Dissolved organic carbon processes

Research into the aquatic chemistry of plutonium has produced information showing how this radioelement is mobilized and transported in the environment. Field studies revealed that the sorption of plutonium onto sediments is an equilibrium process which influences the concentration in natural waters. This equilibrium process is modified by the oxidation state of the soluble plutonium and by the presence of dissolved organic carbon (DOC). Higher concentrations of fallout plutonium in natural waters are associated with higher DOC. Laboratory experiments confirm the correlation. In waters low in DOC oxidized plutonium, Pu(V), is the dominant oxidation state while reduced plutonium, Pu(III+IV), is more prevalent where high concentrations of DOC exist. Laboratory and field experiments have provided some information on the possible chemical processes which lead to changes in the oxidation state of plutonium and to its complexation by natural ligands. 

Torrents A, BG Anderson, S Bilboulian, WE Johnson, CJ Hapeman (1997) Atrazine photolysis mechanistic investigations of direct and nitrate-mediated hydroxyl radical processes and the influence of dissolved organic carbon from the Chesapeake Bay. Environ Sci Technol 31 1476-1482. 

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. 

Such processes lead to the formation of adsorbable halogenated organic compounds (AOX) in high concentrations. Typical concentrations found in a continuous antifelt treatment are shown in Table 4. The high dissolved organic carbon (DOC) determined in the baths is one of the sources for the formation of high concentrations of chlorinated compounds. The formation of chlorinated products is the result of chemical reactions directly with the fiber, with organic compounds released from the fibers, and with added auxiliaries. 

A subsurface peak in HgT was evident at 2-4 cm in most cores. A mechanistic explanation for this observation is not clear. Dissolved organic carbon (DOC) concentrations ranged from about 2.5 to 4 mg/L and generally increased with increasing depth of the core. Thus, a clear correlation was not seen between Hg and DOC (38). Similarly, there was no apparent relationship between dissolved Hg and dissolved Fe or Mn. The distribution of Hg in aqueous and solid phases is the net result of many geochemical processes (e.g., redox, complexation, and solubility). Information available to our group thus far cannot explain the observed subsurface peak in the pore-water Hg profile. 

Estuaries with high inputs of organic waste products may exhibit processes which are different from those described above. Decomposition of organic matter is found to occur in such estuaries. This is seen from studies done on samples collected from the Ems-Dollart estuary (Fig. 12). The samples were collected at intervals of approximately 1 °/°° salinity. Dissolved organic carbon and carbohydrates determined on the samples indicate (Fig. 17) that between salinities 0 and 4°/ there is a net consumption of these two species. This is calculated from the area between the theoretical mixing line and the observed concentrations. 

Aitkenhead, J. A., D. Hope, and M. E Billett. 1999. The relationship between dissolved organic carbon in streamwater and soil organic carbon pools at different spatial scales. Hydro-logical Process 13 1289-1302. 

Grieve, I. C. 1991a. A model of dissolved organic carbon concentration in soil and stream waters. Hydrological Processes 5 301-307. 

McDowell, W. H., and T. Wood. 1984. Podzolization Soil processes control dissolved organic carbon in streamwater. Soil Science 137 23-32. 

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