| Climate warming has been one of the largest global environmental problems in the world. After the Copenhagen meeting, greenhouse gas emissions reduction is universal concerned by international community. As important greenhouse gases, the radiative forcing capacities of N2O and CH4 are less than CO2, but their greenhouse effect are 300 times and 20-30 times of CO2 respectively.Estuary wetland influenced strong by physical and biological factors, on the intersection area of the sea and land, whose most basic habitat characteristic is the junction of salt and fresh water and directly or indirectly tides influence, is an ecological fringe area of high biodiversity. Estuary wetland, as the natural barrier of accommodating purification land-sourced pollutants and cutting them into the sea, plays a very important role in controlling estuarine and coastal water nutritional status and global carbon,nitrogen cycle. In recent years, studies have shown that N2O fluxes from sea are responsible for 13% of the global total. Although estuaries and shore areas account for only 20% of the marine areas, but produce more than half of marine N2O flux.CH4 emissions from natural wetlands account for more than 21% of the world. As the intensification of human activities, carbon and nitrogen load rise of river shore and littoral environment effect N2O and CH4 emissions by stimulating microorganism life process in the environment.The main researches that scholars have advanced on N2O and CH4 emissions in wetland ecosystems have focused on large area of estuarine wetlands, however, many small area, salt and fresh water tidal wetland of scattered distribution haven't been given more attention, especially in current international the lack of N2O and CH4 tidal flux data from coastal wetland of China. Currently, N2O and CH4 emissions from estuaries and littoral wetland ecosystem are short of continuous, systematic, long-term observation data and the mechanisms of N2O and CH4 emissions research are insufficient. So, the assessment about N2O and CH4 emissions of estuarine and coastal zones may be incredible.Daguhe estuarine wetland of jiaozhou bay is the biggest wetland of Qingdao, whose vegetation includes Phragmites australis, Zoysia japonica, Spartina anglica, Imperata cylindrical, et, al. In September 2009 to August 2010 period, we, chosing two different type wetlands of Daguhe estuarine as object of study, have study N2O and CH4 emissions of Daguhe estuarine two different types of wetlands by using the static box-gas chromatography and some main environmental influencing factors (temperature, soil temperature, pH, salt degree, etc.). The study has demonstrated that different types of estuary wetland ecosystem N2O and CH4 flux characteristics, diurnal and seasonal variation laws and key factors, established a set of jiaozhou bay estuarine wetland' relative complete data on N2O and CH4 emissions, and provided scientific basis for perfecting our estuary wetland greenhouse gas emissions list.The major findings are as follows:1,The trends of diurnal variation between Phragmites australis and weeds wetland were generally identical at all seasons. N2O fluxes were low in the morning then began to increase. There was an emissions peak at about 12 o'clock and after that N2O fluxes started to decline. After the second peak occurred at around 21 o'clock, N2O fluxes gradually decreased once again.Because of the comprehensive effect of various environmental factors, the daily variation trends of two different types'wetlands were respectively different at all seasons, however, the trends of diurnal variation between two different types'wetlands were resemble in the same season.2,N2O fluxes in Phragrmites australis wetland had a large fluctuation, however, N2O emissions from weeds wetland changed slightly. N2O fluxes in Phragrmites australis wetland were not significantly correlated with 10cm ground temperature, box temperature, but the relation between N2O fluxes in weeds wetland and 10cm ground temperature, box temperature was significant (P<0.05), the correlation coefficients were 0.241*,0.208* respectively. Similarly, the relation between CH4 fluxes in Phragrmites australis wetland and 5cm,10cm ground temperature, air temperature, box temperature was not significant, whereas CH4 fluxes in weeds wetland were highly significant correlation with them (P<0.01), the correlation coefficient were 0.370**,0.315**,0.349**,0.376** respectively.3,Apart from February, May and August, N2O fluxes were higher in Phragrmites australis wetland than the weeds wetlands in one year. Because experiment base' temperature maintained below 0℃and microbial activity was low, N2O emissions were low. On the whole, two types of wetlands showed weak absorption. The temperature fell in August, Phragrmites australis wetland over all observation period was in the flooded state, which limited the formation and emissions of N2O by creating a strictly anaerobic environment, so N2O emissions couldn't be detected obviously even represented absorbing N2O. Among 12 months Phragrmites australis wetland had more CH4 emissions than weeds wetlands except January. And, two different type wetlands performed emission condition.4,Seasonal N2O Fluxes were not consistent for two different types of wetlands. N2O Fluxes size of Phragrmites australis wetland were the winter> autumn>spring>summer and N2O emissions size in weeds wetland were the summer> autumn> spring> winter in four seasons. However, the maximum value of methane emissions was in summer, followed by autumn and spring, and the minimum was in winter in two different type wetlands.5,Seasonal N2O and CH4 fluxes from Phragrmites australis were much more than weeds wetland which caused by different hydrologic characteristics of wetlands and the different types of vegetation. Seasonal N2O emissions in spring, summer, autumn and winter were 43.84,36.54,56.32,63.38 mg-m-2 in Phragrmites australis wetland, and 7.13,11.07, 10.45,3.08 mg·m-2 in weeds wetland respectively; seasonal CH4 emissions in spring, summer, autumn and winter were 392.91,1020.83,821.70,140.62 mg·m-2 in Phragrmites australis wetland, and 156.94,417.24,159.46,19.10 mg·m-2 in weeds wetland respectively. Phragrmites australis wetland and weeds wetland in the Dagu river estuary of Jiaozhou Bay were the "source" of atmospheric N2O and CH4 in four seasons.6,There was no correlation between N2O and CH4 fluxes and the pH value of the soil, moisture content and conductivity. |
PDF Full Text Request