The Distribution And Evaluation Of Sediment Nitrogen Forms In Urban Lakes Of Yixing City,Western Taihu Lake

Sanjiu lake was the watershed of rivers in western Taihu lake,was also a typical urban lake.The combined forms and spatial distribution characteristics of sediments in Sanjiu lake were conducive to analyze the sources and transmission process of Taihu lake,as well as to provide scientific basis for comprehensive development of city water body.In this paper,the spatial distribution characteristics and influence factors of different nitrogen forms in the sediments of Sanjiu lake were studied,the nitrogen migration law between the sediments and water body was discussed and the pollution level was also evaluated by single factor index method and organic index method.The main research conclusions were as follows:?1?In the interstitial water,the concentrations of NH₄⁺-N were much higher than that of overlying water and the contents of NO₃^--N were far lower than that of overlying water.The sediments were the“source”of NH₄⁺-N and the“sink”of NO₃^--N of overlying water.The concentration of total nitrogen?TN?was in the range of 306¹035mg/kg,and its spatial distribution was consistent with the distribution of sediment organic matter.The concentration of TN in Tuanjiu was higher than that in Dongjiu and Xijiu,and the content in Dongjiu was in line with Xijiu.The concentration of extractable nitrogen?TTN?accounted for 59.5%of TN,therefore,it would result in huger potential hazard to the water.The WAEF-N was the dominant form of TTN.In addition,in the sediments of Dongjiu and Xijiu,IEF-N and WAEF-N were the main forms of nitrogen,therefore,its risk of endogenous release is greater.Different sediment forms can be transformed into one another and its content distribution was depended on the mutual influence of the physical,chemical properties of sediments and the pH,conductivity and TN of the overlying water.Among those factors,the influence of organic matter was the most significant.?2?The vertical distribution of TN of the columnar sediment showed obvious consistency and the content of surface sediments was higher than the bottom layer.The IEF-N was the dominant form of convertible nitrogen in columnar sediments,which was different from surface sediment.In most profiles,IEF-N and WAEF-N were the main forms of nitrogen,which were consistent with the surface sediments.The endogenous risk was great in each sedimentary period.?3?According to the results of pollution evaluation,in Sanjiu Lake,the organic pollution of sediments was light.Relatively speaking,the nitrogen and phosphorus pollution were more serious,which would be great harmful to the environment.The phosphorus pollution was most serious in Dongjiu lake and the nitrogen pollution was most serious in Tuanjiu lake.In the two lakes,nitrogen and phosphorus pollution were great in most sampling sites,which were belong to the degree of severe pollution.