Aquatic humic substances dissolved organic matter

The combination of analytical pyrolysis, molecular modeling, and computational chemistry has also been stressed in investigating the structure of HS. It was reported that computational chemistry which allows to draw, construct and optimize in 3D space biomacromolecules, e.g., aquatic and terrestrial humic substances, with precise bond distances, bond angles, torsion angles, nonbonded distances, hydrogen bonds, charges, and chirality is a powerful tool, and molecular visualization and simulation can also be used to further understand the structure and dynamics of humic and dissolved organic matter. 

Benner, R. H. 1998. Cycling of dissolved organic matter in the ocean. In Aquatic Humic Substances (D. O. Hessen and L. J. Tranvik, Eds.), pp. 317—331. Springer-Verlag, Berlin. 

For decades in aquatic ecology, the apparent chemical recalcitrance of humic substances that dominated the instantaneous bulk DOC of standing and running waters led to the belief that these compounds were poorly used by microbiota. To be sure, loss rates are slow, but consistently in the range of 0.5-2% per day under many different environmental conditions (Fig. 2). Often rates of degradation of total dissolved organic matter are greater than 2% per day. 

Direction 6. Less direct but important biogeochemical interactions of dissolved organic matter in aquatic systems are also important but poorly studied at the ecosystem level. Continued intensive study of natural dissolved organic substances in aquatic ecosystems is also resulting in improved understanding of the many ways in which these diverse compounds, particularly humic compounds, can interact with other important metabolic components. For example, dissolved organic compounds can function in the following ways ... 

Humic substances represent a large fraction of what is termed chromophoric dissolved organic matter (CDOM) in aquatic systems around the world. Aquatic humic substances can be further categorized as fulvic acids, humic acids, and humin based on theis solubility in acid and base solutions. 

Tranvik, L.J. (1998) Degradation of dissolved organic matter in humic waters by bacteria. In Aquatic Humic Substances Ecology and Biogeochemistry (Hessen, D.O., and Tranvik, L.J., eds.), pp. 259-278, Springer-Verlag, New York. 

Schulten H.-R. (1999) Analytical pyrolysis and computational chemistry of aquatic humic substances and dissolved organic matter. J. Analyt. Appl. Pyrol. 49, 385-415. 

Tremendous work has been done on the characterization of humic substances in the aquatic environment (2,19,20) and much analytical data on the concentration of humic substances in natural waters is reported (2,21- 5). Special attention has been paid to the physico-chemical processes governing behaviour of metals and dissolved organic matter during estuarine mixing (6,26-28). 

Schulten, H.-R. and Gleixner, G., Analytical pyrolysis of humic substances and dissolved organic matter in aquatic systems structure and origin. Water Res., 33, 2489-2498, 1999. 

After T720 was tentatively characterized as an aquated electron with nitrous oxide and electron transfer studies, the quantum yield for the production of the aquated electron In dilute natural waters containing dissolved organic matter and In humic substance extract was measured by the comparlslon method. In this method the literature value for the extinction coefficient of the solvated electron at 720 nm was used (21). The excited state absorption of T720 was measured. These were used In algebraic ratio to an actlnomlter for which a quantum yield had already been thoroughly determined. 

Humin s insolubility obviates its presence in a dissolved organic matter aquatic sample. In aquatic systems, the operational definitions of humic and fulvic acids are stated somewhat differently [4]. Humic acid and fulvic acid are defined by the aqueous solution pH necessary to desorb them from XAD-8 resin fulvic acid can be desorbed with water humic acid is desorbed with an alkaline aqueous solution. However, the defining operational characteristic, solubility in an aqueous solution as a function of pH, is consistent in both operations. Thus, the use of the term fulvic acid in this paper refers to the humic substance fraction soluble in aqueous solution at any pH value, and the term humic acid refers to the humic substance fraction soluble in alkaline aqueous solution but insoluble under acidic conditions. 

Table 2.1. Commonly referenced peak and region locations for components of excitation-emission matrices (EEMs) obtained for aquatic humic substances and dissolved organic matter...

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