Influence of selected biotopes on chironomid-based bioassessment of the Swartkops River, Eastern Cape, South Africa

Influence of selected biotopes on chironomid-based bioassessment of the Swartkops River, Eastern Cape, South Africa ON Odume1*, CG Palmer1, FO Arimoro2 and PK Mensah1 Unilever Centre for Environmental Water Quality, Institute for Water Research, Rhodes University, P.O Box 94, Grahamstown, South Africa 2 Department of Biological Sciences, Federal University of Technology, P.M.B 65, Minna, Nigeria 1 ABSTRACT Impact of pollution on aquatic biota is usually assessed by comparing the assemblage at an impacted site with those at a control or reference site. In South Africa, except in rivers where not all biotopes are represented, the characterisation of a macroinvertebrate-based pollution effect is usually based on samples collected from three distinct biotopes, i.e., stones, vegetation and sediments. In this study, the influence of reducing the numbers of biotopes on chironomid-based bioassessment of pollution in the Swartkops River was investigated. This paper addresses the following questions: (i) can the chironomid species assemblage from any single distinct biotope analysed separately provide sufficiently accurate results similar to those of the composite-biotope group assemblage, and (ii) can chironomid community types be identified based on their biotope preferences? Chironomid larvae were sampled seasonally from three distinct biotopes: stones (stone-inand-out-of-current), vegetation (marginal and aquatic), and sediment (gravel, sand and mud, GSM) at one upstream control site, i.e., Site 1, and three downstream sites, i.e., Sites 2, 3 and 4. Site 2 in Uitenhage was impacted by diffuse pollution sources including runoff from road networks. Site 3, also in Uitenhage, was impacted by wastewater effluent discharges as well as diffuse pollution sources, while Site 4 in Despatch was about 2.5 km downstream of Site 3. The multivariate analysis of similarity (ANOSIM) indicated that the chironomid species assemblages based on the composite biotopes were significantly different between all site pairs in terms of species composition and abundance. However, when the assemblages were analysed separately for each of the three distinct biotopes, only the stone-based assemblage indicated significant differences between all of the site pairs similarly to those of the composite biotopes. Thus, the results suggest that, when resources are limited, sampling only the stony benthos could still provide bioassessment results similar to benthos from all three biotopes combined. Keywords: bioindicators, biotopes, chironomid, pollution, Swartkops River, South Africa. * To whom all correspondence should be addressed. ☎ +27 (73) 030-2687; e-mail: Received 4 April 2014; accepted in revised form 5 March 2015 the structure and distribution of chironomid assemblages (Príncipe et al., 2008; Rosa et al., 2011). In South Africa, Dallas (2007) characterised the relationship between biotopes and macroinvertebrates in selected rivers and found that differences exist between macroinvertebrate assemblages collected from different biotopes within the same river. However, the Dallas (2007) study was based on familylevel taxonomic resolution and all species within the family Chironomidae were lumped together as one taxon, thereby obscuring the potential influence of biotopes on chironomid species-based bioassessment. Thus, the extent to which biotope availability could influence chironomid species-based bioassessment of stream pollution is yet to be characterised in any South African stream or river. With the exception of rivers and streams where not all three distinct biotopes, i.e. stones, vegetation and sediments, are represented, macroinvertebrate-based bioassessment of South African lotic ecosystems is often undertaken by sampling all three distinct biotopes, and the overall health of the river calculated based on the collected assemblages (Dickens and Graham, 2002; Odume and Muller, 2011). Since impact of perturbation on aquatic biota is usually assessed by comparing the assemblage structure of an impacted site with a reference or control site (Karr and Chu 2000, Bonada et al. 2006, Odume et al. 2012), it is important to investigate whether assemblage based on any single biotope can provide similar discrimination between the reference and impacted sites as assemblages based on the combination of all three distinct biotopes. If the assemblage based on any of the biotopes can provide similar results as those of all biotopes combined, then, in the face of limited resources, sampling can be restricted to such a biotope. http://dx.doi.org/10.4314/wsa.v41i3.06 Available on website http://www.wrc.org.za ISSN 1816-7950 (On-line) = Water SA Vol. 41 No. 3 April 2015 Published under a Creative Commons Attribution Licence 343 INTRODUCTION The biophysical habitat structures such as available biotopes are among the important factors that could potentially influence bioassessment of aquatic pollution (Dallas, 2007). Aquatic ecosystems with diverse and complex habitat structures are likely to support more biodiversity than systems with less habitat complexity and diversity (Lencioni and Rossaro, 2005; Epele et al., 2012). Consequently, bioassessment protocols usually include biophysical habitat assessment to aid the interpretation of results (e.g. Barbour et al., 1999; Dickens and Graham, 2002). Chironomids have potential for bioassessment of stream pollution because of their high species diversity and wide tolerance to different types and levels of pollutants (Armitage et al., 1995; Cranston, 1996; Ferrington, 2008; Odume and Muller, 2011). A review of chironomid global diversity revealed that 4 147 species in 339 genera are unambiguously aquatic in their immature stages (Ferrington 2008). Chironomid larvae occur in most aquatic habitats, inhabit all available biotopes, and dominate the abundance and species richness of macroinvertebrate samples taken from most freshwater ecosystems (Harrison, 2003, Ferrington, 2008). At the reach scale in freshwater ecosystems, available biotopes, i.e. microhabitats, can influence chironomid distribution and species diversity (Syrovátka et al., 2009; Epele et al., 2012). Consequently, studies elsewhere have investigated the role of biotopes in determining • • Thus, this paper addresses the following questions: Can the chironomid species assemblage from any single distinct biotope analysed separately provide a sufficiently accurate result, similar to those of the composite-group species assemblage? (That is, what is the effect of reducing biotope number on the utility of Swartkops River chironomid species assemblage to demonstrate biotic impairment?) ‘Compositegroup’ refers to combined data from all three biotopes. Can chironomid community types be identified based on their biotope preferences in the Swartkops River? Therefore, in this study we investigate whether biotope availability influences chironomid species-based bioassessment of pollution in the Swartkops River, (...truncated)