On the use of diatom-based biological monitoring Part 2: A comparison of the response of SASS 5 and diatom indices to water quality and habitat variation

On the use of diatom-based biological monitoring Part 2: A comparison of the response of SASS 5 and diatom indices to water quality and habitat variation PA de la Rey1*, H Roux2, L van Rensburg1 and A Vosloo3 1 School for Environmental Science and Development, North-West University, Potchefstroom, South Africa 2 Department of Agriculture Conservation and Environment, North West Province, South Africa 3 School of Biological and Conservation Science, University of KwaZulu-Natal, Durban, South Africa Abstract Due to the fact that South Africa is a water-scarce country, integrated water resource management based on sound information is essential. Bio-indicators have provided valuable information for water resource management in recent years and have enjoyed increasing popularity. Bio-indicators especially stepped to the forefront with the realisation that aquatic eco-systems are not only a source of water but also deliver several goods and services, as well as being essential for industrial growth and quality of life of many South Africans. This study aimed to quantitatively test two kinds of biomonitoring tools namely diatom-based (SPI and BDI) and macro-invertebrate based (SASS 5) in order to assess their applicability in South African River systems; and whether any additional information can be gained by using the two tools in tandem. The results showed that diatom indices are affected more by changes in water quality than SASS 5, while SASS 5 displayed a higher dependency on habitat quality, as measured by IHAS, than the diatom indices. It is therefore suggested that the two indices be utilised as complementary indicators for integrated assessment of river health. Keywords: diatoms; Bacillariophyceae; bioindicators; SASS 5; species diversity indices; water quality Introduction Species of flora and fauna present in riverine ecosystems reflect both the present and past history of the water quality at a particular point in the river, allowing detection of disturbances that might otherwise be missed (Eekhout et al., 1996). Aquatic communities (e.g. fish, riparian vegetation, macro-invertebrates) can integrate and reflect the effects of chemical and physical disturbances that occur in river ecosystems over extended periods of time. Walmsley et al. (2000) stated that bio-indicators are ideal means of monitoring aquatic ecosystems, leading towards integrated water resource management, and that bio-indicators provide a summary of conditions ‘rather like temperature and blood pressure are used to measure human health’. The South African Department of Water Affairs and Forestry (DWAF), as custodians of the water resources of the country, initiated the development of a National Aquatic Ecosystem Biomonitoring Programme (also called the River Health Programme or RHP) during 1995 (Roux, 1997). Examples of such indicators include the Fish Assemblage Integrity Index (Kleyn hans, 1999), the Riparian Vegetation Index (Kemper, 2001) as well as the South African Scoring System, better known as SASS (Chutter, 1998). Although some methods have been available for many years, biomonitoring has only recently become a routine tool in the management of South Africa’s inland waters (Davies and Day, 1998). The SASS biomonitoring system has * To whom all correspondence should be addressed. Alternative address: Africa Geo-Environmental Services, PO Box 19460, Potchefstroom 2522, South Africa  +27 18 297 6588; fax: +27 18 297 4813; e-mail: Received 30 October 2006; accepted in revised form 28 November2007. Available on website http://www.wrc.org.za ISSN 0378-4738 = Water SA Vol. 34 No. 1 January 2008 ISSN 1816-7950 = Water SA (on-line) gained a large body of support as a rapid and fairly accurate system of evaluating water quality in streams and rivers, and is currently in its 5th revised form namely SASS 5 (Dickens and Graham, 2002). Recently diatom-based indices such as the Specific Pollution Index (SPI) and Biological Diatom Index (BDI) have come into the spotlight as potential additions to more established bio-indicators such as SASS 5. Several papers have been published in the past few years exploring the potential use of diatoms as bioindicators such as Taylor et al. (2007b), De la Rey et al. (2004) and Harding et al. (2005). A standard protocol for assessment using diatoms has also been published (Taylor et al., 2005) to facilitate comparability of diatom index results. The value of diatoms as indicators has been recognised to the point that it has been included in the state of the rivers report for the Crocodile (West) – Marico River Water Management Area (Taylor et al., 2007c; River Health Programme, 2005). In a recently published article, Ashton et al. (2005) called for a shift in thinking from a point where water is seen as simply a commodity to recognising that it is an integral part of a larger ecosystem, and that such an ecosystem approach demands an understanding of the various components of the hydrological cycle as well as the inter-relationships of these various components. For this reason it is believed important to understand how different bio-indicators respond to the various changes in the aquatic ecosystem. With the above-mentioned in mind, it is also important to evaluate biological indices in terms of their relationship to habitat characteristics. In this study, the Integrated Habitat Assessment System: Version 2 (McMillan, 1998) was used as indicator of habitat condition. This assessment focuses on sampling habitat, especially habitat that can be utilised by invertebrate fauna, as well as other stream characteristics, such as water quality, which may be modified by anthropogenic or natural impacts. 61 This paper represents the second part of a study that aims to evaluate the efficacy of diatom-based indices in river systems in South Africa. The paper follows from Part 1 (De la Rey et al., 2008) which concluded that aut-ecological indices should be preferentially used as they respond in a linear fashion to environmental water quality gradients. Part 2 of this paper aims to compare the relationship of the SASS 5 invertebrate index and diatom indices to chemical water quality and habitat availability. There are several questions that the current paper strives to answer. Firstly whether there is a significant difference in the response of SASS 5 and diatom-based aut-ecological indices to changes in stream habitat and water quality. If the two indices respond similarly, and to the same extent, to water quality variables, there would be no additional benefit to be found in using both indices for monitoring changes and impacts in rivers. Secondly the present paper aims to evaluate the dependency of index response on variation in habitat and seasonal changes. The answers gained from such analysis can assist in the application and interpretation of results gained when using the various bio-indicators evaluated in this paper. Materials and methods Sampling localities For (...truncated)