> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-3-nutrients-pesticides/phosphorus/phosphorus-in-the-shallow-aquifer.md).

# Phosphorus in the Shallow Aquifer

Groundwater flow entering the main channel from the shallow aquifer can contain soluble phosphorus. With SWAT+ the soluble phosphorus pool in the shallow aquifer is not directly modeled. However, a concentration of soluble phosphorus in the shallow aquifer and groundwater flow can be specified to account for loadings of phosphorus with groundwater. This concentration remains constant throughout the simulation period.

Table 3:2-5: SWAT+ input variables that pertain to phosphorus in groundwater.

| Variable Name | Definition                                                    | Input File |
| ------------- | ------------------------------------------------------------- | ---------- |
| GWSOLP        | Soluble phosphorus concentration in groundwater flow (mg P/L) | .gw        |