Table 3.
Comparison of soil F&T mechanisms for mechanistic watershed models. Loading sources are excluded from the table as they are generally consistent for all models, including fertilizer, manure application, and atmospheric deposition of N. All models that span multiple media, except for CARMEN, consider biological N fixation. F&T processes that move nutrients into and out of the soil compartment are distinguished from those that transform nutrients between nutrient forms.
[(+) or (−) refers to an increase or decrease in concentration of associated species in the water column]
| Model Name | ||||||
|---|---|---|---|---|---|---|
| Criteria1 | CARMEN | He et al. 2011 | NEWS 2 | SWAT | IMAGE-GNM | |
| Soil Nutrient Pools | Nitrogen | TN | BN, DN, HN, NH4, NO3 | DON, DIN, PN | NH4, NO3, DN, HN, PON, BN | TN |
| Phosphorus | TP | - | DOP, DIP, PP | DP, HP, PO4, POP, BP, PIP | TP | |
| Transport and Removal Mechanisms (into and out of grid cells) | Export, Retention | - | N (−) | DIP, DIN, DON, DOP | - | - |
| Surface runoff | TN | NO3 | - | NO3, PO4 | TN, TP | |
| Lateral flow | TN | NO3 | - | NO3 | TN | |
| Erosion | TP | - | PN, PP | PIP, PON | TN, TP | |
| Deep groundwater | TN | - | - | NO3 (−) | - | |
| Revaporization | - | - | - | NO3 (+) | - | |
| Volatilization | - | NH4 (−) | - | NH4 (−) | TN (−) | |
| Nitrification | - | NO3 (−) | - | - | - | |
| Denitrification | - | NO3 (−) | - | NO3 (−) | TN (−) | |
| Vegetative Cycling | TN (−), TP (−) | NH4 (−), NO3 (−), BN (+/−), DN (+) | DIN (−), DIP (−) | NO3 (−), PO4 (−), BN (+), BP (+), DN (+), DP (+) |
TN (−), TP (−) | |
| Groundwater use | - | - | - | NO3 (−) | - | |
| Nutrient Species Transformation Processes (within grid cells) | Adsorption | TP (−) | - | - | PO4 (−) | - |
| Weathering | - | - | DIP (+) | - | TP (+) | |
| Mineralization | - | DN (−), HN (−), NH4 (+) |
- | PO4 (+), DN (+/−), DP (+/−), HN (−), HP (−), NO2/NO3 (+) | - | |
| Nitrification | - | NH4 (−), NO2/NO3 (+) | - | NH4 (−), NO2/NO3 (+) | - | |
| Humus Stabilization | - | DN (−), HN (+) | - | DN (+/−), DP (+/−), HN (+/−), HP (+/−), PIP (+/−) | - | |
| Decay | - | - | - | DN (−), DP (−), HN (+), HP (+) |
- | |
| Groundwater decay | - | - | - | NO3 (−) | - | |
TP - total phosphorus, TN - total nitrogen, DON - dissolved organic nitrogen, DIP - dissolved inorganic phosphorus, DOP - dissolved organic phosphorus, PP - particulate phosphorus, PN - particulate nitrogen, NO2 - nitrite, NO3 - nitrate, NH4 - ammonium, NH3 - ammonia, PO4 - phosphate, BN - biological nitrogen, BP - biological phosphorus, DN - detrital nitrogen, DP - detrital phosphorus, HN - humic nitrogen, HP - humic phosphorus, POP – particulate organic phosphorus, PON – particulate organic nitrogen