[129]I cycling in terrestrial and coastal marine environments /
Natural levels of radioactive ¹²⁹I have been overwhelmed by anthropogenic inputs such as nuclear bomb testing and nuclear fuel reprocessing. Due to its biophilic nature, iodine is expected to be associated with organic matter. Therefore, colloidal material from the Mississippi River was examined to...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731980991&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Natural levels of radioactive ¹²⁹I have been overwhelmed by anthropogenic inputs such as nuclear bomb testing and nuclear fuel reprocessing. Due to its biophilic nature, iodine is expected to be associated with organic matter. Therefore, colloidal material from the Mississippi River was examined to determine the amount of ¹²⁹I associated with colloidal organic carbon (COC). ¹²⁹I and ¹²⁷I isotopes were shown to be mostly associated with COC with the majority in the filter passing (<0.45 []m) fraction, and a small portion ([] 10%) associated with suspended particulate matter. Mississippi River water was further analyzed over a two-year period to ascertain the input of ¹²⁹I to the Mississippi Delta region where sediment cores were collected. A relatively constant ¹²⁹I input into the Mississippi River was observed which produces an inverse correlation between ¹²⁹I (and ¹²⁹I/¹²⁷I) and flow rate. The concentration of ¹²⁹I in Mississippi River water varied with seasonal discharge rates, which could be attributed to a delayed signal from spring flushing of soils. Distinct bomb fallout ¹²⁹I, ¹³⁷Cs, and ²³⁹²⁴⁰Pu signatures were found in a sediment core from the Mississippi Delta. A second core collected closer to the Mississippi River mouth provided a 10-15 year record of recent inputs, and followed the same general trends observed in the first core, also indicating primarily bomb fallout inputs. While high ¹²⁹I/¹²⁷I ratios were measured in U.S. rivers away from known point sources for ¹²⁹I indicating atmospheric input from European fuel reprocessing plants, neither core showed significant fuel reprocessing input. This is likely due to the differences in chemical forms of reprocessing and bomb fallout ¹²⁹I. A conceptual model is presented to account for low ¹²⁹I/¹²⁷I ratios found in the sediment cores as caused by geochemical I-isotope fractionating processes during organic carbon leaching from soils in the Mississippi River watershed. The ratio of ¹²⁹I/¹²⁷I is fixed on different organic carbon fractions based on the affinity of the different chemical forms of ¹²⁹I to different organic carbon fractions. This organic carbon-rich material with fixed isotope ratio is subsequently transported in the river, and possibly further fractionated during depositional processes in the river delta. |
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| Item Description: | Vita. "Major Subject: Oceanography". |
| Physical Description: | xiii, 143 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 125-133). |