, Volume 337, Issue 1–3, pp 123–132 | Cite as

Carbon flux between an estuary and the ocean: a case for outwelling

  • Paul E. D. Winter
  • Thomas A. Schlacherl
  • Dan Baird


The classical outwelling hypothesis states that small coastal embayments (e.g. estuaries, wetlands) export their excess production to inshore marine waters. In line with this notion, the present study tested whether the Swartkops estuary acts as source or sink for carbon. To this end, concentrations of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and particulate organic carbon (POC) were determined hourly during the first monthly spring and neap tides over one year in the tidal waters entering and leaving the estuary. Each sampling session spanned a full tidal cycle, yielding a total of 936 concentration estimates. Carbon fluxes were calculated by integrating concentrations with water flow rates derived from a hydrodynamic model calibrated for each sampling datum. Over the year, exports to marine waters markedly exceeded imports to the estuary for all carbon species: on the basis of total spring tidal drainage area, 1083 g m−2 of DIC, 103 g m−2 of DOC, and 123 g m−2 of POC left the estuary annually. Total carbon export from the estuary to the ocean amounted to 4755 tonnes, of which 83% was in the inorganic form (DIC). Thus, the bulk of carbon moving in the water column is inorganic - yet, DIC seems to be measured only rarely in most flux studies of this nature. Salt marshes cover extensive areas in this estuary and produce some carbon, particularly DOC, but productivity of the local Spartina species is low (P:B=1.1). Consequently, the bulk of carbon exported from the estuary appears to originate from the highly productive macroinvertebrate and the phytoplankton component and not from the salt marsh plants.

Key words

carbon tidal flux estuary outwelling 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Baird, D., 1988. Synthesis of ecological research in the Swartkops estuary. In D. Baird, J. F. K. Marais & A. P. Martin (eds), The Swartkops Estuary. South African National Scientific Programmes Report No. 156, C.S.I.R.: 41–56.Google Scholar
  2. Baird, D., P. E. D. Winter & G. Wendt, 1987. The flux of particulate material through a well-mixed estuary. Cont. Shelf Res. 7: 1399–1403.CrossRefGoogle Scholar
  3. Borey, R. B., P. A. Harcombe & F. M. Fischer, 1983. Water and organic carbon fluxes from an irregularly flooded brackish marsh on the Upper Texas coast, USA. Est. Coast. Shelf Sci. 16: 379–402.Google Scholar
  4. Boto, K. G. & J. S. Bunt, 1981. Tidal export of particulate organic matter from a Northern Australian mangrove system. Est. Coast. Shelf Sci. 13: 247–255.Google Scholar
  5. Branch, G. M. & J. A. Day, 1984. Ecology of Southern African estuaries: Part XIII. The Pahniet River estuary in the south-western Cape. S. Afr. J. Zool. 19: 63–77.Google Scholar
  6. Brown, J., A. Colling, D. Park, J. Phillips, D. Rothery & J. Wright (Open University. Oceanography Course Team), 1989. Waves, Tides and Shallow-water Processes. Pergamon Press, Oxford: 187 pp.Google Scholar
  7. Chrzanowski, T. H., L. H. Stevenson & J. D. Spurrier, 1982. Transport of particulate organic carbon through the North Inlet ecosystem. Mar. Ecol. Prog. Ser. 7: 231–245.Google Scholar
  8. Daly, M. A. & A. C. Mathieson, 1981. Nutrient fluxes within a small north temperate salt marsh. Mar. Biol. 61: 337–344.CrossRefGoogle Scholar
  9. Dame, R., T. Chrzanowski, K. Bildstein, B. Kjerfve, H. McKellar, D. Nelson, J. Spurrier, S. Stancyk, H. Stevenson, J. Vemberg & R. Zingmark, 1986. The outwelling hypothesis and North Inlet, South Carolina. Mar. Ecol. Prog. Ser. 33: 217–229.Google Scholar
  10. Dame, R., D. Childers & E. Koepfler, 1992. A geohydrologic continuum theory for the spatial and temporal evolution of marsh-estuarine ecosystems. Neth. J. Sea Res. 30: 63–72.CrossRefGoogle Scholar
  11. Dye, A. H., 1978. Epibenthic algal production in the Swartkops estuary. Zool. Afr. 13: 157–161.Google Scholar
  12. Els, S., 1982. Distribution and abundance of two crab species on the Swartkops estuary salt marshes and the energetics of the Sesarma catenata population. M. Sc. Thesis, University of Port Elizabeth.Google Scholar
  13. Hanekom, N., D. Baird & T. Erasmus, 1988. A quantitative study to assess standing biomasses of macrobenthos in soft substrata of the Swartkops estuary, South Africa. S. Afr. J. mar. Sci. 6: 163–174.Google Scholar
  14. Hardisky, M. A. & R. J. Reimold, 1977. Salt marsh plant geratology. Science 198: 612–614.Google Scholar
  15. Heinle, D. R. & D. A. Flemer, 1976. Flow of materials between poorly flooded tidal marshes and an estuary. Mar. Biol. 35: 359–373.Google Scholar
  16. Hilmer, T., M. M. B. Talbot & G. C. Bate, 1988. A synthesis of recent botanical research in the Swartkops estuary. In D. Baird, J. F. K. Marais & A. P. Martin (eds), SANCOR Report No. 156, C.S.I.R.: 25–40.Google Scholar
  17. Hopkinson, C. S., J. G. Gosselnik & R. T. Parrondo, 1978. Above ground production of seven marsh plant species in coastal Louisiana. Ecology 59: 760–769.Google Scholar
  18. Huizinga, P., 1985. A dynamic one-dimensional water quality model. CSIR Res. Rep. 562: 1–23.Google Scholar
  19. Kokkinn, M. J. & B. R. Allanson, 1985. On the flux of organic carbon in a tidal salt marsh, Kowie River estuary, Port Alfred, South Africa. S. Afr. J. Sci. 81: 613–617.Google Scholar
  20. Mosterd, S. A., 1983a. Photochemical procedure used in South Africa for the photometric determination of dissolved carbon in seawater. S. Afr. J. mar. Sci. 1: 57–60.Google Scholar
  21. Mosterd, S. A., 1983b. Procedure used in South Africa for the automatic photometric determination of micronutrients in seawater. S. Afr. J. mar. Sci. 1: 189–198.Google Scholar
  22. Nixon, S. W., 1980. Between coastal marshes and coastal waters: a review of twenty years of speculation and research on the role of saltmarshes in estuarine productivity and water chemistry. In P. Hamilton & K. B. MacDonald (eds), Estuariee and Wetland Processes, with Emphasis on Modelling. Plenum Press, New York: 437–525.Google Scholar
  23. Odum, E. P., 1980. The status of three ecosystem-level hypotheses regarding salt marsh estuaries: tidal subsidy, outwelling, and detritus-based food chains. In V. S. Kennedy (ed.), Estuarree Perspectives. Academic Press, New York: 485–495.Google Scholar
  24. Odum, W. E., J. S. Fisher & J. C. Pickral, 1979. Factors controlling the flux of particulate organic carbon from estuarine wetlands. In R. J. Livingston (ed.), Ecological Processes in Coastal and Marine Systems. Plenum Press, New York: 69–80.Google Scholar
  25. Ott, J., 1988. Meereskunde. Ulmer (UTB), Stuttgart: 386 pp.Google Scholar
  26. Pakulski, J. D., 1986. The release of reducing sugars and dissolved organic carbon from Spartina alterniflora Loisel in a Georgia salt marsh. Est. Coast. Shelf Sci. 22: 385–394.Google Scholar
  27. Pierce, S. M., 1979. The contribution of Spartina maritima (Curtis) Fernald to the primary production of the Swartkops estuary. M.Sc.thesis, University of Port Elizabeth.Google Scholar
  28. Pomeroy, L. R., K. Bancroft, J. Breed, R. R. Christian, D. Frankenberg, J. R. Hall, L. G. Maurer, W. J. Wiebe, R. G. Wiegert, R. L. Wetzel, 1976. Flux of organic matter through a salt marsh. In M. Wiley (ed.), Estuariee Processes, Vol. 2. Academic Press, New York: 270–279.Google Scholar
  29. Teal, J. M., 1962. Energy flow in the salt marsh ecosystem of Georgia. Ecology 43: 614–623.Google Scholar
  30. Winter, P. E. D. & D. Baird, 1988. Diversity, productivity and ecological importance of macrobenthic invertebrates in selected eastern cape estuaries. In M. N. Bruton & F. W. Gess (eds), Towards an Environmental Plan for the Eastern Cape. Rhodes University, Grahamstown: 149–154.Google Scholar
  31. Wolaver, T. G., S. Hutchinson & M. Marozas, 1986. Dissolved and particulate organic carbon in the North Inlet estuary, South Carolina: What controls their concentrations? Estuaries 9: 31–38.Google Scholar
  32. Wolaver, T. G. & J. D. Spurrier, 1988. Carbon transport between a euhaline vegetated marsh in South Carolina and the adjacent tidal creek: contributions via tidal inundation, runoff and seepage. Mar. Ecol. Prog. Ser. 42: 53–62.Google Scholar
  33. Woodwell, G. M. & D. E. Whitney, 1977. Flax Pond ecosystem study: exchanges of phosphorus between a salt marsh and the coastal waters of Long Island Sound. Mar. Biol. 41: 1–6.Google Scholar
  34. Woodwell, G. M., D. E. Whitney, C. A. S. Hall & R. A. Houghton, 1977. The Flax Pond ecosystem study: exchanges of carbon in water between a salt marsh and Long Island Sound. Limnol. Oceanogr. 22: 833–838.Google Scholar
  35. Yelverton, G. F. & C. T. Hackney, 1986. Flux of dissolved organic carbon and pore water through the substrate of a Spartina alterniflora marsh in North Carolina. Est. Coast. Shelf Sci. 22: 255–267.Google Scholar

Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • Paul E. D. Winter
    • 1
  • Thomas A. Schlacherl
    • 1
  • Dan Baird
    • 1
  1. 1.Department of ZoologyUniversity of Port ElizabethPort ElizabethSouth Africa

Personalised recommendations