FLUXES OF CO2 AND CH4 UNDER DIFFERENT TYPES OF COASTAL SALT MARSHES OF THE YELLOW RIVER DELTA: DYNAMIC CHANGES AND DRIVING FACTORS ACROSS DIFFERENT SEASONS - Salt Marshes - page 44

P. australis community were positively correlated with soil electric conductivity at deep
depths (15cm); Except for the significantly positive correlations between CH 4 fluxes and soil
electrical conductivity at 5 cm, there was no significant correlation between them (Table 4).
CO 2 fluxes from T. chinensis communities had notable negative correlation with TN and
TC (Table 5). While negative correlations between CO 2 fluxes in S. glauca and P. australis
and TN were only observed in the deep soil (20 cm). No significant correlation was found
between NO 3 -N and NH 4 -N in different soil depths and CO 2 flux (Table 5); However CH 4
fluxes from P. australis community were significantly correlated to NO 3 --N at 0-10 cm and
NH 4 + -N at 10-20 cm depth. And the other correlations between CH 4 and sediments were not
notable.
4. D ISCUSSIONS
4.1. Variations of CO 2 and CH 4 Fluxes
In this study, we found that high CO 2 emissions occurred during summer and autumn
and low fluxes occurred during spring and winter. The results were similar with other studies
in different coastal ecosystems around the world (Table 6). Compared with the results of
these researches, the values of CO 2 fluxes in the Yellow River estuary were lower than those
in the Yangtze River estuary and the Min River estuary, higher than those in Savannah River
and Bay of Fundy, however the variation were similar with each other. The CO 2 and CH 4
fluxes from salt marsh were much lower than those in wetland and intertidal zone (table 6).
The CO 2 mainly comes from the respiration of vegetation and soil, thus the difference of the
vegetation (such as dominant species, individual density) and soil property would lead to the
different CO 2 fluxes. The high salinity decreases the quantity of plant biomass and microbial
diversity, which may be the main reason in explaining the CO 2 fluxes were lower than those
in wetland. CH 4 fluxes from wetland are the result of CH 4 production, consumption and
transportation from the anaerobic zone to the atmosphere (Bubier et al., 1994). The
magnitudes of CH 4 fluxes from salt marshes in the Yellow River estuary were lower than
those in wetland too. That may be related to the difference of soil moisture, soil permeability
and the vegetation.
4.2. Influence of Environmental Factors on CO 2 and CH 4 Fluxes
Many studies (Sha et al., 2011; Wang et al., 2003) have found that, CO 2 fluxes were
closely related with temperature, heating can promote the emission of CO 2 . In this study,
temperature promoted the CO 2 emission significantly. Suitable temperature can promote the
microbial activity, organic carbon mineralization and gas diffusion speed, and then speed up
the CO 2 emissions. Deep soil temperature accelerated the bare land CO 2 emission in winter,
indicating that the low temperature on the surface soil limited the CO 2 emission and the CO 2
mainly came from the respiration of deep soil (Jiang, 2012); Some studies showed that the
relationship between temperature and CH 4 fluxes were complex (Jin et al., 2012; Sun et al.,
2013), some found that CH 4 flux was not correlated with temperature (Segarra et al., 2013).