Re: Nitrates vs. DOCs

["David A. Youngker" <nestor10@mindspring.com>]

From: David Shim
Sent: Thursday, April 29, 1999 4:18 PM


> What is the theory/logic behind the definition of DOCs and
> distinction from TOCs?

In a nutshell, the DOCs are most likely to remain suspended within the water
column as opposed to settling out. They are a prime source of food for those
bacteria directly competing with other organisms for available oxygen within
the water, as well as an eventual source of waste compounds after
consumption.

The following is extracted from an article by Morten Søndergaard, one of the
researchers at the Freshwater Biological Laboratory, University of
Copengagen, Denmark. It is written in light of studies undertaken on lakes,
but can be extrapolated to streams and deposition to marine bodies as well:

"New measurements of bacterial secondary production have identified
bacterial utilisation of dissolved organic carbon (DOC) as a main metabolic
pathway in aquatic systems. The carbon demand of pelagic bacteria in lakes
can be as high as or higher than phytoplankton primary production, and input
of organic substrates from terrestrial and littoral sources must be included
to fully comprehend water column metabolism. Dissolved organic carbon is the
largest organic carbon pool in most lakes, but temporal variations in
concentrations are small compared with the high removal rates by bacteria.
Only a small part of the large concentration of organic carbon is available
for bacteria, despite the dominance of small molecules. Substrate for
bacteria must accordingly be produced and removed at similarly high rates.
Direct release of organic carbon by primary producers is an important source
of substrate for bacteria, but recycling of organic carbon due to grazers
and cell lysis can be equally important. The biological structure of the
plankton is shown to be of decisive importance for the major routes of
substrate production..."

-Y-

David A. Youngker
http://www.mindspring.com/~nestor10
nestor10@mindspring.com





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