Suspended algal biomass is assumed to be directly proportional to chlorophyll . Therefore, the algal biomass loading to the stream can be estimated as the chlorophyll loading from the land area. Cluis et al. (1988) developed a relationship between the nutrient enrichment index (total N: total P), chlorophyll , and algal growth potential in the North Yamaska River, Canada.
4:5.1.1
where is the algal growth potential (mg/L), is the chlorophyll concentration in the surface runoff (/L), is the surface runoff flow rate (m/s), is the total Kjeldahl nitrogen load (kmoles), is the total phosphorus load (kmoles), is a coefficient and is an exponent.
The chlorophyll concentration in surface runoff is calculated in SWAT+ using a simplified version of Cluis et al.’s exponential function (1988):
if or and 4:5.1.2
if or ( and ) 4:5.1.3
if , and 4:5.1.4