Abstract
To examine the spatial and temporal variability of sediment grain size in exposed tidal wetlands with ample sediment supply, we sampled sediments and measured hydrodynamics, accretion/erosion rates, and vegetation characteristics in the Yangtze Delta. Sediment grain size exhibited a landward/upward decreasing trend. This trend is mainly attributed to attenuation of hydrodynamics. A 630-day series of daily surface sediment sampling at a fixed site on an unvegetated intertidal flat revealed significant seasonal and storm-cyclic changes in grain size. This temporal variability was related to alternating accretion/erosion events, with erosion associated with coarser grain size. Such temporal dynamics were not present in vegetation, where sediment remained fine grained throughout the year. In the marsh, vegetation cover enables the trapping of fine-grained sediments in the following ways: (a) adherence of suspended sediments onto plants; (b) deposition of suspended sediments stimulated by attenuation of hydrodynamics through plant obstruction; and (c) prevention of resuspension of fine-grained deposits due to the protection of the plant canopy. The influence of vegetation on sediment grain size was clearly seen when comparing sediment trapped by different vegetation types and seasonal patterns of trapped sediment on different vegetation canopy densities. The relatively high plant biomass of the recently introduced Spartina alterniflora enhanced the trapping effect, whereas plant degradation due to buffalo grazing reduced the trapping effect. We conclude that for exposed tidal wetlands with ample sediment supply such as the Yangtze Delta, the spatial and temporal variability of sediment grain size is governed predominantly by physical controls on the unvegetated flat and predominantly by biophysical interaction of hydrodynamics and vegetation in the salt marsh, rather than by sediment supply.
Original language | English |
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Pages (from-to) | 657-671 |
Number of pages | 15 |
Journal | Estuarine, Coastal and Shelf Science |
Volume | 77 |
Issue number | 4 |
DOIs | |
Publication status | Published - 10 May 2008 |
Bibliographical note
Funding Information:We thank A. Gao, H. Liu, Z.G. Gao, X.M. Zhai, J.H. Gu, H.P. Li, and L. Yuan for their assistance in field work, and J.R. Zhu for providing us with the wind dataset at the Weather Station in Eastern Chongming. We are also indebted to L.Q. Zhang for instrumental support. This study was funded by the Natural Science Foundation of China (40671017), the Ministry of Science and Technology of China (2004CB720505, 2002CB412403), the Ministry of Education of China (PCSIRT0427), and the Programme Strategic Scientific Alliances between the People's Republic of China and the Netherlands (PSA 04-PSA-E-01). The authors would like to thank Dr Carl Friedrichs and one anonymous reviewer for their detailed comments that helped improve the paper greatly.
Funding
We thank A. Gao, H. Liu, Z.G. Gao, X.M. Zhai, J.H. Gu, H.P. Li, and L. Yuan for their assistance in field work, and J.R. Zhu for providing us with the wind dataset at the Weather Station in Eastern Chongming. We are also indebted to L.Q. Zhang for instrumental support. This study was funded by the Natural Science Foundation of China (40671017), the Ministry of Science and Technology of China (2004CB720505, 2002CB412403), the Ministry of Education of China (PCSIRT0427), and the Programme Strategic Scientific Alliances between the People's Republic of China and the Netherlands (PSA 04-PSA-E-01). The authors would like to thank Dr Carl Friedrichs and one anonymous reviewer for their detailed comments that helped improve the paper greatly.
Keywords
- deposition
- grain size
- salt marsh
- sediment
- tidal wetland
- Yangtze (Changjiang) Delta