# Nitrogen in Rainfall

Lightning discharge converts atmospheric $$N_2$$ to nitric acid which can then be transferred to the soil with precipitation. The chemical steps involved are:

&#x20;step 1: ![](https://lh6.googleusercontent.com/3XMDvTeoE9aIcQR4KDsQ_7yNE0fTI_CUsiCn5ze-Sfae7y0IFjBX8XVlnVOnVFjgRtFdaHuB7C_3hHvgtrV62LQRIKxqazsg94gynejyY4MUmRtsqoXBFjknV_zHJMsItjIrLTQo)        (monoxide)

step 2: ![](https://lh6.googleusercontent.com/aKJfA96M3P5oCdV5yMDJGR47_I544FbwnsMu_94Yi0fOfR4ShS0FJ4TC-bICr5A6mkcVkzA3n2EPKh6jbN7C6hLKuOdKR3_ZTUYZ5CWgdhxjn5IctBjdgkMVrIhsUvdumF0TYmBz)         (dioxide)

step 3: ![](https://lh4.googleusercontent.com/GITs42wAWNQ2AarEgs2J4h7TDYUBjcJZiwktnxW6OGitoJXtqMEgjaC6zxUtTIASmT7Ruw38GMkvR5QQgpjjyJPiqZ0vNDOgfFZHqlWHzYOimcgqiGl4LZrr7zVDCmHyqpqzxkqj) (nitric acid and monoxide)

More nitrogen will be added to the soil with rainfall in areas with a high amount of lightning activity than in areas with little lightning.

The amount of nitrate added to the soil in rainfall is calculated:

$$NO_{3rain}=0.01*R_{NO3}*R_{day}$$                                        3:1.5.1

where $$NO_{3rain}$$ is nitrate added by rainfall (kg N/ha), $$R_{NO3}$$ is the concentration of nitrate in the rain (mg N/L), and $$R_{day}$$ is the amount of precipitation on a given day (mm H$$_2$$O). The nitrogen in rainfall is added to the nitrate pool in the top 10 mm of soil.

&#x20;The amount of ammonia added to the soil in rainfall is calculated:

&#x20;      $$NH_{4rain}=0.01*R_{NH4}*R_{day}$$                                 3:1.5.2

where $$NH_{4rain}$$ is nitrate added by rainfall (kg N/ha), $$R_{NH4}$$ is the concentration of ammonia in the rain (mg N/L), and $$R_{day}$$ is the amount of precipitation on a given day (mm H$$_2$$O). The nitrogen in rainfall is added to the ammonia pool in the top 10 mm of soil.

Table 3:1-4: SWAT+ input variables that pertain to nitrogen in rainfall.

| Variable Name | Definition                                                            | Input File |
| ------------- | --------------------------------------------------------------------- | ---------- |
| RCN           | $$R_{NO3}$$: Concentration of nitrogen in the rain (mg/L)             | .bsn       |
| rammo\_sub    | Atmospheric deposition of ammonium (mg/L) values for entire watershed | .atm       |
| Rcn\_sub      | Atmospheric deposition of nitrate (mg/L) for entire watershed         | .atm       |



