[Sources and transformations of nitrogen in the Fuhe River of the Baiyangdian Lake]

The sources and transformations of nitrogen in the Fuhe River were investigated by application of nitrogen isotope methods. The results showed that the values of delta15N in ammonium and nitrate were 1.35 per thousand-8.01 per thousand and -6.69 per thousand-8.36 per thousand, respectively. The industrial and municipal wastewater from the Baoding City contributed high ammonium to the river. In drying season, the processes of nitrification and denitrification were affected by both of water and sediment. In wetting season, ammonium was mainly absorbed by plants, and loss rate of nitrate was about 86.3%. The nitrate removal by denitrification reached 44.6%, whereas that by plant uptake was 55.4%, indicating the importance of vegetation in nitrogen removal. Thus, restoration of local vegetation in the river would be the key to relieve eutrophication in the lake.