Agronomy, 115: 181-214.
- Matocha, C.J., Pyzola, S.M., and Dhakal, P. 2011. Transformations of Nitrate and Nitrite by Iron(II)-Bearing Minerals. International Annual Soil Science Society of America meetings symposium, San Antonio, TX.
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Progress 08/01/10 to 07/31/11
Outputs
OUTPUTS: We have further explored the strong coupling of the nitrogen cycle with soil iron and carbon. Addition of nitrate to soil under iron(III)-reducing conditions led to a reoxidation of iron(II) coupled to nitrate reduction. This past year, activities have included conducting laboratory and field experiments to investigate the contribution of chemical and biological iron(II) oxidation by nitrite and nitrate to the overall process of nitrate-dependent, iron(II) oxidation. The results derived from these activities have been disseminated via three presentations at the annual American Society of Agronomy Meetings in San Antonio, TX. These results have also been incorporated into an undergraduate soil science class in the section dealing with the nitrogen and iron cycles. One Ph.D. graduate student, one M.S. graduate student, and one undergraduate research assistant have contributed to the project. PARTICIPANTS: The project director (Chris Matocha) has provided oversight for the project with the help of the research analyst (Martin Vandiviere). One Ph.D. student (Prakash Dhakal) has been involved in the role of surface Fe(II)/goethite and magnetite in nitrite and nitrate reduction. One M.S. student (Stephanie Pyzola) has worked in assessing the contribution of soil iron(II) oxidation to nitrate reduction as influenced by electron donor amendments. One undergraduate researcher (Morgan Barnes) has helped collect and interpret data. TARGET AUDIENCES: The unique results from the research project, the involvement of iron with the nitrogen cycle, have been incorporated into the graduate-level soil chemistry course and undergraduate-level soil science course. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Slurries from a moderately well-drained soil (Sadler silt loam) were incubated anaerobically in the lab to reduce all indigenous soil Fe(III) to Fe(II) prior to nitrate addition which required 28 d. Acetate was the predominant water-soluble organic carbon species which emerged during the anoxic incubation, ranging from 190 to 350 micromolar. This represented only a small fraction of the total dissolved organic carbon in the anoxic soil slurries. Nitrate was added under anoxic conditions and relevant redox-active species were followed. At early times (5 min- 6 h), water and acid-extractable fractions of iron(II) decreased with concomitant nitrate reduction and there was little change in acetate concentrations. The rate of dissolved Fe(II) oxidation was 7.26 micromolar/hr and the rate of nitrate reduction was 3.5 micromolar/hr during the first 6 h of reaction. Nitrite was not detected in the soil slurries as an intermediate product of nitrate reduction. Nitrous oxide accumulated during the first 6 h of the reaction and decreased to negligible levels at longer time periods (>24 h). Dinitrogen was measured as the predominant product of nitrate reduction. At longer reaction times (24 h-72 h), acetate concentrations decreased drastically with a steady oxidation of iron(II) in the acid-extractable fraction as nitrate was reduced. Fourier transform infrared analysis of the clay fraction seems to indicate that phyllosilicate iron(III) might be the source of the iron utilized during nitrate reduction. Another interesting discovery is that reduced manganese(II) is also oxidized during nitrate reduction. We are currently utilizing 15N stable isotope analysis to tease out chemical from biological iron(II) oxidation. It is plausible that chemical and biological iron(II) oxidation coupled to nitrate reduction operate simultaneously at early time periods, whereas biological pathways may predominate at longer times. Another interesting finding is that nitrate-dependent iron(II) oxidation also occurred in a well-drained soil, indicating that this process could be occurring on a broader scale. These results will help predict the fate of fertilizer nitrate in soils under iron(III)-reducing conditions.
Publications
- Dhakal, P., and C.J. Matocha. 2011. Reactions of nitrite with goethite and surface iron(II)-goethite complexes. 103rd Annual Meetings of SSSA, San Antonio, TX. (Abstract No. 347-2).
- Pyzola, S.M., and C.J. Matocha. 2011. Nitrate reduction coupled to iron(II) oxidation in an agricultural soil. 103rd Annual Meetings of SSSA, San Antonio, TX. (Abstract No. 351-4).
- Matocha, C.J., P. Dhakal, and S.M. Pyzola. 2011. Transformations of nitrate and nitrite by Fe(II)-bearing minerals. 103rd Annual Meetings of SSSA, San Antonio, TX. (Abstract No. 281-13).
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Progress 08/01/09 to 07/31/10
Outputs
OUTPUTS: Addition of nitrate fertilizer to soil under iron(III)-reducing conditions can lead to reoxidation of iron(II) coupled to nitrate reduction, however, the mechanisms involved are unclear. This inspired us to characterize nitrate-dependent, iron(II) oxidation in an agricultural soil by following relevant iron, nitrogen, and carbon fractions. This past year, activities have included conducting laboratory and field experiments to investigate the contribution of chemical and biological iron(II) oxidation by nitrite and nitrate to the overall process of nitrate-dependent, iron(II) oxidation. The results derived from these activities have been disseminated via one invited presentation at a symposium at the annual Soil Science Society of America meetings in Long Beach, CA, one volunteered presentation by the Ph.D. student on the project at the Geological Society of America meeting in Denver, CO, and a USDA-NRI project director meeting in Washington, DC. These results have also been incorporated into an undergraduate soil science class in the section dealing with the nitrogen and iron cycles. One Ph.D. graduate student, one M.S. graduate student, and one undergraduate research assistant have contributed to the project. PARTICIPANTS: The project director (Chris Matocha) has provided oversight for the project with the help of the research analyst (Martin Vandiviere). One Ph.D. student (Prakash Dhakal) has been involved in the role of surface iron(II)/goethite in nitrite and nitrate reduction. One M.S. student (Stephanie Pyzola) has worked on identifying different dissolved organic carbon fractions in nitrate-dependent iron(II) oxidation. An undergraduate research assistant (Morgan Barnes) has helped characterize the soils in the study. TARGET AUDIENCES: Results from this research project have been incorporated into the PDs graduate-level soil chemistry course and undergraduate-level soil science course when the nitrogen, iron, and carbon cycles are discussed. The soil redox chemistry section in the lectures and laboratory have included the intersection of nitrogen with the iron and carbon cycles. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
In laboratory activities, soil slurries were incubated in an anaerobic chamber to reduce all indigenous soil Fe(III) to Fe(II) prior to nitrate addition which required 28 d. Acetate was the predominant water-soluble organic carbon species which emerged during the anoxic incubation, ranging from 190 to 350 micromolar. This represented only a small fraction of the total dissolved organic carbon in the anoxic soil slurries. Nitrate was added under anoxic conditions and relevant redox-active species were followed. At early times (5 min- 6 h), water and acid-extractable fractions of iron(II) decreased with concomitant nitrate reduction and there was little change in acetate concentrations. The rate of dissolved Fe(II) oxidation was 7.26 micromolar/hr and the rate of nitrate reduction was 3.5 micromolar/hr during the first 6 h of reaction. Nitrite was not detected in the soil slurries as an intermediate product of nitrate reduction. Nitrous oxide accumulated during the first 6 h of the reaction and decreased to negligible levels at longer time periods (>24 h). Dinitrogen was measured as the predominant product of nitrate reduction. At longer reaction times (24 h-72 h), acetate concentrations decreased drastically with a steady oxidation of iron(II) in the acid-extractable fraction as nitrate was reduced. We are currently utilizing 15N stable isotope analysis to tease out chemical from biological iron(II) oxidation. It is plausible that chemical and biological iron(II) oxidation coupled to nitrate reduction operate simultaneously at early time periods, whereas biological pathways may predominate at longer times. These results will help predict the fate of fertilizer nitrate in soils under iron(III)-reducing conditions.
Publications
- Matocha, C.J., J.H. Grove, and A.D. Karathanasis. 2010. Nitrogen Fertilizer Effects on Soil Mineralogy in an Agroecosystem. International symposium "Soil Minerals in Natural and Agroecosystems", ASA-CSSA-SSSA International Annual Meetings, Long Beach, CA (Abstract No. 245-1).
- Dhakal, P., C.J. Matocha, S. Pyzola, M. Vandiviere, and J.H. Grove. 2010. Changes in soil chemical properties during short-term reducing conditions followed by nitrogen fertilizer application. Geological Society of America Program and Abstract, Denver, CO (Abstract No. 228-5).
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Progress 08/01/08 to 07/31/09
Outputs
OUTPUTS: Field and laboratory studies have documented that the iron and nitrogen cycles are closely coupled in soil and sediment environments. Nitrate-dependent, iron(II) oxidation is an important process in the inhibition of soil iron(III) reduction and the removal of nitrate from water. However, the mechanisms of this process are poorly understood. Two proposed pathways include chemical reoxidation of iron(II) by nitrite and biological iron(II) oxidation coupled to nitrate reduction by lithotrophic microorganisms. This past year, activities have included conducting laboratory and field experiments to investigate the contribution of chemical and biological iron(II) oxidation by nitrite and nitrate to the overall process of nitrate-dependent, iron(II) oxidation. The results derived from these activities have been disseminated via two presentations at the annual American Society of Agronomy Meetings in Pittsburgh, PA and a USDA-NRI project director meeting in East Lansing, MI. Two undergraduate research assistants and one Ph.D. graduate student have contributed to the project. PARTICIPANTS: The PI (Chris Matocha) has provided oversight for the project and participated in laboratory and field activities relevant to nitrate-dependent, iron(II) oxidation. Two undergraduate research assistants (Jon Bott and Stephanie Pyzola) and an exchange student (Louis Chailloux) have been supported by the project. These students have generated data and assisted in interpretation. One Ph.D. student (Prakash Dhakal)is involved and has worked on the chemistry of surface iron(II) on gibbsite and goethite. This project has afforded the opportunity for training the undergraduate students and Ph.D. student in research techniques such as wet chemical methods, spectroscopic methods, and data reduction/interpretation. In addition, a collaboration has developed between the PI and Dr. Ravi Kukkadapu from the Environmental Molecular Sciences Laboratory to perform Mossbauer spectroscopy. TARGET AUDIENCES: Results from the research project have been incorporated into the PIs graduate-level soil chemistry course. The soil redox chemistry section in the lecture and laboratory has been modified to include interactions of nitrogen and iron. A widely-held tenet is the clear separation of redox processes in the field, however, our results challenge this view. Efforts have been made to include an updated framework for the students in the course to better understand redox chemistry. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
In laboratory activities, we have shown that a naturally occurring iron(II) mineral, siderite, is involved in chemical nitrite reduction. The nitrogen is lost as nitrous oxide, an important greenhouse gas. Siderite is oxidized by nitrite to form an iron(III) mineral, lepidocrocite. These findings change the way we view the nitrogen cycle because historically iron was assumed to be unimportant in nitrogen transformations. The fundamental rate data generated from this research can be incorporated in models that account for nitrate-dependent iron(II) oxidation in soils and sediments and help optimize nitrogen fertilization practices. Another potentially reactive pool is surface iron(II). We have explored the chemical structure of surface iron(II)-gibbsite slurries and found that iron(II) sorption were characterized by a fast reaction step followed by a slower reaction with time. An estimated rate coefficient for the rapid sorption step was 0.0075/s at 12 g/L gibbsite and pH 6.5. The sorption data of the slower stage were fitted with pseudo-first order kinetics and the rate coefficient was 0.00221/s. The sorption of iron(II) on gibbsite was strongly pH-dependent and was not affected by ionic strength. This indicates a minimal contribution of coulombic forces to the overall free energy change of Fe(II) sorption. Particle mobilities and optical spectra measured for surface iron(II)-gibbsite slurries suggest that iron(II) binds to gibbsite surfaces as an inner-sphere surface complex. These results will help predict the fate of iron(II) in soils under iron(III)-reducing conditions and its impact on fertilizer nitrate behavior.
Publications
- Rakshit, S., Matocha, C. J. and Coyne, M.S. (2008). Nitrite Reduction by Siderite. Soil Science Society of America Journal, 72:1070-1077.
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Progress 08/01/07 to 07/31/08
Outputs
OUTPUTS: The overall goal of this project is to understand the mechanism of inhibition of soil iron(III) reduction by nitrate, an important plant nutrient. During the first year of this project, results were disseminated via two oral presentations at the annual American Society of Agronomy meetings. The first presentation dealt with iron(II) carbonate reactivity with nitrite, an intermediate of nitrate. The second talk covered surface iron(II) reactions with gibbsite followed by reactivity with nitrite. PARTICIPANTS: One undergraduate student (Jon Bott) and one technician (Martin Vandiviere) have worked on the project. In addition, the principal investigator (Chris Matocha) traveled to the Environmental Molecular Science Laboratory to work with the collaborator (Ravi Kukkadapu) on the project to perform Mossbauer spectroscopy. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Iron is the fourth most abundant element in mineral soils and nitrate is an important plant nutrient. Our results have shown that nitrate reduction is closely coupled to iron(II) oxidation. Thus, these findings will impact the way fertilizer nitrogen is applied to soil environments. It is anticipated that a better understanding of the nitrate-iron couple will allow the more efficient use of nitrogen fertilizer. This information is timely given the rising cost of nitrogen fertilizer and the concern for preventing nitrate contamination of water supplies.
Publications
- Matocha, C.J., and Coyne, M.S. (2007). Short-term Response of Soil Iron to Nitrate Addition. Soil Science Society of America Journal, 71:108-117.
- Rakshit, S., Matocha, C.J., and Coyne, M.S. (2008). Nitrite Reduction by Siderite, Soil Science Society of America Journal, 72:1070-1077.
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