14-33. Reconstructing River Flow and Climate Using Stable Isotope Ratios in Riparian Trees
We seek a postdoctoral fellow to use stable isotopes in riparian tree rings for reconstructing river flow and drought in the northern Great Plains. Predicting future effects of Global Change on water supplies requires an understanding of past variation in river flow. One of the most important resources for reconstruction of past flow variation is the rings of long-lived trees (Friedman and Lee 2002, Meko et al. 2007, Merigliano et al. 2012). Because tree rings respond to many different environmental influences, however, it is essential to supplement ring-width data with other lines of evidence in order to isolate the flow signal. An important rapidly developing opportunity to obtain additional information from tree rings is stable isotope analysis.
In dry conditions, stomatal closure reduces discrimination by the leaf against 13C. As a result the 13C/12C ratio increases in a season of drought (McCarroll and Loader 2004, Leavitt et al. 2011). Until recently, examination of interannual variation in carbon isotope fractionation of tree rings was limited by large sample mass requirements and time necessary to process a sample (Leffler and Evans 1999). Development of online analysis of carbon isotopes, however, now allows the analysis of thousands of samples smaller than an individual tree ring (Schulze et al. 2004). This makes it possible to treat within- and between-year variation in carbon stable isotope fractionation on a par with ring-width variation in a multi-proxy study of tree response to variation in climate and flow (Silva and Anand 2012). Analysis of annual variation in stable isotopes of hydrogen and oxygen as well as trace elements and radiogenic isotopes are also now feasible.
Because old trees are scarce at low elevations in the arid inland western United States, ring-based flow reconstructions in large rivers are usually based on conifer trees in the mountains, where most of the run-off is derived. Such chronologies are important, but incomplete because they do not integrate events and hydrologic processes lower in the watershed. Ongoing work has shown that the dominant riparian tree in the lowland western United States, cottonwood (Populus spp.), is long-lived (as old as 370 years), cross-dates well, and has growth strongly correlated with surface-water flow (Merigliano et al. 2012, Friedman et al. 2012, Edmondson et al. 2013). Cross-dated sets of cottonwood cores from the northern Great Plains are now available for stable isotope analysis and past work in this genus has shown a strong relation between carbon isotope fractionation and drought stress (Leffler and Evans 1999). This presents the possibility of conducting multi-proxy studies using ring widths, stable isotopes, and possibly trace elements and radiogenic isotopes of both low-elevation cottonwoods and high-elevation conifers.
Developing strong relations among tree growth, carbon isotope fractionation, and surface-water flow also allows prediction of the effects of future changes in flow, precipitation and temperature on tree growth and survival. Down-scaled climate predictions can be used to drive river watershed models providing the daily flow predictions necessary for such assessments. Because Populus is a dominant plant in western riparian ecosystems this approach makes it possible to predict effects of climate change on habitat quality for dependent species such as migratory birds.
The Mendenhall Fellow is expected to develop tree-ring proxies of flow and climate in the northern Great Plains, where such records are currently sparse. These records would be used for prediction of ecosystem response to climate change and for flow reconstruction in rivers of great importance to ecological systems and human water supply (e.g. the Yellowstone River) in a region subject to current and expected future drought. Such records are essential for distinguishing the effects of ongoing century-scale climate variation from those of human-induced climate change and for predicting ecosystem response to climate change.
Questions that may be addressed within the course of the Mendenhall project include: How do stable isotope ratios in riparian trees vary within annual rings, between years, as a function of tree age, between trees, across a flood plain and between sites? Can climate and flows be reconstructed from tree rings based on annual variation in stable isotope fractionation and ring width? How can contributions of montane and low-elevation catchments to prehistoric river flow be distinguished? What effects does climate change have on river flow and riparian tree growth and survival? How does varying water availability affect cottonwood growth, xylem cavitation and stable isotope fractionation? Can novel elemental or isotopic records in tree rings reflect variable chemical and environmental conditions that could further refine climate reconstruction?
The Fellow will have the opportunity to combine resources of four major laboratories focused on – riparian ecology; stable isotope analysis; tree-ring research; and hydrologic/watershed modeling, as well as a facilities for analyzing trace-elements and trace-metal isotopes by laser-ablation ICP-MS.
Edmondson, J.R., Friedman, J.M., Meko, D.M., Touchan, R., Scott, J.A., and Edmondson, A., 2013, Dendroclimatic potential of plains cottonwood (Populus deltoides ssp. monilifera) from the Northern Great Plains, USA: Tree Ring Research, in review.
Friedman, J.M., Edmondson, J.R., Griffin, E.R., Meko, D.M., Merigliano, M.F., Scott, J.A., Scott, M.L., and Touchan, R., 2012, Cottonwood tree rings and climate in western North America: American Geophysical Union 2012 Fall Meeting, San Francisco, CA.
Friedman, J.M., and Lee, V.J., 2002, Extreme floods, channel change and riparian forests along ephemeral streams: Ecological Monographs, v. 72, p. 409-425.
Leavitt, S.W., Woodhouse, C.A., Castro, C.L., Wright, W.E., Meko, D.M., Touchan, R., Griffin, D., and Ciancarelli, B., 2011, The North American Monsoon in the U.S. Southwest: Potential for investigation with tree-ring carbon isotopes: Quaternary International, v. 235, p. 101-107.
Leffler, A.J., and Evans A.S., 1999, Variation in carbon isotope composition among years in the riparian tree Populus fremontii: Oecologia, v. 119, p. 311-319.
McCarroll, D., and Loader, N.J., 2004, Stable isotopes in tree rings: Quaternary Science Reviews, v. 23, p. 771-801.
Meko, D.M., Woodhouse, C.A., Baisan, C.H., Knight, T., Lukas, J.J., Hughes, M.K., and Salzer, M.W., 2007, Medieval drought in the Upper Colorado River Basin: Geophysical Research Letters, v. 34 (10, L10705), doi:10.1029/2007GL029988.
Merigliano, M.F., Friedman, J.M., and Scott, M.L., 2012, Tree-ring records of variation in flow and channel geometry, in Shroder, J., Jr., Hupp, C.R., and Butler, D., eds. Treatise on Geomorphology: Academic Press, v. 12, in press.
Schulze, B., Wirth, C., Linke, P., Brand, W.A., Kuhlmann, I., Horna, V., and Schulze, E.D., 2004. Laser ablation-combustion-GC-IRMS—a new method for online analysis of intra-annual variation of δ13C in tree rings: Tree Physiology, v. 24, p. 1193-1201.
Silva, L.C.R., and Anand, M., 2012, Probing for the influence of atmospheric CO2 and climate change on forest ecosystems across biomes: Global Ecology and Biogeography doi: 10.1111/j.1466-8238.2012.00783.x.
Proposed Duty Station: Denver, CO; Fort Collins, CO
Areas of Ph.D.: Dendrochronology, Geochemistry, Ecology, Hydrology or related fields (candidates holding a PhD in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications: Applicants must meet one of the following qualifications - Research Biologist, Research Botanist, Research Chemist, Research Ecologist, Research Forester, Research Geologist, Research Hydrologist.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant’s background, education, and research proposal. The final classification of theposition will be made by the Human Resources specialist).
Research Advisors: Jonathan Friedman, (303) 541-3017, firstname.lastname@example.org.; Craig Stricker, (303) 236-7908, email@example.com.; James Paces, (303) 236-0533, firstname.lastname@example.org.; David Meko, (520) 621-1608, email@example.com. (U Arizona); Eleanor Griffin, (303) 541-3041, firstname.lastname@example.org.
Human Resources Office Contact: Jennifer Daberkow, (303) 236-9566, email@example.com
|Summary of Opportunities|