The Spatial Temporal Change Of Nitrification And Denitrification In Liaohe Estuary Sediments And Influencing Factors Of Nitrogen Removal

Nitrification and denitrification are important processes in nitrogen cycle, andthey are the processes of transfering the available nitrogen in land and water systeminto gaseous nitrogen（N2or N2O）, which play an important role in the global nitrogencycle. They have a Key role in keeping nitrogen balance among the lithosphere，hydrosphere,biosphere and atmosphere.Estuary wetland as the natural barrier can accommodate and purify pollutantsand reduce the volume of pollutants into the sea, which take a very important part incontrolling nutrition status of estuaries and offshore water and global nitrogen cycle.Recent years, industries, agriculture and aquaculture are developing rapidly; at thesame time, with the increase of human activity intensity, the emission of industrialwastewater and domestic wastewater are going up year by year, leading into thenitrogen content in the estuarine wetlands increasing obviously, coastal wetlands havebeen severely polluted, especially the nitrogen and phosphorus pollution, which makethe phenomenon of red tide happen frequently. Therefore, it is high time for us tostudy the nitrification and denitrification in wetland of Liaohe estuary. It will provideimportant reference for further understanding the influence of the estuary wetland onthe marine environment and the ecological restoration of the wetland ecosystem.We take estuary wetland as the research object, using the method of on-sitesimulation to explore the similarities and differences between the vegetated wetland（A group） and non-vegetation wetland（B group） in all aspects,and make a comparativeanalysis between them; we draw a deep analysis of nitrification and denitrification ofwetlands in different seasons,at the same time, we analysize the impacts of carbonand nitrogen ratio of sediments on nitrification and denitrification rates,meanwhile,weelaborate the variation on the nitrogen removal rate in different seasons and discuss the influence of some environmental factors （temperature, salinity, pH, etc.） onnitrification and denitrification. Expecting provide some reference on wetlandnitrogen cycle and bioremediation of degraded wetlands, we have made the followingfindings.（1）The nitrification and denitrification rates of liaohe estuary wetlands changeobviously with the seasons in natural conditions. The nitrification rate of vegetation（reed） wetlands range from9.05to13.44mg kg^-1 d^-1, the non-vegetation wetlandsrange from5.83to7.14mg kg^-1 d^-1, it appears that the nitrification rates of all thevegetation wetland and non-vegetation wetland increase from June to September,while they decrease in October. When it comes to denitrification, denitrification rateof vegetation wetland range from4.48to6.90mg kg^-1 d^-1, the non-vegetation wetlandrange from3.48to5.29mg kg^-1 d^-1.（2） In the case of different carbon and nitrogen ratio, the nitrification intensity ofthe vegetation sets appear that: AC10（10:1）>AC15（15:1）>AC5（5:1）, the optimumcarbon-nitrogen ratio is10, the maximum value is24.51mg kg^-1 d^-1; whlie thedenitrification intensity of non-vegetation sets appear that:BC15（15:1）> BC10（10:1）>BC5（5:1）, the maximum intensity is13.77mg kg^-1 d^-1. But whether it is the vegetationwetland or the novegetation wetland, the changing trend of nitrification anddenitrification intensities are similar.（3） It was found that the TN removal rate of reed wetlands was much higher thanthe naked wetlands in natural state; the C/N ratio significantly increased the TNremoval rate, and this effect in naked wetlands is more remarkable than reedswetlands; The results show that TN removal rate increased in peak in August orSeptember; the TN removal rate is maximum in reed wetlands when the C/N ratio is10:1,while in naked wetlands the optimum C/N ratio is15:1. Based on field survey,thepH、moisture content、salinity and temperature are the important factors that influenceTN removal rate.（4） We can conclude that the nitrification intensity of vegetation wetlandsobviously higher than the non-vegetation by comparing the various characteristicfeatures of vegetation and non-vegetation wetlands, which illustrates that the nitrification and denitrification abilities of non-vegetation wetlands are weak.