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Chemical characterization of high molecular weight dissolved organic matter in fresh and marine waters 总被引：1，自引：0，他引：1
Daniel J. Repeta Tracy M. QuanLihini I. Aluwihare AmyMarie Accardi 《Geochimica et cosmochimica acta》2002,66(6):955-962
The high molecular weight fraction of dissolved organic matter in a suite of lakes, rivers, seawater, and marine sediment interstitial water samples was collected by ultrafiltration and characterized by molecular level and spectroscopic techniques. Proton nuclear magnetic resonance spectra of all samples show a high degree of similarity, with major contributions from carbohydrates, bound acetate, and lipids. Molecular level analyses of neutral sugars show seven monosaccharides, rhamnose, fucose, arabinose, xylose, mannose, glucose, and galactose, to be abundant, and to occur in comparable relative amounts in each sample. Previous studies have emphasized the distinctive composition of dissolved humic substances in fresh and marine waters, and have attributed these differences to sources and transformations of organic matter unique to each environment. In contrast we find a large fraction of freshwater high molecular weight dissolved organic matter (HMWDOM; > 1kD) to be indistinguishable from marine HMWDOM in bulk and molecular-level chemical properties. Aquatic HMWDOM is similar in chemical composition to biologically derived acylated heteropolysaccharides isolated from marine algal cultures, suggesting a biological source for some fraction of persistent HMWDOM. High molecular weight DOC contributes 51 ± 26% of the total DOC, and monosaccharides 18 ± 8% of the total HMWDOC in our freshwater samples. These contributions are on average higher and more variable, but not significantly different than for surface seawater (30% and 16% respectively). Biogeochemical processes that produce, accumulate, and recycle DOM may therefore share important similarities and be broadly comparable across a range of environmental settings. 相似文献
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Dr. Luigi Accardi 《Pure and Applied Geophysics》1952,22(1-2):84-88
Riassunto Viene fatta la descrizione di un nuovo sensibile apparecchio registratore per la misura del campo elettrico atmosferico che offre la possibilità di una registrazione differenziata dei campi positivi e negativi. Vengono presentate inoltre alcune registrazioni di campo elettrico atmosferico nelle più varie condizioni, ottenute col discritto apparecchio nell'Istituto di Fisica Terrestre dell'Università di Napoli.
Summary The Author describes a new highly sensitive recording instrument for the measurement of the atmospheric electric field, which enables a separated registration of the plus and minus fields. Furthermore the author presents some registrations of the atmospheric electric field obtained in the most various conditions at the Institute for terrestrial physics of the University of Naples.相似文献
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