The application and testing of diatom-based indices in the Vaal and Wilge Rivers, South Africa

JC Taylor,MS Janse van Vuuren,AJH Pieterse

doi:10.4314/wsa.v33i1.47871

Abstract

Chemical monitoring of water resources is time-consuming and comparatively expensive and may not always provide a composite reflection of actual water quality. Biotic indices using faunal elements, such as macroinvertebrates and fish, are already in place in South Africa as part of the National Biomonitoring Programme for Aquatic Ecosystems (NBPAE). As yet periphyton communities are not included in this programme due to perceived difficulties in the application of these methods. Diatom samples were collected from 10 sites in the Vaal and Wilge Rivers for a period of one year. Diatom cells from these communities were enumerated and diatom-based indices were calculated using OMNIDIA v.3. Diatom index scores were correlated to physical and chemical water quality variables over different time periods and at different concentrations. It was found that the tested diatom indices in general have the best correlation with average chemical data for a one-month period, starting six weeks prior to biological sampling. The Biological Diatom Index showed the strongest relationship to general water quality, while the Eutrophication and Pollution Index showed the strongest relationship to dissolved inorganic phosphorus. Results of correlation analyses obtained in South Africa were comparable to those obtained in several European studies. Hence, it is concluded that diatom-based indices, if implemented in South Africa, will provide a valuable addition to South Africa's suite of tools for the biological monitoring of water quality.

Highlights

The assessment of the general quality of a water resource requires regular monitoring
Of the 176 nondominant taxa encountered, a further three taxa are possibly endemic to Southern Africa namely Navicula microrhombus Archibald, Thalassiosira duostra Pienaar & Pieterse and a species as yet not identified leaving a total of 240 out of 245 (98%) cosmopolitan taxa
These results are in agreement with Bate et al (2004b) who found that most dominant diatom species found in South African rivers were already recorded in international literature

Summary

Introduction

The assessment of the general quality of a water resource requires regular monitoring. Chemical components in a river system may be diluted by inflows of rainwater or augmented from runoff from point (mine, sewage, storm water drainage) and diffuse sources (agricultural runoff, groundwater seepage from settling ponds), or become concentrated during times of drought and low flow These factors make it difficult, if not impossible, to provide anything other than a fragmented overview of the state of a river along its complete length using conventional chemical monitoring techniques. The monitoring of South African waterways has traditionally been carried out by two means, firstly by chemical analysis determining the water quality, and more recently by the use of various biomonitoring techniques such as the South African Scoring System (SASS) and the Fish Health Index (FHI) These techniques were introduced as part of routine monitoring programmes due to certain shortcomings in standard physical and chemical methods. These changes in species composition can in turn be used to reflect changes in water quality in a more integrated manner than traditional chemical sampling

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