Marine humic extraction

Further work on differentiating marine and coastal runoff humic substances was hindered by the lack of suitable isolation techniques for the marine material since concentrations in the open sea rarely exceed 0.25 mg/ L. Sorption of marine humic substances from seawater onto solid phases is now a standard technique and can be used to extract gram quantities of marine humic substances for chemical and physical studies (see Aiken, Chapter 14). Sieburth and Jensen (1968) first used rolled nylon stockings as an adsorbant but the method suffered from contamination. Kerr and Quinn (1975) used a specially treated charcoal and obtained quantitative recovery of the dissolved colored substances in seawater. Riley and Taylor (1969) introduced the use of cross-linked polystyrene resins, specifically Amberlite XAD-2. This polymer is now the most widely used for open-ocean work (Stuermer and Harvey, 1974 Bada et al., 1982 Harvey et al., 1983) and in estuaries (Mantoura and Riley, 1975). These isolation methods have made available sufficient quantities of seawater humic substances for detailed chemical studies. 

The natural marine fulvic acid and marine humic acid were removed from 10 L of seawater with XAD-2 resin (Harvey et al., 1983). After readjusting the pH to 8.2, 5 mg of one of the particular lipids was added to the column effluent every half hour, with stirring, up to a total of 5 mg/L. The solution was allowed to stir for 1, 2, or 7 days, depending on the starting material. The solution was then acidified to pH 2 and extracted as above with XAD-2. The yield of product was 50-100 mg. 

A variety of spectroscopic techniques have been applied to DOC isolated from seawater by cross-flow ultrafiltration or adsorption onto XAD resins. The two techniques isolate very different organic fractions from seawater. Hydrophobic fractions (such as marine humic material) are isolated on XAD resins [48], whereas the organic matter extracted by ultrafiltration is retained primarily on the basis of its molecular size and shape [49], resulting in isolates rich in nitrogen and carbohydrates (polysaccharides). Nuclear magnetic resonance (NMR) spectroscopy has proven successful in distinguishing between the specific structures of XAD-bound humics and the carbohydrates concentrated into colloidal size fractions. 

The structural features of the COC isolated by ultrafiltration are very different from the structure of marine humics. Solid-state C NMR spectra of COC reveal a predominance of oxygen-substituted alkyl carbons that are characteristic of carbohydrates [15]. The NMR spectra also indicate that 11 )iM C (about half) of the COC in surface water is associated with polysaccharides [4] in deep water, only 2.2 pM C is COC associated with polysaccharides. A five-fold decrease in carbon associated with carbohydrates is a strong indication that a major fraction of DOC is cycled in the upper ocean [15]. At this point, however, it should be stressed that ultrafiltration recovers between 10 and 40% of the carbon in DOC [4, 6]. There is still a large fraction (60-90%) of marine DOC that cannot be identified, although Benner [4] has speculated that between 30 and 50% of DOC could be recovered from seawater using a combination of ul-trafiltration and XAD extraction. 

Gillam and Wilson (1983) and Harvey et al. (1984) have performed model studies directed toward the synthesis of marine humic material from its assumed precursor compounds, metabolites from planktonic algae. Gillam and Wilson extracted lipid-soluble materials from a large quantity of the diatom Phaeodactylum tricornutum and compared the humic fraction of the extract to a humic material from coastal... 

Soils in Uzbekistan have an average Co of 17 mg/kg. Total Cu in humic soils is in the range of 18-22 mg/kg, and total Zn is 83 mg/kg. In subdesert soils formed on loessial clayey loams and saline alkali soils, total Mo is 2.6-4.5 mg/kg, and Mo in some soils is as high as 8 mg/kg. Total Zn in subdesert soils varies from 60-112 mg/kg. Sodium acetate-extractable Zn in these subdesert soils is 2.1-3.2 mg/kg, accounting for 2.3-5.1% of total Zn. In saline alkali soils formed on loess and marine clays, total B content is 160 mg/kg. The exchangeable Mn in arid and semi-arid soils is 7-50 mg/kg, accounting for 0.7-7.8% of total Mn. Saline soils in the Ustyurt region contain 42-80 mg/kg of Pb. 

Magni et al. [857] studied the optimisation of the extraction of metal-humic acid complexes from marine sediments. Polyarylamide gels have been... 

Pierce RH Jr, Felbeck GT Jr (1972) A comparison of three methods of extracting organic matter from soils and marine sediments. In Povoledo D, Golterman HL (eds) Humic Substances. Center for Agriculture Publication and Documentation, Wageningen, Netherlands, pp 217-232... 

Pontanen and Morris [8] compared the structure of humic acids from marine sediments and degraded diatoms by infrared and C13 and proton NMR spectroscopy. Samples of marine sediments taken from the Peru continental shelf were extracted with water, sodium hydroxide (0.05mol 1 J) and sodium pyrophosphate (0.05mol l-1) under an atmosphere of nitrogen and fractionated by ultrafiltration. Humic acids of molecular weight 300000 and above were examined. Diatoms were collected from... 

At present, soil derived humic matter and fulvic acids extracted from freshwater are available commercially and are commonly used to test techniques for DOM detection and also used as model compounds for trace metal chelation studies. The results obtained using these model compounds are frequently extrapolated to the natural environment and measurements on "real" samples provide evidence that this DOM is a good model compound. In the past, some investigators also made available organic matter isolated from marine environments using C18 resins. While these compounds come from aquatic sources, this isolation technique is chemically selective and isolates only a small percentage of oceanic DOM. Reference materials are not currently available for these compounds, which inhibits study of the role they play in a variety of oceanographic processes. 

Laane, R.W.P.M. and Kramer, C.3.M., 1984. Complexation of Cu + with humic substances in relation to different extraction procedures of sandy and silty marine sediments. In C.3.M. Kramer and 3.C. Duinker (eds), Complexation of Trace Metals in Natural Waters. Nijhoff/3unk Publ., the Hague, pp. 345-348. 

E. Magi, T. Giusto, R. Frache, Humic acids in marine sediments an extraction procedure for the determination of the complexed metals. Anal. Proc., 32 (1995), 267-269. 

In addition to direct extraction of humic substances, the amount of humic substances has been estimated by subtracting the amount of biochemicals (sum of lipids, amino acids or proteins, and carbohydrates) from the total organic matter in the sediments (Kemp and Johnston, 1979). In this chapter, this difference is called nonbiochemicals, although no doubt there is much overlap between nonbiochemicals and extracted humic substances. As shown in Table 2, nonbiochemicals amount to 42-58% of the total organic matter in two Japanese lake sediments, but in the Great Lake (North America) sediments nonbiochemicals amount to 70-79% of the total organic matter on average. The latter values are close to those observed for marine sediments (Ishiwatari, 1979). 

Extraction of Humic Substances from Marine Sediments... 

The amounts of hydrolyzable organic matter and humic substances extracted by alkaline aqueous solutions decrease with the burial depth of a sediment. This is demonstrated by Hue et al. (1980) on Black Sea sediments where the organic matter is mainly autochthonous (Fig. 12). Boudou (1981), who studied diagenesis of terrestrial organic matter deposited in marine deltaic sediments, also noted this decrease (Table 8). The amount of hydrolyzable organic matter decreases very rapidly as a function of depth. Humic substances disappear more slowly, and their decrease can be followed dur-... 

In this chapter, we consider humin to be the residue after successive extraction of sediments by benzene/methanol to remove lipids, dilute acid IN HCl), and 0.5N NaOH. In marine sediments, further treatment with concentrated HF/HCl (1 1 v/v) is required to concentrate the organic matter by removal of mineral matter. This treatment will partially or totally hydrolyze polysaccharides and proteins while probably having little effect on the humic material (Hatcher et al., 1983a). 

The study of humic substances by nuclear magnetic resonance of the isotope and the proton suggests that aliphatic structures prevail over aromatic structures for the fulvic acids extracted from marine water, contrary to the case for soil fulvic acids. The high values of the H C ratio in marine fulvic acids also point to an aliphatic nature (Stuermer and Payne, 1976). 

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