Environmental Engineering Reference
In-Depth Information
However some asserted that CH
4
emissions from several east coast marshes displayed a weak
reliance on temperature (Wilson et al., 1989). In our study, the similar results were founded.
CH
4
fluxes tended to correlate with the deep soil temperature (Table 2), and the results were
consistent with studies of (Bellisario et al., 1999)and (Wang et al., 2005). CH
4
emissions from
wetlands are usually driven by enhanced temperature (Shindell et al., 2004). Temperature
may affect the activity of methanogenic processes (Zeikus et al., 1976), gas solubility
(Yamamoto et al., 1976), the net ecosystem production and competing terminal metabolisms
(Kotsyurbenko, 2005).
Soil moisture can not only affect the respiration of vegetation roots and microbial, but
also affect the diffusion of the gases (Hirota et al., 2007). Higher or lower soil water content
can inhibit
the decomposition of organic matter and microbial activity. Our studies showed
that the soil moisture of the surface soil promoted the CO
2
fluxes of
T. chinensis
community
in spring and
S. salsa
community in autumn, respectively. While negative relationship was
found between soil moisture in the surface soil and CO
2
fluxes in
P. australis
community.
The surface soil moisture of
P. australis
community was lower than others, which limited the
activities of vegetation and microorganism. These are consistent with the most previous study
results (Awasthi et al., 2005; Li et al., 2004); Soil moisture has been identified as the most
sensitive factor to regulate CH
4
emissions from soils since it directly regulates oxygen
availability in soil pores, which determines the activity of production and oxidation of CH
4
within the soil profile. In our study, the water content at the bottom of soil was significantly
higher than that in the surface soil, and the deep soil moisture promoted CH
4
emissions
obviously in summer. This was consistent with the current study results (Liu et al., 2013;
Neubauer, 2013). Higher moisture can create a reduction condition and that is beneficial for
the production and emission of CH
4
. But in other seasons, the correlations were complex,
which is coherent with the published data of intertidal zone in Yellow River Delta (Jiang et
al., 2012). This may be caused by the complex environment.
As mentioned above, the electric conductivity (EC) in surface soil inhibited the CO
2
emission which was consistent with the other studies (Krasakopoulou et al., 2009; Neubauer
et al., 2013). That may be due to the salinity of the sample were beyond the suitable salinity
range of soil microorganisms, so that reduced the microbial activity. While CO
2
fluxes were
positively correlated with EC in deep soil, and negatively correlated with that in the surface
soil in spring (Table 4). We also found that EC in different depth of soil followed the order:
5cm<10cm<15cm<0cm. These indicated that the increase of EC can promote CO
2
emission
within limits. Similar conclusion was drawn by Marton Marton et al., 2012), which were
inconsistent with the most previous studies. One possible explanation for positive effect was
that the salinity might not completely inhibit the C turnover and the activities of
microorganisms in soil (Lv et al., 2008); EC in winter was higher than that in other seasons,
and EC in winter inhibited the CH
4
emission. The high EC to CH
4
emission can increase the
quantity of electron acceptor and inhibiting the activities of microorganisms (Zeng et al.,
2008). On the whole, CH
4
fluxes in the salt marsh were not significantly related with EC, and
the result was in consistent with the findings of Tong (2013). The possible explanation was
that the well-adaption of the vegetation and microorganism had reduced the influence of
salinity.
Site-level control of CO
2
and CH
4
emission can be attributed to the effects of nutrient
status (Sun et al., 2013). Positive/negative relationships between CO
2
and CH
4
emissions and
