Soluble Phosphorus

The soluble phosphorus model was based on runoff reduction only. The observations censored from (Dillaha et al., 1989) for the nitrates were also censored for soluble phosphorus. The soluble phosphorus model has the weakest relationship of all the nutrient models (R$^2$ = 0.27), yet both the slope and intercept were significant (p = 0.01).

$DP_R=29.3+0.51R_R$ 6:5.1.6

where $DP_R$ is the dissolved phosphorus reduction (%); and $R_R$ is the runoff reduction (%). Like nitrate, there is a significant reduction in soluble phosphorus (29.3%) with no corresponding runoff reduction. Experimental observations of soluble phosphorus reduction at low runoff reductions are highly variable. Dillaha et al. (1989) found reductions in soluble phosphorus ranging from 43% to -31% with near zero runoff reduction. The minimum reduction predicted by equation 6 could be the result of mechanisms similar to those cited for the removal of nitrates, or simply an artifact of experimental variability.