Allochthonous humic material

In principle, this figure is valid for both lakes and running water. In clear lakes, the input of carbon via autochthonous production (and the humification process per se) is of greater significance than in rivers and bogs where allochthonous humic material predominates. 

While specific compounds such as siderophores have been found in natural waters, the bulk of the dissolved organic matter (DOM) is made up of relatively refractory compounds known as humic substances. These substances exhibit complex, ill-defined structures with the actual structure depending markedly on the source of the organic material. DOM in the open ocean is almost entirely authochthonous and formed by condensation, polymerisation and partial oxidation of smaller molecules such as triglycerides, sugars and amino acids and exhibits very little aromatic character [78]. In contrast, the DOM in fresh and coastal waters is largely allochthonous and derived... 

The contribution of allochthonous organic matter to lake sediment humic substances is variable. In this chapter, we did not discuss in depth the contribution of allochthonous materials, such as soil organic matter, to sedimentary humic substances. However, it is important in the study of lake humic substances to determine how much authochthonous or allochthonous organic matter contributes to the formation of lake humic substances. Therefore, a method must be established for estimating the degree of contribution of authochthonous or allochthonous organic matter to lake humic substances. 

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. 

Humic-like fluorescence is predominately but not solely associated with allochthonous organic matter derived from degrading soil and plant matter. Relative to microbial derived material enriched in amino acid-like FDOM, humic-like FDOM is not expected to be preferentially degraded by bacteria, and thus considered to be a proxy for slowly... 

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