Browsing by Subject "isotopic analysis"

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    Carbon, Oxygen, and Nitrogen Isotopic Analysis of Mollusca: Unionidae of the Ohio River System during the Anthropocene
    (Office of the Vice Chancellor for Research, 2014-04-11) Conduitt, Chelsea L
    Isotopic compositions of Obovaria olivaria, Leptodea fragilis, and Quadrula quadrula of the Wabash River contain clues to the anthropogenic modifications they have undergone during the time of the shell formation. In this study we analyzed the isotopic composition of the carbon (δ13C), oxygen (δ18O), and nitrogen (δ15N) in the carbonate sampled from growth bands of the shells. These results are compared to published data, and with accurately documented historical river data to better understand the human impact on river systems in the Ohio River Valley in the last 250 years. Mollusks construct their shells using CO2 and nitrogen that is dissolved in the water. Since mollusks are sedentary animals, their isotopic signatures will reflect the chemistry of the water in which they grow. Comparing the locality in which the mollusks lived to the chemical changes recorded in their shells over time will provide temporal-spatial constraints on the natural variability of the river as well as the influence of anthropogenic inputs. Specifically, the δ13C and δ18O stored in the shells of the mollusks record changes in the environment such as air and river temperature, acidity of the river, changes in the river chemical composition, and may indicate a change in the source of the water. The isotopic analysis of δ15N recovered from the shell can help track changes in nutrient delivery during the time of shell formation. Through this geochemical study we hope to provide a much needed record of the timing and extent of human impact on river systems.
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    Multiple Methods to Partition Evapotranspiration in a Maize Field
    (2017-01) Wu, Youjie; Du, Taisheng; Ding, Risheng; Tong, Ling; Li, Sien; Wang, Lixin; Department of Earth Sciences, School of Science
    Partitioning evapotranspiration (ET) into soil evaporation E and plant transpiration T is important, but it is still a theoretical and technical challenge. The isotopic technique is considered to be an effective method, but it is difficult to quantify the isotopic composition of transpiration δT and evaporation δE directly and continuously; few previous studies determined δT successfully under a non-steady state (NSS). Here, multiple methods were used to partition ET in a maize field and a new flow-through chamber system was refined to provide direct and continuous measurement of δT and δE. An eddy covariance and lysimeter (EC-L)-based method and two isotope-based methods [isotope combined with the Craig–Gordon model (Iso-CG) and isotope using chamber measurement (Iso-M)] were applied to partition ET. Results showed the transpiration fraction FT in Iso-CG was consistent with EC-L at both diurnal and growing season time scales, but FT calculated by Iso-M was less than Iso-CG and EC-L. The chamber system method presented here to determine δT under NSS and isotope steady state (ISS) was robust, but there could be some deviation in measuring δE. The FT varied from 52% to 91%, with a mean of 78% during the entire growing season, and it was well described by a function of LAI, with a nonlinear relationship of FT = 0.71LAI0.14. The results demonstrated the feasibility of the isotope-based chamber system to partition ET. This technique and its further development may enable field ET partitioning accurately and continuously and improve understanding of water cycling through the soil–plant–atmosphere continuum.