| Nitrification is a critical process in global nitrogen cycle. It connects nitrogen fixation and nitrogen removal by oxidating ammonia to nitrate and nitite. The estuarine wetland has an active role on the river pollutants into the sea with a very good retention, storage and purification function. The nitrogen pollutant loads into the Min River estuarine wetlands which make the eutrophical phenomenon of red tide happen frequently are going up year by year with the increase of human activity intensity. In order to better understand the nitrogen recycle mechanisms and provide scientific references of wetland ecological restoration for this area. The purpose of this paper is to research the spatial and temporal characteristics of sediment nitrification and clarify the main environmental influencing factors in different saline-fresh water wetland of Min River estuary. Three saline-fresh tidal flats in Min River estuary (Shanyutan, Bianfuzhou and Tajiaozhou) were selected as the sample sections, and the field sample collections were conducted respectively in October2012, January2013, April2013and July2013. We conducted the nitrification rates research with the method of matrix derivation, as well as relevant laboratory simulation response experiments about environmental factors.The results showed as follows:①The potential nitrification rates (PNR) of3saline-fresh tidal flats in Shanyutan, Bianfuzhou and Tajiaozhou ranged from0.11to5.41μgN·g-1·d-1with an average of2.22μgN·g-1·d-1, ranged from0to2.51μgN·g-1·d-1with an average of0.79μgN·g-1·d-1and ranged from0.06to1.32μgN·g-1·d-1with an average of0.43μgN·g-1·d-1, respectively, which were at the lower level comparing with the results of other estuaries at home and abroad.②There were significant seasonal and spatial differences among the PNR of sediments in these three saline-fresh tidal flats. Spatial variation showed that the largest PNR was observed at0-5cm soil layer, and the PNR of the higher salinity wetland was higher than the lower salinity wetland (Shanyutan> Bianfuzhou> Tajiaozhou). The seasonal PNR order was spring> winter> autumn> summer. ③There were obvious seasonal and vertical spatial variation characteristics among the net nitrogen rates (NNR) of sediments in Shanyutan wetland. The contrast analysis of NNR and PNR showed that:the seasonal variation characteristic of NNR was similar to PNR, and PNR of the surface sediments was significantly higher than NNR, but there was no significant difference between NNR and PNR in the underlying sediments.④The temperature is a restrictive factor of inhibition of Nitrification. In different salinity wetland, the optimum temperature of nitrification of sediments was different, seasonal variation would affect it in the same sampling site as well. In general, the most suitable temperature of nitrification of sediments was found higher in summer and lower in winter. And the optimum temperature of nitrification of sediments in fresh water wetland was lower than brackish water wetland.⑤The temperature within the range of25to35℃was most beneficial to nitrification in Min River estuarine wetland by conducting experiment in simulant condition; The larest nitrification rates of sediments in Shanyutan wetland was found under the condition of the salinity of5, while it was found under the condition of the salinity of0in Tajiaozhou wetland.⑥The critical environmental impact factors of the sediment PNR varied in different saline-fresh wetland, the total nitrogen (TN) and carbon (C):nitrogen (N) ratio were the main environmental impact factors of the PNR in Shanyutan, soil moisture content and soil salinity were the main environmental impact factors of the PNR in Bianfuzhou, and the soil texture was the main environmental impact factors of the PNR in Bianfuzhou.⑦The nitrogen substrate addition of (NH4)2SO4and (NH2)2CO not only significantly improved the PNR, but also prolonged the relative higher nitrification duration, and the most significant influence was showed on the surface sediment. |
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