Study Of Nitrogen Forms And Releasing In The Sediments From Dongchang Lake

Urban lake is an important water form in the cities. It can provide a variety ofimportant ecological support for the city. And it is also the most intense zone ofinteraction between human activities and natural processes. With the rapiddevelopment of the city, the input of a large number of nutrients has seriouslyaffected the normal function that the urban lake water plays and restricted theregional social and economic development.The research work of the nitrogen in theurban shallow lake sediments is of great significance for China’s urban waterenvironmental protection. Meanwhile it is closely linked to the geochemical cyclesof shallow lake sediments and water eutrophication problem. And it has been one ofthe hot spots of scholars from various countries.The paper, in support of the National Key Water Project, Dongchang Lake asthe object of study, mainly using the experimental method of analysis and simulation,studied the existing features and releasing regulation of different nitrogen formsfrom surface sediments of the Dongchang Lake, to provide demonstration of supportand theoretical basis for the protection and management of northern water shortageurban lakes among which the Dongchang Lake is a representative. These are theconclusions of the study:①Dongchang Lake surface sediment is fine and mainlycomposed of silty sand, sandy silt, silt and clay silt. The sorting of the whole lakesurface sediments is poor. Gravels range from middle sharp category to sharpcategory.②In the voyage of April2009, the mean level of Chemical OxygenDemand (CODMn) in Dongchang Lake, was the Ⅲ water standard. The averageconcentration of detected CODMnof the other voyages was higher than the waterstandard IV. TN concentration of Dongchang Lake was consistently high, higher thanthe water standard Ⅲ. In particular, in September2010, TN concentration almostexceeded the water quality standard V1time.③TN content of Dongchang Lakesurface sediment samples ranges from1071.31to1450.55mg kg-1. Nutrient level of Dongchang lakebed mud is not high compared with other lakes that have beenstudied much.④T he average transformable nitrogen（TTN）of Dongchang Lakesurface sediments is963.55mg kg-1, and average non-transformable nitrogen （NTN）is305.09mg kg-1. With the increased levels of sediment contamination, theproportion of nitrogen that TTN accounted TN decreased and nitrogen tended to bestable form. The release order of different forms of TTN was: SAEF-N（50.52%）>SOEF-N（40.87%）>IEF-N（4.52%）>WAEF-N（4.09%）. The correlation relationshipbetween them was significant, and that between them and TN was poor. It showedthat there is a strong mutual transformation between different forms of exchangeablenitrogen. But exchangeable nitrogen had a smaller weights in TN and was not keyfactors that infect TN.⑤A verageexchangeable nitrogen (EN) and mineralizablenitrogen（MN） of sediment was47.68mg kg-1and210.72mg kg-1respectively.With the accumulation of sediment nitrogen pollution in Dongchang Lake, nitrogenbioavailability enhanced and nitrogen utilization increased. Different exchangeablenitrogen in the sediment has an intense mutual transformation process and NH4-Nhad a dominant position in EN.⑥The releasing process of NH4-N of DongchangLake surface sediment was quick at first, then slowed down gradually and reachedreleasing balance after about5h. In the present experimental conditions, neutral orweak alkaline conditions and a high-temperature environment are more beneficial tothe release of NH4-N.⑦T he TN release of Dongchang lakebed mudtrended to besimilar to the releasing of NH4-N. In the present experimental conditions, the TNrelease of samples substantially tends to decrease with increasing pH and increasewith increasing temperature.