Browsing by Subject "Organic matter"

Now showing 1 - 3 of 3
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    An organic geochemical record of inland migration in a coastal marsh, Chesapeake Bay, Maryland, USA
    (2017-05) Van Allen, Rachel
    Organic matter accumulation in marsh soils affects marsh survival under rapid sea level rise (SLR). This work describes the changing organic geochemistry of a salt marsh located in Blackwater National Wildlife Refuge on the eastern shore of Chesapeake Bay that is transgressing inland with SLR. Marsh soils and vegetation were sampled along an elevation gradient from the intertidal zone to the adjacent forest. Stable carbon isotope analysis of bulk organic matter suggests a broad transition towards C4-dominated marsh vegetation over time. Vegetative source of the organic matter shifts along a marsh-upland mixing line from herbaceous angiosperm-sourced lignin in the low marsh to a woody gymnosperm signature at the upper border of the marsh. Stable isotope and lignin chemistry results illustrate that landward encroachment of marsh grasses results in deposition of herbaceous tissues that exhibit relatively little decay. This presents a possible mechanism for organic matter stabilization as marshes migrate inland.
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    Rapid solid phase extraction of dissolved organic matter
    (2014-05) Swenson, Michael M.
    Dissolved organic matter (DOM) is a complex mixture of organic molecules found ubiquitously in freshwater and saltwater environments. Contained within the heterogeneous mixture of DOM lies valuable information content on the source of molecules as well as the biotic mechanisms at work within an aquatic ecosystem. Recent advancements in high resolution mass spectrometry and liquid chromatography have made inroads into determinations of the molecular structures within DOM, which have been largely unknown until recently. Liquid chromatography-mass spectrometry (LC-MS) analysis, however, generally requires a prior step to concentrate/isolate DOM, and this step often limits the number of samples that can be analyzed. This study has developed a fast (<20 min) method to concentrate dissolved organic matter on commercially available online solid phase extraction (SPE) cartridges which can be directly eluted onto an LC-MS system. This method is generally faster and requires far less sample (10-100 mL) than previous SPE methods for DOM isolation. Additionally, this study tested a suite of very different SPE phases to find a combination of phases that could improve DOM recovery as compared with commonly used approaches. When a styrene divinylbenzene phase (RP1) was coupled with activated carbon, recoveries were found to be significantly higher than in previous SPE studies relying upon single phases (either C18 or styrene divinylbenzene-based). The SPE method proposed here was tested for a diverse set of salty and fresh water samples and percent recoveries ranged from 46-78% of the total dissolved organic carbon (DOC).
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    Sources, cycling, and fate of organic matter in large lakes: ingishts from stable isotope and radiocarbon analysis in Lakes Malawi and Superior
    (2014-08) Kruger, Brittany Ruth
    Organic matter (OM) in lake systems is sourced from in situ aquatic primary production (autochthonous), land based plant primary production or detrital material that ultimately originated from photosynthesis (allochthonous), or resuspension of organic rich sedimentary material that was ultimately sourced from a combination of all such sources. Studying the stable and radioisotopic signature of multiple chemical components of lacustrine OM can help elucidate which of the above is the dominant OM source to the lake, as well as how OM is incorporated into and cycles through lake systems. The high organic content and biodiversity in large lakes of the world make them excellent sites to investigate such questions, and this dissertation focuses on such questions in Lake Malawi (SE Africa), and Lake Superior (North America). In Lake Malawi, the organic carbon (OC) recently deposited (within the last 50 years) is largely dominated by aquatic input, and the influence of terrestrial riverine inputs dissipates as distance from shore and water depth increase. This confirms that parameters typically used to investigate historic lake levels (and thereby to infer past climates) can in fact function as robust indicators of distance from shore, and thereby lake level. This is supported by bulk and compound specific stable carbon isotopic and radiocarbon analysis of multiple sediment fractions. Most fractions exhibited isotopic signatures nearshore that were distinct from more offshore, open-lake locations. In Lake Superior, compound specific nitrogen isotope analysis (CSNIA) of specific amino acids from species occupying all levels of the food chain showed that Limnocalanus macrurus, a copepod, occupies a trophic level much higher than expected from known feeding habits, which may indicate the consumption of additional or unique food sources. Bulk radiocarbon analysis of the same suit of species from that lake showed Diporeia, a benthic amphipod, consumes an aged carbon source that does not appear to be significantly incorporated by other (more pelagic) organisms in this study, which rely primarily upon recently synthesized autochthonous organic carbon.