Dissolved nutrient load (kg) from source area k, for precipitation or snowmelt on day t, is given
by:
LDkt = 0.1 Cdkt Qkt Ak
(1.1.15)
Where:
Cdkt = dissolved nutrient concentration (mg/l)
Qkt = runoff 9cm), calculated by CNE (Section 1.1.1.3)
Ak = source area (ha)
0.1 is a units conversion constant
Dissolved Nutrient Concentrations . Dissolved nutrient concentrations (Cdkt) in runoff vary
primarily due to crop type. Secondary considerations include animal waste and manufactured fertilizer
input, soil type, and the timing of precipitation events (Haith and Tubbs, 1981). Local dissolved
nutrient flow-weighted mean concentration or event mean concentration edge-of-field data may be
available for local modeling applications. Use of local data is preferred over the selection of default
values (Table 1.1.2).
Table 1.1.2. Dissolved Flow-weighted Mean
Concentration Nutrients in Agricultural Runoff.
Phosphorus
Land Use
(mg/1)
(mg/1)
Fallow1
2.6
0.10
Corn1
2.9
0.26
Small Grains1
1.8
0.30
Hay1
2.8
0.15
Pasture
13.0
0.25
Barn Yards2
29.3
5.10
0.33
0.00074
Forest
1
Dornbursh, et al. (1974)
2
Edwards, et al. (1972)
3
Johnson (1975)
4
Omernik (1977)
(after Haith and Shoemaker, 1987)
Gilbertson provides additional default Cd values for incorporated and unincorporated manure
and rainfall and snowmelt runoff in Table 1.1.3.
1.1-13
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