Bacteria Decay

A first order decay function is used to calculate changes in bacteria concentrations (Bowie et al., 1985).

$bact_{lpres,i}=bact_{lpre s,i-1}*exp(\mu _{lpres,die})$ 8:5.1.1

$bact_{pres,i}=bact_{pres,i-1}*exp(\mu _{pres,die})$ 8:5.1.2

where $bact_{lpres,i}$ is the amount of less persistent bacteria present in the reservoir on day $i$ (#cfu/100mL), $bact_{lpres,i-1}$ is the amount of less persistent bacteria present in the reservoir on day $i-1$ (#cfu/100mL), $\mu_{lpres,die}$ is the rate constant for die-off of less persistent bacteria in water bodies (1/day), $bact_{pres,i}$ is the amount of persistent bacteria present in the reservoir on day $i$ (#cfu/100mL), $bact_{pres,i-1}$ is the amount of persistent bacteria present in the reservoir on day $i-1$ (#cfu/100mL), and $\mu_{pres,die}$, is the rate constant for die-off of persistent bacteria in water bodies (1/day).

The die-off rate constants are adjusted for temperature using the equations:

8:5.1.3

8:5.1.4

where , is the rate constant for die-off of less persistent bacteria in water bodies (1/day), is the rate constant for die-off of persistent bacteria in water bodies (1/day), is the rate constant for die-off of less persistent bacteria in water bodies at 20C (1/day), is the rate constant for die-off of persistent bacteria in water bodies at 20C (1/day), is the temperature adjustment factor for bacteria die-off/re-growth, and is the water temperature (C).

Table 8:5-1: SWAT+ input variables that pertain to bacteria die-off in the water bodies.