Physicochemical Properties Of Tidal C. Malaccensis Marsh Soil With Different Salinity And Effect Of Simulation Of Saltwater Intrusion On Methane Production Rate In The Min River Estuary

The Min River estuary wetland is one of the most representative and typical estuarine tidal wetlands of south-east China. Cyperus malaccensis is one main native dominant species, and distributes in a series of wetlands with different salinity in the Min River estuary region. We measured the physical and chemical properties of tidal C. malaccensis marsh soil with different salinity and determined the effects of simulation of saltwater intrusion on soil methane prodcution rate in the Min River estuary. The results showed that:(1) Soil bulk density among four wetlands was statistically indistinguishable. Dissolved organic carbon (DOC) was lower in the low salinity C. malaccensis marsh and higher in the high salinity C. malaccensis marsh; In contrast, soil organic carbon (SOC) was higher in the low salinity but lower in the high salinity.The Shanyutan wetland with the highest salinity had the higher microbial carbon (MBC) content, but was not significantly different with other wetlands. Soil particle size showed obvious rule in the salinity gradient:silt and clay gradually increase, while the sand content decreases, reflecting the law of river sediment moving. pH is roughly decreases with the salinity increase.(2) Content of NH4+、SO42-and Cl-of soil pore water were higher, while NO2、NO3-was lower. The content of NO2-and NH4+was not significantly different; NO3-content roughly decreased with salinity increase; the contents of SO42"and Cl-decreased with the salinity increase.(3) Dissolved methane concentrations of soil pore water were334.77±29.17μmol/L,266.67±63.80μmol/L,46.17±7.89μmol/L,9.73±3.11μmol/L in the Xiayangzhou, Bianfuzhou, Tajiaozhou and Shanyutan in winter. From surface to depth of50cm, pore water methane content mostly showed an increasing trend. In summer, pore water methane content firstly decreased and then increased with the soil depth.(4) Soil methane production rate was higher in the depth of10cm in the middle salinity, while in40-50cm depth, the rates decreased with salinity increased (0.1093±0.0179μg·g-1-d-1>0.1035±0.0343μg·g-1·d-1>0.0649±0.0312μg·g-1·d-1>0.0110±0.0035μg·g-1·d-1), which means that methane production rate had a negative correlation with the salinity in situ, in summer, wetlands with the lowest and highest salinity have higher soil methane production rate in the depth of10cm, while the middle salinity wetland had lower methane production rate. Soil methane production rate in summer was generally more than50times than that in winter. In50cm depth, there are no significant differences in soil methane production rate among the four wetlands.(5) Methane production rate of brackish-water marsh reduced when experiencing pure brine/seawater intrusion, while freshwater wetlands methane prodcution rate increased in winter. In summer, when the salinity is more than5‰, seawater can greatly restrain the methane production rate of both kinds of wetlands, which can even lower the rate more than97%. Considering conditions during summer and winter, pure brine/seawater intrusion can inhibit the tidal wetland soil methane production ability greatly.