Clay Mineralogy and Organic Carbon Associations in Two Adjacent Watersheds, New Zealand

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Title: Clay Mineralogy and Organic Carbon Associations in Two Adjacent Watersheds, New Zealand
Author: Lloyd, Kristen Helen
Advisors: Dr. Neal Blair, Committee Member
Dr. Elana Leithold, Committee Chair
Dr. Dean Hesterberg, Committee Member
Abstract: Research conducted on the Waipaoa and Waiapu Rivers on the North Island of New Zealand has recognized and characterized geomorphologic and geochemical processes responsible for the control and delivery of sediment and associated OC to the adjacent margin. Clay mineral compositions from specimens of bedrock, volcanic soils and tephras, suspended river sediment, and recent marine sediments were studied. Identification of the clay minerals was made chiefly by X-ray (XRD), infrared (FTIR), and selective mineral dissolution analyses. Geochemical analyses included organic carbon (OC) concentrations and stable carbon isotopic compositions. Characteristic clay minerals indicative of bedrock contributions include chlorite and illite. Smectite and kaolinite are also present but in lesser quantities. Soil and tephra mineralogy could not be as easily quantified from x-ray diffraction due to the presence of poorly crystalline minerals (i.e. allophane). FTIR spectrometry proved to be a beneficial tool for the identification of clay minerals in the soil. Allophane and the higher concentration of smectite signify material being derived from the soils and tephra. Suspended sediment samples collected during moderate to high river flows exhibited a mixed clay mineral composition derived from both bedrock and soil. Within the Waiapu River, bedrock contributions appeared to be greater due to gullying being the more dominant geomorphologic process. The Waipaoa River showed soil contributions to be as important as rock contributions. Recent marine sediments off the Waiapu River were similar in composition to the suspended Waiapu River sediment. Spatial variability in clay mineralogy associated with cross shelf transport reveal chlorite increases at the expense of illite off the Waiapu shelf. A downcore study was conducted on the Waipaoa shelf to examine temporal variability. The sediments in the flood layer and below resemble the river suspension, with smectite being the dominant clay mineral. The presence of allophane in the flood layers suggests a greater contribution from the soil and subsequent rapid burial. The mineralogy of the top layer resembles that seen in the Waiapu, with illite being the dominant clay. After the clay mineralogy was established, geochemistry was employed to examine contributions from the sources of particulates being delivered to the margin. However, due to the wide range of results, overlap between characteristic isotopic signatures of the sources prevented the successful application of this method. %OC illustrates the mixing of ancient and modern carbon in the rivers and bulk %OC of the rivers is roughly two times greater than the %OC from the rocks. XRD and FTIR results are consistent with and further confirm the mixing of rock and soil particulates in both margins.
Date: 2007-12-07
Degree: MS
Discipline: Marine, Earth and Atmospheric Sciences

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