Impervious surfaces such as rooftops, paved roadways, runways, and parking lots shed rainwater into storm drains and gutters where it accumulates in catch basins in the unsaturated subsoil layer. These hard surfaces shunt rainwater, with its load of dissolved and accumulated particulate nitrogen, away from plant uptake and storage. In areas where soils are not very porous, precipitation with its load of nitrogen may run off of natural areas instead of percolating into the soil. By contrast, Cape Cod's very porous soils promote rapid infiltration of rain so that surface runoff from vegetated areas is not common.