Bacteria can be transported with percolation into the soil profile. Only bacteria present in the soil solution is susceptible to leaching. Bacteria removed from the surface soil layer by leaching are assumed to die in the deeper soil layers.
The amount of bacteria transported from the top 10 mm into the first soil layer is:
bactlp,percβ=10βΟbββdepthsurfββkbact,percβbactlpsolββwperc,surfββ 3:4.3.1
bactp,percβ=10βΟbββdepthsurfββkbact,percβbactpsolββwperc,surfββ 3:4.3.2
where bactlp,percβ is the amount of less persistent bacteria transported from the top 10 mm into the first soil layer (#cfu/m2), bactlpsolβ is the amount of less persistent bacteria present in soil solution (#cfu/m2), wperc,surfβ is the amount of water percolating to the first soil layer from the top 10 mm on a given day (mm HO), is the bulk density of the top 10 mm (Mg/m) (assumed to be equivalent to bulk density of first soil layer), is the depth of the βsurfaceβ layer (10 mm), is the bacteria percolation coefficient (10 m/Mg), is the amount of persistent bacteria transported from the top 10 mm into the first soil layer (#cfu/m), and is the amount of persistent bacteria present in soil solution (#cfu/m).
Table 3:4-3: SWAT+ input variables that pertain to bacteria transport in percolate.
SOL_BD
Οbβ: Bulk density of the layer (Mg/m3)
.sol
BACTMIX
kbact,percβ: Bacteria percolation coefficient (10 m3/Mg)
.bsn