[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[APD] RE: NO3=>NH4 conversion by bacteria

Okay, folks need to know what is going on here with this(DNRA)
biogeochemical cycle.DRNA=> Dissimilatory Nitrate Reduction to Ammonia

First, the players: Obilgate anaerobes, Clostridium and Streptococcus under
highly reduced conditions are able to do this reduction. 
The reaction: NO3(-)+ 10H(+)+ 8e(-)==> 3H2O+NH4(+)
This reaction consumes 8 e's vs 5e's for denitrification.Therefore a much
higher reductive environment will favior DRNA vs Denitrification.
As you can also see, the reaction also consumes 10 protons and therefore
drives the pH up.

There are some other issues also, such as ammonification of Organic source
of N as well but I'll not discuss that here.

DRNA will occur because nitrification is supressed. DRNA is very O2
sensitive. These bacteria also have very low N requirements and are not
efficent at this process vs aerobes/fungi. So the NO3 will much more likely
be lost to N2 gas than converted into NH4+.

These bacteria use NO3 as an alternate electron acceoptor for respiration
in the absense of O2. These microbes require a high availabilty of
electrons to carry out this process. No, not heating cables:-)
These electrons supply the force needed to start this process and carry it
out. The redox level(Eh) is less than 0mv. I think I said -200 to -300mv
which is not quite true but my points where still valid. DN reductases are
membrance bound enzymes and thus only synthesized under anoxic conditions. 
Got it?:)

Flux of NH4 out of the substrate will depend on bioturbiation/mixing of the
sediment, CEC, NH4 production rate, NH4 concentration gradient, intensity
of soil/substrate reduction, temp, adsorption-desorption.

I think folks hear something on the web about NO3=> NH4 and automatically
assume it occurs without reading up on the process.

Correlation does not imply causation.
The same is true for that whole mess with K+ blocking Ca uptake. 
Or PO4 causes algae
High Fe levels cause BBA and all sort of thread algae
Or Plants prefer soft water
Ad nasuem.......... 

Tom Barr

Aquatic-Plants mailing list
Aquatic-Plants at actwin_com