Nitrite

The amount of nitrite ($NO_2^-$) in the stream will be increased by the conversion of $NH_4^+$ to $NO_2^-$ and decreased by the conversion of $NO_2^-$ to $NO_3^-$. The conversion of $NO_2^-$ to $NO_3^-$ occurs more rapidly than the conversion of $NH_4^+$ to $NO_2^-$, so the amount of nitrite present in the stream is usually very small. The change in nitrite for a given day is:

$\Delta NO2_{str}=(\beta_{N,1}*NH4_{str}-\beta_{N,2}*NO2_{str})*TT$ 7:3.2.8

where $\Delta NO2_{str}$ is the change in nitrite concentration (mg N/L), $\beta_{N,1}$ is the rate constant for biological oxidation of ammonia nitrogen (day$^{-1}$ or hr$^{-1}$), $NH4_{str}$ is the ammonium concentration at the beginning of the day (mg N/L), $\beta_{N,2}$ is the rate constant for biological oxidation of nitrite to nitrate (day$^{-1}$ or hr$^{-1}$), $NO2_{str}$ is the nitrite concentration at the beginning of the day (mg N/L), and is the flow travel time in the reach segment (day or hr). The local rate constant for biological oxidation of ammonia nitrogen is calculated with equation 7:3.2.5. The calculation of travel time is reviewed in Chapter 7:1.

The rate constant for biological oxidation of nitrite to nitrate will vary as a function of in-stream oxygen concentration and temperature. The rate constant is calculated:

7:3.2.9

where is the rate constant for biological oxidation of nitrite to nitrate (day or hr), is the rate constant for biological oxidation of nitrite to nitrate at 20C (day or hr), is the dissolved oxygen concentration in the stream (mg O/L), and is the average water temperature for the day or hour (C). The second term on the right side of equation 7:3.2.9, , is a nitrification inhibition correction factor. This factor inhibits nitrification at low dissolved oxygen concentrations.