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How Does the Nutrient Retention Model Handle Huge Lakes?

IceAgeIceAge Member
edited April 2014 in Terrestrial Models
Hi all,
I wondering how the model considers a big lake...
I have a huge one on my Nutrient retention model and it runs but with a very strange results, it seems the water can not be addressed to any "final" direction, as an estuary.
I think could be related with DEM and its analysis inside the Invest code.
So, what could happen in this case?

I attached the Nitrogen retention map below in which the red area (very high retention) represents the lake.
1700 x 2200 - 119K
Post edited by Doug on


  • RichRich Administrator, NatCap Staff
    First of all, this is a beautiful map.

    Secondly, a couple of questions/ideas. Is your lake specified in your land cover map? If so, the behavior will be defined based on the retention and load coefficients you set for that land cover type. Probably you want to set them to 0.0 in that case.

    If the lake is implicit when classifying the stream layer, it will be treated like a stream itself so that when nutrient is routed downhill it'll hit the stream and be exported from the watershed.

    I notice that's a relatively large watershed compared to your others, is it possible that's affecting the amount of output load?

    Is the land cover in that subwatershed a type that has high nutrient loads?

    Finally, you probably want to see what's happening at the pixel level. Take a look at "p_export.tif" and/or "n_export.tif" in your output folder depending on which nutrient you simulated. That'll show you at the pixel level where export is occurring.
  • IceAgeIceAge Member
    Thanks Rich, I'll try to answer your question as you can help me better for mine.
    Yes, my lake is specified in the land cover map and was set to 0.0
    So, if the nutrient routing is based on the DEM, and on that there is no chance for the water to move away from the watershed, how the lake could be treated like a stream?
    No, is not possible that is an "area effect" cause the retention was expressed in kg/ha.
    No, basically inside the problematic watershed there are some others land cover type but the main one was set as water with 0 value retention coefficient.
    At pixel level the situation appears as the picture below shows, strange pattern of the nutrient export compared with all the other sub-catchments.
    The best solution did I find was temporarily remove the problematic catchment.
    What about modify the DEM?
    Cuold be a solution?
  • RichRich Administrator, NatCap Staff
    If the flow accumulation through the DEM where the lake exists is higher than the stream threshold parameter of the model, it could be treated as a stream. In the model this just means any nutrient that hits that stream is washed to the watershed which wouldn't be accurate in your case.

    You said at the pixel level there's a strange pattern? Could you post that? It's possible that your DEM has hydrological pits which dink up the routing in the current version of InVEST. If that's the case, filling the pits in ArcHydro or TauDEM will fix that.
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