Intratidal fluctuations in stratification within a mangrove estuary

Chapter

The Ecology of Mangrove and Related Ecosystems

Volume 80 of the series Developments in Hydrobiology pp 163-171

Title 

Intratidal fluctuations in stratification within a mangrove estuary

• Author 

• R. J. Uncles
• , W.-K. Gong
• , J.-E. Ong

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• Abstract 

• The dependence of salinity stratification on the vertical structure of the longitudinal salinity gradient is investigated by solving the equations of longitudinal momentum and salt conservation. The results are used to interpret measurements made throughout 31 tidal cycles in the Merbok Estuary, Malaysia, as part of an ecological study of a tropical mangrove estuary. The solutions show that a substantial part of the salinity stratification was caused by vertical shear in the currents coupled with advection of the longitudinal salinity gradient. This mechanism led to maximum stratification around low water and minimum stratification around high water. Observed intratidal variations in stratification at neap tides greatly exceeded modelled values when a depth-independent, longitudinal salinity gradient was assumed. Simulations made using a longitudinal salinity gradient of simple depth-dependent, power-law form implied that this difference arose mainly because the near-surface, longitudinal salinity gradient in the field was significantly larger than that near the bed during neap tides and at times of high run-off. The longitudinal, dispersive transport of salt, fresh water and solutes due to vertical shear is shown to be important during periods of stratification at neap tides and during high run-off. The relevance of stratification to mangrove estuaries is discussed.

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• References 

• 1. Boto, K. G. & J. S. Bunt, 1981. Tidal export of particulate organic matter from a northern Australian mangrove system. Estuar. coast. Shelf Sci. 13: 247–255.CrossRef
  2. Boto, K. G., J. S. Bunt & J. Wellington, 1984. Variations in mangrove forest productivity in northern Australia and Papua New Guinea. Estuar. coast. Shelf Sci. 19: 321–329.CrossRef
  3. Bowden, K. F. & P. Hamilton, 1975. Some experiments with a numerical model of circulation and mixing in a tidal estuary. Estuar. coast. mar. Sci. 3: 281–301.
  4. Dronkers, J. & J. van de Kreeke, 1986. Experimental determination of salt intrusion mechanisms in the Volkerak Estuary. Neth. J. Sea Res. 20: 1–19.CrossRef
  5. Dyer, K. R., 1974. The salt balance in stratified estuaries. Estuar. coast. mar. Sci. 2: 273–281.
  6. Fischer, H. B., E. J. List, R. C. Y. Koh, J. Imberger & N. H. Brooks, 1979. Mixing in inland and coastal waters. Academic Press, New York, 483 pp.
  7. Hunkins, K., 1981. Salt dispersion in the Hudson Estuary. J. Phys. Oceanogr. 11: 729–738.CrossRef
  8. Kjerfve, B. & C. Medeiros, 1989. Current vanes for measuring tidal currents in Estuaries. Estuar. coast. Shelf Sci. 28: 87–93.CrossRef
  9. Murray, S. P. & A. Siripong, 1978. Role of lateral gradients and longitudinal dispersion in the salt balance of a shallow well mixed estuary. In: B. Kjerfve (cd.), Estuarine Transport Processes. University of South Carolina Press: 113–124.
  10. Nunes Vaz, R. A., G. W. Lennon & J. R. de Silva Samarasinghe, 1989. The negative role of turbulence in estuarine mass transport, Estuar. coast. Shelf Sci. 28: 361–377.CrossRef
  11. Rattray, M. & J. G. Dworski, 1980. Comparison of methods for analysis of the transverse and vertical circulation contributions to the longitudinal advective salt flux in estuaries. Estuar. Coast. Mar. Sci. 11: 515–536.CrossRef
  12. Ridd, P. V., M. W. Sandstrom & E. Wolanski, 1988. Out-welling from tropical tidal salt flats. Estuar. coast. Shelf Sci. 26: 243–253.CrossRef
  13. Ridd, P., E. Wolanski & Yoshihiro Mazda, 1990. Longitudinal diffusion in mangrove-fringed tidal creeks. Estuar. coast. Shelf Sci. 31: 541–554.CrossRef
  14. Simpson, J. H., J. Brown, J. Mathews & G. Allen, 1990. Tidal straining, density currents and stirring in the control of estuarine stratification. Estuaries 13: 125–132.CrossRef
  15. Simpson, J. H. & J. Sharpies, In press. Dynamically-active models in the prediction of estuarine stratification. In D. Prandle (ed.), Physics of Estuaries and Coastal Seas. Springer-Verlag, Berlin/Heideberg.
  16. Uncles, R. J., R. C. A. Elliott & S. A. Weston, 1985. Dispersion of salt and suspended sediment in a partly mixed estuary. Estuaries 8: 256–269.CrossRef
  17. Uncles, R. J., J. E. Ong & W. K. Gong, 1990. Observations and analysis of a stratification-destratification event in a tropical estuary. Estuar. coast. Shelf Sci. 31: 651–665.CrossRef
  18. Wolanski, E. & P. V. Ridd, 1986. Tidal mixing and trapping in mangrove swamps. Estuar. coast. Shelf Sci. 23: 759–771.CrossRef
  19. Wolanski, E., Yoshihiro Mazda, B. King & S. Gay, 1990. Dynamics, flushing and trapping in Hinchinbrook Channel, a giant mangrove swamp, Australia. Estuar. coast. Shelf Sci. 31: 555–579.CrossRef
  20. Wolanski, E. Personal Communication. Australian Institute of Marine Science, PMB No. 3, Townsville M.C.. OLD 4810, Australia.

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