Fig. 4. Chain of equations that link environmental component variables in the simulation model. Equation 4 calculates the rate of change of fecal coliforms concentration (FC) in a given estuarine sector. FC depends on: (i) the wastewater coliform load into that sector, dependent on population (P) and the level of fecal coliform removal rate (R), (ii) the transport across the estuarine sector, from upstream to downstream, (iii) bacterial decay.