Excessive nutrient levels?

[Cecilie Hansen]

hi,

for a while, i've been struggling with sky-high nutrient levels in the NoBa model. We became aware of it when updating to the new code, but then realized that it has been with us for a while. I've tried 'everything', and am hoping that someone has some good advice that is yet to be tested. Among the things that i've tried (and it has fixed a few issues, so was not a waste of time!) are:

-rebuilding the physics 

-removing any initial level of detritus

-removing all species - i'm now only dealing with ZS, PS, PL, DF, BB, PB and the detritus groups. When I remove the ZS - the nutrient levels are ok, so it's something connected to the biology

-playing with rate of nitrification, growth rates, half-saturation rates of the few species left in the test-model

Any tips or tricks that can help me move on? it's probably just caused by some stupid parameterization combination:) 

(for those wondering what excessive means - i'm starting with levels of NH3 at roughly 14, and within two years it has reach 600 in some of the most problematic polygons - all polygons are at least 10x initial value within 2-3 years, and then levels out, whereas some polygons level off at 100 x initial value....there are only low differences between layers).

best, cecilie

[Cecilie Hansen]

solved:) bug in input file (input.nc), so happy that I finally figured this one out! now i 'just' have to get the phytoplankton to thrive in a less nutrient rich environment;) 

best,

cecilie

[Fulton, Beth (Environment, Hobart)]

G’day

 

Glad to hear you sorted it.

 

If future if anyone hits this issue and its not an in.nc oops something else to watch is the positive feedback you get when nutrients get so high they shut down denitrification. That usually happens because of excessive detritus. If that is happening its usually because you have out of control vertebrate waste generation or large phytoplankton blooms. If you’ve quadruple checked your vertebrate abundances and they are correct for the system and you really do have large seasonal blooms (e.g. in an upwelling) then increase the decay rate of detritus in.nc to mimic burial rates that happen in those systems. That solution should only be used as a last resort however as it is usually actually an indicator of something awry with a parameter setting or initial conditions

 

Cheers

 

Beth

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