Humic substances from river water

Humic substances from groundwater are considerably less colored per unit of carbon than humic substances from surface water their absorbance at 465 nm (a wavelength commonly used for color in Standard Methods, 1971) is 3-10 times less than the absorbance of humic substances from surface water. Table 6 compares absorbances of humic substances from groundwater with absorbances of humic substances from surface water. Absorbances of samples from the Red River, St. Peters, and Laramie-Fox Hills aquifers are considerably less than absorbances of humic substances from an average surface water. Only the Madison and the Biscayne samples are similar in color to humic substances from surface water. The Biscayne is... 

Unfortunately, only two analyses were performed for carboxyl content of humic substances from groundwater, the Biscayne and Laramie-Fox Hills. The Biscayne has a carboxyl content of 6.3 meq/g and the Laramie-Fox Hills has a carboxyl content of 3.8 meq/g. These values span the range that have been found for humic substances from all natural waters, about 3-7 meq/g (see Chapter 7 on humic substances from rivers). 

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. 

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... 

FLUORESCENCE Spectra. Fluorescence data are presented in Table V. All samples derived from drinking water gave an emission maximum between 417 and 430 nm, whereas the excitation maximum ranged between 346 and 365 nm. Miami IB showed an excitation maximum similar to the CFH samples, but the maximum was quite different from the one exhibited by the aquatic humic substances from the Satilla River. The emission maximum of these samples (Table V), however, was very similar. 

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. 

Because of the considerable potential of titration calorimetry as an analytical technique for characterization of the acidic functional groups of humic substances, our studies have been extended to river water humic substances. In this paper, results are presented for the thermochemical characterization of the acidic functional groups of river water humic substances from two quite different river systems 1) the Satilla River in southeastern Georgia, and 2) the Williamson River in southern Oregon. 

As a first step, adsorption isotherms were determined for a commercially available humic substance and for its humic and fulvic acid fraction. Secondly the adsorption of humic substance from a river water and a marshland water was investigated. 

On the basis of few data from a limited range of geographical areas, it appears that humic substances in estuarine zones exhibit many attributes of the transitional nature of the environment. Aquatic humic substances show concentrations and chemical characteristics intermediate between those found in river and ocean waters, indicating relatively little in situ production, consumption, or chemical change. Sedimentary humic substance concentrations are somewhat higher than are usually found in the ocean, reflecting the high primary productivity and shallow water depths, but are chemically similar to either riverine or oceanic endmembers. The actual nature of estuarine humic substances is poorly known, but this problem is no worse than for humic substances from most environments. 

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.

Calculated equilibrium speciation of (a) mercury and (b) copper during estuarine mixing of hypothetical river water with seawater. Hum, humic substance. Note logarithmic scale on y-axis. Source. From Mantoura, R. F. C., et al. (1978). Estuarine and Coastal Marine Science 6, 387 08. 

Black C, produced by wild fires and humic substances (HS), the natural by products of SOM decomposition in soil and water systems, are certainly the classes of organic compounds that most closely approximate this recalcitrant behavior. HS occur widely, being found in large amounts not only in the soil and sediments but also in lakes, rivers, ground waters, and even the open ocean (Stevenson, 1994). Besides these relatively refractory substances, more labile compounds can persist in soil for a much longer time than would be predicted from their inherent recalcitrance to decomposition. SOM stabilization (Figure 5.2) is generally considered to occur by three main mechanisms (i) physical protection, (ii) chemical stabilization, and (iii) biochemical stabilization (Six et al., 2002). 

Photolysis first-order rate constants for photosensitized reactions in water with various humic substances as sensitizers k = 0.17 h-1 with aquatic humus from Aucilla River, k = 0.12 Ir1 with Aldrich humic acid, k = 0.091 Ir1 with Fluka humic acid and k = 0.11 Ir1 with Contech fulvic acid in sunlight, corresponding to half-lives of 4 to 8 h (Zepp et al. 1981) photolysis t,/2 = > 50 yr at 15°C and a pH 5-9 (Torang et al. 2002). Oxidation rate constant k for gas-phase second order rate constants, koH for reaction with OH radical, kN03 with N03 radical and kQ3 with 03 or as indicated, data at other temperatures and/or the Arrhenius expression see reference ... 

Apparent first-order rate constant phototransformation al X > 285 nm, k = (1.38 0.12) x 102 h 1 in purified water, and k = (1.68 0.12) x 10 2 h 1 in Capot river water with t,/2 40 h (Zamy et al. 2004) Oxidation half-life ranged from t,/2 5 h of midday sunlight during summer to t,/2 = 12 h during winter estimated from kinetic data for oxygenation reactions photosensitized by humic substances in water exposed to sunlight (Zepp et al. 1981) ... 

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