| Researches on the pollution of tidal sediment, transferring and transformation of nutrients between sediment-water interface are hotspots of environmental science. Sediment resuspension is a vital process, which can decrease available light for seagrasses, can be deposited in harbours and shipping channels, can result in higher mineralization rate and organic material transformation, and especially can release nutrients and contaminants into the water column and accelerate eutrophication. On the other hand, sediment denitriflcation can attenuate N flux and decelerate water eutrophication.In this thesis, we study the transmitting and transformation of N & P in tidal cycle and sediment denitriflcation in tidal flat along Yangtze estuary. We get following main results:1 We find that tidal circle and its seasonal change have an effect on the environmental parameters, such as temperature, salinity, conductivity, dissolved oxygen, Eh and PH, which showed tidal and seasonal difference. The highest SPM appeared at the beginning of all flood tide, the content of organic material of SPM showed seasonal difference, and had a negative significant correlation with water depth and particulate granularity. PSol of SPM has obviously released at the beginning of flood tide in spring, autumn and winter, the content of PAl were controlled to a certain extent by adsorption of SPM in spring and winter, PCa changed more in whole tidal circle in summer and winter than that in spring and autumn, PFe has been affected by different parameters in different season. 2 DIn, DIP in the water column have been impacted on not only by sediment resuspension, but also by the exchange of fresh water and salt water in tidal process. The concentration of NCV-N have increased during flood tide in spring and autumn, decreased in spring and increased in autumn in ebb tide, changed slowly in summer in the whole tidal circle, and showed complicated change and sediment resuspension promoted nutrients release in winter. The concentration of NO2--N changed very intricately in the tidal circle, and indicated the transforming frequently among each DIN. The concentration of NH4+-N decreased in spring and autumn and increased in summer and winter within 0~20min of flood tide, for NH4+-N release was quickly and the time of first sampling was not well choosed. We found that the release of NH4+-N was controlled by water depth, salinity and other factors in tidal circles. Theconcentration of DIP in ebb tide was higher than that in flood tide in summer, autumn and winter, indicating that tidal suspension can help to the release of P. Comparing all factors in April of 2002 with those in April of 2003, we discovered that there were so many differences between the two tidal circles. Employing Paired-Samples T Test in analyzing all factors, PH, SPM, Psol, PFe, PCa, DIP and NH4+-N had no significant difference, but DO, salinity, temperature, conductivity, Eh, organic material, PAl, nitrate and nitrite had significant difference between the two tidal circles.3 The concentration of SPM, IP of SPM, DIN and DIP in the head of the tidewater showed spatial differences. The release of Psol, PAl and PFe of the sediment was the main sources of DIP, but extracted nitrogen was not important for DIN in the column water.4 The effects on nutrients transferring and transformation between the sediment-water interface changed with seasons and sampling sites under the samecondition of physical disturbance. Disturbance extent had obvious effects on therelease of NH4+-N at site CD, XP and QY, NO3--N, P at site LC, P at site CD,stimulating the release of NO3--N and P at site QY, and had no obvious effect onthe nutrients release at site GL, in winter. The adsorption of SPM weakened theeffects of nutrients release in resuspension events at site CD and QY; sedimentresuspension would stimulate the suddenly release of nitrate at site QY; therelease of nutrients in LC and NH4+-N in GL were controlled by the disturbanceextent, and the release... |
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