Review of Water Quality of Miyun Reservoir

The reservoir's pollution came from soil erosion,waste of animals such as livestock and fish,rubbish and waste water of villages and towns,loss of fertilizer,and nutrient release of the reservoir's deposit.The inorganic pollutants such as total nitrogen and phosphorus in Miyun Reservoir were mainly from Chaohe River basin while organic pollutants such as chemical oxygen demand(COD) and biochemical oxygen demand(BOD) mainly from Baihe River basin.Most of the pollution load came into Miyun Reservoir during the flood season.The concentration of total nitrogen in Miyun Reservoir was higher while that of total phosphorus was lower from 1980 to 2002.Total nitrogen,COD and chlorophyll had an increasing trend year by year.Dissolved oxygen(DO) and transparency(SD) were high,and bacterial,colon bacilli and micro-cystins were low.Water quality of Miyun Reservoir was in mesotrophic condition before 1990s,and reached meso-eutrophic condition after 1990.The first outbreak of blue green algae in Miyun Reservoir happened during the warm season of 2002.