Simplified Model of Nitrogen and Phosphorus Transformation and Transport

The simplified model consists of three components (flow model, transport model, and nutrient (nitrate (NO3), ammonium (NH4), and phosphate (PO43-)) load estimation) implemented in six separate modules as follows:

  • The proto-module (0-Preprocessing) aids in preparing soil datasets derived from the Soil Survey Geographic Database (SSURGO), which includes hydraulic conductivity, porosity, texture, and spatial distribution.

  • The first module (1-Groundwater Flow) consists of a simplified flow model that uses smoothed topography to approximate the water table and calculate the magnitude and direction of groundwater seepage velocity.

  • The second module (2-Particle Tracking) calculates flow paths based on the first module’s results of velocity direction and magnitude.

  • The third module, the Vadose Zone MODel (3-VZMOD), is optional and estimates the vertical soil flow and transformation processes for ammonium (NH4), nitrate (NO3), and phosphate (PO43-) within the Vadose Zone below the OSTDS. This estimation is based on the number of OSTDS points, soil conditions, and the depth between the drainfield and the water table.

  • The fourth module (4-Transport) uses an analytical solution to the advection-dispersion equation to simulate the movement of NH4, NO3, and PO43- plumes. The Transport Module warps plumes along their paths to reflect realistic environmental conditions.

  • The fifth module (5-Load Estimation) calculates the mass load-input, -output, and -removal for NH4, NO3, and PO43- for both surface water bodies and plumes that do not reach water features.

The modules are each described in detail below.

Subsections: - 0-Preprocessing for preprocessing steps. - 1-Groundwater Flow for understanding groundwater flow. - 2-Particle Tracking on particle tracking. - 3-VZMOD for vertical zone modeling. - 4-Transport for transport modeling. - 5-Load Estimation for load estimation techniques.