River water humic substances, isolation

Sample Preparation of Foam and Water Samples and Humic Substances Isolation. All foam and water samples were filtered through 0.45- Lim silver filter using stainless-steel filtration units. Silver filtration of Como Creek and Suwannee River foam samples resulted in build up of a brown extract on the filter paper, which was readily solubilized in 0.1 N sodium hydroxide. This extract was refiltered through silver filters as a sodium hydroxide solution. This fraction was believed to be colloidal in nature and was treated as a separate humic fraction, called the "foam-extract" fraction. A part of the filtered foam was freeze dried directly and considered "raw" foam. Fulvic and humic acids were isolated from foam and stream-water samples via the XAD-8 adsorption technique developed by Thurman and Malcolm (77), freeze dried, and weighed. To obtain a sufficient mass of humic substances, each entire sample was used for one extraction. As multiple samples were not extracted, calculation of the error associated with humic substances isolation cannot be made, and the contributions of humic substances to the DOC content must be regarded as estimates. 

Based on comparison of data from UV, fluorescence, and NMR spectroscopy, and from carbon isotope determination for humic substances isolated from coastal and open ocean environments, the authors have concluded the following (1) other than its metal complexation and redox functions, the only resemblance between humic substances from open ocean (marine) and terrestrial environments is that they are both colored organic acids soluble in water, and (2) marine humic substances are formed in situ and only in the coastal zone is there an admixture of terrestrially derived humic substances from rivers. However, this second conclusion has not yet been reconciled with the observations discussed by Mayer in Chapter 8 that riverine humic... 

The NEXAFS spectroscopic studies conducted on Cl functional groups of humic substances isolated from soils, sediments and river waters showed an intense feature at... 

Figure 46. Is NEXAFS spectra of Cl in humic substances isolated from river water, soils, peat and lignite (taken from Myneni 2002). HA humic acid HA, FA fulvic acid. Different spectra represent (A) Suwannee River FA, (B) Suwannee River HA, (C) soil FA, (D) soil HA, (E) Lake Fryxell FA, (F) peat HA, (G) peat FA, and (H) Leonardite HA.

An extraction method for isolating humic substances from water by using XAD-8 has been proposed by Thurman and Malcolm (9) (see box). Humic substances in natural waters represent almost the entire hydrophobic acid fraction. This method has been used to isolate 4.25 g of humic substances from 24,500 L of ground water from the Fox-hills-Laramie aquifer and to obtain 500 g of humic material from 10,400 L of the Suwannee River (Table II). The sample from the Suwannee River was collected as a reference sample of aquatic humic substances by the International Humic Substances Society. In both of the examples cited, a fc cutoff of 100 was used. 

Little work has been done to compare the nature of ligands in riverine, estuarine, and coastal waters. Preston (1979) found similar selectivity coefficients for copper with humic compounds isolated from different salinity regimes of the Tamar estuary. His results are made uncertain by lack of knowledge of the molecular weights of the compounds, but it appeared that the selectivity for copper decreased with increasing salinity. The stability constant data of Mantoura et al. (1978) also show similar selectivities for copper by aquatic humic substances from river, lake, and marine waters, which would imply that little variation in selectivities should be found along an estuarine salinity gradient. 

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