| CO2, CH4and N2O, having strong warming potentials, are considered to be the primarygreenhouse gases in the atmosphere. Global warming caused by the increasing concentrationsof CO2, CH4, N2O in the atmosphere is one of the hotspots in the study of global change. Thewetland, being sources or sinks of a variety of greenhouse gases, plays an important role instabilizing the global climate change. At home and abroad at present, there are a great many ofstudies on greenhouse gas emission and mechanism of the artificial wetland-rice paddies andnatural wetlands such as peat land, swamp and estuary wetland, while the studies ongreenhouse gas emissions of coastal wetlands are rarely reported. Therefore, this studysystematically investigated the fluxes of CH4, N2O, CO2and soil methane production potentialfrom Scirpus mariqueter wetland (SM), Phragmites australis wetland(PA), Spartinaabcerniflora wetland (SA) and Bare mudflat(BM) in the south of Hangzhou Bay. Therelationships between temperature, soil basic physical and chemical properties such as soilorganic carbon, soil pH and these three greenhouse gas fluxes were analyzed. This studyrevealed the temporal and spatital variation of CH4, N2O, CO2fluxes and spatital distributionof soil methane production potential of Hangzhou Bay wetland, and evaluated the function ofHangzhou Bay wetland on greenhouse gases emission or absorption. The main research resultsare as follows:(1) Static light chamber-gas chromatography method was used to observe the greenhousegas fluxes in situ.The average CH4flux showed as follows: SA (1.085mg·m-2·h-1)>PA (0.582mg·m-2·h-1)>SM (0.096mg·m-2·h-1)>BM (-0.042mg·m-2·h-1). There was no significantdifference of average CH4flux between BM and SM, but significant differences were foundbetween BM, SM and other two wetlands. Overall, BM was a sink of CH4, while SM, PA andSA were sources of CH4, and the highest and lowest values of CH4fluxes were respectively insummer and in autumn or winter in these three wetlands. The average N2O flux was that: PA (0.015mg·m-2·h-1)>SM (0.009mg·m-2·h-1)>SA (0.007mg·m-2·h-1)>BM (0.005mg·m-2·h-1).There was no significant difference of average N2O flux between BM and SM, but both ofthem were significantly different from PA and SA. Overall, four wetlands were emissionsources of N2O, and N2O fluxes varied from different vegetation types. The average CO2fluxwas that: PA (0.245g·m-2·h-1)>BM (0.090g·m-2·h-1)>SA (0.060g·m-2·h-1)>SM (-0.106g·m-2·h-1). There was no significant difference of average CO2flux between BM and SM, butboth of them were significantly different from PA and SA. Overall, BM was an emission sourceof CO2and the highest flux and lowest CO2flux were in winter and autumn respectively. PAwas an emission source of CO2, while SM and SA were sinks of CO2. The average CO2fluxesin BM, PA and SA were the highest in autumn and the lowest in spring. Soil physical andchemical properties such as soil organic carbon, total nitrogen, soil temperature and pH hadimportant effects on greenhouse gas emission. The correlation analysis results showed thatthere was a negative significant correlation between CH4flux and soil pH. Temperatures at15cm and inside the chamber, were significantly and highly significantly positively correlated toCH4fluxes. Soil organic carbon, Eh and total nitrogen were significantly(p<0.05), andextremely significantly positively correlated to CH4flux. Significantly negative correlation wasfound between N2O flux and soil water content. Temperature at all soil layers studied weresignificantly positively correlated to N2O flux. Temperature and other factors had weakcorrelation with CO2fluxes and further analysis and study on temperature and other factors’influences on CO2flux needed to carry out.(2) The indoor anaerobic culture-gas chromatography method was used to study themethane production potential of0~30cm soil depth from Hangzhou Bay Wetland withdifferent vegetation types. The average methane production potential showed that: SA (1.200μg·g-1·d-1)>PA (1.012μg·g-1·d-1)>BM (0.709μg·g-1·d-1)>SM (0.639μg·g-1·d-1). There was nosignificant difference of methane production potential between BM and SM, but significantdifferences were found between BM, SM and other two wetlands.0~5cm soil layer is the mostactive layer for methane production potential in three wetlands with vegetation and methane production potential decreased with soil depth deepening. The maximum and minimum valuesof methane production potential in BM were in10~20cm and5~10cm soil layers, showingthat methane production potential in topsoil was lower than that in deeper soil layers. Inaddition to0~5cm soil layer, methane production potential in SA was significantly higher thanthat in other wetlands. Among the soil physical and chemical factors, total nitrogen content wassignificantly positively correlated to methane production potential; soil organic carbon, Eh, soilelectrical conductivity and ammonium nitrogen content were positively correlated to methaneproduction potential; soil pH was negatively correlated to methane production potential.(3) The annual cumulative emission of CH4in Hangzhou Bay Wetland showed that: SA(9.309g·m-2·a-1)>PA (4.512g·m-2·a-1)>SM (0.449g·m-2·a-1)>BM (-0.795g·m-2·a-1); the annualcumulative emission of N2O showed that: PA (0.110g·m-2·a-1)>SM (0.073g·m-2·a-1)>BM(0.065g·m-2·a-1)>SA (0.040g·m-2·a-1); the annual cumulative emission of CO2showed that:BM (705.6g·m-2·a-1)>PA (195.7g·m-2·a-1)>SM (-630.1g·m-2·a-1)>SA (-718.4g·m-2·a-1); plantgrowth may be more conducive to emission of CH4and N2O. Difference of annual cumulativeemission of CH4between BM and SM was not significant, while the differences between BM,SM and other wetlands were significant. Significant differences of annual cumulative emissionof CO2, N2O were not found among all wetlands. During the observation period, the largestcomprehensive warming potential was found in BM (4153.7kg·hm-2) on the time scale of100years, followed by PA (2571.1kg·hm-2), SA (-3538.8kg hm-2) and SM (-4498.8kg·hm-2). BMand SA were sources of greenhouse gases; SM and SA were sinks of greenhouse gases, whichcould slow down the global warming. |
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