EFDC Explorer v.10.0 Chl-a

For reasons discussed below, I’m still running a model in v.10.0. In this version, it appears to me that conversion from algal biomass to chlorophyll-a is mis-applying the mg-C/ug-Chl-a conversion factor by multiplying instead of dividing. As a result, chl-a output is too low by a factor of roughly 237. Please let me know if I am missing something and whether this has been updated in latest version.I’ve previously executed my model in v.10.0, as well as the latest version (v.10.1.4). Model appears to run faster in new version, but it got bogged down in calibration post-processing and couldn’t compute summary statistics for all of my calibration series at once. For this reason, I have continued to run in v.10.0 for now.

How are you setting the time series in your model? Are you using the carbon to chlorophyll conversion factor of 0.06 provided in table 8.16 of the EFDC+ theory guide: EFDC+ Theory Guide – EE Modeling System

I had previously been using a conversion factor of 0.065, as that was default in a prior version of EFDC+. I have since found that a value of 0.05 better fits my data, though calibration is still in progress.Regardless of which value I use, when I create time series plot with both algal biomass and chlorophyll next to each other, it appears that conversion factor is getting mis-applied. I compared output from the same day to double-check the math.As an example, I just picked out a day in an older model where algal biomass = 3.2 g-C. The chl-a value should be 3.2 g-C / 0.065 g-C/ug-Chl-a = 49 ug-Chl-a/LI am instead seeing a Chl-a concentration of 0.21 ug/L, which suggests to me that the biomass is being multiplied times the factor instead of dividing.I believe that biomass state variable is being handled correctly, but the derived constituent chlorphyll-a looks incorrect to me. I’ve found a work-around (applying same adjustment to my calibration data), but wanted to point this out and see if I’m either missing something and/or if this has been changed in most recent software version. Thanks for your time.

One more note: as best I can tell, this discrepancy only impacts the chlorophyll output. My testing suggests that chlorophyll is being properly calculated in the light extinction formulation.

Chl-a is not used by EFDC+ other than for light extinction. It looks like you are having issues with EE reporting. However, we checked and EE is computing the Chl-a correctly also. One issue may be that you are thinking that you are using just one class of algae, but the WQ computations ALWAYS use all algae classes. The following is from the EE code, which is correct. Maybe you have an initial condition of Carbon for the other classes and they are being used?// Chl-a = AlgaeRatio(Chla:C)*CHC + AlgaeRatio(Chla:C)*CHG + AlgaeRatio(Chla:C)*CHDIt is important to understand exactly where things are not being reported correctly.

Thank you for the response. You are correct in that I am only having issues with EE reporting. Thank you also for posting formula, which is exactly as I thought. When computing Chl-a, the software should be dividing by the C:Chl-a ratio, not multiplying as shown in the formula. Thus, unless the C:Chl-a ratio is first being inverted, the formula should more correctly be as follows:// Chl-a = CHC/AlgaeRatio(Chla:C) + CHG/AlgaeRatio(Chla:C) + CHD/AlgaeRatio(Chla:C)If the default ratio of 0.06 mg C/ug Chl-a is applied to all species, the formula should therefore be// Chl-a = CHC/0.06 + CHG/0.06 + CHD/0.06It looks to me like the software is instead multiplying by the ratio, consistent with my hand calculations.

We have looked at this further and believe your equation above is incorrect. Rather than:// Chl-a = CHC/AlgaeRatio(Chla:C) + CHG/AlgaeRatio(Chla:C) + CHD/AlgaeRatio(Chla:C)It is in fact:// Chl-a = CHC/AlgaeRatio(C:Chla) + CHG/AlgaeRatio(C:Chla) + CHD/AlgaeRatio(C:Chla)Noting that that AlgaeRatio(C:Chla) = 1/AlgaeRatio(Chla:C)You can see from the two attached images that the max value of green algae is 0.4125 and that of chl-a is 6.3413. So the algae to chl-a ratio = 0.065