Modelling Phosphorus

[ArcSWAT]

I am modelling P transport into a reservoir, loacted at the outlet of
a watershed. I have a question regarding the output of SWAT for P. Is
the parameter Mineral P in the output files refers to soluble or
active mineral P.

I would really appreciate your help.

Thank you.

J.

[Jim Almendinger]

SWAT uses the module Qual2E (or a newer variant) to model nutrient processing by streams.  My understanding is that, traditionally, in this model MINERAL_P is interpreted to be the inorganic, soluble P (SRP, or ortho-P, considered to be the same here).  And, ORGANIC_P is considered be everything else -- principally particulate P, whether organic or inorganic.  I'm skeptical, because I don't didn't find whether Qual2E explicitly modeled adsorption / desorption of P from mineral particles -- which one would think ought to be an important form of P in rivers.  

   In addition to MINERAL_P and ORGANIC_P, Qual2E also keeps track of chlorophyll -- which is from algae, and Qual2E assigns a P content to that algal load.  So technically, this is another part of the P load.  

    However, when a reach delivers its load to a reservoir, the reservoir receives the MINERAL_P and ORGANIC_P load -- but I don't think it keeps track of the Chlorophyll load.  I could be wrong here... but in general I would carefully track your output to test whether the model is correctly passing P between reaches and reservoirs.  

   Currently --- I just do not use the stream water-quality routines (Qual2E).  In this configuration, the model keeps good track of P coming off the landscape and what gets routed downstream, both through the reaches and through the reservoirs (and what may be deposited in reservoir sediments).  

-- Jim

Dr. James E. Almendinger, Senior Scientist

St. Croix Watershed Research Station

Science Museum of Minnesota

16910  152nd St. N

Marine on St. Croix, MN  55047

tel: 651-433-5953 X 19

fax: 651-433-5924

email: din...@smm.org

web: www.smm.org/SCWRS/