Inorganic/Soluble Phosphorus
Last updated
Last updated
The amount of soluble, inorganic phosphorus in the stream may be increased by the mineralization of organic phosphorus and diffusion of inorganic phosphorus from the streambed sediments. The soluble phosphorus concentration in the stream may be decreased by the uptake of inorganic P by algae. The change in soluble phosphorus for a given day is:
7:3.3.4
where is the change in solution phosphorus concentration (mg P/L), is the rate constant for mineralization of organic phosphorus (day or hr), is the organic phosphorus concentration at the beginning of the day (mg P/L), is the benthos (sediment) source rate for soluble P (mg P/m-day or mg P/m-hr), is the depth of water in the channel (m), is the fraction of algal biomass that is phosphorus (mg P/mg alg biomass), is the local growth rate of algae (day or hr), is the algal biomass concentration at the beginning of the day (mg alg/L), and is the flow travel time in the reach segment (day or hr). The local rate constant for mineralization of organic phosphorus is calculated with equation 7:3.3.2. Section 7:3.1.2.1 describes the calculation of the local growth rate of algae. The calculation of depth and travel time is reviewed in Chapter 7:1.
The user defines the benthos source rate for soluble P at 20C. The benthos source rate for soluble phosphorus is adjusted to the local water temperature using the relationship:
7:3.3.5
where is the benthos (sediment) source rate for soluble P (mg P/m-day or mg P/m-hr), is the benthos (sediment) source rate for soluble phosphorus at 20C (mg P/m-day or mg P/m-hr), and is the average water temperature for the day or hour (C).
Table 7:3-3: SWAT+ input variables used in in-stream phosphorus calculations.
Variable Name | Definition | File Name |
---|---|---|
AI2
: Fraction of algal biomass that is phosphorus (mg P/mg alg biomass)
.wwq
RHOQ
: Local algal respiration rate at 20C (day)
.wwq
BC4
: Local rate constant for organic phosphorus mineralization at 20C (day)
.swq
RS5
: Local settling rate for organic phosphorus at 20C (day)
.swq
RS2
: Benthos (sediment) source rate for soluble phosphorus at 20C (mg P/m-day)
.swq