Questions about the nutrient delivery ratio model

CharChar Member
edited April 2018 in General
I followed the users's guide to prepare the data for running the nutrient delivery ratio model.Though the coverage area of DEM is bigger than my study area,one side of my study area is facing the sea.The coverage area of others data inputs are the same as my study area.After running the model many times to have a suitable threshold flow accumulation value by comparing the stream.tif output with the stream line of my study area,I got a stream map that can almost match the stream line of my study area. But the outputx_export.tif is odd.The coverage area of it is smaller than my study area.The value of the raster matching the stream is null. The missing part of the study area is mainly distributed on the edge of it,especially the side of the part facing the sea. So could you help me deal with this?The missing part is green.
Looking forward to your reply!
Thank you!
1164 x 1145 - 174K
Post edited by Char on


  • swolnyswolny Member, NatCap Staff
    Hi @Char -

    First, just making sure that all of your other data inputs cover these areas. If you have NoData in a pixel in any of the model inputs, you will get NoData in that pixel in the output.

    It is normal for the NDR output to show NoData in streams. This is because the model does not do in-stream processing, and only routes nutrient until it hits a stream, then stops processing.

    For your other areas that are missing results, I suspect that they don't have output values because a stream is not defined there. Look at your stream.tif output and see if there are streams in those areas. If there is no stream defined, the model does not have anywhere to route nutrient to, so you end up with no export. I have seen this happen before in flat areas that drain to a lake or ocean. Let me know if this seems to be the case.

    ~ Stacie
  • CharChar Member

    Thank you for answering me so soon! I checked my data inputs carefully , all of them have values in my study area . You are right about the missing areas , the value of these areas in the stream.tif is zero and these areas are either ponds or dry lands next to a ocean. I wonder if it's okay to set the values of these areas including streams to zero in the outputx_export.tif. I'm using InVEST 3.4.4 now.I find the new version no longer provides output\n_retention.tif.Since higher nitrogen or phosphorus export values reflect lower water purification services,could I take the result of outputx_export.tif as a ecosystem disservice ? Or there is some way to get the  output\n_retention.tif in the InVEST 3.4.4?
  • CharChar Member
    Or maybe I could use the older version like InVEST 3.2.0 to get output\n_retention.tif?
  • swolnyswolny Member, NatCap Staff
    We really do recommend using the latest version. I know that in particular a bug or two was fixed in NDR between 3.2.0 and 3.4.4. I'm not sure why n_retention was removed from the output, but the way we often use the result is to compare the current landscape with a scenario of land cover change (usually natural vegetation going to ag or pasture or whatever is likely to occur in that place), and the difference between them represents the value of the current landscape for retaining nutrient. 

    ~ Stacie
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