The ratio of direct runoff (DR) to TR was used to examine the effect of DR and base-flow (BF) on nutrient discharge during rainfall
events. TR was divided into DR and BF. The portion of BF was separated from the TR by drawing a horizontal line from the point at
which the DR begins (Viessman and Lewis, 2003). Therefore, in the
present study DR means the increased portion of the runoff during
a rainfall event and contains components such as overland flow,
channel precipitation, soil water, and a portion of the increased
BF. DR/TR for each rainfall event were calculated as