Characteristics of nitrogen and phosphorus losses with surface runoff in typical sub-watersheds of Jiulong River watershed

Five typicl sub-watersheds in the Jiulong River watershed were chosen for monitoring nitrogen and phosphorus losses.Results of the monitoring and analysis show that in the event of storms in agriculture-based watersheds,the N loss with the runoff is dominated with soluble N and the P loss with P combined with silt whereas in natural-forest-based ones,the situation is completely different.Under storms,the maximum total N concentration in the runoff is 2.9-11.3 times as much as that in the runoff normal and the maximum total P concentration 2.9-20.5 times as much.Throughout the entire course of runoff,water volume and N & P concentration vary sharply with the time,showing a similar trend.The concentrations of total N & P and their various forms come up to their respective peaks almost at the same time.The contents of silt N and soluble P fluctated within a limited range whereas those of soluble N and silt P do within a large one.