RayRay you have raised a lot of questions in my thinking of an ecosystem. I have a system very similar to Wally's. Now I am wondering....On land the anaerobic breakdown is good for the soil. The process rejuvenates the system. It encourages the growth of the ecosystem. If my mangroves were grown in soil wouldn't that bacteria be beneficial to their growth? Isn't that the whole purpose of plants in a saltwater system? The main reason I tried Mangroves was to leave nutrients in the system, and eliminate Nitrate sand Phosphates. I have noticed my deep sand bed releasing bubbles from underneath. That has subsided. Fish are happy, SPS and LPS corals are happy. Should I expect a major problem in the future? BTW the sand bed in my dt and sump are over Three years old. HELP!!!
if I recall my biology 101, terrestrial anaerobes fix atmospheric nitrogen gas (N2) in order to incorporate it into amino acids that more advanced organisms need but cant make on their own. On land nitrogen is often the limiting factor, thats why fertilzers are mostly plant-usable forms of nitrogen.
in the marine environment, anaerobic deep sand beds regenerate nitrogen gas, that is likely what the bubbles are, along with sulfur gases, etc.
The 2 combined are the oversimplified global nitrogen cycle.
Mangroves do take up organic nutrients, but usually very slowly compared to algae. So slow that unless you have a Wally-amount of mangroves it probably doesnt make a big difference until the plants root extensively.
But what I was getting at was "old tank syndrome" when the 2+ year old DSB is blamed for the poor performance of a captive reef. Its when really experienced reefers just cant pinpoint the cause of nitrate spikes and the slow and steady decline of their mature system. The rationale is the DSB is like a landfill too full of nutrients and now the waste is leaching back into the system. When every other possible cause has been excluded and changing out the DSB resulted in rapid improvement, the diagnosis is "old tank syndrome."
http://aem.asm.org/content/68/3/1312.short
Production of N2 through Anaerobic Ammonium Oxidation Coupled to Nitrate Reduction in Marine Sediments
ABSTRACT
In the global nitrogen cycle, bacterial denitrification is recognized as the only quantitatively important process that converts fixed nitrogen to atmospheric nitrogen gas, N2, thereby influencing many aspects of ecosystem function and global biogeochemistry. However, we have found that a process novel to the marine nitrogen cycle, anaerobic oxidation of ammonium coupled to nitrate reduction, contributes substantially to N2 production in marine sediments. Incubations with 15N-labeled nitrate or ammonium demonstrated that during this process, N2 is formed through one-to-one pairing of nitrogen from nitrate and ammonium, which clearly separates the process from denitrification. Nitrite, which accumulated transiently, was likely the oxidant for ammonium, and the process is thus similar to the anammox process known from wastewater bioreactors. Anaerobic ammonium oxidation accounted for 24 and 67% of the total N2 production at two typical continental shelf sites, whereas it was detectable but insignificant relative to denitrification in a eutrophic coastal bay. However, rates of anaerobic ammonium oxidation were higher in the coastal sediment than at the deepest site and the variability in the relative contribution to N2 production between sites was related to large differences in rates of denitrification. Thus, the relative importance of anaerobic ammonium oxidation and denitrification in N2 production appears to be regulated by the availability of their reduced substrates. By shunting nitrogen directly from ammonium to N2, anaerobic ammonium oxidation promotes the removal of fixed nitrogen in the oceans. The process can explain ammonium deficiencies in anoxic waters and sediments, and it may contribute significantly to oceanic nitrogen budgets.
... 
