Dissolved organic carbon
Dissolved organic carbon (DOC) is a broad classification for organic molecules of varied origin and composition within aquatic systems. The "dissolved" fraction of organic carbon is an operational classification. Many researchers use the term "dissolved" for compounds below 0.45 micrometers, but 0.22 micrometers is also common, saving colloidal for higher concentrations. A practical definition of dissolved typically used in marine chemistry is all substances that pass through a GF/F filter. The recommended measure technique is the HTCO technique after filtration on precombusted glass fiber filters, typically GF/F filters.
DOC in marine and freshwater systems is one of the greatest cycled reservoirs of organic matter on Earth. The source of DOC depends on the body of water. In general, organic carbon compounds are a result of decomposition processes from dead organic matter such as plants. When water contacts highly organic soils, these components can drain into rivers and lakes as DOC.
DOC is a food supplement, supporting growth of microorganisms and plays an important role in the global carbon cycle through the microbial loop. Moreover it is an indicator of organic loadings in streams, as well as supporting terrestrial processing (e.g., within soil, forests, and wetlands) of organic matter. Dissolved organic carbon has a high proportion of biodegradable dissolved organic carbon (BDOC) in first order streams compared to higher order streams. In the absence of extensive wetlands, bogs, or swamps, baseflow concentrations of DOC in undisturbed watersheds generally range from approximately 1 to 20 mg/L carbon. Carbon concentrations considerably vary across ecosystems. For example, the Everglades may be near the top of the range and the middle of oceans may be near the bottom. Occasionally, high concentrations of organic carbon indicate anthropogenic influences, but most DOC originates naturally.
The BDOC fraction consists of organic molecules that heterotrophic bacteria can use as a source of energy and carbon. Some subset of DOC constitutes the precursors of disinfection byproducts for drinking water. BDOC can contribute to undesirable biological regrowth within water distribution systems.
- Stone, Richard (June 18, 2010). Marine Biogeochemistry: The Invisible Hand Behind A Vast Carbon Reservoir. 328. Science Magazine. pp. 1476–1477. doi:10.1126/science.328.5985.1476. http://www.sciencemag.org/cgi/content/full/sci;328/5985/1476?cookietest=yes&maxtoshow=&hits=10&RESULTFORMAT=&fulltext=refractory+%22dissolved+organic+carbon%22&searchid=1&FIRSTINDEX=0&sortspec=date&resourcetype=HWCIT.
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- ^ Kirchman, David L.; Suzuki, Yoshimi, Garside, Christopher, Ducklow, Hugh W. (15). "High turnover rates of dissolved organic carbon during a spring phytoplankton bloom". Nature 352 (6336): 612–614. doi:10.1038/352612a0. http://www.nature.com/nature/journal/v352/n6336/abs/352612a0.html.
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