A study on periphyton as indicator of water-quality in regulated rivers

[摘要] In the central part of South Africa, where the average rainfall is 400�?00 mm/yrand evaporation far exceeds precipitation, it is important to monitor the limitedfreshwater resources that are available and to keep the aquatic environment inan acceptable state.Excessive nutrients (N and P) lead to algal blooms and deterioration of otheraquatic biota as the water quality declines. Biological monitoring methods andprogrammes have been instrumental in the management and monitoring of thehealth of aquatic ecosystems. Various biomonitoring indices have beendeveloped, using fish, benthic macroinvertebrates, phytoplankton and periphyton(including Bacillariophyta), as site- or non-site-specific indicators of water quality.Periphyton forms the foundation of many food webs. It is adaptable to theavailability of a habitat and is directly affected by changes in water quality. Inunregulated rivers, 'normal flow patterns and disturbance regimes shape thebenthic community composition, while in regulated rivers the 'unpredictability offlow (as an example) adds extra stress to the ecosystem.The overall objective of this study was to determine the position of periphyton (asa group) as a biomonitoring tool and which of its components would be bestsuited as indicators of water quality. This study was carried out over two periodsof 24 months each at two sites on the Modder River and one on the RenosterSpruit. The sites were selected because SASS5 (standard benthicmacroinvertebrate index of water quality) could be carried out on 'stones incurrent, as this is the preferred habitat for sampling periphyton.The physical and chemical factors sampled were temperature (°C), turbidity(NTU), flow (m/s), dissolved oxygen (mg/�?and % saturation), electricalconductivity (μS/cm) and total dissolved salts (mg/�?, pH, redox potential (mV),nutrients (including dissolved inorganic phosphorus and nitrogen) and chlorophyll-a. The biotas sampled were periphyton, phytoplankton and benthicmacroinvertebrates. Statistical analyses were carried out on all sampled data.Correlations and patterns between the periphyton values and the physical,chemical and biological conditions were investigated. The effect of seasonalityon the periphyton and the influence of hydrological phases (dry and wet periods)on the periphyton were examined.Results indicate that the composition of the periphyton is shaped by seasons.An increase of Bacillariophyta was found during winter, and Chlorophyta andCyanophyta during summer. The increase of flow during wet periods had anegative effect on the biovolume of periphyton, as fewer filamentous and colonialalgae were present during the wet period. The cell and chlorophyll-aconcentration also decreased because of dislodgement during high flow. Eventhough the nutrients had an influence on all the periphytic algal components, thebest correlations were found with the periphytic chlorophyll-a concentration.The periphyton composition and concentration were compared to thebiomonitoring indices used on the sampled rivers and sites, namely FRAI (fish)and SASS5 (benthic macroinvertebrates), as well as phytoplankton.To conclude, it was found that periphyton could be used as a biomonitoringindicator in the monitoring and management of water quality. However, as thestandard biomonitoring indices operate on different spatial scales and measures,the best results would be obtained if all, or a combination of indices, were used.

[发布机构] University of the Free State