Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

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    Whole stream nitrogen uptake and denitrification in a restored stream of the Chesapeake Bay
    (2007-08-10) Klocker, Carolyn Ann; Kaushal, Sujay S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Little is currently known about the effects of stream restoration practices on in-stream processing and nitrogen removal. This study quantified nitrate retention in a survey of two restored and two unrestored streams in Baltimore, MD using unenriched nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length was significantly correlated to surface water velocity, which was lowest in restored streams. In situ denitrification rates in Minbank Run were 153 mg NO3--N m-2 d-1, and approximately 40% of the daily load of nitrate could be removed over a distance of 220.5 m. Stream restoration projects that decrease water velocity and increase residence time may lead to considerable rates of nitrate removal through denitrification.
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    THE INVESTIGATION OF MERCURY REDOX CHEMISTRY IN NATURAL WATERS AND THE DEVELOPMENT OF A NEW METHOD FOR INCUBATION EXPERIMENTS
    (2005-04-26) Whalin, Lindsay; Mason, Robert P; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The redox processes that control Hg speciation in natural waters are poorly understood and study results often disagree, primarily a consequence of varied and often flawed methodologies. An incubation method was developed utilizing PFA Teflon® bag reaction vessels to reduce sources of error, and additions of isotopically labeled Hg to quantify rate constants. With low measures of error and duplicate bag reproducibility, this method was applied via incubations of natural waters in ambient sunlight to test three theories; 1) Hg oxidation and reduction are photochemically mediated, 2) Hg reduction is correlated to [DOC], and 3) Hg oxidation is enhanced by halides. The former was proven through the detection of redox chemistry during daylight and its absence in the dark. Results indicate the importance of both redox processes in natural waters, but failed to prove the latter two theories, potentially due to greater than expected [DOC] in one experiment.