Miyun Reservoir has become the most important source of drinking water for Beijing area.In the past 20 years

with the economic growth and development

nutrient load of Miyun Reservoir increased gradually

which will result in an increasing risk of the bloom of harmful algae.To address this issue

water samples collected from the river basins at different scales were analyzed.Total nitrogen(TN)

nitrate(NO3--N)

ammonium (NH4+-N)

total phosphorus(TP)and index of potassium permanganate(CODMn)were measured to estimate flux and occurrence of nutrients.Based on the analysis of hydrological processes for each basin

the sources of nutrients that entered into the Miyun Reservoir were estimated.The results showed that TN concentrations in almost all the samples exceeded the environmental quality standards for drinking surface water of China. Concentrations of TP in 15.9%samples were exceeded the standards.It was estimated that 40.3%of nutrients in Miyun reservoir were from point-source pollution

while the other 59.7% were from non-point source pollution.Meanwhile

50.1%of the TN

49.1%of the NO3--N

39.0%of the NH4+-N

26.5%of the TP and 36.8%of the CODMn that entered into the Miyun reservoir were from point-source pollution

while 49.9%of the TN

50.9%of the NO3--N

61.0% of the NH4+-N

73.5% of the TP and 63.2% of the CODMn that entered into the Miyun Reservoir were from non-point source pollution.