remote sensing techniques for nitrogen stable isotope analysis … · 2016-05-03 · stable isotope...
TRANSCRIPT
• Aeroponic growth experiments of Buckwheat (Fagopyrum esculentum)
subjected to 15N labeled ammonium nitrate mixed with SeaCom (no
nitrogen) liquid fertilizer compared to control of standard fertilizer.
• Hand held or lab bench spectroscopy instruments
Analytical Spectral Devices Field Spec Pro (ASD) field portable
spectrometer (350-2500 nanometers (nm) / 28,571 to 4,000 cm-1)
Agilent Technologies Exoscan field portable Fourier transform infrared
(FTIR) spectrometer (4000-650 cm-1)
Nicolet 6700 lab FTIR spectrometer (Optimized for 4500 to 500 cm-1)
The highly variable natural abundances in most stable isotopes in contrast
to their standard elemental concentrations make their analysis particularly
useful in many applications, particularly in chemical fingerprinting and the
identification of source signatures. Usually, to obtain accurate nitrogen
stable isotope data for a given portion of organic matter in the laboratory,
isotope-ratio mass spectrometry (IRMS) is the analytical tool of choice.
IRMS is very high in precision; however, sample run times and instrument
calibrations are time consuming, costly and represent data from a single
location on the Earth’s surface at a particular time and performed only in
laboratory conditions. Alternatively, field based Fourier-Transform
infrared spectroscopy (FTIR) based spectroscopy can be performed
rapidly, at a lower cost, and provide geospatially robust data. Isotopic
shifts within the infrared spectrum have traditionally been measured using
lab based FTIR spectroscopy. Three major methods are employed here:
a traditional approach of isotope measurement using IRMS, FTIR
spectroscopy, and a nontraditional computational approach, all of
which aim to quantify isotopic downshifts within the spectra of several
plant pigments. This will provide researchers with faster and cheaper
measurements that could cover broader areas and eventually be translated
to use with airborne or space-based instruments in order to provide
biogeochemical understanding at larger spatial scales not possible by
current instrumentation and techniques.
ABSTRACT
BACKGROUND
Validate the spectral downshifts that have been
observed experimentally through computational
modeling and IRMS measurements.
OBJECTIVE
Spectral absorption feature shifts due to heavier isotope uptake of labeled
plants (black) versus the control (red).
A 19 cm-1 down shift in the SWIR of the ASD 1st derivative data
A 7 cm-1 down shift in the Exoscan data
A 102 cm-1 down shift in the Nicolet data
(Overlaid with library spectra of the Chlorophyll b molecule)
Chlorophyll molecule – Modeling at Rivanna
Modeling isotope-induced frequency downshifts using molecular modeling
software and ultra-high performance computing capabilities at UVA’s
Rivanna cluster.
EXPERIMENTAL RESULTS CURRENT RESEARCHValidation of isotope-induced frequency shifts
though molecular modeling at Rivanna
Fertilizer sources identification with isotopes helps to
• Understand nutrient loads and origins, as anthropogenic
impacts are often hard to quantify in the environment.
• Isotope analysis when linked with water samples in nearby
streams and rivers enable researches to better differentiate
agricultural fields that have been applied with organic fertilizers
• Better identify nonpoint source polluters in waterways.
• Development of future remote sensors to provide
biogeochemical understanding at larger spatial scales.
• Areas of high anthropogenic nitrogen loading could be mapped
and efforts taken to mitigate the adverse environmental effects.
REFERENCESElmore, A. J., & Craine, J. (2011). Spectroscopic analysis of canopy nitrogen and nitrogen isotopes in
manages pastures and hay land. IEEE Transactions on Geoscience and Remote Sensing , 49 (7), 2491-
2498.
Kleinebecker, T., Schmidt, S., Fritz, C., Smolders, A., & Holzel, N. (2009). Prediction of c13C and c15N
in plant tissues with near-infrared reflectance spectroscopy. New Phytologist , 184 (7), 732-739.
Shearer, G., & Kohl, D. (1986). N2 fixation in field settings: Estimation based on 15N natural
abundance . Austrian Journal of Plant Physiology , 13, 699-756.
Wang, L., Okin, G. S., & Macko, S. A. (2010). Remote Sensing of Nitrogen and Carbon Isotope
Compositions in Terrestrial Ecosystems. In J. B. West, G. J. Bowen, T. E. Dawson, & K. P. Tu,
Isoscapes: Understanding movement, pattern, and process on Earth through isotope mapping (pp. 51-
70). New York: Springer.
Wang, L., Okin, G., Wang, J., Epstein, H., & Macko, S. (2007). Predicting lean and canopy 15N
compositions from reflectance spectra. Geophysical Research Letters , 34, L02401.
Yun, S.-I., Ro, H.-M., Choi, W.-J., & Chang, S. X. (2006). Interactive effects of N fertilizer source and
timing of fertilization leave specific N isotopic signatures in Chinese cabbage and soil. . Soil Biology
and Biochemistry , 38 (7), 1682-1689.
HOW:
Concentrations of the different isotope abundances, reported as ratios of
the different forms of the element can be used to explain many
biogeochemical processes. In plant matter, the stable isotope ratio of
nitrogen can used to understand the nitrogen cycle. Nitrogen (N) fertilizer
sources can be identified in plant matter and the surrounding soils as
organic manure based fertilizers are more enriched in 15N versus Haber
process inorganic urea fertilizers (Yun et al. 2006). Also, in areas with high
levels of nitrogen availability and increased rates of nitrogen leaching there
is 15N enrichment (Shearer & Kohl, 1986). Most researchers still rely
heavily on the IRMS for stable isotope analysis but some are investigating
alternative methods such as using handheld spectrometers for
measurements to be performed in a non-destructive manner and capable in
the field environment (Wang et al. 2010). There is a general consensus
among the stable isotope community that a larger spatial scale, including
regional analysis of isotope concentrations would be beneficial.
Spectroscopic analysis and remote sensing capabilities for stable isotopes
is currently being suggested and the possibility researched (Elmore &
Craine, 2011; Kleinebecker et al. 2009 and Wang et al. 2007). Stable
isotopes inherently have different masses that cause them to behave
distinctly within the electromagnetic continuum. Specifically they generate
isotope effects in their bonds with other elements where a bond with a
heavier isotope will vibrate at a different spectral band (Hoefs, 2009).
Declan McCarthy, Sonja Long, Stephen A. Macko
Department of Environmental Sciences, University of Virginia
Remote Sensing Techniques for Nitrogen Stable Isotope Analysis in Plant Matter
MATERIAL AND METHODS