Streams fulvic acid from

FIGURE 3. The cross-polarization, magic-angle-spinning, solid-state "C NMR spectrum of stream fulvic acid from the Ogeechee River near Louisville, Georgia during December 1981. 

Klenke et al. [5] described a technique for extraction of humic and fulvic acids from stream sediments and outlined methods for their determination. By means of flame atomic absorption spectrometry, the levels of environmentally important heavy metals (cadmium, copper, chromium, cobalt, nickel and lead) in the fulvic and humic acid extracts were compared with those in the original sediment samples. The pattern distribution of the respective metals in the two cases showed very close agreement, suggesting that the combined extract of humic and fulvic acids could be used as an indicator of the level of heavy metal pollution in flowing waters. 

We found consistent differences in the fluorescence properties of fulvic acids from streams where fulvic acids are terrestrially derived and from lakes where fulvic acids are microbially derived (McKnight et al., 2001). The upper maximum in microbially derived samples is more sharply defined and... 

NMR. Quantitative liquid-state carbon-13 nuclear magnetic resonance ( 3c NMR) spectra were recorded for humic and fulvic acid from Como Creek foam and for stream and foam fulvic- and humic- acid samples from the Suwannee River at the U.S. Geological Survey, laboratory in Arvada, CO. C NMR could not be performed on other humic substances due to insufficient sample or instrument availability. The acquisition parameters used were as follows C NMR spectra were recorded on a Varian XL-300 NMR spectrometer at 75 MHz. Each sample (200 mg of freeze-dried material) was dissolved in deuterated water and deuterated sodium hydroxide was added to ensure solution a total solution volume of approximately 6 to 7 mL. Spectra were recorded using a 30,000 Hz spectral window, a 45 pulse width, a 0.199 second acquisition time, and a pulse delay of 10 seconds for quantitative spectra. The number of transients was 10,000, and line broadening was 50 Hz. 

Titration Measurements. The carboxyl and phenolic hydroxyl content of humic and fulvic acids from stream, foam, and foam-extract samples was determined by titration using carefully calibrated O.IN sodium hydroxide. Briefly, 20 mg of freeze-dried sample were dissolved in 10 mL of distilled water, then titrated to pH 8.0 and pH... 

Although visually the C NMR spectra of stream and foam humic substances from Como Creek and Suwannee River samples appear quite different from one another (e.g., broader, smoother peaks for all Suwannee samples), the quantitative contributions of each spectral region are comparable between the sampling sites. In particular, the fulvic acids from Como Creek and Suwannee River foam samples show great similarities, as do foam humic acids. This would indicate that, in terms of general aliphaticity and aromaticity between the two sites, the foam humic substances are comparable. 

From a practical standpoint, stream fulvic acids which comprise over 90% of the stream humic substances are not an important food source for aquatic organisms, but all stream humic and fulvic acids are positive influences on biological growth in respect to phosphorus and nitrogen nutrient cycling, trace metal availability, and limiting potential metal toxicity. 

FIGURE 3 Depth profiles for 14C age and sulfur-to-carbon (S/C) ratios for fulvic acid samples isolated from Lake Fryxell, a permanently ice-covered lake in the McMurdo Dry Valleys, Antarctica (from Aiken et al., 1996). In the upper water column, the fulvic acids have a modern signal. This young fulvic acid derives from perennial algal mats in glacial meltwater streams. At depth, the fulvic acids are quite old (about 3000 years) and are possibly derived from organic material in sediments. The ratio of S/C increases with depth as conditions in the water column become anoxic. 

The photodegradation of an aqueous solution of terbuthylazine was not only accelerated, but was also more extensive in the presence of humic acids isolated from soil (Mansour et al., 1997). In the absence of humic acids, only hydroxyterbuthylazine (OBET) was formed (Sanlaville et al., 1996), whereas in the presence of humic acids, dealkylated products (CBAT, CBDT, CEAT, CAAT, OAAT) were formed (Table 23.2) (Sanlaville et al., 1996 Mansour et al., 1997). In contrast, fulvic acids isolated from stream water slowed the photolysis of terbuthylazine, most likely reflecting differences in structure between the soil- and stream-derived materials. The photodegradation of atrazine and its initial photoproduct OEIT (Table 23.2) in artificial sea water containing humic acids was also accelerated compared to photolysis in distilled water (Durand et al., 1990,1991). 

Lignin Analysis. Lignin present in fulvic and humic acids from stream, foam, and foam-extract samples from Como Creek and the Suwannee River were oxidized to phenolic oxidation products by copper oxide oxidation via the method described by Hedges and Ertel (24). These phenolic oxidation products then were derivatized to trimethyl silyl derivatives for GC/MS analysis. 

Fulvic and humic acids from Como Creek and Suwannee River stream samples contained phenolic hydroxyl contents within the typical range shown in Table V. However, the phenolic hydroxyl content of Como Creek samples was highly variable from stream, to foam, to foam-extract fractions and between fulvic and humic acids, and did not show any clear trends. Suwannee River foam samples were much more uniform in concentration between stream, foam, and foam-extract fractions, with humic acids consistently higher than fulvic acids in all samples. The variable phenolic hydroxyl content of Como Creek samples and lack of clear trends compared to the more consistent content of Suwannee River samples indicates that in contrast to carboxyls, the phenolic hydroxyl moiety may not play a very important role in controlling surface activity or in affecting foam formation. 

Table VI. NMR integration results (reported as a percentage of peak area) for fulvic and humic acids from stream and foam...

Surface Activity Measurements. The surface activity displayed by solutions of humic substances and raw foam samples from Como Creek and Suwannee River stream and foam samples was compared to the surface activity of an impure standard of commercial surfactant sodium dodecyl sulfate (SDS) and surface-tension measurements for both sites are shown in Figures 3a and 3b. Como Creek raw foam and foam-extract humic acid showed the greatest surface activity, with foam humic acid contributing to a lesser extent (Figure 3a). In contrast, Como Creek foam and foam-extract fulvic acid and stream humic substances showed little surface activity. Fulvic and humic acids from Suwannee River foam and foam extract showed comparable surface activity to the raw foam, and all samples were less surface active than the SDS (Figure 3b). Stream humic substances showed little surface activity and were comparable to Como Creek stream humic substances. 

Summary of Biomarker Analyses. The combination of phospholipid fatty acids, steroids, and lignin phenols indicates that the chemical makeup of raw foam includes input from bacterial, algal, diatoms, fungal, and higher plant sources. The total of these compounds account for less than 5% of the organic carbon present in raw foam, and it is not possible, therefore, to assess which is the largest source. These compounds however, do reveal interesting compositional trends between the raw foam and the stream and foam humic substances. The compositional complexity of humic substances increases from stream, to foam, to foam extract and from fulvic acids to humic acids. 

A third issue is that even though the soil is one source of stream humic substances, it is not necessary that soil and stream humic substances have the same composition. If they were of the same composition, then stream humic substances would be primarily humic acids, because the humic cidjo J fulvic acid ratio in soil is approximately 3 1. However, as previously dis- -cussed in this chapter, stream humic substances are approximately 90% fulvic acids. One may say that fulvic acids are leached from soils in preference to humic acids. This may be true, but no one has shown water leachates of soil to contain fulvic acid of the same composition as in the bulk soil. Beck et al. (1974) state that meteoric waters percolating through soil will selectively mobilize nonrepresentative fractions of the soil organic matter. It should be emphasized that even if stream humic substances are the same as soil humic substances, one can not infer that one is the source of the other, but that the same precursors and humification process are probably operable in both soil and stream environments. 

The first needs no theoretical discussion it merely assumes that stream humic substances consist of soil fulvic acid which has been leached or eroded from soils. 

A third theory speculates that stream humic substances are soil fulvic acids leached from soil in the initial stages of humification and then modified, transformed, or aged by stream humification processes which result in humic substances unique to this aquatic environment. 

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