PHOSPHORUS EXPORT FROM A LOW-DENSITY RESIDENTIAL WATERSHED AND AN ADJACENT FORESTED WATERSHED

Low density residential subdivisions (< 4.0 units/ha) constitute the majority of new development in Maine's lake watersheds. This study investigates the effect of such development on phosphorus export from adjacent low density residential and forested watersheds. Total phosphorus and discharge measurements were taken of stormwater runoff from a 3.5 ha watershed with uniform, low density residential development. Annual areal phosphorus export from the watershed was 0.44 kg/ha in 1982, a relatively dry year, and greater than 1.5 kg/ha in 1983. In 1983, simultaneous total phosphorus and discharge measurements were taken of stormwater runoff from the residential watershed and an adjacent 2.4 ha forested watershed during eight storm events. For these storm events, the geometric mean of the ratios between developed and forested watersheds for runoff volume was 1.7:1; for peak discharge, 2.6:1; for mean flow-weighted phosphorus concentration, 4.3:1; and for phosphorus export, 7.2:1.