The Research On The Nitrogen Pollution Status And Transmission Flux In Lanzhou Section Of The Yellow River

Nitrogen is one of the key elements which cause eutrophication.The nitrogen content in the river has been greatly increased,causing eutrophication and many other environmental problems.Study on the nitrogen pollution characteristics and transmission fluxes of the rivers are of great significance for the restoration of river health and recognition the Impact of human activities intensity and scale on the the ecological environment.To research the changes of the nitrogen pollution in the Yellow River in Lanzhou City,Xincheng Bridge section and Yaner Bay section were selected along the Yellow River in Lanzhou City.Through monthly sampling and measuring nitrogen concentrations(total nitrogen and dissolved inorganic nitrogen-DIN)in 2007,the nitrogen pollution level was analysisd and evaluated,also the nitrogen content transformation characteristic was disscussed and N transmission fluxes were calculated.The Xincheng Bridge section:TN content was 1.531～2.373mg/L.Organic nitrogen content was 0.81～1.689mg/L,accounting for 49.26～72.23 percent of the total nitrogen;nitrate nitrogen content was 0.302～0.875mg/L,accounting for 16.80～45.13percent of the total nitrogen;NH₄⁺-N content was 0.030～0.311mg/L, accounting for 1.96～15.03 percent of the total nitrogen.The Yaner Bay section:TN content was 2.378～3.682mg/L.Organic nitrogen content was 0.9901～1.8815mg/L,accounting for 36.01～60.24 percent of the total nitrogen;nitrate nitrogen content was 0.769～1.37mg/L,accounting for 25.49～47.86 percent of the total nitrogen;NH₄⁺-N content was 0.250～0.822mg/L,accounting for 10.51～26.94 percent of the total nitrogen.Nitrogen concentrations were higher in the downstream than in the upstream.TN content was 24.67～42.68 percent,organic nitrogen content was 2.15～34.96 percent, nitrate nitrogen content was 18.69～60.73 percent,and NH₄⁺-N content was 52.3～85.44 percent higher in the downstream than in the upstream.The Xincheng Bridge section:in the dry seasons(from May to October),TN content was 2.1338 mg/L,organic nitrogen content was 1.257 mg/L,nitrate nitrogen content was 0.669mg/L,NH₄⁺-N content was 0.208mg/L;in the wet seasons(from November to April of the next year),TN content was 1.861 mg/L,organic nitrogen content was 1.257 mg/L,nitrate nitrogen content was 0.609 mg/L,NH₄⁺-N content was 0.157 mg/L.TN content was 12.78 percent,organic nitrogen content was 12.89 percent,nitrate nitrogen content was 8.97 percent,and NH₄⁺-N content was 24.52 percent higher in the dry seasons than in the wet seasons. The Yaner Bay section:in the dry seasons(from May to October),TN content was 3.3845 mg/L,organic nitrogen content was 1.467 mg/L,nitrate nitrogen content was 1.134 mg/L,NH₄⁺-N content was 0.783rag/L;in the wet seasons(from November to April of the next year),TN content was 2.7977mg/L,organic nitrogen content was 1.329 mg/L,nitrate nitrogen content was 1.000 mg/L,NH₄⁺-N content was 0.468mg/L.TN content was 17.34 percent,organic nitrogen content was 9.41 percent,nitrate nitrogen content was 11.82 percent,and NH₄⁺-N content was 40.23 percent higher in the dry seasons than in the wet seasons.In 2007,nitrogen transmission fluxes across the Xincheng Bridge section were 61696.03 tons,which contained 59.65 percent of organic nitrogen,31.51percent of NO₃^--N,8.84percent of NH₄⁺-N.nitrogen transmission fluxes across the Yaner Bay section were 95117.97 tons,which contained 46.78 percent of organic nitrogen, 34.84percent of NO₃^--N,18.38percent of NH₄⁺-N.Transmission fluxes of nitrogen accross the Yaner Bay section were 35.14 percent higher than the Xincheng Bridge section.The result show that transmission fluxes of nitrogen of the Yellow River in Lanzhou City are closely related with human production and daily life activities.