| Nansi Lake located in Weishan county, is the largest lake in Shandong province and the northern area of China, which consists of four lakes (Nayang Lake, Dushan Lake, Zhaoyang Lake, Weishan Lake) without clear demarcation of the lake district from north to south and is an important buffer lake of the South-to-North Water Diversion Project (east route). The water quality of the lake district has great influence on industrial and agricultural production, the ecological environment, and the water quantity of he South-to-North Water Transfer East Route Project. The water quality should meet national grade Ⅲ(GB3838-2002) according to the pollution planning contents and Implementation of the South-to-North Water Diversion Project (east route).Under the effective control of external source pollution, Nansi Lake is threatened with nitrogen and phosphorus accumulated in the sediment under the joint actions of physical, chemical and biological factors. Therefore, the study of the distribution characters of sedimental pollution and its release rule seem to be particular importance for the preservation of water quality. Some researches have been done on the distribution characters of phosphorus and heavy metal pollution and its release rule. Whereas, the special studies of nitrogen which is another limiting factor of the eutrophication of water bodies is relatively less.Based on above,"research-simulation experiment" idea was used, physical and chemical properties of water body and sediment were analyzed, as well as adsorption/desorption characteristics of N was studied. Major conclusions were described as follows:The quality of water which is heavily polluted meet the Grade Ⅲ, IV of the China surface water quality standard (GB3838-2002), The water of the lake is affected by light pollution and medium pollution. This shows the ability of wastewater dilution and dispersion is limited in Nansi Lake. The contradiction between the ecological environment and natural resources on the one hand and economic and social development on the other is becoming increasingly conspicuous.Different nitrogen forms in the seven surface sediments of Nansi Lake were separated by means of sequential extraction, and analyzed their contents, distribution characteristics and related factors. The transferable nitrogen can be divided into four forms, ion exchangeable form (IEF-N), weak acid extractable form (WAEF-N), strong alkaline extractable form (SAEF-N) and strong oxidant extractable form (SOEF-N) and analyzed their contents, distribution characteristics and influencing factors. The results indicate that the content of total nitrogen and different translate nitrogen fractions (except SAEF-N) in the upper Nansi Lake is higher than the lower lake district. The ratio of TTN, TN in the lower lake is higher than the upper Nansi Lake. Nitrogen mainly combines with grained sediments in Nansi Lake. There is no significance correlation of TN, ammonia nitrogen between sediments and water, which proves that most of the nitrogen comes from its main inflow rivers. As a result, the N/P ratio in sediments is only about1.5-4.5below Redfield index, while the N/P ratio in water is13.7-24.1higher than Redfield index, which farther illustrates that the nitrogen and phosphorus come from its main inflow rivers in Nansi Lake. Although the concentration of TN descended greatly in the last one decade, phosphorus is the most restricting nutritious element.Sorption isotherms of Gummonium and adsorption thermodynamics parameter on surface sediments taken from Nansi Lake were determined in laboratory. The results of ammonia nitrogen adsorption dynamics on sediments showed that the adsorption included two phases:fast and slow adsorption. The adsorption on sediment mainly occurred within0-6h. Langmuir equation couldn’t simulate or simulate results couldn’t reach remarkable level while the ammonium adsorption isotherms curves were fitted to Henry equation and Freundlich equation and simulate well. The Henry model can well describe the results of the ammonium sorption isotherms at low concentrations, and the adsorption-desorption equilibrium concentration varied from0.98to4.16mg/L.The research on the effect of the different temperature and pH values on the exchange law of the nitrogen in the interface between sediment and water was observed.It is found that the ability of adsorption increases when temperature decreases. The adsorption is not only a physical adsorption process but also a chemical process related to heat-exchange.When the ammonia nitrogen balance concentration is less than1.5mg/L, the influence of pH value on the adsorption quantity is not obvious.But when the ammonia nitrogen balance concentrations is more than1.5mg/L and the pH altered from5to9, the adsorption ability of ammonium was bigger than that in acidic condition.Results of ammonia nitrogen release indicated that the first order kinetic equation can well describe ammonia nitrogen release characteristics of sediment from Nansi Lake. Process of ammonia nitrogen release from studied samples mainly occurred within0～360min, and then amount of released ammonia nitrogen attended to a dynamic equilibrium gradually. Parameters of ammonia nitrogen release kinetics of the studied samples were related to composition, there was significant positive correlation with content of total nitrogen and total phosphorus while relationship with the content of organic matter and sand size fraction was not significant. Parameters of ammonia nitrogen release kinetics of sediment were related to nitrogen forms, there was significant positive correlation with content of transformed nitrogen while relationship with non-transformed nitrogen was not significant.The pH value have significant effeets on exchange of ammonia nitrogen in the interface between sediment and water. The release of ammonia nitrogen from the sediment would be promoted in the acid or alkaline water-body. Thus, the control of the pH value of water body could effectively inhibit the secondary pollution of sediment to water-body. The amount of ammonia nitrogen release increased with tile temperture rising. |
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