The sources and magnitude of agricultural nutrient export from a catchment are not identical. Nitrogen and phosphorus export patterns and their Critical Source Areas (CSAs) were identified in a 1.74-km 2 mountainous agricultural catchment. During baseflow the concentration of nitrate nitrogen (NO3-N) increased downstream, but dissolved reactive phosphate (DRP) concentration decreased downstream from the uppermost site to the outlet. The upstream area—segment 1 is a CSA for DRP export, but the outlet areas—segments 6, 7 are CSAs for NO3-N loss during baseflow. Two precipitation events with a similar precipitation magnitude but different duration were used to test the AGricultural Non-Point Source (AGNPS) model. During stormflow, CSAs for both N0 3 -N and DRP, defined through the AGNPS model tested, are side-slope areas where citrus has been planted.