Impacts Of Main Disturbance Factors On The Key Processes Of Sediment Nitrogen Transformation In The Tidal Marsh Of The Min River Estuary

The Min River estuary is one of the important estuaries in the southeast coast of China.This estuary wetland was disturbed by man-made and natural factors of interference recently and the interference factors of Spartina alterniflora invasion,reclamation and aquaculture,salt water intrusion and acid deposition are more prominent.This study take the sediments of Cyperus malaccensis as the research object to explore impacts on main interference factors on the key processes of sediment nitrogen transformation in the tidal marsh of the Min river estuary through field investigation and laboratory control experiment.The main research results are as follows:1.Effects of the Spartina alterniflora invasions processes on the key of sediment nitrogen transformationThe study investigated the differences of spatial distribution of Spartina alterniflora invasion sequence on soil carbon and nitrogen in a Cyperus malaccensis marsh.We analyzed a non-invaded C.malaccensis wetland(A),S.alterniflora-invaded patch edge(B),and S.alterniflora-invaded wetland(C)of the Min River Estuary,by using new-generation space-time methods.The results showed that invasion of S.alterniflora significantly reduced the content of NO3--N in sediment(P<0.05),but increased the NH4+-N content.The invasion increased the content of TN and C/N ratio of sediment.Comparing the C.malaccensis community and the invasive plate edge,the stock of TN was increased by 10.22%and 17.87%.The rates of nitrification and denitrification ranged froml.90 to 16.6 mg.kg-1.d-1 and 24.82?54.38 mg.kg-1.d-1 in the three studied sites,respectively.The nitrification rates in the three sites sediments demonstrated the following order:B>C>A,whereas the denitrification rates showed the increasing order of C>B>A.The results showed that the invasion of Spartina alterniflora had changed the original level of sediment mineralization of Cyperus malaccensis wetland from temporal and spatial distribution in Min River estuary.The nitrogen mineralization of sediment was enhanced by the invasions in a certain extent.2.Effects of the reclamation and aquaculture on the key processes of sediment nitrogen transformation(1)The mineralization rate remained the trend of increase first and then decreased in different periods of the shrimp pond and the maximum value appeared in the middle period.Compared with the transformation in early period,the mineralization rate of reclamation and aquaculture was weaker in mineralization.(2)The trend of nitrification rate was consistent for the first increase and then decreased in different periods and the nitrification activity of each period showed a decreasing trend after the first increase.Reclamation and aquaculture weakened nitrification intensity of the native wetland.(3)The relationship between denitrification rate and denitrification activity and time showed the first increase and then decrease in different periods and tended to be stable last.Land use change played an important role on denitrification and significantly enhanced denitrification rate compared with the transformation in early period.3.Effects of the salt water intrusion on the key processes of sediment nitrogen transformation(1)Salinity promoted the mineralization of nitrogen in a certain range and the mineralization was inhibited when the salinity was too high.(2)The increase of salinity inhibited the sediments nitrification in the Min River estuary wetland and this inhibition increased with salt concentration in a certain range,but the excessive salinity caused the inhibition of nitrification slightly.(3)The increase of salinity had inhibitory effects on the nitrification rate in a certain range.4.Effects of pH on the key processes of sediment nitrogen transformation(1)The mineralization rate had no regularity basically in the control of pH single factor in the Min River estuary wetland.The mineralization rate of wetland may be controlled by multiple factors.(2)The trend of nitrification rate increased first and then decreased and increased last with the time variation under different pH conditions,but there was no significant difference in pH gradients.Nitrification activity is very low in acidic environment and the nitrification activity is significantly inhibited for pH(pH=2.5).(3)The denitrification rate was not controlled by pH,and the denitrification rate decreases with the incubation time.While denitrification activity was increased with the incubation time,the low pH(pH=2.5)has an inhibitory effect on the denitrification activity.