| Nitrogen was one of the most limited elements of plant photosynthesis and primary production processes in terrestrial ecosystems. Inorganic nitrogen content ware generally maintained at a relatively low level in wetland sediment, which is often the most important limiting nutrients. Nitrification was an important part of nitrogen biogeochemical cycles in wetland sediments. The study of nitrification in wetland sediments was not only revealed the wetland nitrogen biogeochemical behavior and its ecological significance, but also has significance to explore the wetland eco-system productivity and the processes of nitrogen interface processes.In order to understood the role of nitrification in pollution purification and nitrogen cycle in Liaohe estuary reed wetland sediments, and further offered references for ecosystem restoration and management of Liaohe wetland estuary. In this paper, Nitrobacteria, nitrification and its impact factors were discussed based on the method of on-site incubation and laboratory simulation in Liaohe estuary wetland sediments in June, August and September 2009, respectively. It is also that the selected several major factors (temperature, pH, salinity, ammonia concentration, organic matter and petroleum hydrocarbon content) on nitrification were analyzed by the control experiments designed used single-factor analysis method. The net nitrification rate was determined by the method of on-site simulation cultivation column, the potential nitrification rate was determined by the method of laboratory liquid simulation cultivation, the number of AOB was determined by the method of MPN-Griess. The relationship between nitrification and environmental impact factors was analyzed by correlation analysis and regression analysis of SPSS13.0 software. The results showed as follows:(1) In Liaohe estuary reed wetland sediments, the number of ammonia-oxidizing bacteria(AOB) ranged from 0.54×104 to 5.69×104 cells·g-1 with an average of 2.21×104 cells·g-1 in June and ranged from 1.90×104 to 7.90×104 cells·g-1 with an average of 3.61×104 cells·g-1 in August and ranged from 0.12×104 to 0.36×104 cells·g-1 with an average of 0.21×104 cells·g-1 in September, the potential nitrification rates ranged from 9.72 to 16.45 mmol·m-2·h-1 with an average of 12.54 mmol·m-2·h-1 in June and ranged from 14.66 to 24.62 mmol·m-2·h-1 with an average of 18.71 mmol·m-2·h-1 in August and ranged from 8.22 to 12.37 mmol·m-2·h-1 with an average of 9.69 mmol·m-2·h-1 in September, the net nitrification rates was 0.41mmol·m-2·h-1 in June and ranged from 0.20 to 0.53 mmol·m-2·h-1 with an average of 0.35mmol·m-2·h-1 in August and 0.23 mmol·m-2·h-1 in September. Potential nitrification rates were significantly higher than the net nitrification rates. The AOB abundance, potential nitrification rates and net nitrification rates were demonstrated highest in August and lowest in September. The nitrification was accelerated by reed rhizosphere effects.(2) Temperature, dissolved oxygen, ammonia concentration in the overlying water and pH, organic matter, total nitrogen content, ammonia nitrogen content and the number of AOB were the main environmental impact factors on nitrification by SPSS 13.0 statistics analysis(p<0.05) in Liaohe estuary wetland sediments, and it also showed ammonia concentration in the overlying water and pH, ammonia nitrogen content in sediments were key impact factors on nitrification by partial correlation analysis in study area.(3) Selected several key impact factors such as temperature, pH, ammonia concentration, salinity, organic matter and petroleum hydrocarbon content, explained its impact on nitrification by single-factor analysis, and also analyzed their degree of influence on nitrification using linear regression and path analysis. The results showed the size of order is:salinity>petroleum hydrocarbon content>ammonia concentration >organic matter content>pH value> temperature.(4) Nitrification played an important role in nitrogen cycle in Liaohe River estuary wetland. Combined with the measured data of this study, it is estimated that the Liaohe estuary wetland sediment could change 1.02×105kg ammonia to nitrate per day, were equivalent to 44.2% and 10.9% of NH4+-N and NO3--N flux into the sea from the Liaohe River Basin, which has significant impact on the nitrogen cycle in Liaohe estuary reed wetland.
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