Nutrient export chemistry

[F i s h y]

Im trying to wrap my head around a statement that I see on the forums quite often regarding nutrient export in a refugium.

"Have you harvested Cheato to export nutrients" The person posting essentially saying that in order to see a drop in No3 or Po4 that you have to physically remove the macro algae you are growing because that removes the nutrients. I don't really want to get into the effectiveness of a refugium for nutrient export, especially since every system is different, but is that statement true at all?

Perhaps I am thinking about this incorrectly but isn't the No3 and Po4 already being used in natural biological processes by the macro, therefore it would no longer be a part of the testable, detectable nutrient value of the system? Wouldn't it also stand true that by not harvesting, there is more macro there to consume more nutrients, making the refugium more effective as the volume of macro increases? Making the above statement of you have to harvest to export nutrients false?

Is it possible that by harvesting, we are allowing for new growth and its the new growth consuming more nutrients that creates a drop? Does new growth use more than mature macro? Similar to when a reefer might clean an ATS?

Can anyone science me with actual information that proves or refutes the statement that macro must be harvested to remove nutrients?

 

[Subsea]

Im trying to wrap my head around a statement that I see on the forums quite often regarding nutrient export in a refugium.

"Have you harvested Cheato to export nutrients" The person posting essentially saying that in order to see a drop in No3 or Po4 that you have to physically remove the macro algae you are growing because that removes the nutrients. I don't really want to get into the effectiveness of a refugium for nutrient export, especially since every system is different, but is that statement true at all?

Perhaps I am thinking about this incorrectly but isn't the No3 and Po4 already being used in natural biological processes by the macro, therefore it would no longer be a part of the testable, detectable nutrient value of the system? Wouldn't it also stand true that by not harvesting, there is more macro there to consume more nutrients, making the refugium more effective as the volume of macro increases? Making the above statement of you have to harvest to export nutrients false?

Is it possible that by harvesting, we are allowing for new growth and its the new growth consuming more nutrients that creates a drop? Does new growth use more than mature macro? Similar to when a reefer might clean an ATS?

Can anyone science me with actual information that proves or refutes the statement that macro must be harvested to remove nutrients?

If seaweed only sequestered inorganic nutrients then your hypotheses would be correct.

However, during photosynthesis, the organic & inorganic world come together where seaweed absorbs inorganic nutrients and produces glucose. Also, during photosynthesis, seaweed leaks dissolved organic carbon.

I suspect you are correct in that new, fast growing seaweed will absorb more inorganic nutrients than old mature seaweed.

 

[Randy Holmes-Farley Verified Community Expert]

If you never remove it, it will eventually stop growing and nutrient uptake will cease. It will fill the space, shade itself, etc.

 

[drewzaun]

I’m no botanist but it is my understanding that plants and algae do not directly release nitrates and phosphates. So in effect not removing algae should not have a testable impact on water quality.

However if that algae should slow down in growth it will reduce the amount of nutrients it pulls out, and should it die it will release all those nutrients back into the water column.

 

[Subsea]

Not exactly. During photosynthesis, seaweed absorbs inorganic nutrients and at the same time seaweed exudates are DOC (dissolved organic carbon) and that will not show up on your ICP test results.

I’m no botanist but it is my understanding that plants and algae do not directly release nitrates and phosphates. So in effect not removing algae should not have a testable impact on water quality.

However if that algae should slow down in growth it will reduce the amount of nutrients it pulls out, and should it die it will release all those nutrients back into the water column.

 

[Dan_P]

Im trying to wrap my head around a statement that I see on the forums quite often regarding nutrient export in a refugium.

"Have you harvested Cheato to export nutrients" The person posting essentially saying that in order to see a drop in No3 or Po4 that you have to physically remove the macro algae you are growing because that removes the nutrients. I don't really want to get into the effectiveness of a refugium for nutrient export, especially since every system is different, but is that statement true at all?

Perhaps I am thinking about this incorrectly but isn't the No3 and Po4 already being used in natural biological processes by the macro, therefore it would no longer be a part of the testable, detectable nutrient value of the system? Wouldn't it also stand true that by not harvesting, there is more macro there to consume more nutrients, making the refugium more effective as the volume of macro increases? Making the above statement of you have to harvest to export nutrients false?

Is it possible that by harvesting, we are allowing for new growth and its the new growth consuming more nutrients that creates a drop? Does new growth use more than mature macro? Similar to when a reefer might clean an ATS?

Can anyone science me with actual information that proves or refutes the statement that macro must be harvested to remove nutrients?

Nitrate and phosphate removal by living things like macro algae happens because they are growing and creating biomass which uses up nitrate and phosphate in the water. Until this biomass is removed from the system, the consumed nutrients even though they have been transformed into biomass are technically still in the system. The harvesting part is important because the aquarium can support just so much macro algae. Particularly, the aquarium has limited space, water flow becomes more sluggish around large dense growth and there is a limited amount of light per square inch. This means at some point the vigorously growing plant starts to die and leak nutrients back into the water, though these nutrients are likely first digested by bacteria before become nitrate and phosphate again.

Make sense?

 

[Koty]

Most efficient refuge is where the macro algae is at some kind of log growth phase where growth is maximal as there is no limiting factor namely PO4 , NO3, trace elements, light and space to grow into . Moreover the after trimming starting point is a factor as well (where it starts from)

 

[Faurek]

Yes and no. The seaweed will take the nutrients from the water, once you remove the seaweed you are removing the nitrate and phosphate that the seaweed consumed not the one in the water, problem being is if you don't harvest you could end up in these situations:
1. Seaweed gets less effective, the best of the two situations.
2. It just keeps growing and then crashes, basically it just dumps it all back.
Which one you end up depends on the type of seaweed, Caulerpa would be a number 2 and Ulva would be a 1, mostly like this simplified.