Nitrogen Forms And Distribution In The Sediment Cores Of Dianchi Lake

Dianchi Lake has been one of the most eutrophic lakes in China since1980s. It's a hard problem for the control of Dianchi Lake eutrophication that the lake was totally deprived of self-purification under the severely internal pollution for a long time. The form and distribution of nitrogen in sediment are the basis for estimation of internal nitrogen load and prediction on the transfer behavior of nitrogen at the sediment-water interface, it's very important for learn about the pollution situation, trace the pollutant source, and predict the trend of deposition evolution, because the sediment is a recorder of the evolution of lake's ecological environment.The content of total nitrogen and various nitrogen form in eleven sediment cores(0-50cm) sampled in the Waihai section of Dianchi Lake were measured in the research. It was shown that the content of TN was relative higher than the other domestic and foreign lakes'. The average content of TN in all the samples was2319.20±387.27mg/kg. Trans-N was the main part of TN and the SOEF-N was the main form of Trans-N, the average content of Trans-N was1230±148.52mg/kg. The order of the content of four transferrable nitrogen form in the sediment was SOEF-N>WAEF-N>SAEF-N>IEF-N; and the WAEF-N made the most contribution to lake eutrophication than the other nitrogen forms'.Dianchi Lake was divided into three part by the content of TN to study the nitrogen's horizontal distribution:northern lake, central lake and southern lake. The order of the content of TN in this three part was southern>northern>central. However, the order of Trans-N's content was northern> southern≈central, and the nitrogen pollution level was northern> southern> central in order from on a whole.The vertical profiles of TN and various nitrogen form are as follows:the content of TN was relative lower at0-5cm, and increased to the highest level at5-15cm in the most of sediment cores, and then changed little with the depth. The contents of IEF-N at different depositions were always low; the content of WAEF-N was relative high at0-5cm, and decreased significantly at5-15cm, then changed a little with the depth; the content of SAEF-N was relative low at0-5cm and increased sharply at5-15cm, then remained stable below; the content of SOEF-N was very low at0-5cm and increased sharply at10-20cm, the changed a little below.The internal nitrogen load and its bio-availability were estimated in the study. The weight of TN in the0-15cm deposition of Dianchi Lake was45353.6t, and IEF-N's was4125.3t, WAEF-N's was6680.5t, SAEF-N's was3623.9t, SOEF-N's was9926.3t; the Trans-N's was24356t, FN's was20997.6t. The weight of bio-available nitrogen was about14429.7t, accounted to TN31.8%averagely. The results were showed that the weight of TN at10-15cm, which was deposited in1972-1988approximately, was highest than the other depositions', it was agreed with the contamination history of Dianchi Lake. In addition, the transfer behaviors of nitrogen at the sediment-water interface and the effect to the water caused by implementing the Diversion Project from Niulanjiang River to Dianchi Lake was predicted and analyzed.