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Classification of South African
Rivers. Volume 1

S Eekhout, JM King & A Wackernagel.

1997

Department of Environmental Affairs and Tourism. Pretoria

ISBN 0-621-27963-3


Executive Summary

BACKGROUND

The ever growing demand for water to provide for South Africa's burgeoning population has resulted in increasing pressure being placed on lotic ecosystems in the country and the concomitant need for tools to aid in the management and conservation of lotic ecosystems. Ecologists and resource managers frequently make use of classifications in order to organize information and thereby enhance understanding of complex systems and a classification of the rivers of the country has been identified as a potentially useful management tool. The findings of a research project, the aim of which was to develop a biotic classification of the rivers of South Africa, are documented in this report.

Classification can be broadly defined as a process in which a set of objects, systems or ideas (entities) are divided into a number of discrete groups on the basis of some measure of their similarity or difference with respect to one or more pre-defined criteria. Classification of ecological systems is complex because these systems are in general characterised by indistinct boundaries i.e. their characteristics (potential criteria for classification) vary continuously rather than discretely. This inevitably creates problems, as implicit in any classification is the assumption that relatively distinct boundaries exist and that these may be identified by a limited set of criteria.

It is important to appreciate that the product of the process of classification, namely the groups identified (usually referred to as the classification), is artificial in nature and in no way an inherent property of the entities being classified. Indeed, to a large extent the classification produced will be determined by the nature of the criteria used to measure similarities or differences between the entities. Thus there is a vital need for initial clarity on what the classification will be used for so that the appropriate criteria can be chosen. Every effort was made by project staff to ensure that potential end-users of the classification were involved in the development of the project in order to ensure that the resultant classification would indeed be of practical use.

PROJECT AIMS AND THEIR ACHIEVEMENT

The objective of the project "Classification of South African Rivers" as broadly stated in the project proposal was as follows:

To develop a classification for the rivers of South Africa, as a guide to water managers, developers, scientists, conservators and other decision-makers on the number, distribution, variety, regional characteristics and sensitivity to development of the rivers and river zones of the country.

As a result of feedback from potential users of the classification and the project advisory committee this objective was refined and the revised objectives accepted by the project advisory committee are listed below, with comment on the extent to which they were achieved.

  1. To develop a regional, biotic classification for the rivers of South Africa by:

    1. Creating a national database of riverine fauna and flora

      A database was developed using the Microsoft Access software package. The database currently contains some 15 000 distribution records for species of riparian vegetation (200 species), fish (93 species), molluscs (72 species), mayflies (91 species), caddisflies (151 species) and blackflies (39 species). Distribution records were extracted from scientific publications, unpublished reports and theses and the distribution databases of the National Botanic Institute, the Albany Museum, the JLB Smith Institute, the National Mollusc Collection and Transvaal Nature Conservation.

    2. Adapting or developing a methodology for classifying the country's rivers, using this database

      The methodology that was adopted to produce the classification involved the use of hierarchical agglomerative cluster analysis using untransformed data and the Bray Curtis similarity index. Secondary catchments were used as the spatial unit for classification and similarity between catchments was based on the presence or absence of each of the 646 species for which distribution data were collated.

    3. Using the classification to create a map of biotic regions

      A map of biogeographic regions was constructed using the results of the cluster analyses. In essence this map identifies regions (groups of secondary catchments) which have similar species composition. This map is available as a PC ARC-INFO GIS coverage.

  2. To explore the comparability and potential usefulness of integrating the results of the regional biotic analyses and the outputs from independent projects examining regional patterns of flow and water chemistry.

    Research funded by the Water Research Commission has recently resulted in the production of maps which identify water quality management regions for the country and regions of homogenous flow-types. At the outset of this project it was envisaged that it would be advantageous if these regional classifications could be integrated with the biogeographic regionalisation in order to produce a composite classification. During the course of this project it became evident that such an integration was neither feasible nor desirable.

  3. To investigate, using existing biotic data, the possibility of objectively delineating biotic sub-regions.

    The possibility of delineating biotic sub-regions within the biogeographic regions was investigated and the results obtained indicated that such delineation was indeed possible and that the sub-regions which could be recognised reflected the longitudinal zonation of rivers within a biogeographic region.

MAJOR RESULTS AND CONCLUSIONS

The requirements of potential end-users of a national river classification were diverse. In broad terms the need of scientists and consultants was for a classification that grouped like systems based on their natural attributes and primarily related to their need for baseline data in order to determine natural "pristine" conditions and to determine the limits for extrapolation of research results. On the other hand, resource managers and conservation officials in most cases appeared to require a rating system which attached a value of some kind to a river or part of a river. The biogeographic classification developed within this project probably satisfies the requirements of the first of these groups fairly well and also provides a convenient framework within which the rating systems required by resource managers and conservation officials can be used.

The checklists and distribution maps which were constructed in order to create the data matrix which was used for the classification analyses, and which are presented in Volume 2 of this report, make a valuable contribution to our knowledge of the patterns of distribution of the riverine fauna and flora of South Africa. Although it must be appreciated that for many of the species these maps provide only a first estimate of distribution they do provide a useful basis for further work in this field and serve to identify high priority areas for future survey work.

Cluster analysis performed using a data matrix of presence/absence of 645 species of riverine flora and fauna in 137 secondary catchments resulted in the identification of ten biogeographic regions (groups of secondary catchments) within with species composition was relatively homogeneous. The ten regions identified were:

  1. Arid north-west
  2. Arid Interior
  3. Namaqua Capensis
  4. Capensis
  5. Karroid Capensis
  6. Eastem seaboard
  7. Sub-tropical east coast
  8. Interior uplands
  9. Basuto highlands
  10. Temperate/sub-tropical north-east

The biogeographic classification is coarse, but does account for differences in the biotic character of rivers which are a consequence of biogeographic history, as well as large-scale variation in environmental variables. It provides a first approximation of areas within which extrapolation of ecological data may be valid and also provides an ecological framework around which assessment systems can be developed and used. The classification has recently been successfully used, in a modified form, as a basic framework upon which site selection for a national biomonitoring network has been based.

The integration of the biogeographic classification with classifications which have recently identified water quality management regions for the country and regions of homogenous flowtypes was considered to be neither feasible nor desirable. The three classifications individually serve different purposes and independently provide potential users with more information than a composite classification would. In addition, there are considerable data limitations attached to each of the classifications which would in all likelihood be compounded within an integrated classification.

A desktop study was undertaken in order to investigate the possibility of delineating biotic sub-regions within each of the biogeographic regions. This pilot study made use of data which detailed benthic invertebrate community composition at specific sites on various rivers within the Capensis biogeographic region. Multivariate analysis (cluster and ordination procedures) of these data indicated that individual sites tended to group together on the basis of position along the river. In other words biotic sub-regions which reflected the longitudinal zonation of rivers within the biogeographic region could be identified. It is suggested that the sub-regions thus identified could be delineated and mapped using one or more environmental correlates. The most promising correlates appear to be altitude and gradient.

RECOMMENDATIONS

There is an urgent need for the development of a national policy regarding access to and use of public domain databases which are currently housed within various museums and research institutes. The issue of custodianship of the biogeographic database developed during this project needs to be addressed.

There is an urgent need for further taxonomic studies particularly in the case of the riverine invertebrates. Associated with this is the need, in particular for the rivers within the former homelands of Transkei and Ciskei and those of the and interior of the country, for baseline survey and inventory studies.

The delineation of biotic sub-regions within the biogeographic regions should be regarded as a research priority. The desktop study undertaken within this project as well as initiatives undertaken under the auspices of the National Biomonitoring programme for riverine ecosystems provide a suitable framework for further work in this area.

Provision should be made for updating of the database and for re-analysis of the data matrix and revision of the boundaries of the biogeographic regions at 5-yearly intervals.


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