Dissolved organic substances, sources

Data in this and other reports indicate three sources for dissolved organic substances in rivers, lakes, and reservoirs lignins, carbohydrates, and lipids. This study and others using degradative approaches (24) clearly established lignin as a precursor for dissolved humic substances. Similarly, carbohydrates are known to be a component of dissolved organic substances in natural waters (I). 

A two-dimensional numerical model was developed to describe the transport of dissolved organics originating from nonaqueous phase liquid pool dissolution in saturated porous media in the presence of dissolved humic substances. The model assumes that the dissolved contaminant (NAPL dissolved in the aqueous phase) may sorb onto the solid matrix as well as onto humic substances suspended in the aqueous phase, contaminant-humic particles and humic substances may sorb onto the solid matrix, the dissolved contaminant may undergo first-order decay, and humic substances are introduced into the aquifer from a line source. 

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... 

Skopintsev (1982) has pointed out the enormous potential of marine humic substances as an organic nutrient resource (15 x 10 kcal). We are unaware of any published work demonstrating that dissolved humic substances can serve as a heterotrophic food source. Microbial enzymes should be capable of using the free carboxyl end of the marine humic substances as a simple fatty acid. However, this is conjecture and should be investigated by microbiologists and planktologists. 

It follows that the content of dissolved oxygen is an important indicator of the quality of streams, as one of the first indications of surface water pollution by organic substances is a decrease in the oxygen content downstream from the source of poUution. Oxygen in water is of vital importance for fish, a concentration of 3-4 mg 1 is usually considered to be the lower limit, but this depends on the sensitivity of fish. The salmon-like fish require a concentration of approximately 6 mg... 

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