Analysis of daily phosphorus yield and streamflow data collected before and after implementation of agricultural best management practices in the Johnson Brook watershed in south-central Maine indicated statistically significant reductions in phosphorus loading in all flow categories. Reduction of median loadings for five flow categories ranged from 26% to 90%. The annual total phosphorus yield was reduced 17% after implementation of the best management practices. The observed phosphorus yield reduction is considerable because of two streamflow factors. First, the period after implementation of the best management practices had eight more storms. Periods of storm runoff in the post-implementation period had 31 days with greater than average streamflow, and a maximum daily streamflow more than three times greater than those observed in the pre-implementation period. Second, the annual streamflow was 128% greater in the year after the management practices were implemented. Because the potential for phosphorous transport increases with runoff, and greater yields are possible when the volume of water increases, a higher phosphorus yield would be expected in the post-implementation period than during the pre-implementation period, if other factors had remained unchanged. The reductions in phosphorous yield in the study area are not expected to have a significant effect on the eutrophic conditions observed in Lovejoy Pond. Phosphorous concentrations in the pond will continue to be capable of supporting algal blooms. However, the intensity and duration of blooms are expected to be less than those observed before best management practice implementation. (Author 's abstract)
