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

[摘要] ENGLISH ABSTRACT: The primary aim of this study was to assess and compare the ecological integrity of the Lourens, Palmiet andHout Bay Rivers (South Western Cape, South Africa) by examining the macroinvertebrate communitystructure at a series of representative sampling sites along the course of each river, using the South AfricanScoring System - Version 5 (SASS-5) rapid bioassessment method. Secondary aims included anexamination of the effects of seasonal variability, biotope availability and site-specific environmentalvariables on the macroinvertebrate community structure at sampling sites, as well as the preliminary testingof 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 thethree rivers was consistently good. The Hout Bay River in the upper portions of the Orange Kloof Reservewas 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 significantdeterioration in the ecological integrity of all three rivers due to a number of probable causes. Results basedon recorded SASS Scores and Average Score per Taxon (ASPT) values, using 'biological bands' generatedfrom reference sites in the South Western Cape, were generally similar to and supported by thecorresponding multivariate analyses undertaken. From the results of the various analyses undertaken in thisinvestigation and some of the problems encountered in interpreting the data, a number of recommendationsare made regarding future bioassessment studies based on the SASS within the national River HealthProgramme (RHP).To test the IHAS, secondary data were obtained from reference sites in the Mpumalanga and Western CapeProvinces 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 correlationanalyses were undertaken between SASS-4/5 Scores and IHAS scores, using Kendall's Rank-correlationCoefficient (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) andunsatisfactory, with no significant correlations (p < 0.05) for two-thirds of the data sets analysed and a widedegree of scatter generally observed amongst data points in respective scatter plots. The performance of theIHAS varied between geomorphological zones and biotope groups, with the Foothill: Gravel-bed Zone inMpumalanga showing the best results, particularly when the stones-in-current biotope group was analysedseparately. Further testing of the IHAS is required to confirm its relative performance in differentbioregions/ecoregions, geomorphological zones and biotope groups, which should be undertaken as apriority research area within the RHP. Unsuccessful attempts to test the IHAS by means of multipleregression analyses were undertaken, suggesting that such techniques should be avoided in further testingof the IHAS.

[发布机构] Stellenbosch University