Characteristics of nitrogen and phosphorus discharge with runoff from a watershed in the northern subtropical low hilly areas

The study was carried out in the Meicun Watershed,Xuancheng County,Anhui Province,in the northern subtropical low hilly areas by monitoring stream water,in order to illustrate characteristics of nitrogen and phosphorus discharge with surface runoff.The results show that nitrate was the main form of the nitrogen discharged,accounting for 60% of the total lost nitrogen,while particulate-associated phosphorus（PAP）was the main form,accounting for more than 90% of the total phosphorus discharged.There existed positive linear relationships between NO^-₃-N,NH⁺₄-N and total nitrogen（TN）.The discharge of PAP was correlated well with suspended particulates.A significant logarithmic relationship was observed between the discharges of dissolved phosphorus（DP）and PAP.A dramatic seasonal change of nitrogen and phosphorus discharges with runoff was found,showing a decreasing sequence of summer>spring>autumn>winter as a result of seasonal rainfall distribution.Furthermore,rainstorms contributed the most to the discharge of nutrients.Therefore,soil erosion control should be an effective countermeasure in limiting nitrogen and phosphorus loss in the rainy season.