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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Spatial and Interannual Variability in Export Efficiency and the Biological Pump in an Eastern Boundary Current Upwelling System with Substantial Lateral Advection

Unknown Date (has links)
Estimating interannual variability in carbon export is a key goal of many marine biogeochemical studies. However, due to variations in export mechanisms between regions, generalized models used to estimate global patterns in export often fail when used for intra-regional analysis. We present here a region-specific model of export production for the California Current Ecosystem (CCE) parameterized using intensive Lagrangian process studies conducted during El Niño-Southern Oscillation (ENSO) warm and neutral phases by the CCE Long-Term Ecological Research (LTER) program. We find that, contrary to expectations from prominent global algorithms, export efficiency (e-ratio = export / primary productivity) is positively correlated with temperature and negatively correlated with net primary productivity (NPP). We attribute these results to the substantial horizontal advection found within the region, and verify this assumption by using a Lagrangian particle tracking model to estimate water mass age. We further suggest that sinking particles in the CCE are comprised of a recently-produced, rapidly-sinking component (likely mesozooplankton fecal pellets) and a longer-lived, slowly-sinking component that is likely advected long distances prior to export. We determine a new algorithm for estimating particle export in the CCE from NPP (Export = 0.08 x NPP + 72 mg C m-2 d-1). We apply this algorithm to a two-decade long time series of NPP in the CCE to estimate spatial and interannual variability across multiple ENSO phases. Reduced export during the warm anomaly of 2014-2015 and El Niño 2015-2016 resulted primarily from decreased export in the coastal upwelling region of the CCE; the oligotrophic offshore region exhibited comparatively low seasonal and interannual variability in flux. The model resolves intra-regional patterns of in situ export measurements, and provides a valuable contrast to global export models. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2018. / April 13, 2018. / California Current ecosystem, carbon export, El Nino, plankton, sinking particles / Includes bibliographical references. / Michael Stukel, Professor Directing Thesis; Sven Kranz, Committee Member; Angela Knapp, Committee Member.
2

Coupling the effects of dissolved organic matter and nutrient stoichiometry with nutrient uptake in boreal forest headwater streams

Fjare, Dana 23 October 2015 (has links)
<p> Discontinuous permafrost affects the hydrology of boreal forest streams by restricting flow path depth where permafrost is present. Stream water chemistry, such as flux of inorganic nutrients and dissolved organic matter (DOM), is subsequently affected by permafrost distribution. Headwater streams in the boreal forest are dependent on allochthonous inputs of energy and nutrients, and as a result are dominated by heterotrophic processes. A warming climate may change the distribution of permafrost in high latitude ecosystems, with consequences for nutrient availability. Herein, we investigated how nutrient stoichiometry interacts with the availability of labile carbon to control nutrient uptake. We hypothesized that 1) the carbon, nitrogen, and phosphorus (C:N:P) ratio in DOM affects nutrient uptake due to stoichiometric constraints on autotrophic and heterotrophic nutrient assimilation, and 2) labile DOM affects nutrient uptake by increasing heterotrophic production. We tested these hypotheses using a series of instantaneous nutrient additions with a factorial design manipulating both C:N:P ratios and DOM source (acetate or birch leaf leachate) in nine headwater streams in interior Alaska. We added N and P (as NH4+ and PO43-) alone, simultaneously, and in combination as DOM. Uptake velocities (<i>V<sub>f-amb</sub></i>) for C, N, and P were within the upper range of literature values from other ecosystems, ranging from 4.1 &ndash; 67.2 mm/min for N, 4.0 &ndash; 25.0 mm/min for P, and 4.2 &ndash; 34.5 mm/min for acetate. <i>V<sub>f-amb</sub></i> was in part explained by ambient stream chemistry, with N <i>V<sub>f-amb</sub></i> weakly positively correlated with ambient P concentration, while uptake velocity for SRP and acetate was weakly negatively correlated with ambient inorganic N and ambient dissolved organic carbon (DOC), respectively. In addressing our nutrient stoichiometry hypothesis, we found uptake efficiency (UE) was similar for N and P added alone, in co-additions, and with DOM. For our labile DOM hypothesis, acetate and birch-derived DOM had similar effects on N and P UE during in-stream additions. During laboratory incubations both carbon sources were very labile with &ge; 70% of acetate and birch-DOM mineralized over 30 days. Overall, our results were inconclusive as to whether DOM stoichiometry or source affected uptake, but the addition of inorganic nitrogen increased DOC loss from birch DOM. High demand for nutrients in boreal forest headwater streams suggests that uptake could increase concurrently with greater inorganic nutrient flux following a loss in permafrost extent, and that response in stream nutrient uptake is relatively flexible to changes in DOM source and nutrient stoichiometry.</p>
3

VARIATIONS IN ORGANIC GEOCHEMISTRY OF ANOXIC-OXIC BLACK SHALE - CARBONATE SEQUENCES IN THE PENNSYLVANIAN OF THE MIDCONTINENT, USA (KANSAS, OKLAHOMA)

WENGER, LLOYD MILLER, JR. January 1987 (has links)
Two cores containing thin organic-rich phosphatic black shale members, the Excello and Little Osage shales, and transitional lithologies from Pennsylvania cyclothems of southeast Kansas and northeast Oklahoma were characterized by geochemical and organic petrographic methods by very detailed sampling. Variations in relative amount of primary organic material, i.e. liptinitic versus humic, exerts a major control on the nature and quality of the organic profiles. Organic petrography, Rock-Eval pyrolysis, n-alkane and isoprenoid distributions, and C$\sb{27}$/C$\sb{29}$-sterane ratios indicate that shallow-water, more oxic facies (e.g. fossiliferous shales and limestones) contain dominantly terrestrial organic matter while "deep" water phosphatic organic-rich black shales contain significant proportions of marine algal organic matter. Pyrolysis Transformation Ratios ${\rm (S\sb 1/S\sb 1 + S\sb 2)}$ were lower for facies with significant marine components sugesting differential kinetics of bitumen generation for marine versus terrestrially-derived kerogen. Vitrinite reflectance (%R$\sb{\rm o}$) values were suppressed in liptinite-rich anoxic black shale facies relative to the coal "benchmark." Anoxia levels varied within the sequences and had significant influence on several geochemical parameters. Oxidized facies, although having low total organic carbon (TOC) contents, tended to have increased TOC-normalized bitumen and hydrocarbon contents and increased diasterane/normal sterane ratios. Anoxic facies had higher TOC and bitumen contents, contained larger proportions of non-hydrocarbon extractables, and had lower diasterane/normal sterane ratios than oxidized facies. Highly (negatively) fractionated $\delta\sp{34}$S values for pyrite (and polar bitumen) in organic-rich black shale facies indicates extensive open-system sulfate reduction operated during diagenesis. Enrichment of V and Ni, and especially an increasing V/Ni + V ratio, coincide with increased anoxia. A reversal of conventional "terrestrial lighter than marine organic matter" carbon isotope relationships in organic-rich black shales was linked to utilization of isotopically-light "recycled CO$\sb 2$", derived from organic matter decomposition. Eustatic sea level rise and rapid transgression over the craton, with flooding of adjacent brackish-marine (peat) swamps and resultant influx of large supplies of nutrients and humic detritus, appears to be the key geologic control of black shale deposition. The nutrients fostered high algal productivity while terrestrially-derived organic matter provided a sink for oxygen which enhanced anoxia.
4

Assessing the relationship between soil reduction and methane emission in Texas rice fields

Lewis, Sandra Tracey January 1995 (has links)
Reduction processes and methane emissions have been observed in six rice fields along a sand-clay-silt gradient for one growing season. Variations in reduction processes occurred by depth and upon field draining, as well as among fields of differing soil sand content. Analysis at four 2.5 cm-intervals revealed that greater microbial activity appears to be occurring close to the surface of the soil, and decreases with depth. This may be due to greater substrate availability through decomposition of organic matter from roots and dead plant material at that location. Also, it was observed that the re-entry of oxygen upon field draining decreases the amount of reduction occurring, as well as the levels of methane emitted. In this study, greater amounts of emitted methane were measured from the sandy soil extreme. Reduction processes, however, were found to be similar in both clayey and sandy soils.
5

Carbon-13/carbon-12 ratios in surface water and sea ice organic matter-variability and contributions to the sediments of the Ross Sea, Antarctica

Rogers, Jennifer Carol January 1995 (has links)
Elemental and carbon isotopic analyses of suspended and sea ice particulate organic matter (POC) from Antarctica show enrichments in $\sp{13}$C unrelated to atmospheric CO$\sb2$ variations. Phytoplankton bloom-related POC from the southwestern Ross Sea during 1992 had a range in $\delta\sp{13}$C of 7$\rm\perthous.\ \delta\sp{13}C\sb{POC}$ collected from pack ice had an 11$\rm\perthous$ range, with highest values found in the Bellingshausen and Amundsen Seas and lower values found in Ross Sea pack ice. Organic matter $\delta\sp{13}$C from phytoplankton blooms in the southwestern Ross Sea is strongly correlated with POC concentration, suggesting high rates of bloom-related CO$\sb2$(aqueous) drawdown that may cause disequilibrium as a result of stable stratification of the upper water column and partial isolation of the surface water CO$\sb2$ pool. Isotopic and organic carbon composition of surface sediments is similar to the upper water column, thus primary isotopic signals are preserved. Surface sediment $\delta\sp{13}$C values are 1 to 3$\rm\perthous$ enriched in $\sp{13}$C relative to surface water POC $\delta\sp{13}$C. Highest isotopic values were found in areas that receive large amounts of phytoplankton bloom detritus. Future downcore carbon isotopic analyses may prove useful as tracers of bloom dynamics and sea ice production.
6

Interactions between suspended sediments, nutrients and freshwater inflow in Texas estuaries

Paudel, Bhanu 07 October 2014 (has links)
<p> The objectives of the present study were to identify the effects of freshwater inflow (FWI) on sediment transport and nutrients supply to estuaries, and the effects of sediments on nutrient supply at sediment-water interface. The Nueces River and its estuary, the Guadalupe River and its estuary, and the Lavaca-Colorado Estuary were selected for field studies. Laboratory experiments were conducted to test the study hypotheses, and data was analyzed using multivariate modeling and statistical approaches. </p><p> In the Guadalupe Estuary, variability of suspended solids and nutrients were correlated with FWI, whereas in the Nueces and Lavaca-Colorado Estuary they were related with seasonal differences. Suspended solids in the estuaries increased during frontal events and during windy days. In some of the field samplings, stations closer to the Gulf of Mexico had higher suspended sediments than the stations closer to the river. The increase in suspended sediments increased ammonia concentration in the Guadalupe Estuary, phosphorus and silicate concentrations in the Nueces Estuary, and silicate concentration in the Lavaca-Colorado Estuary. The presence of silicate minerals in the estuaries maintains silicate concentration as well. Organic matter and calcium carbonate shells in sediments of the estuaries can bind phosphate, thus, may have played role in decreasing phosphate concentration in the water. Guadalupe River sediments, when transported to the estuary, can release ammonia at higher concentrations the river water concentration. Salinity in the estuary, thus, has a significant role in controlling nutrient concentrations. </p><p> The release of ammonia by organic matter decomposition was lower in the Guadalupe Estuary than in the Nueces Estuary. The high inflow volumes in the Guadalupe Estuary may have washed away organic matter from the sediments and may have disturbed bacterial community resulting in the lower release of ammonia from Guadalupe Estuary sediments. The research performed here demonstrates the importance of sediments, organic matter, and inflow in maintaining nutrient concentrations in estuaries. Fluctuation of these nutrients can affect water quality, and hence, may influence the ecology of the estuary.</p>
7

Exploring the controls on the cycle of carbon in the Ross Sea, Antarctica

Tagliabue, Alessandro. Unknown Date (has links)
Thesis (Ph.D.)--Stanford University, 2006. / (UMI)AAI3235361. Adviser: Kevin R. Arrigo. Source: Dissertation Abstracts International, Volume: 67-09, Section: B, page: 4933.
8

High-resolution biogeochemical study of organic-rich sediments from the Early Aptian oceanic anoxic event at Shatsky Rise, ODP Leg 198

Dumitrescu, Mirela. January 2006 (has links)
Thesis (Ph.D.)--Indiana University, Dept. of Geological Sciences, 2006. / Title from PDF t.p. (viewed Nov. 18, 2008.) Source: Dissertation Abstracts International, Volume: 67-12, Section: B, page: 6959. Adviser: Simon C. Brassell.
9

Carbon, nitrogen and phosphorus additions to a temperate hardwood forest effects on below ground processes /

Smith, Candice M. January 2008 (has links)
Thesis (Ph.D.)--Indiana University, School of Public and Environmental Affairs, 2008. / Title from PDF t.p. (viewed on Oct. 7, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 0900. Adviser: J. C. Randolph.
10

Controls on dissolved organic carbon at Hubbard Brook Experimental Forest and its effects on stream acid-base chemistry

Wellington, Brian Ishmael. January 2002 (has links)
Thesis (Ph. D.)--Syracuse University, 2002. / "Publication number AAT 3065205 "

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