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stable isotopes

Sensitivity of precipitation isotope meteoric water lines and seasonal signals to sampling frequency and location

The Watershed Hydrology lab will be out in force for the Geological Society of America annual meeting in Vancouver in October. Over the next few days, we’ll be sharing the abstracts of the work we are presenting there.

SENSITIVITY OF PRECIPITATION ISOTOPE METEORIC WATER LINES AND SEASONAL SIGNALS TO SAMPLING FREQUENCY AND LOCATION

REYNOLDS, Allison R., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44242, areyno13@kent.edu and JEFFERSON, Anne J., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44240
Every precipitation event has its own isotopic signature, making it useful for hydrology purposes, like estimating transit time or identifying seasonality of groundwater recharge. Our purpose is to compare the seasonal signal and local meteoric water line (LMWL) generated by one year of event-based sampling to those resulting from multi-year monthly sampling at the closest Global Network of Isotopes in Precipitation (GNIP) stations. The question we seek to answer is whether data from different sampling strategies, periods, and locations within the eastern Great Lakes region in North America converge on a regional-scale LMWL and seasonal signal.
From October 2012-present precipitation samples were collected in Kent, Ohio, filtered and analyzed by a Picarro L-2130i at Kent State University. The closest GNIP sites are Coshocton, Ohio, USA and Simcoe, Ontario, Canada; monthly data was downloaded from a database. For each site, we graphed the ?18O versus ?2H and added a linear trendline to represent the LMWL and fit sine waves to the data to assess seasonal isotopic signal.
Based on the event data, Kent has the most isotopically depleted precipitation, but when looking at monthly samples, it falls between Simcoe to the north and Coshocton to the south. This suggests that, in this region, isotopically light precipitation events are more important in terms of their frequency than their amount. LMWLs for each site were similar. Comparing the LMWLs generated from the event samples and monthly data, monthly data had a slightly lower slope and d-excess. For Coshocton, amplitude of the seasonal sine wave for ?18O is 6.2‰, for Simcoe the sine wave is 4.3 ‰. For the Kent dataset, event-based data produced a sine wave with amplitude of 6.1‰, while monthly data resulted in a 4.9‰ amplitude wave. While it is possible that the amplitude of a wave fit to monthly data would increase with data points that represent isotopically extreme months, it is likely that curves fit to monthly data will frequently under-represent the variability in precipitation isotopes as measured at event and sub-event timescales. Both the LMWL and seasonal signal analysis suggest a greater variability in precipitation isotope signatures during the winter relative to the summer in the eastern Great Lakes region.

Rayleigh isotope distillation module – development and transferability in geoscience education

The Watershed Hydrology lab will be out in force for the Geological Society of America annual meeting in Vancouver in October. Over the next few days, we’ll be sharing the abstracts of the work we are presenting there.

RAYLEIGH ISOTOPE DISTILLATION MODULE – DEVELOPMENT AND TRANSFERABILITY IN GEOSCIENCE EDUCATION

GRIFFITH, Elizabeth M., Earth and Environmental Sciences, University of Texas at Arlington, 500 Yates St, Arlington, TX TX 76019, lgriff@uta.edu, ORTIZ, Joseph D., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44242, JEFFERSON, Anne J., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44240, DEES, David, Faculty Professional Development Center and School of Foundations, Leadership and Administration, Kent State University, 231 Moulton Hall, Kent, OH 44242, and MERCHANT, William, Department of Evaluation and Measurement, Kent State University, 111L Nixon Hall, Kent, OH 44242
Rayleigh distillation is an important concept in geochemistry – applied to isotopic and elemental systems ranging from crystallization in magma chambers to oxygen isotope stratigraphy across glacial-interglacial periods. A teaching module that allows students to discover first-hand consequences of isotopic fractionation and Rayleigh distillation was developed, peer-reviewed, modified and used in thre upper-division geoscience courses: Sedimentology/Stratrigraphy, Environmental Geochemistry and Paleoceanography. In the module “Rayleigh isotope effect in the oceans: building glaciers” students perform (or are given data from) a simple batch distillation experiment that they model using open system Rayleigh isotopic fractionation. Insight on isotopic fractionation during phase transitions and a fundamental understanding of oxygen isotope stratigraphy is learned first-hand by the students preforming simple experiments and analyzing the data on sophisticated equipment. The teaching module is adaptable for the geoscience curriculum, including upper division courses and introductory courses. The module has only been tested in three upper division courses, but future work adapting and implementing the activity in an Introduction to Oceanography lab is planned.
Funding by the NSF Division of Undergraduate Education allowed us to study the impact on student learning and motivation from teaching the material within the module using different pedagogical approaches including a paper-based data analysis activity and hands-on data collection with and without access to the water isotope analyzer. Assessment techniques were developed and implemented through the close collaboration with a faculty expert within the educational field. The 3-year project is in its second year and initial quantitative results and reflections from the faculty and students will be presented. Both faculty noted a difference in the classroom dynamic with the students performing the experiments vs those completing the paper-based data analysis. Additional strategies will be highlighted for the transferability of the hands-on experiment to institutions and departments without access to the water isotope analyzer.

Hands-on experiences with stable isotopes in the geosciences curriculum

The Watershed Hydrology lab will be out in force for the Geological Society of America annual meeting in Vancouver in October. Over the next few days, we’ll be sharing the abstracts of the work we are presenting there.

HANDS-ON EXPERIENCES WITH STABLE ISOTOPES IN THE GEOSCIENCES CURRICULUM

JEFFERSON, Anne J.1, GRIFFITH, Elizabeth M.2, ORTIZ, Joseph D.1, DEES, David3, and MERCHANT, William4, (1) Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44242, ajeffer9@kent.edu, (2) Earth and Environmental Sciences, University of Texas at Arlington, 500 Yates St., Arlington, TX 76019, Arlington, TX TX 76019, (3) Faculty Professional Development Center and School of Foundations, Leadership and Administration, Kent State University, 231 Moulton Hall, Kent, OH 44242, (4) Department of Evaluation and Measurement, Kent State University, 111L Nixon Hall, Kent, OH 44242

Over the past thirty years, environmental and geoscience research has increasingly utilized stable isotope ratios to understand problems as diverse as paleoclimates, magma genesis, and processes in the hydrosphere and critical zone. New laser-based technology for measuring isotope ratios has significantly reduced the cost of setting up and maintaining an isotope lab. The new technology is also easier to use with students than traditional isotope ratio mass spectrometers, so there is strong potential to introduce hands-on experiences into the geoscience curriculum.
This project, funded by the NSF Division of Undergraduate Education, assessed the impact that different pedagogical approaches have on student learning of stable isotope concepts in upper-division geoscience courses (Watershed Hydrology; Sedimentology/Stratigraphy; Environmental Geochemistry). Groups of students were exposed to this content via (1) a lecture-only format; (2) a paper-based data analysis activity; and (3) hands-on data collection, sometimes including spectrometer analysis. Pre- and post-tests measured gains in content knowledge while approaches to learning and motivational questionnaires instruments were used to identify the effects of the classroom environment on learning approaches and motivation. Focus group interviews were also conducted to verify the quantitative data. Preliminary findings of this study, currently in year two of three, include: a) a common decrease in student motivation as the semester progresses, b) relatively minor changes in student approaches to learning regardless of pedagogical strategy, and c) students’ positive responses to professor passion.
Peer review of modules and activities has been used to ensure high quality content is being delivered. Close collaboration between geosciences and education faculty at all project stages has enabled deployment of robust measures of student learning, increased responsiveness of the research to developments in the classroom, and facilitated exploration of unexpected project results. In its final year, the project will focus on high-impact dissemination of developed curriculum and project results, through workshops and on-line repositories.

Virtual workshop on laser isotope technology applications in hydrology

CUAHSI is the consortium of universities for the advancement of hydrologic science, inc. and Kent State University became a full member of the consortium in December 2013. That’s good timing, because for the last year I’ve been sitting on the organizing committee for a virtual workshop sponsored by CUAHSI and USGS, and I’m super excited to announce that it’s finally happening and starting soon.

This workshop focuses on field hydrology and biogeochemistry applications of laser-based isotope technology. This may sound like an esoteric topic, but this technology is rapidly expanding the affordability and availability of stable isotope analyses. When I was in graduate school, the only way to get water isotope data was off an expensive and hard to use isotope ratio mass spectrometer. I traveled 10 hours to access one and I swore I’d never have one in my lab. Now, I walk upstairs to use the slightly less expensive and somewhat easier to use laser spec purring along in my lab. Viva technology!

Over the course of 5 weeks, we’ll have presentations from the manufacturers of the two main laser specs (Picarro and Los Gatos Research), commentary on the technology from experts at the USGS and IAEA, examples of applications from experienced users, and a poster session where we can share our data and experiences. The workshop will occur entirely on the web (thanks, sequester) and you can participate in real time or watch recordings of the talks.

The flyer below gives a lot of the information, but you can out even more at the CUAHSI webpage for the workshop.

LaserSpec_Instrumentation_Flyer_01.07.2014

I’m looking forward to learning a ton of information during the workshop, sharing some hot-off-the-instrument data that my undergraduate student and I have been collecting, and hopefully sharing the neat ways we’re integrating the technology into our undergraduate geosciences curriculum at KSU. I hope to see you (virtually) there!