Study Of Nitrogen Transformation Process Of Wetlands And Overlying Water In Pearl River Estuary

This paper take the Pearl River estuary wetland as the research object, using the laboratorysimulation experiments to explore the migration and transformation rule of nitrogen in mangrove,phragmites and tidal flats areas wetlands, the impacts of salinity, nitrogen, carbon and nitrogenratio, hydrodynamic load conditions on nitrification and denitrification systematically, andcompare the denitrifying enzyme activity and nitrogen removal of the load of different types ofwetland sediments, at the same time, make a comparative analysis in diversity of microbialcommunity structure between different types of wetland sediments. Expecting lay the foundationon wetland nitrogen cycle and ecological restoration of the Pearl River estuary. The results of thestudy are as follows.In the Pearl River estuary, the ammonia nitrogen adsorption of sediments in mangrove,phragmites and tidal flats areas present obvious difference, the load-bearing capacity of ammoniain the plant area’s sediments was stronger than tidal flats area. Along with the increase of salinityin overlying water and sediment from storage media gradually became source of ammonia. Andshort time disturbance of water contributed to adsorption. In addition, the adsorption increasedwith the ammonia concentration in overlying water, but the adsorption rate was decreasing, thechange of the nitrogen adsorption in the plant area sediments was more obvious.The nitrification and denitrification rate of mangrove and phragmites wetland were higherthan tidal flats. Denitrification in sediment interstitial water was more obvious than in sedimentsoverlying water, and in sediments overlying water, nitrification was more outstanding. Increasethe salinity could promote nitrification and denitrification under the condition of low salinity (0to10‰), and high salinity (10to30‰) could inhibit the nitrification and denitrification process.Nitrification rate and denitrification rate increased by the rise of ammonia nitrogen and carbonnitrogen ratio. High dissolved oxygen concentration would accelerate nitration process andinhibit denitrification process. Among them, the dissolved oxygen is the key factor ofnitrification rate, and the influence of carbon nitrogen ratio conditions on the denitrification ismost significant.The denitrifying enzyme activity of mangrove sediments was higher than tidal flats. Theincrease of salinity and dissolved oxygen could inhibit the denitrifying enzyme activity, and the increase of nitrogen load and carbon nitrogen ratio could improve the denitrifying enzymeactivity. While, the increase of salinity and dissolved oxygen was not conducive to nitrogenremoval of load, the change of the concentration of ammonia nitrogen had no significant effecton removal efficiency of nitrogen load, but improve the carbon nitrogen ratio could increasenitrogen load removal efficiency.In order to further verify the above conclusion, through the mangroves and tidal flatswetland sediment microbial diversity analysis found there were many kinds of nitrifying bacteriaand denitrifying bacteria existed in mangroves and tidal flats wetland sediment. In addition,relative to the tidal flats wetland, the flora structure of mangroves wetland is more stable, andhas higher species richness and community similarity. As a result, the mangrove wetland isstronger than tidal flats wetlands in nitrogen load carrying capacity.