Water Humic substances, Surface

Sun L., Perdue E.M., McCarthy J.F. (1994), Using reverse osmosis to obtain organic matter from surface waters. Humic Substances in the Global Environment and Implicadons on Human Health, (Ed. N. Senesi, T.M. Miano), Elsevier Science, 901-910. 

They constitute 75% w/w of the organic matter in most soils and 50% of the organic carbon in surface waters. Humic substances are composed of complex heterogeneous mixtures of organic compounds and are characterized as being yellow to brown in color, of high relative molecular mass, and refractory. Unlike many other natural organic products, they cannot be described in terms of unique chemical structures and are operationally defined by the technique used for their extraction and fractionation. 

Complexation Partly Humic substances are very significant factors in near-surface complexation processes, probably less so in die deep-well environment. Data on complexation in saline waters are probably most relevant. 

The amphiphilic nature of dissolved humic substances (DHS) lends them the ability to associate with both hydrophobic organics and polar or ionic species [62-64]. Inorganic ions or mineral colloids in solution will interact with the electrically active surface of humic material in solution or in the solid phase according to the same bonding forces which lead to the association between SP0M and the solid mineral matrix. Humic matter in water is associated with... 

Dissolved humic substances (DHS) are the main constituents of the dissolved organic carbon (DOC) pool in surface waters (freshwaters and marine waters), groundwaters, and soil porewaters and commonly impart a yellowish-brown color to the water system. Despite the different origins responsible for the main structural characteristics of DHS, they all constitute refractory products of chemical and biological degradation and condensation reactions from plant or animal residues and play a crucial role in many biogeochemical processes. 

Water table should be more than several feet from the land surface. Humic substances in the soil can interfere with the process. 

A conceptual DOM pie diagram (Fig. 1) represents the chemical view of the DOM pool of a typical riverine sample. The specific chemical classes or wedges can be separated based upon several different operational fractionation schemes (Thurman and Malcolm, 1981 Aiken, 1985 Aiken et al., 1992 Benner, 1998). For typical natural waters, the dominant fraction comprising DOM is fulvic acid, which is defined as the yellow, moderate molecular weight organic acid fraction of aquatic humic substances that is soluble at all pH values (Aiken et al., 1985). In surface waters receiving... 

Voelker, B. M., F. M. M. Morel, and B. Sulzberger. 1997. Iron redox cycling in surface waters Effects of humic substances and light. Environmental Science Technology 31 1004-1011. 

The presence of humic substances (HS) in the environment has long been recognized (Kononova, 1966 Schnitzer and Khan, 1972 Orlov, 1985 Frimmel and Christman, 1988). The term humic substances refers to a category of naturally occurring materials found in, or extracted from, soils, sediments, and natural waters and constitute one of the most abundant forms of organic matter (OM) on the surface of the earth (Woodwell and Houghton, 1977 Woodwell et al., 1978). 

Also, Schmidt et al. (2005) found a significant increase in root hair density by working with Arabidopsis thaliana, which were treated with water extractable humic substances (WEHS), suggesting that these substances induce a nutrient acquisition response that favors the uptake of nutrients via an increase in the absorptive surface area. Furthermore, a phenotypical analysis of an array of mutants harbouring defects in root epidermal patterning revealed that root hair density of the ttg and gl2 mutants, defective in cell specification, was significantly modified, indicating an effect at/or downstream of the determination of the cells. 

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