Abstract: Mojiagou Watershed was chosen to study small watershed comprehensive control. It is one subbasin in Shitoukoumen Reservoir Watershed which is the important drinking water sourcr for Changchun City, the capital city of Jilin Province. Five structure management practices, i.e. contour farming, terrace cultivation, grain to green, chemical fertilizer reduction, and constructed wetland, are selected to reduce pollution loads. The optimal management complete model consisits of two interacting components: an objective function and many constraints. The objective function is to minimize the measure construction coast. The constraints are: the resevoir water quality standards, the area to be transformed and nonnegative. The decisive factors are: the area constructed with terraces and the fertilizer applied. The optimal management model is used to simulate pollutant concentration in Mojiagou Watershed under three stages of twenty-one possible schemes. The resulting practical scenarios for three atages are achieved. In 2011 to 2020, the concentration for TP can meet grade III standard (≤0.05 mg • L^-1) in resevoir when the corn fields of less than five degree in gradient are farmed along the contour line, terrace area no change and other fields turn grain to green. To attain TP grade II (≤0.025 mg • L^-1) in 2021 to 2030, there is a need of 0.03 km² constructed wetland based on the first strategy. With all corn fields be turned to grow trees and no fertilizer application, the water quality will meet TP grade I standard in 2031 to 2050. The modeling framework developed (≤0.01 mg • L^-1) in the present study is an efficient tool for planning a watershed-wide implementation of pollution control practices for mitigating runoff pollution impact on the receiving water bodies.

Key words: Non-point source pollution, optimal management model, management scheme, small watershed, TP