Nutrient Delivery Ratio: Nutrients Retained

Software Support
1

Hi all,

I am new to the Nutrient Delivery Ratio Model and I am having trouble identifying which output would represent the amount of nutrients retained in each pixel. In other words the amount filtered. Would this be effective_retention_x?

Thank you for the help!

Sarah

2

Hi @sarahhalperin ,

I believe you are correct. The intermediate output effective_retention_{p|n} (depending on phosphorous or nitrogen) is the effective retention per pixel. It pertains to the eff_i equation in the Users Guide. However, these models were developed at the watershed and sub-watershed scale, so looking at pixel values should only be used to better understand the model and system and not for exact measurements.

When looking at scenarios with different LULC inputs it is easier to compare relative retentions at the watershed level by looking at the differences in export.

Hopefully this helps!

Doug

3

Hi @dcdenu4,

Thank you! That is very helpful! The reason I ask is I am interested in the amount of {p | n} that is retained as this would be the ecosystem service. So if I am understanding correctly there isn’t an output of the amount of {p | n} in kg/pixel absorbed only an export. I guess one could look at the inverse of the export.

I really appreciate your help!

Best,

Sarah

4

HI @sarahhalperin -

As @dcdenu4 noted, the way that we usually quantify nutrient “retention” is to take the difference between a baseline landscape/management practices and a scenario. The model itself doesn’t really quantify the total amount of nutrient retained on each pixel from what comes at it from downslope + what is generated on the pixel.

Check out this forum post, which has a discussion about nutrient retention that you might find interesting. It’s for NDR 3.7.0, but I believe that the same is still true about 3.9.0.

~ Stacie

2 Likes
5

Hi @swolny !

I want to estimate the contribution of different types of natural environments (e.g. wetlands) to nutrient retention (in tons) at the city scale. From what I understand from the questions previously asked, it is not really possible to estimate the retention of each pixel - unless you go through the difference between a baseline landscape and a scenario. I was wondering if you see a problem with the following approach :

  1. Run the model once to get the total nutrient retention for the whole territory with the baseline land use layer.

  2. Assuming that nutrient retention and export from bare soil is zero, reclassify the land use layer to convert wetlands (or other natural environment type of interest) to bare soil. This would give the total nutrient retention for the whole area, but with the contribution of wetlands removed.

  3. To obtain the wetland contribution (nutrient retention in tonnes/year), subtract the result obtained in step 1 from that obtained in step 2.

Is this what you are referring to by using a scenario?

Thank you very much!

Anne-Sophie