Author: Hongmei Chen
Publisher:
ISBN:
Category : Electrodialysis
Languages : en
Pages : 344

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Author: Xiaping Li
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 73

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The objective of the present study was to provide better understanding of the effects of watershed land use on molecular composition of streamwater DOM and molecular transformations associated with photochemical and microbial processing of DOM. We compared DOM from headwater streams draining forest-dominated watersheds (FW) and pasture-dominated watersheds (PW) in the lower Chesapeake Bay region (Virginia, USA). Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry analysis was conducted on streamwater DOM prior to and after laboratory incubations: 1) bacteria-only incubations; 2) light-only incubations; and 3) combined light+bacterial incubations. Results showed that DOM in FW streams and PW streams differed in molecular characteristics--the former was characterized by greater structural complexity and aromaticity, higher proportions of condensed aromatic molecules and black carbon-like components, while the latter was higher in the proportions of lipid-like components, protein-like components and aliphatic compounds. Relative to DOM from FW streams, DOM from PW streams was more reactive to bacterial transformation. Protein-like components, lipid-like components and unsaturated hydrocarbon-like components are primarily responsible for the changes associated with bacterial transformation of DOM. However, similar behavior was also observed for DOM in FW streams and PW streams under the influence of bacterial and photochemical processes. Bacterial transformation reduced the proportions of lipid-like components but increased the proportions of lignin-like components and carboxyl-rich alicyclic molecule-like components, indicating that lipid-like components was a bioreactive class while lignin-like components and carboxyl-rich alicyclic were resistant to bacterial processing. Photochemical processes, alone or combined with microbial alterations, increased the proportions of protein-like components, which may be due to the light stimulation of autochthonous production of protein-like components, and increased the relative abundance of carboxyl-rich alicyclic molecule-like components, which indicates the refractory nature of these molecules. Photochemical processes also significantly reduced the amount of dissolved black carbon-like components, which suggests dissolved black carbon was a photoreactive class, countering the conventional view that black carbon was an inter group in carbon cycle. Collectively, these findings suggest that human land use in upstream watersheds may lead to alterations to the molecular composition of streamwater DOM as well as to its behavior to photochemical and microbial processing.

Author: John Robert Helms
Publisher:
ISBN:
Category : Carbon cycle (Biogeochemistry)
Languages : en
Pages : 438

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Author: Jasper Daniel Hendrik van Heemst
Publisher:
ISBN:
Category : Seawater
Languages : en
Pages : 178

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Author: N. Handa
Publisher: Springer Science & Business Media
ISBN: 9401713197
Category : Science
Languages : en
Pages : 561

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Over the past decade the scientific activities of the Joint Global Ocean Flux Study (JGOFS), which focuses on the role of the oceans in controlling climate change via the transport and storage of greenhouse gases and organic matter, have led to an increased interest in the study of the biogeochemistry of organic matter. There is also a growing interest in global climate fluctuations. This, and the need for a precise assessment of the dynamics of carbon and other bio-elements, has led to a demand for an improved understanding of biogeochemical processes and the chemical characteristics of both particulate and dissolved organic matter in the ocean. A large amount of proxy data has been published describing the changes of the oceanic environment, but qualitative and quantitative estimates of the vertical flux of (proxy) organic compounds have not been well documented. There is thus an urgent need to pursue this line of study and, to this end, this book starts with several papers dealing with the primary production of organic matter in the upper ocean. Thereafter, the book goes on to follow the flux and characterization of particulate organic matter, discussed in relation to the primary production in the euphotic zone and resuspension in the deep waters, including the vertical flux of proxy organic compounds. It goes on to explain the decomposition and transformation of organic matter in the ocean environment due to photochemical and biological agents, and the reactivity of bulk and specific organic compounds, including the air-sea interaction of biogenic gases. The 22 papers in the book reflect the interests of JGOFS and will thus serve as a valuable reference source for future biogeochemical investigations of both bio-elements and organic matter in seawater, clarifying the role of the ocean in global climate change.

Author: Christopher L. Osburn
Publisher: Frontiers Media SA
ISBN: 2889450813
Category :
Languages : en
Pages : 244

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A substantial increase in the number of studies using the optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) as a proxy for its chemical properties in estuaries and the coastal and open ocean has occurred during the last decade. We are making progress on finding the actual chemical compounds or phenomena responsible for DOM’s optical properties. Ultrahigh resolution mass spectrometry, in particular, has made important progress in making the key connections between optics and chemistry. But serious questions remain and the last major special issue on DOM optics and chemistry occurred nearly 10 years ago. Controversies remain from the non-specific optical properties of DOM that are not linked to discrete sources, and sometimes provide conflicting information. The use of optics, which is relatively easier to employ in synoptic and high resolution sampling to determine chemistry, is a critical connection to make and can lead to major advances in our understanding of organic matter cycling in all aquatic ecosystems. The contentions and controversies raised by our poor understanding of the linkages between optics and chemistry of DOM are bottlenecks that need to be addressed and overcome.

Author: Marc Einsporn
Publisher:
ISBN:
Category :
Languages : en
Pages : 102

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Zeitungsausschnitte.

Author: Johanna Sjöstedt
Publisher: Frontiers Media SA
ISBN: 2889711021
Category : Science
Languages : en
Pages : 255

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Author: Xianyu Kong
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Dissolved organic matter (DOM) in the ocean is a complex mixture of molecules derived from autochthonous (marine) or allochthonous (terrestrial) origins. DOM plays an important role in marine biogeochemical cycles by attenuating light available for primary production, serving as an energy and nutrient source for heterotrophic communities, regulating the ultraviolet and visible light absorption, undergoing photochemical processing, and acting as a trace metal ligand. DOM in the Central Arctic Ocean (CAO) is influenced by increased freshwater input and associated terrestrial materials in recent decades due to rapid climate change. The quantification of DOM sources (terrestrial versus marine) in the water column of the CAO is not well constrained. Few studies have systematically investigated the seasonality and spatial variability of DOM by combining optical and molecular-level analytical techniques in the CAO, especially during winter. State of the art chemical characterization of DOM is subject to major challenges: Solid phase extraction (SPE) that is often used to desalt and pre-concentrate marine DOM introduces chemical fractionation effects, which limits the comparability between analytical results for original samples and those carried out for SPE-DOM. There is no specific method to quantify fractionation effects, nor specific guidelines to avoid fractionation. Using mass spectrometry, quantitative DOM analyses is challenged by selective ionization of molecules and the large number of unresolved structural isomers that prevent classical external calibration. In the first part of this thesis, a method was developed to quantitatively track optical or chemical fractionation during SPE and investigate the potential mechanisms. We found a decrease in extraction efficiency of dissolved organic carbon (DOC), fluorescence and absorbance, and polar organic substances with increasing carbon loading on the SPE column. As the surface loading of the solid-phase increased, the dominant extraction mechanism shifted from PPL physisorption to increased DOM self-assembly, resulting in optical and chemical fractionation. The relative DOC loading (DOCload) was used to assess the carbon loading during SPE, and a double sigmoid model was applied to our online permeate fluorescence data as a function of DOCload, which allowed us to assess the degree of variability induced by DOCload. This finding has ample implications for the future processing and previous interpretation of chemical characteristics in SPE-DOM of aquatic organic matter. For the second part of the thesis, original water samples were acquired from the “Multidisciplinary Drifting Observatory for the Study of Arctic Climate” (MOSAiC) expedition. The water column samples covered a full year (2019 / 2020) and included the regions Amundsen Basin, western Nansen Basin and Yermak Plateau and Fram Strait. Samples were analyzed using optical spectroscopy to determine chromophoric DOM (CDOM) and fluorescent DOM (FDOM). In addition, a new method was applied that used Fourier transform ion cyclotron resonance mass spectrometry hyphenated to high performance liquid chromatography (LC-FTMS). The method allowed DOM analysis in original filtered water and thus avoided the chemical fractionation introduced by SPE. During the MOSAiC expedition, DOC concentrations and CDOM characteristics in the water column were primarily influenced by regional differences. These differences were largely dependent on terrestrially-derived DOM (tDOM) input by the transpolar drift (TPD) as indicative of average 136% and 45% higher aCDOM(350) and DOC concentration, respectively, in the Amundsen compared to the western Nansen Basin and Yermak Plateau, and slightly modified by seasonal changes. Despite the convenient identification of tDOM, optical spectroscopy was not suitable to quantify the contribution of tDOM to bulk DOC or to track sea ice derived DOM in the water column. In contrast, using LC-FTMS, we found quantitative linear correlation between the summed mass peak magnitudes for each sample (intsum) and DOC concentration. By combing LC-FTMS and source identification with optical parameters, we were able to quantify DOM sources (terrestrial versus marine) in the water column: 83% of the summed peak magnitude of all samples could be related to marine or terrestrial sources. tDOM contributed ∼17% (or 8 μmol kg-1) to deep DOC (~2000 m) in the CAO and was more refractory and had a higher state of unsaturation compared to marine DOM. The quantitative characterization of DOM in original seawater from different origin is a major step in the field of research. It provides a unique and new insight into the molecular changes in marine DOM composition and an improved understanding of the terrestrial DOM distribution in the CAO.