anchor.diff:              Rsm(iFeOB)=Rsm(iFeOB)+R(21)
               
               F(i,50)=F(i,50)-dz(i,k)*R(21)         !FeOA
  +!
  +!  - Re-oxydations using SO4
  +!
  +           !R(23)=K23*poro(k)*pw(i,k,iwCH4)*pw(i,k,iwSO4)         
   !
   !  Add reaction
   !
  
positive.code:             Rpw(iwSO4)=Rpw(iwSO4)+R(19)
              
              F(i,48)=F(i,48)-dz(i,k)*R(19)*4.0d0   !S0 
  
              R(20)=K20*cff1*sm(i,k,iMnOA)
              Rsm(iMnOA)=Rsm(iMnOA)-R(20)
              Rsm(iMnOB)=Rsm(iMnOB)+R(20)
  
negative.code:             
              F(i,19)=F(i,19)-dz(i,k)*R(6)          !NH4
              F(i,20)=F(i,20)-dz(i,k)*R(6)*2.0d0    !O2
              
             !R(7)=K07*cff1*(sm(i,k,iFeOA)+sm(i,k,iFeOB))*pw(i,k,iwPO4) ! (B)
              R(7)=K07*cff1*sm(i,k,iFeOA)*pw(i,k,iwPO4) ! (A)
              Rsm(iFeOA)=Rsm(iFeOA)-R(7)
              Rpw(iwPO4)=Rpw(iwPO4)-R(7)
              Rsm(iFeOP)=Rsm(iFeOP)+R(7)
              
              F(i,21)=F(i,21)-dz(i,k)*R(7)         !FeOA
              F(i,22)=F(i,22)-dz(i,k)*R(7)         !PO4
  !
  !  - Re-oxydations using MnO2
  !
             !R(8)=K08*cff1*pw(i,k,iwFe_)*(sm(i,k,iMnOA)+sm(i,k,iMnOB)) ! (B)
              R(8)=K08*cff1*pw(i,k,iwFe_)*sm(i,k,iMnOA) ! (A)
  