Program
 
Special Session 2: Changing ocean environment: from the sedimentary perspective -- processes and records
 

 
 
1130
Biogeochemical processes and material exchange in the silty intertidal sediment of an open-coast tidal flat (Chongming Eastern Flat, China)
Wednesday 11th @ 1130-1145
Room 4
Yu-Shih Lin* , Department of Oceanography, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
Hang Gao, School of Ocean and Earth Science, Tongji University, Shanghai 200092, P.R. China
Longhui Deng, Department of Oceanography, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
Jia-Jang Hung, Department of Oceanography, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
James T. Liu, Department of Oceanography, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
Huaiyang Zhou, School of Ocean and Earth Science, Tongji University, Shanghai 200092, P.R. China
Chen-Tung Arthur Chen, Department of Oceanography, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
Chin-Chang Hung, Department of Oceanography, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
Presenter Email: yushih@mail.nsysu.edu.tw
Most tidal flats in South and East Asia and South America belong to the category of open-coast tidal flats. Linked to tide-dominated deltas or estuaries of large rivers, open-coast tidal flats are frequently dominated by fine-grained deposits. The Yellow and Yangtze Rivers together nourish one of the longest stretches of open-coast tidal flats in the world, but the biogeochemical properties of the silt-dominated sediment remain to be explored. We studied the basic biogeochemistry of silty intertidal sediment (mean size = 44 米m; permeability = 2℅10每11 m2) from the Chongming Eastern Flat, and compared the results to those of sand- and clay-dominant flats to discuss the underlying hydrodynamic mechanisms required to sustain the reactions. The organic-lean sediment (total organic carbon content = 0.08㊣0.02%) had stable carbon isotopic signatures (汛13C = 每22.3㊣0.5㏑) of marine organic matter. The downcore distribution of chlorophyll-a suggests the presence of microphytobenthos on the sediment surface and shallow penetration depths (< 1 cm) of fresh organic particles. Dynamics of pore-water NO3每 concentrations over the tidal cycles indicates interfacial solute exchange down to 4 cm via flow- and topography-induced advection during inundation, whereas the temporal variations of NH4+ and dissolved inorganic carbon (DIC) accords to the presence of deep (down to 10 cm) but less vigorous density-driven convection. The net areal rates of nitrate removal (2.0每5.0 mmol m每2 d每1), ammonium accumulation (0.8每2.1 mmol m每2 d每1) and DIC production (16每143 mmol m每2 d每1), derived by the use of a reaction-transport model to account for the effect of percolation during flat emergence, were comparable to those reported for sandflats. The seasonal pore-water salinity data, in combination with the previously reported frequent change in bed level, pointed to physical reworking of the fine-grained sediment as the mechanism to replenish degradable organic matter for sustaining the high remineralization activity in deeper sediment. We conclude that the silty intertidal sediment exhibits an intermediate behavior by showing solute exchange similar to those of sandflats and particle exchange close to those of mudflat. The role of the intertidal sediment in the biogeochemistry of the East China Sea shelf system is also discussed.