Study On Biochemical Processes Of Nitrogen Transformation On The Interface Between Water And Sediment

Entrophication of water is one of the most important problems presently.The basic reason of entrophication is the excessive nutrients in water. The endogenous pollution becomes the principal facter which has bad effect on source water quality after the extraneous pollution has been effectively eliminated.The eutrophication level of reservoir water is due to the release of nitrogen-phosphorus nutrients from sediments.The exchange of nitrogen-phosphorus nutrients in the interface of sediment-water is affected by the characteristics of overlying water, microorganisms, etc.And the mechanism and process is much more complex.So it is necessary to do further study about the inner pollution of sediment.Taking different point of sediment samples of Tangyu reservoir in Xi'an City as an example. Study about the distribution characteristics of nitrogen-phosphorus forms.The results about nitrogen showed that the transferable nitrogen's mean content covers 41% of total nitrogen conten.SOEF-N,which covers 69% of transferable nitrogen,is the dominant form of transferable nitrogen. In the other three transferable nitrogenIEF-N,WAEF-N and SAEF-N,NH4+-N is the dominant form. Study about the distribution of phosphorus speciation showed that total phosphorus is in a high level. The average content of inorganic-phosphorus(IP) account for about 70% of TP,which is also the main form of TP.The experiment is about the sediment of Xi'an Heihe Jinpen Reservoir water.Through the indoor static simulation of sediment-water interface environment, study about the effects of microorganisms on nitrogens in sediments under the comparison of non-sterilization and sterilization series.(1) Through the natural sealing process to achieve the anaerobic condition in low temperature,it showed the effect of microorganisms is one of the processes in transformation of nitrogens.There was also physical-chemical process in it.But microorganisms is more important in nitrogen releasing process.In addition,under the effect of microbiology,nitrogen can release from the interface as gas under anaerobic conditions,which is called denitrification.(2) The analysis of organic matter in overling water showed that dissolved organic matter is increased and then decreased in the experiment.At the first part of the experiment,lots of dissolved organic matters released into pore water,then spread into the overlying water.Especially the intermediates are increased greatly because of decomposition of microorganisms and then decomposed into small molecules. So at the end of experiment,the fluorescence signal become weaken in the overlying water.UV type matters and intermediate matters are disappeared,which is all because the activity of microorganisms.(3)The tests of total nitrogen and organic matter of the sediment before and after the experiment showed that both of them were decreased in non-sterilized and sterilized series.In non-sterilized series,total nitrogen released for 41μg/g,organic matter decreased for 0.53%.In sterilized series,total nitrogen released for 20μg/g,organic matter decreased for 0.24%. Both were enough to explain that the microorganism played a significant role in nitrogen releasing and organic matter decomposing.The study of the influence factors about nitrogen release from sediment showed that the reactor which add carbon source released the most quality nitrogen from sediment.It means raising C/N in water had a good effect in promoting nitrogen released from the interface between water and sediment.The reactor which add nitrate is also affect a lot,but weaken than the reactor added carbon source.