Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The River Health Programme (RHP) is an assessment tool for monitoring the ecological state of
rivers to ensure that they remain fit for use by present and future generations. This study, forming
part of a RHP assessment conducted on the south-western Cape Hout Bay, Lourens and Palmiet
Rivers, has the aim to (1) zone the rivers for representative site selection, (2) assess their habitat
integrity (HI), (3) determine the influence of land use on riverine HI and (4) assess the river water
quality at the time of the RHP assessments.
(1) The desktop geomorphological zonation method used in RHP assessments has not been
sufficiently previously tested on short rivers draining the Western Cape Mountains. The
Lowland River Zone of the rivers studied, as well as the Hout Bay River’s Upper Foothill Zone,
were found to have steeper gradients than expected, probably due to these rivers being shorter
and consequently steeper than any on which the method was previously tested. The notion of
one gradient river classification system being applicable throughout South Africa, with its
diverse geology and climate, is unlikely. Rather a classification system modified for various
physiographic features regions or by a factor based on river length is more realistic.
(2) Although there is a general longitudinal decrease in HI downstream along the Hout Bay and
Lourens Rivers, coinciding with increased anthropogenic activities, HI improves in the Palmiet
River’s lower reaches through the Kogelberg Nature Reserve. Surrounding land use thus seems
to be a major determinant of HI. Although the Index of Habitat Integrity (IHI) used appears to
achieve its aim, it was found to be subjective. Categorisation of the IHI scoring is suggested.
(3) The amount of natural versus disturbed land use occurring upstream of a site at a regional and
local scale, is a good predictor of riverine HI. Regional alien forestry and local urbanisation
have significantly strong negative effects on instream (r2 = -0.80, r2 = 0.80, p<0.05) and riparian
(r2 = -0.81, r2 = -0.83, p<0.05) HI. Different land use types therefore appear to affect riverine HI
at differing scales and thus managers must not only think on a local but also a catchment scale.
(4) In the Hout Bay River, a filtering system (e.g. wetland) appears to improve the water quality
between the middle and lower reaches. Along the Lourens River, high total dissolved salts,
conductivity and inorganic nitrogen concentrations in the middle reaches are cause for concern.
Along the Palmiet River there appeared to be insufficient oxygen to support most aquatic life
forms at Grabouw. Impoundments in the middle reaches act as sinks for nutrients and salts, but
the Huis and Krom tributaries downstream then appear to degrade the water quality of the
Palmiet River’s lower reaches within the Kogelberg Nature Reserve.
Together with the results of simultaneous biotic assessments, these results should be used to
develop management actions to improve the ecological health of these rivers. The results have been
used in a State-of-Rivers Report for the south-western Cape. / AFRIKAANSE OPSOMMING: Die Riviergesondheidsprogram (RGP) is 'n asseseringsinstrument wat die ekologiese stand van
riviere monitor om te verseker dat hulle steeds bruikbaar bly vir huidige en toekomstige geslagte.
Hierdie studie maak deel uit van 'n RGP-assessering van die Lourens-, Houtbaai- en Palmietrivier in
die Suidwes-Kaap en het ten doel om (1) die riviere te soneer vir verteenwoordigende
terreinseleksie, (2) die habitat-integriteit (HI) te assesseer, (3) die invloed van grondgebruik op
rivier-HI te bepaal en (4) die kwaliteit van rivierwater tydens die RGP-assesserings te bepaal.
(1) Die geomorfologiese-soneringsmetode wat in RGP-assesserings gebruik word, is nog nie
voorheen genoegsaam vir die kort riviere wat die Wes-Kaapse berge dreineer, getoets nie. Daar is
bevind dat die studiegebied riviere in die laagland-sones skerper gradiënte het as verwag, gehad het.
Dit kan moontlik toegeskryf word aan die riviere wat korter en dus steiler is as enige van dié wat
voorheen met die metode getoets is. Die moontlikheid dat een gradiëntklassifikasiestelsel vir riviere
regdeur Suid-Afrika met sy diverse geologie en klimaat toegepas kan word, is onwaarskynlik. 'n
Klassifikasiestelsel aangepas vir verskillende fisiografiese streke of met 'n faktor gebaseer op
rivierlengte, is meer realisties.
(2) Alhoewel HI stroomaf langs die Lourens- en Houtbaairivier in die algemeen longitudinaal saam
met die toename in antropogeniese aktiwiteite afneem, verbeter die Palmietrivier se HI waar dit laer
af deur die Kogelbergnatuurreservaat vloei. Die gebruike van aanliggende grond blyk dus 'n
belangrike bepaler van HI te wees. Die Indeks van Habitatintegriteit (IHI) bereik klaarblyklik die
vereiste doel, maar is te subjektief. Kategorisering van die IHI-waardes word voorgestel.
(3) 'n Goeie voorspeller van rivier-HI is die hoeveelheid natuurlike teenoor versteurde grondgebruik
stroomop van 'n terrein op 'n streeks- en lokale skaal. Die sterk negatiewe effek van uitheemse
plantegroei in die omgewing en lokale verstedeliking op stroom- (r² = -0.80, r² = 0.80, p<0.05 ) en
oewer-HI (r² = -0.81, r² = -0.83, p<0.05) is beduidend. Verskille in tipe grondgebruik beïnvloed
rivier-HI op verskillende vlakke; bestuurders moet dus plaaslik en aan die opvanggebied dink.
(4) In die Houtbaairivier lyk dit asof 'n filtreringstelsel (bv. vleigrond) die waterkwaliteit tussen die
middel- en lae gedeeltes verbeter. In die loop van die Lourensrivier is hoë totale opgeloste soute,
geleidingsvermoë en anorganiese stikstofkonsentrasies in die middelgedeelte 'n rede tot kommer. In
die Palmietrivier by Grabouw was die suurstof te min om die meeste akwatiese lewensvorme te
onderhou. Opgedamde water in die middel gedeeltes dien as 'n sink vir voedingstowwe en soute,
maar dit lyk asof die Huis- en Kromrivier die waterkwaliteit van die Palmietrivier stroomaf in die
Kogelbergnatuurreservaat degradeer.
Saam met die resultate van gelyktydige biotiese assesserings, kan hierdie resultate gebruik word vir
die ontwikkeling van bestuursaksies om die ekologiese toestand van hierdie riviere te verbeter. Die
resultate is gebruik in 'n toestand-van-riviere-verslag vir die Suidwes-Kaap.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16297 |
| Date | 12 1900 |
| Creators | Dawson, Emily Kathleen |
| Contributors | Van der Merwe, J.H., Boucher, C., University of Stellenbosch. Faculty of Science. Dept. of Earth Sciences. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xv, 167, 34 leaves : ill. |
| Rights | University of Stellenbosch |
Page generated in 0.003 seconds