Responses of soil CO2 and CH4 emissions to changing water table level in a coastal wetland

Global climate change and in particular sea level rise have resulted in water table level rise in the coastal wetland, which may alter the magnitude and direction of carbon flux. However, the degree to which different water table level affects soil CO2 and CH4 emissions remains uncertain in coastal wetland. Here, a soil microcosm experiment with five water table levels (−40, −30, −20, −10, 0 cm) was conducted in the Yellow River Delta, China. The water table level was controlled by manual. The soil CO2 and CH4 emissions of each water table levels were measured during 150-days incubation in 2018. Our results showed that water table level rise decreased soil CO2 emissions, while increased soil CH4 emissions. However, there was no significant difference in soil CO2 and CH4 emissions from −20 to −40 water table levels, respectively. In addition, water table level rise significant alter soil physical and chemical properties in the uppermost soil layer (0–10 cm) in coastal wetland, in particular soil moisture and salinity, which probably jointly affected soil CO2 and CH4 emissions. Furthermore, cumulative soil CH4 emission was positively significantly correlated to soil organic carbon and total carbon, suggesting that carbon component can supply energy and nutrients and benefit for soil CH4 production. Additionally, there was a significant relationship between cumulative soil CO2 emission and dissolved organic carbon, which indicated that CO2 was mainly contributed from dissolved organic carbon. Cumulative soil CO2 emission was significantly correlated with soil microbial biomass carbon, suggesting that microbial activity played an important role in CO2 emissions in coastal wetlands. Our results also indicate that water table level rise caused by sea level rise may contribute to the storage of soil organic carbon and produces a lower global warming potentials of CH4 and CO2 in the further climate change. Therefore, it is necessary to estimate the effect of hydrological, especially water table level on carbon cycles in coastal wetland when evaluating the climate–carbon feedback scenarios. The rise of water table level caused by sea level rise decreased linearly soil CO2 emissions, while increased exponentially soil CH4 emissions. However, there was no significant difference in soil CO2 and CH4 emissions from -20 to -40 water table levels, respectively. Water table level rise significant affect soil moisture and salinity at surface soil layer in coastal wetland, w