I grew up amongst the subdivisions and strip malls of Greenwood, Indiana. While in high school, a backpacking trip in the Colorado Rockies opened my eyes to the magnificence and fragility of nature, and instilled in me the desire to preserve it for future generations. In my coursework, I found it fascinating how chemistry explained so many natural phenomena and decided to pursue a degree in Chemistry at St. Olaf College in Northfield, Minnesota. In addition to my chemistry courses, I took biology and environmental science courses and completed a summer research internship in soil chemistry at the University of Idaho, through which I discovered the way environmental chemistry links physical, biological, and geological process at the molecular scale. Though fascinating, this complexity makes molecular-level analysis of soils challenging, thus they are excellent candidates for using and developing advanced analytical techniques. I enjoy employing advanced instrumentation such as synchrotron X-ray absorption spectroscopy and ultrahigh resolution mass spectrometry in analysis of soil processes. In my free time, I enjoy rock climbing, hiking, cooking, and knitting.
Temperature effects on natural organic matter sorption to iron oxide coated minerals
Natural organic matter (NOM) makes up the largest terrestrial pool of carbon and is twice the size of the atmospheric carbon pool. Understanding the processes that govern NOM stabilization and degradation are crucial for accurate modeling of carbon cycling and for predicting the impacts of climate change. Sorption to mineral surfaces has been implicated as an important mechanism for long-term preservation of NOM. Iron, the fourth most abundant element in Earth’s crust, creates oxide minerals and surface coatings that act as effective sorbents of NOM. While NOM sorption to iron oxides has been extensively investigated, less is known about how changes in climate, such as an increase in temperature, will affect sorption behavior.
In this study, I am assessing the impact of temperature on the sorption and desorption behavior of various humic substance standards on iron oxide coated sand in packed columns. Liquid fractions collected from the columns are analyzed to determine NOM and organic carbon concentration, and Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS) and carbon near edge x-ray absorption fine structure (C NEXAFS) spectroscopy will be used to determine the chemical differences between bound and unbound fractions of NOM. Because microbes more readily degrade certain types of organic compounds, alterations in the chemical composition of the available carbon pool due to changes in sorption behavior may affect overall NOM degradation rates.
Fe(II) stabilization and complexation by NOM
Iron is an essential mineral nutrient for nearly all organisms, but the low solubility of ferric iron limits its bioavailability in most natural environments. At neutral pH, ferrous iron is several orders of magnitude more soluble than ferric iron, but it rapidly oxidizes in the presence of molecular oxygen. Intriguingly, Fe(II) has been discovered in association with natural organic matter (NOM) in particles collected from oxygen-rich environments favorable of Fe(II) oxidation. Recent laboratory studies of Fe-NOM redox chemistry, however, have yielded contradictory results as to whether NOM enhances, inhibits, or has no effect upon the rate of Fe(II) oxidation. Accordingly, molecular mechanisms by which NOM inhibits or enhances Fe(II) oxidation are not clearly understood. We use X-ray absorption spectroscopy (XAS) to determine the coordination environment of Fe(II) adsorbed to (chemically) reduced and unreduced NOM and investigate the effect of NOM complexation upon Fe(II) oxidation kinetics.
This project is done in collaboration with Drs. Benjamin Gilbert and Peter Nico at Lawrence Berkeley National Laboratory.
The role of Fe-NOM interactions in Fe and C cycling in subalpine wetlands
Wetlands are hotspots of biogeochemical activity that influence the cycling of carbon, nitrogen, iron, and other nutrients. The saturated soil environment limits the diffusion of oxygen, resulting in regions of variable redox conditions. Cycling of iron and organic carbon is intimately linked in these systems and is sensitive to temperature and precipitation changes associated with climate change. Thus, it is important to characterize molecular-level compositions of Fe-NOM complexes as a function of soil warming, redox conditions, and hydrology. Recent studies in redox-cycled wetlands show the preferential complexation of aromatic and pyrogenic compounds by precipitating iron, leaving aliphatic acids dissolved in the more mobile surface water. However, investigation of Fe(II)-NOM complexation and the effects of temperature on Fe-NOM complexation in wetlands has not been conducted. Our goal is to elucidate the molecular composition of organic matter associated with iron mineral phases and aqueous Fe(II) in various subalpine wetlands in Fraser Experimental Forest in Colorado using high resolution synchrotron and mass spectrometry techniques.
This project is done in collaboration with Dr. Céline Pallud at UC Berkeley and Dr. Chuck Rhoades at the US Forest Service.
For more details about the research conducted in the Borch group please click here.
Dr. Benjamin Gilbert, Earth Science Division, Lawrence Berkeley National Laboratory
Dr. Peter Nico, Earth Science Division, Lawrence Berkeley National Laboratory
Dr. Céline Pallud, Department of Environmental Science, Policy and Management, University of California, Berkeley
Dr. Charles Rhoades, Rocky Mountain Research Station, United States Forest Service
Fraser Experimental Forest, United States Forest Service