Abstract: Nitrogen (N) and phosphorus (P) migration and transformation are complex in the watersoil interface. It is significant to probe the characteristics of N and P losses in watersheds for managing nonpoint source pollution. In this paper, five runoff plots (5 m×20 m) were set to examine runoff in a Moso bamboo (Phyllostachys edulis) forest stand around the Fushi Reservoir watershed in northern Zhejiang Province from May 2012 to October 2013, and the migration characteristics of N and P losses were analyzed in the Moso bamboo forest stand. The results showed that, in the 16 observed surface runoff events, the differences in surface runoff amount were obvious among the different plots, with the maximum runoff being 0.98 m3. N was the main lost nutrient element in the Moso bamboo forest stand. The concentrations of NO₃^--N, NH₄⁺-N, TN and TP in the runoff water ranged from 0.039-1.017, 0.039-2.547, 2.069-5.393 and 0.020-1.205 mg·L^-1, respectively. These variables were greatly influenced by the rainfall and runoff water. Moreover, the correlation between N or P loss and runoff amount was properly fitted by a quadratic equation. On October 12th, 2012, due to typhoon “FITOW”, the runoff reached the maximum with an average of 0.81 m³, and the losses of TN and TP were 2.300 and 1.716 g, respectively. Hence, we concluded that during the period of plant nongrowing season and heavy rain, there was a great risk of N and P losses with runoff in this region, causing potential nonpoint source pollution around the Fushi Reservoir.

Key words: ¹³C, ¹⁵N, elevated CO₂, organic matter decomposition, nitrogen mineralization, oak