open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi all,

When checking the t3d-aed2 example I found the unit of WQ variables is mmol/m3, while the field data measured are usually in mg/L. More details could be find in the table below. Could the moderators or anyone explain the unit conversion from (mg/L) to (mmol/m3)?

Variable	Measured	AED2
PO4	mg/L	mmol P/m3
NH4/NO3	mg/L	mmol N/m3
phytoplankton	mg/L(Chla)	mmol C/m3

Take chlorophyll a as an example, since the molar mass of Chla (C55H72MgN4O5) is 893.51g/mol, to my knowledge the conversion should be: 1 g/m3 = 1/893.51*55*1000 mmol C m/3, is that right?

Any suggestion is greatly appreciated.
Yunhao

Hello Yunhao,

Sorry for the delay.

Here is an answer from Javier, a colleague of mine, who better knows about water quality processes than me.

Hope this helps,

Chi-Tuan

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Hi Yunhao,
For all the variables, except for phytoplankton, your approach is right. For example, for the Oxygen (O2) since the molar mass of O2 is 32 g/mol you can convert mg/L (or ug/m3) to mmol/m3 as follows (after converting mg to g and L to m3):

1 mg O2/L = (1/32)*1000 = 31.25 mmol O2/m3

However, for the phytoplankton, the model calculates the biomass of phytoplankton expressed in mmol C/m3. That means all the content of C in the phytoplankton and not only within the Chlorophyll. For doing so, you ‘just’ need to fix a carbon to chlorophyll ratio (mg C/mg chla) that is included in the parameters list of phytoplankton:

Ycc [real]: carbon to chlorophyll ratio (mg C/mg chla)

You might need to find some bibliographic values for your simulated species. And, of course, it is a questionable way of doing so, since the carbon to chlorophyll ratio is not even constant for the same species; but the conversion from chloa to biomass is never easy...

Good luck with your simulations,