NDR subsurface phosphorus output is 0?

Hi,

I did not find this problem in other topics. The NDR model runs great and outputs look good, but each time I run it, no matter how I tweak the calibration parameters, I get zeros in the column “Sub_p_Id”, and high values in “Sub_n_Id”. And I don’t see notable differences in the biophysical table between N and P that could explain this. Do you know if it’s a normal result in the NDR model?

I can share the data with you if you need,
Thank you!
Raphaël

Hey @Raph117 ,

It looks like this is expected for the NDR model. From the NDR User’s Guide:

Because phosphorus particles are usually sediment bound and less likely to be transported via subsurface flow, the model uses the subsurface option only for nitrogen …

It does seem strange that the Users’s Guide mentions phosphorous in some of the Data Needs sections related to subsurface. I’ll get more clarification here, but hopefully that helps.

Doug

Well that cleared up my confusion, thanks! But yes, my questioning started when the User’s Guide mentioned subsurface phosphorus in the data section.

I have one last question related to NDR outputs. My comprehension is that “x_exp_tot” in the watershed shp output is the sum of nutrient that reaches the stream, but this phrase in Overview section “At the watershed/subwatershed outlet, the nutrient export is computed as the sum of the pixel-level contributions.” makes me think that “x_exp_tot” is actually the sum at the watershed outlet, which is not the same thing.

Do you know if it’s the sum of nutrient export at the watershed outlet, or the sum of nutrient export that reaches the stream?

Thanks again!
Raph

Hi @Raph117 -

I agree that it does not make sense to have subsurface P inputs to the model if the model only models subsurface N, this has confused me for a long time.

As for the watershed results, x_exp_tot is calculated by doing a sum over the x_export.tif raster, within each watershed. So it represents the total amount of nutrient reaching a stream, within the watershed flowing to a particular outlet. NDR does not model in-stream processes, so the assumption is that once nutrient reaches a stream anywhere within the watershed, it’s a problem at the watershed outlet.

~ Stacie

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Hi @swolny

Excellent, thanks to you and @dcdenu4 for the quick feedback. Really appreciate you work for this community.

Raph

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