Caulerpa vs Cheato Phos by Dry Weight

[YankeeTankee]

1. I read Randy's article on P which referenced a study showing 5.6% N to 0.08% P removal by weight with caulerpa. Is there another reference that shows the dry weight of chaeto? I am wondering if it removes more or less P relative to N, and both overall.

2. Help with the math, what would the N and P reductions be in PPM (the unit for both right?), if you removed 10 grams of caulerpa and how large of a ball would 10g dry be when its wet? Meaning what does 10grams of dry caulerpa look like when you just pulled it out wet in terms of size?

 

[Dan_P]

1. I read Randy's article on P which referenced a study showing 5.6% N to 0.08% P removal by weight with caulerpa. Is there another reference that shows the dry weight of chaeto? I am wondering if it removes more or less P relative to N, and both overall.

2. Help with the math, what would the N and P reductions be in PPM (the unit for both right?), if you removed 10 grams of caulerpa and how large of a ball would 10g dry be when its wet? Meaning what does 10grams of dry caulerpa look like when you just pulled it out wet in terms of size?

Macro algae is mostly water. The amount varies, but pick a number between 70 and 90% for a quick and dirty estimate. 100 g of wet alga would then be between 10 and 30 g dry. I am math challenged so I will pick 90% wet.

5.6% of 10 g is 0.56 g or 560 mg N. If that nitrogen came from nitrate, you would have removed about 4 times that weight, 2.2 g or 2200 mg. If that much nitrate came from a 100 L system (roughly 25 gallons), it would represent a reduction of 2 ppm...EDIT: just saw Randy’s reply and realized that 2200/100 =20 ppm!

If I got the numbers right, you need to harvest a lot of biomass to export nitrogen this way.

Now that I think about it, you have to wonder about how carbon dosing works to reduce nitrate levels. No one has ever reported hundreds of grams a bacteria being skimmed off, assuming the stoichiometry is similar.

 

[Randy Holmes-Farley Verified Community Expert]

I do not recall seeing specific chaeto numbers, and would have used them if I had had them when I wrote my nitrate article, but note the comment I made in the middle about many species being roughly similar:

For those interested in knowing how much nitrate is being exported by macroalgae, this free PDF article in the journal Marine Biology has some useful information. It gives the phosphorus and nitrogen content for nine different species of macroalgae, including many that reefkeepers typically maintain. For example, Caulerpa racemosa collected off Hawaii contains about 5.6% nitrogen and 0.08 % phosphorus by dry weight. Harvesting 10 grams (dry weight) of this macroalgae from an aquarium would be the equivalent of reducing the nitrate content by 2.5 grams, or 10 ppm in a 67-gallon aquarium. All of the other species tested gave similar results (plus or minus a factor of two). Interestingly, using the same paper’s phosphate data, this export would also be the equivalent of removing 24 mg of phosphate from the water column. That amount would reduce the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67-gallon aquarium.

 

[YankeeTankee]

Thanks Randy and Dan, anyone ever actually test the wet vs dry weight of cheato or caulerpa?

 

[Dan_P]

Thanks Randy and Dan, anyone ever actually test the wet vs dry weight of cheato or caulerpa?

I haven’t, but I imagine someone with an electronic balance and the seaweed could get the data, at least a good approximation.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy and Dan, anyone ever actually test the wet vs dry weight of cheato or caulerpa?

I measured some chaetomorpha years ago (for an iodine uptake study) to be about 87% water by weight.

 

[taricha]

I did a similar exercise once.
Using very very rough math I got daily chaeto export numbers for N and P that were the same order of magnitude as my N & P food inputs.
I used data from the "Down the Drain" article on exports that gives the numbers for wet weight caulerpa.

So if I feed 1 cube of mysis + 1 cube of something else, I get a daily food input of around
40-55mg N, and 2.5-5.5mg P
0.7-0.9ppm NO3 and 0.03-0.06ppm PO4

This seems reasonable to me because my exports average around 30g chaetomorpha a day, which if the numbers are around those cited for caulerpa here, then I'm exporting about 30mg of N and 2.4mg of P per day through chaeto. So it might be very wrong but nice to see the food inputs and algae exports around the same scale.

and here's what 30g of wet weight chaeto looks like. I remember reading somewhere that chaeto is on the 90% water end of the scale.

so you'd need over 3 times that much to get to 100g wet - 10g dry weight.