UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Highly Siderophile Elements, 187Re-187Os and 182Hf-182W Isotopic Systematics of Early Solar System Materials: Constraining the Early Evolution of Chondritic and Achondritic Parent Bodies
    (2016) Archer, Gregory Jude; Walker, Richard J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Highly siderophile element (HSE) abundances and 187Re-187Os isotopic systematics for H chondrites and ungrouped achondrites, as well as 182Hf-182W isotopic systematics of H and CR chondrites are reported. Achondrite fractions with higher HSE abundances show little disturbance of 187Re-187Os isotopic systematics. By contrast, isotopic systematics for lower abundance fractions are consistent with minor Re mobilization. For magnetically separated H chondrite fractions, the magnitudes of disturbance for the 187Re-187Os isotopic system follow the trend coarse-metal
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    RECRUITMENT RESPONSES OF BENTHIC INFAUNA TO MANIPULATED SEDIMENT GEOCHEMICAL PROPERTIES IN NATURAL FLOWS
    (2004-05-18) Engstrom, Steven John; Marinelli, Roberta L; Marine-Estuarine-Environmental Sciences
    Recent studies have shown that local variation in sediment geochemistry can have significant effects on settlement rates of benthic invertebrates. For example, elevated porewater ammonium concentrations in soft-sediment benthic systems may result in decreased recruitment rates of settling larvae. Recruitment responses of the benthic polychaete Arenicola cristata and the bivalve Mercenaria mercenaria to varying ammonium concentrations were measured in realistic flow environments. Experiments made novel use of ammonium-spiked polyacrylamide gels placed beneath field-collected sediment, which produced predictable porewater ammonium concentrations. Post-larval arenicolids and Mercenaria were allowed to settle in an annular flume containing sediment treatments with varying ammonium concentrations. Porewater ammonium data indicated successful manipulation of geochemical properties without contamination of overlying water. In Mercenaria trials, recruit retention was low. For Arenicola trials, significant retention differences were observed as a function of ammonium concentration, and indicate that ammonium plays a significant role in determining recruitment patterns and hence juvenile abundance.