Humic material/substances soil/terrestrial

NOM is common in sediments, soils, and near ambient (<50 °C) water. The materials result from the partial decomposition of organisms. They contain a wide variety of organic compounds, including carboxylic acids, carbohydrates, phenols, amino acids, and humic substances (Drever, 1997, 107-119 Wang and Mulligan, 2006, 202). Humic substances are especially important in interacting with arsenic. They result from the partial microbial decomposition of aquatic and terrestrial plants. The major components of humic substances are humin, humic acids, and fulvic acids. By definition, humin is insoluble in water. While fulvic acids are water-soluble under all pH conditions, humic acids are only soluble in water at pH >2 (Drever, 1997, 113-114). 

Aquatic humic substances may be found in groundwater, river water, lakes, marshes, bogs, swamps, and seawater. The source of the humates may be autochthonous or allochthonous that is, the humates may be formed from phytoplankton in the water or they may be leached into the aquatic environment from terrestrial plants, leaf litter, soil, or subsurface deposits. Relatively undisturbed marine environments have humic and fulvic acids formed almost entirely from native phytoplankton inland surface waters contain major contributions from allochthonous sources. Mixing of the two types of materials may occur, as in the estuaries of rivers. 

H/C ratios are clustered around 1.0 for most soil and aquatic humates and fulvates. Lake and marine sedimentary humic substances have somewhat higher H/C ratios than their soil or water counterparts (Ishiwatari, 1975a). A plot of EJE(, ratios versus H/C ratios shows a direct correlation for terrestrial humic acids (Ertel and Hedges, 1983). The magnitude of the EjEe ratio is inversely proportional to the degree of condensation or the molecular weight (Chen et al., 1977). Ratios above 1.3 indicate that the material may be a nonhumic substance. 

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