Enrichment ratio for phosphorus losses

[Manal Askar]

Hello,

I am trying to figure out the original source of the enrichment ration equation in SWAT+. On the website they mention that it is obtained from Menzel 1980 but I couldn't find the equation. All I could found is the equations below from a different reference showing different equations than what is used in SWAT. They are also using the sediment yield rather that the sediment concentration used in the SWAT+ model.

Quoting from Sharpley 1980 --> "From a review of published data on enrichment ratios, Menzel (1980) concluded that the logarithmic relationship 

In (enrichment ratio) = 2 — 0.2 In (sediment discharge)

appeared to hold for a wide range of soil and vegetative conditions. In the present study, a general relationship of 

In (enrichment ratio)= 2.48 - 0.27 In (sediment discharge)

was obtained for all P amendments, slopes, and rainfall intensities studied. The general relationship calculated from the present study is similar to that suggested by Menzel (1980)."

Your help is greatly appreciated.

Thanks,

Manal