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Nutrient export coefficients

jgoldsteinjgoldstein Member
edited October 2014 in RIOS
We are using RIOS in the Florida Panhandle as part of a watershed planning process. From the Florida Dept of Environmental Protection, we have obtained good information on nutrient export coefficients for LULC categories in the format of Event Mean Concentrations (mg/l). But RIOS wants inputs as annual values (e.g., kg/ha/yr).

We are working on a process to convert the Event Mean Concentrations (EMC) to annual values - not fully sure yet how to do this and welcome any input if you've done this before.

But more to the point, my question is - since RIOS produces relative scores and normalizes input layers based upon min/max values, maybe it's okay to use the EMC values? My sense is that the conversion of EMC to annual values would result in roughly the same relative differences between values. I can't confirm that without going further... but if I'm right about this, I wanted to see if my logic that using EMC values would in fact be fine and would not distort anything in the RIOS analysis.

Thanks for any input you can provide!
Josh Goldstein


  • adrianvogladrianvogl Member, NatCap Staff
    Hi Josh,

    EMCs are a measure of concentration (unit pollutant per unit of water), whereas the load is a measure of mass (unit pollutant per unit of area). The relative amounts of EMCs for different land uses can change when converting to a load, depending on the size of the watersheds for which they are measured and the flow rates. If these are standardized when the EMCs are defined, then your sense is correct that the relative loads (kg/ha/yr) will stay in the same proportions. But, if the EMCs for different land uses are associated with different size contributing areas and storms, then you should do the conversion to ensure that the load sizes are standardized.

    To convert EMCs (mg/L) to kg/ha/yr, it is necessary to know the flow rate and the size of the contributing area. The conversion is then:
    load (kg/ha/yr) = EMC * Q * 86,400 sec/yr * 1kg/1e6mg * 1/A
    where Q = flow rate (L/sec)
    A = contributing area (ha)

    Let me know if you have any more questions on this.

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