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Background Information

In March 1993 a co-ordinated research programme on decision support for the conservation and management of estuaries was launched under the auspices of the Consortium for Estuarine Research & Management (CERM) and funded by the Water Research Commission (WRC). A procedure was developed whereby decision support systems were to be structured around certain key issues, with currently available information and wisdom providing the basis for individual decision support modules. A collation of available scientific information on individual southern African estuaries was identified as a high priority in order to facilitate subsequent components of the CERM contract with the WRC. The WRC Report No. 577/1/95 entitled Available Scientific Information on Individual South African Estuarine Systems was published in 1995 and has been widely used over the past five years.

In June 1999 it was suggested that an updated version of the above WRC Report be prepared for installation on the CERM web page. This task was completed in December 1999 and now provides researchers, planners and managers with an easily accessible source of scientific information on the various South African estuaries. In addition to providing valuable data sources for individual systems, this document also highlights those estuaries for which little or no information is available. Most of the former Ciskei and Transkei estuaries fall into the latter category, and systems within these regions should therefore be targeted as priorities in future information gathering exercises. A section dealing with references having wider relevance to estuaries of a particular region or even to the subcontinent has also been included.

The categories chosen for this review of information are, of necessity, very broad and the contents of a number of papers cover more than one category. Although published works in scientific journals and books have received the most attention, numerous reports synthesizing both published and unpublished information on South African estuaries are also given. Although much of the ‘grey’ literature which is readily accessible has been included in this document, a number of documents were excluded on the basis that this type of information is not available to either scientists or managers (e.g. unpublished honours projects). Abstracts from conference proceedings are also excluded from the data base since these often cover preliminary findings of studies which are published in detail at a later date.

Reference to the proceedings of estuarine workshops is linked to the editor(s) of such workshops and not to the individual scientists who may have contributed to the proceedings. Where an unpublished report or progress report duplicates information provided by the same author in a published article, the former document is excluded from this analysis. Likewise, if preliminary reports are followed by final reports which include the information given previously, then only the final document is indexed. Taxonomic papers dealing with the descriptions of species have not been included in this database. Selected references from both the marine and freshwater environment have been included where they contain considerable information directly relevant to estuaries or typical estuarine organisms.

Information availability on each estuarine system is categorized as nil, poor, moderate, good or excellent, based on the scope and depth of available scientific publications and reports. A preliminary analysis of the estuarine information database in the different biogeographic regions is shown in Table 1. Indications are that the status of information on 68% of the South African estuaries was classified as nil or poor, with 22% having moderate information and only 10% having good or excellent information. One third of the nil or poor returns are from the former Transkei, where 59 (87%) of the 68 estuaries have little or no published information. A similar situation pertains to the former Ciskei, where 11 (85%) of the 13 estuaries have little or no published information.

For the purposes of this literature review, South African estuarine systems have been divided into three major biogeographic regions, viz. subtropical from the Kosi Estuary in KwaZulu-Natal to the Mbashe Estuary in the Eastern Cape, warm temperate from the Mendu Estuary in the Eastern Cape to the Silwermyn Estuary in False Bay, and cool temperate from the Krom Estuary on the Cape Peninsula to the Orange River mouth on the Northern Cape coast. Each estuary has been placed in one of the three biogeographic categories described above, a map of which is shown in Figure 1.

Map of South Africa

Figure 1. Map of southern Africa showing the three major biogeographic regions used in this document.

Table 1. Synthesis of available information categories from individual estuaries in each biogeographical region.  

REGION
INFORMATION
Cool Temperate
Warm Temperate
Subtropical
South Africa
N
%
N
%
N
%
N
%
Nil    
4
3
21
17
25
10
Poor
5
50
81
64
65
54
151
58
Moderate
2
20
26
20
28
23
56
22
Good
3
30
10
8
5
4
18
7
Excellent    
7
5
2
2
9
3
Total
10
100
128
100
121
100
259
100

Systems which do not function as estuaries using the widely accepted definition of Day (1980) were not included in this review, viz. Langebaan, Papkuils, Buffels Wes, Elsies, Mossel, Rooi, Skaapkop, Meul, Grooteiland, Kranshoek, Crooks, Brak, Witels, Geelhoutbos, Kleinbos, Bruglaagte, Langbos, Sanddrif, Eerste, Klipdrif, Boskloof, Mjihelo, Mlambomkulu, Mkambati and Mlazi. According to Harrison et al. (1994a) the following Northern and Western Cape systems do not perform the functions normally attributed to estuaries; Holgat, Buffels, Swartlintjies, Spoeg, Bitter, Groen, Brak, Sout (Noord), Jakkals, Wadrif, Verlore, Papkuils, Dwars (Noord), Dwars (Suid), Modder, Jacobsbaai, Lêerbaai, Bok, Silwerstroom and Sout (Suid). Verlorenvlei may have functioned as an estuarine lake system before the creation of artificial restrictions to water exchange with the marine environment but definitive evidence is lacking (Fromme 1985a, Sinclair et al. 1986).

The following extremely small systems have catchments arising within the immediate coastal environment, are seldom linked to the sea, and make a minimal contribution (in some instances a zero contribution) to the overall estuarine biota of southern Africa; Sewejaarskop, Booiskraal, Helpmekaars, Klip, Kaapsedrif, Freshwater Poort, Blue Krans, Shwele-Shwele, Mvubukazi, Ngqenga, Imtwendwe, Timba, Mbokotwana, Nebelele, Kwa-Goqo, Ku-Nocekedwa, Nqabarana, Ngomane, Mendwana, Dakana, Kwa-Suku, Sundwana, Ku-Amanzimnyana, Nqakanqa, Lubanzi, Mhlahlane, Mtonjane, Ku-Bomvu, Thsani, Mtonga, Ndluzula, Tyityane, Ntloboba, Gxwaleni, Mnenga, Manzana, Gugu, Ingo, Ntyivini, Dakane, Mguga, Kwa-Nyambalala, Sikatsha, Cutweni, Maviti, Tezana, Magogo, Mbaxeni, Butsha, Kwa-Nondindwa, Daza and Mtolane. All the systems listed above are excluded from this review because of their limited estuarine functions but this does not imply that they are unimportant ecosystems. Previously functional estuaries such as the Sout, Bakens, Papkuils, Ngcura and Sipingo, which have been drastically altered as a result of canalization, industrialization, etc., are included in this analysis because of the potential for rehabilitation.

The estuarine classification system used in this review follows that of Whitfield (1992), viz. permanently open estuaries, temporarily open/closed estuaries, estuarine lake systems, estuarine bays and river mouths. Individual estuarine systems may change from one type of estuary to another under the influence of natural events or anthropogenic influences. Human induced changes have resulted in rapid and dramatic alterations to a number of systems, e.g. Richard's Bay has been transformed from an estuarine lake into two estuarine bays through harbour development. It should be noted that an estuarine water body must have a water surface area exceeding 1000 ha to be considered as an estuarine lake or estuarine bay system. It should also be noted that permanently open estuaries and river mouths do sometimes close during prolonged drought periods but under normal seasonal river flow conditions they remain open. Increasing freshwater abstraction from perennial river systems for agricultural, domestic and industrial use will inevitably lead to changes in sediment scouring patterns and mouth dynamics, with concomitant changes in the future classification of these estuaries.

The condition of each estuary, which is based on the degree to which human activities have changed the functioning or viability of a particular system, is broadly classified as poor, fair, good or excellent. These assessments are based on the opinions of scientists from the different regions as well as use of the literature data base presented in this document. The following criteria acted as guidelines in the designation of the condition of a particular estuary:
Excellent - estuary in a near pristine condition (negligible human impact).
Good - no major negative anthropogenic influences on either the estuary or catchment (low impact).
Fair - noticeable degree of ecological degradation in the catchment and/or estuary (moderate impact).
Poor - major ecological degradation arising from a combination of anthropogenic influences (high impact).

Vertical and oblique aerial photographs/slides are a useful tool in documenting changes to estuarine systems and are therefore of value to both scientists and managers. Contact individuals and organizations possessing substantial photographic records are provided to facilitate access to this database.