||Since the Industrial Revolution, large quantity of air pollutants are emitted to and accumulated in the atmosphere, which cause the elevated concentrations of greenhouse gases (GHGs) in the atmosphere, resulting in global warming due to greenhouse effect. Such global worming related issues have attracted much attention globally. “The Wetland Conservation Act” of ROC has been legislated in February 2, 2015, showing Taiwan’s emphasis on wetland issues. The decomposition of water pollutants in aerobic and anaerobic environments could release carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from the wetlands to the atmosphere.|
From the fall of 2015 to the summer of 2016, this study in-situ monitored GHGs emitted from the mangrove wetlands and the Da-Tam constructed wetlands, in Dapeng Bay National Scenic Park. This study applied a self-designed floating chamber to collect GHGs through a Teflon tube connected to the top of the chamber, and in-situ monitored GHGs with a continuous monitoring instrument (Teledyne Analytical Instruments, Series 7600) to continuously monitor GHG emissions, estimate its CO2 equivalent (CO2-e) and carbon budget, and investigate the seasonal variation and spatial distribution of GHGs, which assist us to further understand the potential impact of saline wetlands on global warming. Integrating water quality and atmospheric quality data, this study further analyzed the correlation between GHGs and water quality, combined the GHG data and net primary production data to understand the carbon budget of saline constructed wetlands.
This study revealed that the seasonal concentrations of CO2 emitted from saline constructed wetland ranged from 424.9±20.3~476.8±24.2 ppm. Diurnal variation of GHG concentrations showed that GHG concentrations in the daytime were lower than those at night time. CH4 emitted from saline constructed wetlands ranged from 3.7±1.4~28.6±7.6 ppm, while N2O emitted from saline constructed wetlands ranged from 3.1±2.6~0.9±0.6 ppm. Diurnal variation of CH4 and N2O concentrations showed that they were higher in the daytime than those at night time.
The CO2 equivalent (CO2-e) emission fluxes at the mangrove and the Da-tam constructed wetlands were further determined. The CO2-e emitted from the mangrove wetland (5409.6 g CO2 m-2 yr-1) was higher than the Da-tam constructed wetland (3470.8 g CO2 m-2 yr-1), mainly due to the fact that the concentrations of N2O emitted from the mangrove wetland were 58% more than those at the Da-tam constructed wetland.
The net primary production and carbon budget of the mangrove wetland were 1987.4 g C m-2 yr-1 and 1923.3 g C m-2 yr-1, respectively, while those of the Da-tam constructed wetland were 1877.7 g C m-2 yr-1 and, 1803.4 g C m-2 yr-1, respectively. Both wetlands were characterized as carbon sink wetlands.
The soil carbon stock showed that soil carbon was mostly distributed in the soil depth of 0~10 cm in the saline wetlands. Soil carbon stocks of the mangrove wetlands was 226.9 tC, while soil carbon stocks of the Da-Tam wetland was 222.5 tC.