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No algal booms!!!

Wed, 02/25/2004 - 11:04am — InesTrindade
Helo. I am calibrating the model for a reservoir.At this time, I am trying to calibrate OD and simultaniously algae, BOD, NH4 e P. The waterbody has 3 branches and 2 tributaries. I know the initial concentrations for each one, since there are quality monitoring stations in it The distributed concentrations I have estimated then.I introduced the algal concentrations from the chla values that were measured. I run the model, and I do not have any significant algal production, excepting for few days in the summer, and the values calulated for the model to chla a are really small, compared to those one measured in the reservoir. I have already made analysis of the data collected, and I am in presence of an eutrophic lake. I can not understand why this is hapenning, since I do not have any limiting factor for algal grouth! I suspect that the distributed concentrations are probably to small, but I would like to see your opinion. Another question is that I have the depths of the Secchi disc. When I try to put the EXC option on, the pre processor doesn
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Water Quality
Thu, 02/26/2004 - 6:43am — Tom

Well, the model will definitely reproduce algal blooms quite accurately on a eutrophic system if the boundary conditions, initial conditions, and kinetic coefficients are set up correctly (see the Rimov Reservoir algal bloom comparisons in the User's Manual). You can look at the limiting factor for algal growth in the snapshot output file if you turn LIMC on in the control file to ON. This will tell you what is limiting algal growth. One piece of information that is not output is the effect of temperature on algal growth. Make sure that the values for AT2 is set to a temperature that the epilimnion reaches during the observed algal bloom and that AK2 is set to 0.99. If you are comparing to observed chl a values, make certain your ratio is for OM to chl a and not C to chl a as the model state variable is g/m^3 of dry weight algal biomass. You will have to be more specific with the error message you are getting when running the model. Also, keep in mind that the preprocessor does not check for all potential errors in the input files. It is simply too difficult to think of all sources of errors and check for them.[addsig]
Thu, 02/26/2004 - 9:16am — InesTrindade

Hi Tom! Thank you for your answer . I will follow your guidances. About the error, I can not be more precise, since the model just do not run! I introduce the extinction coefficients (calculated from the Secchi disc measurements) as a function of time, entered at difference frequencies... Well, I will see with the changes what will be my new results! Then I will tell you. Thank you in the same! [addsig]
Thu, 02/26/2004 - 1:04pm — Tom

You have to get some error message unless the computer locks up on you. What is the error message?[addsig]
Fri, 02/27/2004 - 8:57am — InesTrindade

Hi Tom. The error message I get is run-time error M6203 MATH - exp OVERFLOW error Image PC Routine Line Source W2.exe 0064BBA9 Unknown Unknown Unknown W2.exe 0064BA07 Unknown Unknown Unknown W2.exe 0064BB61 Unknown Unknown Unknown W2.exe 00654578 Unknown Unknown Unknown W2.exe 0067CF1E Unknown Unknown Unknown W2.exe 00671FC8 Unknown Unknown Unknown W2.exe 0063C809 Unknown Unknown Unknown W2.exe 0052108C CE_QUAL_W2 4815 w2_generic.f90 W2.exe 00683909 Unknown Unknown Unknown W2.exe 00666839 Unknown Unknown Unknown kernel32.dll 77E614C7 Unknown Unknown Unknown. Can you help me please?Thank you very much [addsig]
Mon, 03/01/2004 - 7:00am — Tom

Well, you are getting an math overflow in the exponentiation routine. Send me all the input files (do not zip them up) and I will take a look. I'm fairly certain that you have something wrong in the inputs that the preprocessor did not catch in order to get this message.[addsig]
Fri, 03/05/2004 - 11:48am — Tom

In case anyone is following this post, Ines had set the nitrogen half-saturation values for algal growth three orders of magnitude greater than what they should have been. As a result, the model did exactly what he was telling it to do - be severely nitrogen limited for algal growth. The values he was using were flagged in the preprocessor output. Lesson to be learned - always run the preprocessor and take the warnings seriously.[addsig]
Tue, 09/04/2007 - 7:39am — yingmei liu

The reservoir I work on has 4 branches and 2 tributaries. I compare the simulated chla value with observed data and find that the algae growth at two stations in the main branch close to dam is normal. But, there are few algae production by the model at another two stations at the upstream of the two tributaries. We normally do not observe algae in the inflow. So,I set the algae inflow from the two tributaries to be zero and let the initial algae concentration in the waterbody drive the algae growth. By the way, I simulate three algae growths including blue-green, green and diatom. After running the model, I find blue-green alage dominate all the time. There are green algae growth sometime but no diatom at all. This is not true for the real world. The model indicates the limiting factor for blue-green and green is light and diatom for Si. I have tried changing kinetic parameters for three algae groups and initial algae concentrations but didn't solve the problem. Would you please let you know your opinion about the two questions? Thanks.
Tue, 09/04/2007 - 2:01pm — chris

Hi Yingmei, It's been my experience that if one algae group is dominating that indicates that kinetic parameters you've given that group provides it with a big competitive advantage. I'd look over the growth rates, half saturation concentrations, light saturation values, respiration rates, etc. of the algae compartments and make the values for the greens and diatoms closer to that of the blue-greens. Also check the temperature coefficients. chris
Fri, 09/14/2007 - 8:54am — nick

From your description you mention diatoms are limited by silica. Be sure silica (DSI and PSI) are included in the simulation, check the inflow and in-situ concentrations, and check the silica half-saturation for diatoms.