Rapid bioassessment of the ecological integrity of the Lourens, Palmiet and Hout Bay Rivers (South Western Cape, South Africa) using aquatic macroinvertebrates

Ollis, Dean Justin (2005-12)

Thesis (MSc)--University of Stellenbosch, 2005.

Thesis

ENGLISH ABSTRACT: The primary aim of this study was to assess and compare the ecological integrity of the Lourens, Palmiet and Hout Bay Rivers (South Western Cape, South Africa) by examining the macroinvertebrate community structure at a series of representative sampling sites along the course of each river, using the South African Scoring System - Version 5 (SASS-5) rapid bioassessment method. Secondary aims included an examination of the effects of seasonal variability, biotope availability and site-specific environmental variables on the macroinvertebrate community structure at sampling sites, as well as the preliminary testing of the Integrated Habitat Assessment System (IHAS) for aquatic macroinvertebrates. According to results obtained, the ecological integrity of sampling sites in the Mountain Stream Zone of the three rivers was consistently good. The Hout Bay River in the upper portions of the Orange Kloof Reserve was particularly near-pristine, with this area having been identified in this study as a potential biodiversity ‘hot-spot’ for aquatic macroinvertebrates. Downstream of the Mountain Stream Zone, there was a significant deterioration in the ecological integrity of all three rivers due to a number of probable causes. Results based on recorded SASS Scores and Average Score per Taxon (ASPT) values, using ‘biological bands’ generated from reference sites in the South Western Cape, were generally similar to and supported by the corresponding multivariate analyses undertaken. From the results of the various analyses undertaken in this investigation and some of the problems encountered in interpreting the data, a number of recommendations are made regarding future bioassessment studies based on the SASS within the national River Health Programme (RHP). To test the IHAS, secondary data were obtained from reference sites in the Mpumalanga and Western Cape Provinces of South Africa. Assuming that SASS Scores at reference sites are the highest scores attainable, one would expect to find a positive relationship between SASS Scores and IHAS scores at reference sites. The assumption in this investigation was that this relationship should be linear. Non-parametric correlation analyses were undertaken between SASS-4/5 Scores and IHAS scores, using Kendall’s Rank-correlation Coefficient (τ), with separate analyses undertaken for different geomorphological zones and biotope groups. Correlations between SASS Scores and IHAS scores were generally weak (τ-values mostly < 0.3) and unsatisfactory, with no significant correlations (p < 0.05) for two-thirds of the data sets analysed and a wide degree of scatter generally observed amongst data points in respective scatter plots. The performance of the IHAS varied between geomorphological zones and biotope groups, with the Foothill: Gravel-bed Zone in Mpumalanga showing the best results, particularly when the stones-in-current biotope group was analysed separately. Further testing of the IHAS is required to confirm its relative performance in different bioregions/ecoregions, geomorphological zones and biotope groups, which should be undertaken as a priority research area within the RHP. Unsuccessful attempts to test the IHAS by means of multiple regression analyses were undertaken, suggesting that such techniques should be avoided in further testing of the IHAS.

AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie studie was om die ekologiese toestand van die Lourens-, Palmiet- en Houtbaairiviere (Suidwes Kaap, Suid Afrika) te bepaal en te vergelyk deur die bestudering van die makroinvertebraatgemeenskapstruktuur by verteenwoordigende monsterpunte langs die riviere, met gebruik van die “South African Scoring System” – Weergawe 5 (SASS-5) snelle biologiese bepalingsmetode. Sekondêre doelwitte het die bepaling van die gevolge van seisoenele veranderlikheid, biotoop beskikbaarheid en ligging-bepaalde omgewingsveranderlikes op die makroinvertebraatgemeenskapstruktuur by monsterpunte ingesluit, asook die inleidende toetsing van die “Integrated Habitat Assessment System” (IHAS) vir watermakroinvertebrate. Volgens die resultate verkry, was die ekologiese toestand van monsterpunte in die Bergstroomsone van die drie riviere konsekwent goed. Die Houtbaairivier in die boonste gedeelte van die Oranjekloofreservaat was veral feitlik onversteurd en hierdie streek is in die studie as ‘n potensiaal biodiversiteit “hot-spot” vir watermakroinvertebrate geidentifiseer. Stroomafwaarts van die Bergstroomsone was daar ‘n beduidende verswakking in die ekologiese toestand van al drie riviere, as gevolg van ‘n aantal moontlike oorsake. Resultate gebaseer op bepaalde “SASS Scores” en ‘Gemiddelde Waarde per Takson’ (“Average Score per Taxon” - ASPT) waardes, met gebruik van ‘biologiese bande’ wat van verwysingsmonsterpunte in die Suidwes Kaap afgelei is, was oor die algemeen soortgelyk aan en gestaaf deur die ooreenstemmende multiveranderlikke (“multivariate”) statistiese analises wat gedoen is. Uit die resultate van die verskeie analises wat in hierdie ondersoek gedoen is en sommige van die probleme wat in die dataverklaring gevind is, is ‘n aantal aanbevelings gemaak met betrekking tot toekomende biologiese bepalingstudies vir die nasionale Riviergesondheidsprogram (“River Health Programme” - RHP) wat op die SASS gebaseer is. Om die IHAS te toets is sekondêre data van verwysingsmonsterpunte in die Mpumalanga en Wes Kaap Provinsies van Suid Afrika verkry. As aangeneem word dat die “SASS Scores” by verwysingsmonsterpunte die hoogste moontlike tellings is wat bereik kan word, sou ‘n positiewe verwantskap tussen “SASS Scores” en IHAS tellings by verwysingsmonsterpunte verwag word. Die veronderstelling in hierdie studie was dat dié verwantskap lineêr moet wees. Nie-parametriese korrelasieanalise tussen “SASS-4/5 Scores” en IHAS tellings is gemaak, deur gebruik van Kendall se Rangkorrelasiekoëffisiënt (τ), met afsonderlike analises vir verskillende geomorfologiese sones en biotoopgroepe verrig. Korrelasies tussen “SASS Scores” en IHAS tellings was algemeen swak (τ-waardes < 0.3) en onbevredigend, met geen beduidende korrelasies (“p” < 0.05) vir twee-derdes van die datastelle wat geanaliseer is nie en ‘n wye verspreiding tussen datapunte in die onderskeie “scatter plots” wat waargeneem is. Die funksionering van die IHAS was verskillend tussen geomorfologiese sones en biotoopgroepe. Die beste resultate is vir die Voorheuwel: Gruisbeddingsone in Mpumalanga verkry, veral indien die klippe-in-stroom biotoopgroep afsonderlik geanaliseer is. Verdere toetsing van die IHAS is nodig om die relatiewe funksionering in verskillende biostreke/”ecoregions”, geomorfologiese sones en biotoopgroepe te bevestig en dit behoort voorangs te geniet binne die RHP. Pogings om die IHAS deur middel van veelvoudige regressie analise te toets het misluk, wat aandui dat sulke tegnieke vermy moet word in verder toetsing van die IHAS.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/20937
This item appears in the following collections: