Planted sand bed and the sulfur cycle?

[eddiesylas]

http://reefkeeping.com/issues/2005-12/rhf/index.php

Upon reading this article I now have words to describe some of the processes that inevitably occurs in anoxic zones in my sand bed. What I was unable to draw out of the article was the role that a Seagrass ryzome and root system play in this cycle. I have always assumed destinct color boundaries were a sign of devercity in the sand bed ecosystem. Is this desireable in a grass bed?

 

[3D-Reef]

The sulfer cycle depends on the amount of organics in the substrate.Some discoloration of the sand (light gray)shows that denitrification is happening at a level benifitual to the plant.

Too much organics in the sand bed and it will go completly anoxic (black).Which will kill the plant.

Some of the grasses have a system by which they "pump" O2 down into the substrate in order to medigate the side effects of H2S.

 

[eddiesylas]

Is there any benefit to dosing iron directly into the sand bed to interrupt the cycle?

 

[Plantbrain]

O2 is only sent down to the sediments during the day cycle for aquatic plants. At night, only a minor amount is transferred.

I'm not sure if anyone has done much with O2 and Rhiziod transport, but seems the Rhizordial macro algae in soft sediments MUST have some method to get some O2 to those cells.

They do respire after all.

A dense rug of Caulerpa should have a higher Redox value than say an open region with macro algae. You'd need to leave the redox probe and likely best yet, a platinum tip 1/2 cell and leave in place for say 8-10 weeks and measure that one and then the other in the open region. And if you want some stat's to support it, use say 4-5 Platinum tips 1/2 cell probes in each treatment. Measure the Redox weekly over 8-10 weeks after placing then in the tank.

This is okay for a Refugium, folks would not mind having say 8-10 plastic probes for a few weeks.

Mangroves also, they have all those prop roots which help add O2 to the sediments also, but more likely, their main role is more as stated: prop roots. Keep them from washing away. They get tidal flux so the roots are exposed 2x a day to air and O2. But the sediments below are very reductive in those systems as a rule.

Not much in aquariums. We really do not have that much loading.
If you want H2S, stuff a potato wedge down there.

 

[3D-Reef]

Is there any benefit to dosing iron directly into the sand bed to interrupt the cycle?

In one study iron enrichment of the sediment lead to an increased leaf production by 55% and a 78% increase in alkaline phosphatase activity (APA).Nutrient incorporation increased 46-91%.Sulfate reduction rate was lowered by 71%,but,the overall pool of sulfides remained 9x's higher at the organic enriched site.

So you may get a temperary bump in grass production but over all it won't disrupt the sulfur cycle in the long term.