Where Cj is the concentration of solute j ;\(\theta\) is the water content; q is the Darcy velocity
vector; D is the hydrodynamic dispersion coefficient
tensor; \(R_{j}\) is the reaction rate of solute j .
Multicomponent reactions involved in the model included aerobic
respiration (AR), nitrification (NI) and denitrification (DN). The
organic matter (DOC) was represented by the chemical formula ”CH2O”. All
the reaction equations are as follows: