Abstract
The National Water Act (Act 36 of 1998) in South Africa recognizes basic human water requirements as well as the need to sustain the country's freshwater and estuarine ecosystems in a healthy condition for present as well as future generations. In this Act, provision is made for a water reserve to be estimated prior to the authorization of water use (e.g., for agriculture, large volume residential and industrial uses) through licensing. This reserve is the water required to satisfy basic human needs (i.e., 25 1 person−1 d−1) and to protect aquatic ecosystems to ensure present and future sustainable use of the resource. This led the Departments of Water Affairs and Forestry and estuarine scientists throughout South Africa to develop a method to determine the freshwater inflow requirements of estuaries. The method includes documenting the geographical boundaries of the estuary and determining estuarine health by comparing the present state of the estuary with a predicted reference condition with the use of an Estuarine Health Index. The importance of the estuary as an ecosystem is taken from a national rating system and together with the present health is used to set an Ecological Reserve Category for the estuary. This category represents the level of protections afforded to an estuary. Freshwater is then reserved to maintain the estuary in that Ecological Reserve Category. The Reserve, the quantity and quality of freshwater required for the estuary, is determined using an approach where realistic future river runoff scenarios are assessed, together with data for present state and reference conditions, to evaluate the extent to which abiotic and biotic conditions within an estuary are likely to vary with changes in river inflow. Results from these evaluations are used to select an acceptable river flow scenario that represents the highest reduction in freshwater inflow that will still protect the aquatic ecosystem of the estuary and keep it in the desired Ecological Reserve Category. The application of the Reserve methodology to the Mtata estuary is described.
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Literature Cited
Adams, J. B. andG. C. Bate. 1994. The freshwater requirements of estuarine plants incorporating the development of an estuarine decision support system. Water Research Commission Report No. 292/2/94. Water Research Commission, Pretoria, South Africa.
Adams, J. B., G. C. Bate, andM. O'Callaghan. 1999b. Estuarine primary producers, p. 91–118.In B. R. Allanson and D. Baird (eds.). Estuaries of South Africa. Cambridge University Press, Cambridge, U.K.
Adams, J. B., W. T. Knoop, andG. C. Bate. 1992. The distribution of estuarine macrophytes in relation to freshwater.Botanica Marine 35:215–226.
Adams, J. B. andM. M. B. Talbot. 1992. The influence of river impoundment on the estuarine seagrassZostera capensisSetchell.Botanica Marina 35:69–75.
Adams, J. B., S. Taljaard, J. K. Turpie, andA. K. Whitfield. 1999a. Volume 5: Estuarine Ecosystems, Version 1.0.In H. Mackay and B. Weston (eds.). Resource Directed Measures for Protection of Water Resources. Department of Water Affairs and Forestry, Pretoria, South Africa.
Allanson, B. R. andG. H. L. Read. 1995. Further comment on the response of Eastern Cape Province estuaries to variable freshwater inflows.Southern African Journal of Aquatic Science 21:56–70.
Arthington, A. H., J. M. King, J. O'Keeffe, S. E. Bunn, J. A. Day, B. J. Pusey, B. R. Bluhdorn, andR. Tharme. 1992. Development of an holistic approach for assessing environmental flow requirements of riverine ecosystems, p. 69–76.In J. J. Pligram and B. P. Hooper (eds.). Water Allocation for the Environment. The Centre for Water Policy Research, University of New England, Armidale.
Bate, G. C. andJ. B. Adams. 2000. The effects of a single freshwater release into the Kromme estuary: Overview and interpretation for the future.Water SA 26:329–332.
Bickerton, I. B. andS. M. Pierce. 1988. Estuaries of the Cape. Part 2: Synopsis of available information on individual systems. Report No. 22 Krom (CMS 45), Seekoei (CMS 46) and Kabejous (CMS 47). A. E. F. Heydron and P. D. Morant (eds.). Council for Scientific and Industrial Research Research Report 432. Environmentek. Stellenbosch, South Africa.
Colloty, B. M., J. B. Adams, andG. C. Bate. 2000. The botanical importance of estuaries in the former Ciskei and Transkei regions. Report 812/1/00. Water Research Commission, Pretoria, South Africa.
Department of Water Affairs and Forestry (DWAF). 1995. South African Water Quality Guidelines for Coastal Marine Waters, Volume 1: Natural Environment. DWAF, Pretoria, South Africa.
Department of Water Affairs and Forestry (DWAF). 1996. South African Water Quality Guidelines, Volume 7: Aquatic Ecosystems. DWAF, Pretoria, South Africa.
Dunbar, M. J., A. Gustard, M. C. Acreman, andC. R. N. Elliott. 1998. Review of overseas approaches to setting river flow objectives. Environment Agency R&D Technical Report W6B(96)4. Institute of Hydrology. Wallingford, U.K.
Grange, N. andB. R. Allanson. 1995. The influence of freshwater inflow on the nature, amount and distribution of seston in estuaries of the Eastern Cape, South Africa.Estuarine, Coastal and Shelf Science 40:403–420.
Harrison, T. D., J. A. G. Cooper, and A. E. L. Ramm. 2000. State of South African estuaries. Geomorphology, ichthyofauna, water quality and aesthetics of South African estuaries. Department of Environmental Affairs and Tourism, State of the Environment Series Report, Document 2. Pretoria, South Africa.
Howard-Williams, C. andB. R. Allanson. 1981. An integrated study on littoral and pelagic primary production in a southern African coastal lake.Archiv fur Hydrobiologie 92:507–534.
Howard-Williams, C. andM. R. Liptrot. 1980. Submerged macrophyte communities in a brackish South African estuarine-lake system.Aquatic Botany 9:101–116.
MacKay, H. M. 2000. Moving towards sustainability: The Ecological Reserve and its role in implementation of South Africa's water policy. Proceedings of the World Bank Water Week Conference. Washington, April 2000. World Bank, Washington.
Pitman, W. V. 1995. Towards improved utilisation of South Africa's water resources. Proceedings of the 7th South African National Hydrology Symposium, Grahamstown, September 1995. Rhodes University, Grahamstown, South Africa.
Plumstead, E. E., J. F. Prinsloo, andH. J. Schoonbee. 1989. A survey of the fish fauna of Transkei estuaries. Part three: The Mtata River estuary.South African Journal of Zoology 24:282–289.
Reddering, J. S. V. 1988. Prediction of the effects of reduced river discharge on the estuaries of the south-eastern Cape Province, South Africa.South African Journal of Science 86:425–428.
Richter, B. D., J. V. Baumgartner, J. Powell, andD. P. Braun. 1996. A method for assessing hydrologiciteration within ecosystems.Conservation Biology 10:1163–1174.
Schlacher, T. A. andT. H. Wooldridge. 1996. Ecological responses to reductions in freshwater supply and quality in South Africa's estuaries: Lessons for management and conservation.Journal of Coastal Conservation 2:115–130.
Stalnaker, C. B. 1990. Minimum flow is a myth, p. 31–33.In M. B. Bain (ed.). Ecology and Assessment of Warm Water Streams: Workshop Synopsis. U.S. Fish and Wildlife Service, Washington, D.C.
Turpie, J. K. 2002. Classification and prioritization of South African estuaries on the basis of health and conservation importance for the determination of the estuarine water reserve. Report submitted to Social and Ecological Services, Department of Water Affairs and Forestry, Pretoria, South Africa.
Turpie, J. K., J. B. Adams, A. Joubert, T. D. Harrison, B. M. Colloty, R. C. Maree, A. K. Whitfield, T. H. Wooldridge, S. J. Lamberth, S. Taljaard, andL. Van Niekerk. 2002. Assessment of the conservation priority status of South African estuaries for use in management and water allocation.Water SA 28:191–206.
Whitfield, A. K. 1999. Icthyoplankton diversity, recruitment and dynamics, p. 209–217.In B. R. Allanson and D. Baird (eds.). Estuaries of South Africa. Cambridge University Press, Cambridge, U.K.
Whitfield, A. K. andM. N. Bruton. 1989. Some biological implications of reduced freshwater inflow into eastern Cape estuaries: A preliminary assessment.South African Journal of Science 85:691–694.
Whitfield, A. K. andT. H. Wooldridge. 1994. Changes in freshwater supplies to southern African estuaries: Some theoretical and practical considerations, p. 41–50.In K. R. Dyer and R. J. Orth (ed.). Changes in Fluxes in Estuaries: Implications from Science to Management. Olsen and Olsen, Fredensborg, Denmark.
Wooldridge, T. H. 1999. Estuarine zooplankton community structure and dynamics, p. 141–166.In B. R. Allanson and D. Baird (eds.). Estuaries of South Africa. Cambridge University Press, Cambridge, U.K.
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Adams, J.B., Bate, G.C., Harrison, T.D. et al. A method to assess the freshwater inflow requirements of estuaries and application to the Mtata estuary, South Africa. Estuaries 25, 1382–1393 (2002). https://doi.org/10.1007/BF02692232
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DOI: https://doi.org/10.1007/BF02692232