[Modelling pollutant loads and management alternatives in Jiulong River watershed with AnnAGNPS]

The modelling package Annualized Agricultural Nonpoint Source Model (AnnAGNPS) was used to predict pollutant loads, and simulate catchment processes and management practices in Jiulong River watershed, a medium-sized mountainous watershed in southeast of China. Four typical sub-watersheds were primarily chosen to calibrate AnnAGNPS model by data collected from storm events during the period of April to September, 2003. The model was further validated in the two biggest branches of Jiulong River watershed, i.e. West river and North river by the data regarding climate, and land using condition in 2002 - 2003. The simulation results show that annual total nitrogen load was 24.76kg/(hm2 x a) and 10.28kg/(hm2 x a) in the West river and North river, respectively, and annual total phosphorus load was 0.67 kg/(hm2 x a) and 0.40 kg/(hm2 x a) in the West river and North river, respectively. With the support of AnnAGNPS model, several management alternatives were separately simulated in the typical sub-watersheds, West river and North river. In the specific cell with cell-ID of 92 in Tianbao and Xiandu sub-watershed, after reforesting in sloping field, runoff surface, sediment yield, total nitrogen load and total phosphorus load cut down with 21.6%, 25.9%, 96% and 79.2%, respectively. In West river, with the cultivation plant changing from banana into rice, the total nitrogen, dissolved nitrogen, total phosphorus and dissolved phosphorus cut down with 23.83%, 25.44%, 9.08% and 19.84%, respectively. In North river, when removing all the hoggerys, nitrogen and dissolved nitrogen cut down with 63.54% and 76.92% , respectively.