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jerrcarlson
05/19/2014, 02:15 PM
Hey y'all, I have read endless articles, opinions on carbon dosing. Just trying to educate myself on the process. Does anyone know with vodka etc dosing where the bacteria reside. I have read they reside in the water column but I was also under the impression they were more anaerobic bacteria that preferred low o2 environments. Can anyone shed any light on the nature of these bacteria for me? Thanks!

Jerry

disc1
05/19/2014, 02:40 PM
I think you've got a few different things confused together. The bacteria that can convert nitrate to nitrogen are anaerobic and live in the low oxygen areas, but these aren't the guys we're feeding with Vodka.

The beneficial bacteria that run your nitrogen cycle live in the rocks and sand and surfaces, but these aren't the guys we're feeding with vodka either.

When we feed vodka we're trying to cause a little bloom of bacteria so we end up with a lot of bacteria in the water that we can skim out to export nutrients. These will be whatever opportunistic critters happen to get to the vodka first. Those are the bugs that will be floating off in the water column.

Randy Holmes-Farley
05/19/2014, 05:12 PM
I have read they reside in the water column but I was also under the impression they were more anaerobic bacteria that preferred low o2 environments. Can anyone shed any light on the nature of these bacteria for me?

I don't think anyone has ever identified exactly what species are driven by organic carbon dosing, or where they primarily grow. :)

tmz
05/19/2014, 09:30 PM
I believe they are facultative( use free oxygen preferentially but when it's gone go to nitrate for it) heterotrophic bacteria which are found on surfaces but are also found in the water column.

chema
05/20/2014, 03:55 AM
This is a difficult issue. The current paradigm is that denitrification is an anaerobic process. As O2 is a competing electron acceptor for NO3 respiration, oxygen would inhibit the enzymes involved in the denitrification pathways, and thus the process would require complete anoxic conditions. However there are multiple reports of lab experiments showing that denitrification takes place with oxygen present (up to 90 microM). It seems that, instead of being a completely ON or OFF process, there is a fine tuning which depends on O2 concentration. The higher the O2 concentration, the lower denitrification rate, and viceversa.

There is a nice paper describing this, not in a lab experiment, but in permeable sediments of the Wadden Sea: http://www.nature.com/ismej/journal/v4/n3/full/ismej2009127a.html

tmz
05/20/2014, 09:01 AM
I think the bacteria will assimilalte nitrogen in either oxic or hypoxic( nitrate is present) environments. However, denitrification increases in the hypoxic environment as the facultative bacteria switch from aerobic to an anaerobic mode reducing NO3 to N and N2 gas,removing additional nitrogen in that way. The bacteria are able to form hypoxic areas as they consume available oxygen in a shallow substrate or even in their mulm.When that happens they keep going on lthe O from NO3.

Thanks for the link.

jerrcarlson
05/20/2014, 11:10 AM
Thanks tmz and chema! Great information and great article chema. I agree tmz I was assuming they were heterotrophic bacteria especially since they reproduce so quickly and have to reside at least partially in the water column. But I was under the impression that they would start to consume the No3 only when the O2 was gone. But the article seems to indicate that it is not an absolute. Very interesting. Thanks again for the information.

tmz
05/20/2014, 01:37 PM
You are welcome.
It's not all proven information but seems to fit the experiences associated with carbon dosing . There are still many things to learn. A few thoughts:

If they didn't appear in the water column there wouldn't be bacterial blooms or export via skimming. Colonies of brownish mats are common on surfaces too ; the basis for pellets in reactors fits in with benthic colonization as well.

If they weren't heterotrophic they wouldn't need organic carbon.

A few papers indicate they take ammonia directly for nitrogen. If so, less NO3 would be produced via ammonia oxidation. Whether NO3 anaerobic reduction plays out from the bacteria responding to organic carbon or not or in combination with another facultative species is unclear .

This one may be of interest:

http://ag.arizona.edu/azaqua/ista/ISTA7/RecircWorkshop/Workshop%20PP%20%20&%20Misc%20Papers%20Adobe%202006/7%20Biofiltration/Microbial%20Floc%20Systems/2006%20Roanoke%20-%20Understanding%20Trophic%20Systems%20%20Ebeling.pdf