Review: The Knysna Basin Project
Dr Brian Allanson
Organisation of the month is the Knysna Basin Project. Knysna is a
particularly beautiful area of the South African coast, midway between Cape Town
and Port Elizabeth along the famous Garden Route. The Knysna lagoon is the
largest on the south coast and possesses the highest plant and animal diversity
of all South African estuaries. But urban and industrial development threatened
the delicate environmental status of the lagoon. Since the 90s the Knysna Basin
Project has literally turned the tide - the research continues.
Throughout the 90's there was an increasing realisation by the general public,
or at least some of the non-governmental organisations (NGO's), that the rivers
and estuaries of the coastal rimland of South Africa were threatened by poor
land management, urban and industrial development and the effluents which they
generate.
By 1990 many of the NGO's concerned over the fate of the Knysna ‘lagoon"
as a consequence of rapid urbanisation within the "lagoon" basin
argued that the system was fast approaching a critical environmental status or
condition. Some went as far as to conclude that the "lagoon" was
dying!
To assess the reality of this view, the Outeniqualand Trust (an NGO founded
in 1974 to keep watch over the impact of development along the Garden Route, set
up the Knysna Basin Project (KBP) at the instigation of Dr Brian Allanson,
formerly Professor of Zoology and Director of the IWS at Rhodes University.
Earlier research studies on the coastal lakes and estuaries of the south
coast of the Western Cape during the 1970's by the Institute of Freshwater
Studies (now the Institute for Water Research) at Rhodes University,
Grahamstown, and the seminal work by Professor John Day and his colleagues at
the University of Cape Town, during the late 1940's, provided the opportunity to
assess the changes (if any) in the structure and biodiversity of the tidal
wetlands of the south coast over a period of some 50 years.
Initially, the Project was planned as an holistic catchment study involving
the river and its estuary which opened into a large marine embayment. And as the
largest urban development was taking place within the littoral of the tidal
areas of the ecosystem, and funds were limited our research effort was directed
towards a description of the hydrographics, chemical and biological
characteristics of the estuary, lagoon and marine embayment.
The emphasis was placed upon understanding the biophysical features of the
tidal water column and intertidal sediments. Without this background the impact
of increasing urbanisation upon the environmental status of the tidal areas
would not be possible.
A notable feature of the Knysna estuarine complex is that it is the largest
on the south coast and possesses the highest plant and animal diversity of all
South African estuaries. The studies of John Day established the importance of
quiet, wave reduced tidal flow and gently shelving intertidal shore, the latter
with its rich array of plant and substratum habitats, which together give
shelter, food and protection to a wide spectrum of animals, invertebrate and
vertebrate.
The funds to support the minimal research were obtained through public and
corporate sponsorship for a period of three years. Serious work started in
1994/95 and continued through extreme of climatological events - drought and
1:50 year floods to the end of 1998. The spread of the studies undertaken is
given in the scientific report, published as volume 55 (2) of the Transactions
of the Royal Society of South Africa, 2001. The development of specific
investigations arising from these studies, particularly to do with the role of
eelgrass (Zostera capensis) wetlands in nitrogen and phosphorus metabolism is
being undertaken by Mr Todd Switzer of the Department of Oceanography at the
University of Cape Town.
Through this collaboration of colleagues from the universities of Cape Town,
Western Cape and Rhodes and Dr Richard Barnes of Cambridge University, a deeper
understanding of the biophysical environment of the estuary has emerged. For
example, there is good evidence that the overall biodiversity has not decreased
over 50 years since the days of the original survey (although some of the faunal
components have changed). However, the threat of poor land management in the
contiguous catchments; increase in stormwater volumes as the non-absorptive
urban areas expand, and the complementary increase in mineralised sewage
effluent upon the ecological integrity of the system is real.
These are not unique environmental issues, but the published work does offer,
in quantitative terms, an improved understanding of the roles tidal exchange,
intertidal wetlands and varying river flow play in ameliorating these impacts.
Of particular significance is the magnitude of the tidal prism - 18 - 19 x 10 6
m 3 at spring tide - the largest among South African estuaries. The dimensions
and structure of the tidal embayment are such that it is irrigated at every
tide; the middle lagoon sector has a somewhat longer exchange time and the true
estuary of the Knysna River remains largely dependent upon river inflow. The
large tidal prism saves the estuarine complex, and particularly the embayment,
from destructive domestic enrichment and allows the re-distribution of land
derived sediments during river and stream floods.
We have concluded that the principal physical, chemical and biological
processes within the ecosystem are working near maximum efficiency and sustain
an acceptable environmental quality, but for how long? Fortunately new
legislation in the shape of the National Water Act of 1998 linked to the work of
the Knysna Basin Project provides both the law and facts, which local government
and developers should take cognisance of if this national treasure is to be
protected and sustained.
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