Spatial and temporal variations of the greenhouse gas emissions in coastal saline wetlands in southeastern China.

Coastal wetlands are crucial to global climate change due to their roles in modulating atmospheric concentrations of greenhouse gases (GHGs) (CO2, CH4, N2O). Under a warming climate, we investigated spatial and temporal variations of GHGs emissions over the coastal wetlands in southeastern China during 2012-2014. Five dominant land cover types in coastal wetlands have been considered, including the bare mud flat (BF), the Spartina alterniflora flats (SAF), the Suaeda glauca flats (SGF), the Phragmites australis flat (PAF), and the Scripus triqueter flat (STF). The results showed that the annual average CO2 fluxes were 305.8, 588.8, 370.2, and 136.5 mg m-2 h-1 from spring to winter. CH4 fluxes presented to be a sink in spring (- 0.02 mg m-2 h-1), and functioned as a source in the following seasons. Correlation analysis indicated that the surface air temperature and the cumulative precipitation could be two main factors that influenced the seasonal and inter-annual variations of GHGs emissions. In addition, we provided a regional budget of GHGs emissions that suggested the variations of GHGs emissions under a warming climate.

[Temporal and Spatial Dynamics of Greenhouse Gas Emissions and Its Controlling Factors in a Coastal Saline Wetland in North Jiangsu].

Although coastal wetlands play an important role in governing the atmospheric concentrations of CO2, CH4, and N2O, thus control the global warming, research of the greenhouse gas emissions conducted in the coastal wetlands were not well-documented because of the difficulty in fieldwork in these harsh environments, and the complicated controlling factors affecting the greenhouse gas emissions. The temporal and spatial variations of CO2, CH4, and N2O were investigated simultaneously in the coastal saline wetland in North Jiangsu during the period from April, 2014 to March, 2014, using the closed static dark chamber method. And the results showed that seasonal variations of CO2, CH4, and N2O were higher in summer, and lower CO2 and N2O fluxes were observed in winter, while for CH4 in spring, it presented the sink in the coastal wetland. The annual average CO2 emission derived from the Spartina alterniflora flat (SAF) was the highest, with the value of (766.3±496.9) mg·(m2·h)-1, and for CH4 and N2O, the highest values were found in Phragmites australis flat (PAF), with the values of (0.420±0.900) mg·(m2·h)-1 and (17.4±5.0) µg·(m2·h)-1, respectively. The bare mud flat (BF) presented the sink of CH4, and the source of CO2 and N2O, with the lowest emission rates across all the tidal flats. The global warming potential (GWP) from the coastal wetlands in north Jiangsu was observed higher in SAF[68841.280 kg·(hm2·a)-1], which was 1.41 and 3.02 times higher compared with those of PAF and SGF, the GWP of BF was the lowest, with the value of 5002.100 kg·(hm2·a)-1. Furthermore, significant correlations were found between CO2 fluxes and temperature, including air temperature (AT), soil temperature (ST), and temperature inside the chamber (CT), however, for CH4 and N2O, the correlations were not so obvious. Above all, the temporal variations of CO2, CH4, and N2O were mainly controlled by the temperature and characteristics of vegetation, the spatial variations of CO2, CH4, and N2O were determined by the characteristics of vegetation. Furthermore, we may safely draw the conclusion that the invasive S. alterniflora increased the global warming potential dominantly through increasing the CO2 emission rates, compared with the native plant.

Quantifying the anthropogenic and climatic contributions to changes in water discharge and sediment load into the sea: A case study of the Yangtze River, China.

Based on data from the Datong hydrological station and 147 meteorological stations, the influences of climate change and human activities on temporal changes in water discharge and sediment load were examined in the Yangtze River basin from 1953 to 2010. The Mann-Kendall test, abrupt change test (Mann-Kendall and cumulative anomaly test), and Morlet wavelet method were employed to analyze the water discharge and sediment load data measured at the Datong hydrological station. The results indicated that the annual mean precipitation and water discharge exhibited decreasing trends of -0.0064 mm/10 yr and -1.41×10(8) m3/yr, respectively, and that the water sediment load showed a significant decreasing trend of -46.5×10(6) t/yr. Meanwhile, an abrupt change in the water discharge occurred in 2003. The sediment load also exhibited an abrupt change in 1985. From 1970 to 2010, the climate change and human activities contributed 72% and 28%, respectively, to the water discharge reduction. The human-induced decrease in the sediment load was 914.03×10(6) t/yr during the 1970s and 3301.79×10(6) t/yr during the 2000s. The contribution from human activities also increased from 71% to 92%, especially in the 1990s, when the value increased to 92%. Climate change and human activities contributed 14% and 86%, respectively, to the sediment load reduction. Inter-annual variations in water discharge and sediment load were affected by climate oscillations and human activities. The effect of human activities on the sediment load was considerably greater than those on water discharge in the Yangtze River basin.