5.6 Necessary Reductions

It is helpful to look at TMDLs in terms of reductions necessary to meet the standards. Watershed runoff phosphorus loads need to be reduced 62% overall, with reductions varying from 43% to 69% for individual watershed portions. The same reduction percentages apply to average export and concentrations (Table 5.6). The runoff TMDLs are based on requiring the same runoff concentration (183 μg/L) for each watershed portion.49

The atmospheric load is the only load that is not included in Table 5.6; all other loading, including the watershed load’s WLA portion, are represented. Internal load is zero due to Canfield-Bachman model incorporating as implicit in BATHTUB.