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Anaerobicity in substrates

>Date: Sun, 18 May 1997 19:09:07 GMT
>From: Sparrow <spug at intlog_demon.co.uk>
>Subject: Re: Aquatic Plants Digest V2 #715
>>From: Dan Q <dqallwet at avana_net>
>>Subject: Re: Response to Sparrow from Dan
>>I've tried the same experiment and got the same results, so yes this is
>>what is suppose to happen. You lost me in the "..facilitating aerobic
>>conditions". I suspect most substrates are anaerobic, and this would not
>>be an exception.   
>Most substrates are NOT anaerobic, otherwise nitrobacter and nitrosoma
>not live there, and H2S and other nasties would prevail

I'll only address this question, not other points and counterpoints made in
this thread.

I think if you measured the oxygen content within the substrate of most
aquatic streams, lakes, and ponds, you'd find it quite anaerobic.  This
isn't a problem for aquatic plants, as they deliver the necessary amounts
of O2 for their needs through air channels in their tissues.  Additionally,
an aerobic substrate doesn't seem to be compatible with aquatic plants'
root hairs.  Given the choice, I'd want to have an anaerobic substrate.

<itty-bitty, unsignificant bit of information>
Recent research, written about in AFM and on the web as well (I don't have
the URL, but it should be fairly easy to locate via search) used genetic
probes to learn more about nitrifying bacteria in aquatic environments.
Although we know that nitrifiying bacteria do exist, the nitrobacter and
nitrosomonas bacteria that are found in soils (and claimed for the last 30
years to be the reason for nitrification in aquaria) were not found in
cycled freshwater aquaria, to which ammonia was added regularly and the
aquarium cycled, and only one of these (I think it was nitrosomonas) was
found in marine aquaria in the same set of tests.  Further research will
hopefully identify the bacteria that are actually responsible for aquatic
nitrification.  It was a very interesting article and made me realize how
much is just taken for granted within the aquaria hobby.
</itty-bitty, unsignificant bit of information>

Although nitrifying bacteria probably help somewhat in an aquarium, many
aquatic gardeners do not depend on them for ammonium processing because the
plants do it so well.  Also, I've found that any ammonium added to my
aquarium is quickly either consumed or converted to nitrates even though my
substrate is quite anaerobic.  I suspect that enough nitrifying bacteria
live on the surface of my substrate and on my plants that I really don't
need to worry about adding oxygenated surface area to my tanks for a
nitrification bed.

H2S will only be evolved in a substrate if the substrate is anaerobic, if
there are undecomposed organic compounds in the substrate to decay, and if
no nitrates are present.  Nitrates will be reduced by anaerobic bacteria
before sulfates are reduced.  H2S in the substrate will convert to FeS if
reduced iron exists in the anaerobic substrate in equal quantities.  Fish
droppings that rest on top of the substrate and then get shuffled
underneath by trumpet snails or other processes usually are pretty well
composted prior to being placed in an anaerobic environment.  Roots left in
the substrate after plant removal, fish droppings sucked into a UGF and
then left to rot when the UGF is turned off or clogs up, or organics added
to fertilize the substrate are among the most likely sources of
decomposition and H2S evolution within the substrate.

David W. Webb           Corporate Business Systems
Texas Instruments Inc.  Dallas, TX USA
(972) 575-3443 (voice)  dwebb at ti_com
(972) 575-4853 (fax)    http://www.dallas.net/~dwebb
(214) 581-2380 (pager)  2145812380 at alphapage_airtouch.com