Support for the proximity theory on sand beds vs bioballs and denitrification

[Randy Holmes-Farley]

Many folks have questioned the proximity theory that I've expounded on for the reason that bioballs may release nitrate while sand beds may not.

I just ran across this reference that seems to strongly support the idea when natural sediments are examined. i have bolded the appropriate passage:

Coupling the 15N/14N and 18O/16O of nitrate as a constraint on benthic nitrogen cycling. Lehmann, Moritz F.; Sigman, Daniel M.; Berelson, William M. Department of Geosciences, Princeton University, Princeton, NJ, USA. Marine Chemistry (2004), 88(1-2), 1-20.

Abstract

We report 15N/14N and 18O/16O ratios of nitrate in benthic chamber incubations in the continental shelf sediments of the Santa Monica Bay (SMB) to deconvolve the effects of nitrification and denitrification. Ests. of denitrification rate from benthic flux stoichiometry is 0.9-2.5 mmol N/m2-day. Between 46 and 100% of the total denitrification can be explained by nitrate or nitrite from nitrification. In general and independent of the denitrification rate and the fraction of remineralized N being denitrified, nitrate 15N/14N and 18O/16O ratios do not change significantly with progressive nitrate depletion in the chambers. A lack of change in nitrate 15N/14N could be due to either the lack of effective N isotope fractionation assocd. with sedimentary denitrification or the balancing of a denitrification isotope effect by the addn. of low-15N/14N nitrate from nitrification. However, the lack of an increase in nitrate 18O/16O indicates that the isotopic fractionation specifically assocd. with sedimentary denitrification is, in fact, negligible. The coupled N and O isotope measurements also indicate that there is no significant gross efflux of 15N-depleted nitrate from nitrification, leading to the conclusion that nitrification is closely coupled to denitrification, even in the bioturbated sediments of the SMB.

[Boomer]

OK, I bite :D What makes you think or what evidence do you have Randy that makes you believe bioballlls may release NO3.

[Randy Holmes-Farley]

:blown:

[jfinch]

It would be very interesting to see a nitrogen balance done on a typical reef aquarium.

How much ammonia is converted to nitrate by bacteria?
How much nitrogen is exported via organics through the skimmer or AC?
How much nitrogen (via DOM) is consumed by plants/animals?
How much ammonia is consumed by plants?
How much nitrate is converted to N2 by bacteria?
How much nitrate is consumed by plants?
How much nitrate is consumed by other bacteria and removed by the skimmer?

I wonder which of these processes dominate in my tank?

Randy, what comments do you have on Hovanec's study on reef filtration systems
http://www.marineland.com/seascope/ss2003_issue2.pdf ?

It's been my experience that bioballs/biowheels (highly oxygenated high surface area filters) can lead to nitrate issues. Proximity to denitrifiying bacteria is an intriguing theory and does make sense. Another idea is that the bioballs are so efficient at nitrification that the instant ammonia is produced it's oxidized in the biofilter. When you remove this biofilter, the ammonia is given more time to float around and find other pathways out of the system (such as plant uptake)...

Anyways, this is an interesting topic.

[Boomer]

Be careful there Randy, you are playing with an IED (Improvised Explosive Device )and may hurt yourself :D You may need, in the end, the assistance of an IEED ( Improvise Explosive Device) Disposal) Technician........That would be me of course ;) I'm rather pricey also :lol:

[Boomer]

Ok, time to stop playing games in case someone gets lost here. About all bioballs do is release Nitrate into the water column, for if they didn't, there would be no nitrate present in the water column to measure and there is lots of it, hence the name "Nitrate Factory" :D

[thackray]

I did a search on “Hovanec� back to the time the article that Jon referenced appeared. It seems that no discussion of that article took place here on Reef Central. Am I not finding something?

In the end, Tim’s “study� seems to support those who believe that all the “filter� you need is lots of live rock and a good skimmer.

Phil

[jfinch]

What I got from Tim's study was that denitrification plays a minor role to the consumption of nitrate by plants. If that is true and my experience with bioballs leading to high nitrates it also true then some of those primary consumers must prefer ammonia to nitrate...

[Bomber]

Originally posted by jfinch
It would be very interesting to see a nitrogen balance done on a typical reef aquarium.

How much ammonia is converted to nitrate by bacteria?
How much nitrogen is exported via organics through the skimmer or AC?
How much nitrogen (via DOM) is consumed by plants/animals?
How much ammonia is consumed by plants?
How much nitrate is converted to N2 by bacteria?
How much nitrate is consumed by plants?
How much nitrate is consumed by other bacteria and removed by the skimmer?

I wonder which of these processes dominate in my tank?

This one. :)

How much N is introduced by N fixing bacteria.

[jfinch]

How much N is introduced by N fixing bacteria.

Are you saying my tank is full of cyano? :D

So are you saying N fixing bacteria are the dominating exporter of nitrogen? I wasn't even considering N2 as a source of nitrogen... but if they're fixing their own N from N2 how are they helping export nitrogenous waste?

[a4]

Can N be fixed in an aerobic environment? How about a low oxygen environment? Will any oxygen present block the conversion?
Thankyou

[Randy Holmes-Farley]

Can N be fixed in an aerobic environment?

Yes

How about a low oxygen environment?

I'm not sure, but I'd expect so.

Will any oxygen present block the conversion?


Not that I know of.

[Boomer]

To add some info to Randy's comments;

Some species of bacteria can maintain an intracellular anoxic environment under aerobic conditions, due to large amounts of mucous they secrete combined with high rates of O2 consumption in excess of energy needs.

Don't forget about N fixing symbiotic bacteria, found on the "roots" of macro's and even on just the surface of macro's. Some starved macor's can release DOC's , which break down the bacteria cell wall, thus releasing fixed nitrogen which the plants can use.

Nitrogen fixation by aquatic sediment bacteria is even less likely than NO3 assimilation.

Paraphrasing from;
Bacterial Biogeocehmistry, King & Blackburn (1998)

In the end, Tim’s “study� seems to support those who believe that all the “filter� you need is lots of live rock and a good skimmer.

I support that :D It was a theroy of mine 20 years ago and I was laughed at. I'm also a believer of Randy's "proximity theroy" and have said so may times, years ago and long before RC was here. It is covered in an old Aquatic Microbiology book from the early 1980's, where I got it from ;)

[Bomber]

Thanks Boom.

In the end, Tim’s “study� seems to support those who believe that all the “filter� you need is lots of live rock and a good skimmer.

Welcome to Starboard Reef