How to input nutrient loadings instead of concentrations?

I have Total Phosphorus loadings, whose unit is metric ton. So it’s appropriate for me to click “use time variable point source MASS loadings” (Fig.a). However, after choosing this option, when I edit the input time series, it seems that what I input is still considered of “concentration” (see mg/L unit in Fig.b), instead of “mass”. What should I do? By the way, where can I find the units in EE about the data I input (I have to click the “current” to see the vertical axis now, I don’t think this is a good method)?
a-2.jpg
b-2.jpg

Please don’t forget this question when you have time. Thanks!

Please don’t forget this question when you have time. Thanks!