phytoplankton growth below thermocline

Question

Hi Chris,

I have two groups (Cyanobacteria, using stokes migration) and (F-diatoms, using constant settling) who are calibrated and show a good agreement with measured data. However, they do not grow below thermocline (~10m), while we see some chla concentration there in the measured data. The limits (incl. light) and growth rate show there must be no problem below 10m, however, I always see zero concentration of the both groups below 10m. I tried to adjust many different parameters in wq_files, including temperature limits, sedimentation speed, light attenuation, light limitation, etc. But the outcome is basically the same.

I would be glad to know your idea about it.

Thanks

Behnam

Answer 1

Okay, I found the reason and I am writing it here for any similar case that might happen for others. The reason was the negative settling velocity. In CAEDYM we used to set the settling velocity as negative numbers.  However, in AEM3D the settling velocity of the CONSTANT migration model must be set positive. Otherwise the particles sink upwards and no settling happens. So, just a positive sign does the job.

Behnam