Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman Research article Treated acid mine drainage and stream recovery: Downstream impacts on benthic macroinvertebrate communities in relation to multispecies toxicity bioassays M. Steyn a,* , P.J. Oberholster a , A.M. Botha b , B. Genthe a , P.E. van den Heever-Kriek c , C. Weyers d a CSIR, Natural Resources and the Environment, P.O. Box 320, Stellenbosch, 7599, South Africa b Department of Genetics, University of Stellenbosch, Stellenbosch, South Africa c Department of Health Sciences, Central University of Technology, Free State, South Africa d Department of Life Sciences, Central University of Technology, Free State, South Africa ARTICLE INFO Keywords: Land use Metals Longitudinal impacts Toxicity bioassays Macroinvertebrates Stream recovery ABSTRACT The success and long term effectiveness of extensive and expensive engineering solutions to restore streams impacted by Acid Mine Drainage (AMD) is rarely tested. Concentrations of pollutants were measured in water along a longitudinal gradient from a stretch of the Tweelopie stream, South Africa, that receives pH-treated acid mine drainage (AMD) from an abandoned gold mine. The biotoxic effects of treated AMD were determined through macroinvertebrate biotic indices (SASS5) and a battery of toxicity bioassays. These included the L. sativa, A. cepa, D. magna toxicity and Ames mutagenicity tests, as well as an in vitro human liver cancer cell line HepG2. Even though the Tweelopie stream was moderately to severely degraded by multiple anthropogenic stressors, the impact of the treated AMD was masked by the improvement in the system downstream after mixing with the domestic wastewater effluent receiving stream, and subsequent further dilution as a result of the karst springs downstream. The general improvement of the system downstream was clearly shown by the decrease in the ecotoxicity and mutagenicity in relation to the in-stream macroinvertebrates. PCA multivariate analysis successfully displayed associations between the different environmental variables and the decrease in toxicity and subsequent ecosystem improvement downstream. This study indicated that environmental management of AMD remediation should consider long term assessment strategies, including multiple factors, to promote bio- logical ecosystem recovery. 1. Introduction Globally, land use activities and anthropogenic pollution associated with mining, agriculture and industry, have resulted in multiple pres- sures on freshwater ecosystems, with severe loss of biodiversity and ecological functioning. Remediation efforts to minimize the effects of AMD on stream ecosystems are occurring worldwide (Gunn et al., 2010), and has become a rather large and profitable business (Bernhardt et al., 2005). Monitoring the success of remedial actions usually involves both chemical and biological sampling (DeNicola and Stapleton, 2014), with responses of in-stream communities superior to that of chemical measurements (Adams et al., 2002; Gunn et al., 2010; Kruse et al., 2013). The reduction in diversity and abundance of mac- roinvertebrates by acid mine drainage (AMD) is well established and commonly used as ecological indicators (Gray, 1998; Chambers and Messinger, 2001; He et al., 2015). To date, only a few studies have examined the impacts of pH-treated AMD on macroinvertebrates, with mixed results. DeNicola and Stapleton (2002) observed reduced mac- roinvertebrate density as a result of AMD exposure and subsequent increase after AMD treatment system installation. Nevertheless, the increased macroinvertebrate densities observed after treatment were not comparable to controls at most sampling sites and taxa richness remained low (DeNicola and Stapleton, 2014; DeNicola and Stapleton, 2016; Gunn et al., 2010). In contrast, Perrin et al. (1992) reported no effect of treated AMD on macroinvertebrate numbers or number of taxa. In particular, treated AMD will tend to be diluted as it moves farther downstream, gradually alleviating toxic effects on biota (Oberholster et al., 2013). According to Covich et al. (1999) macroinvertebrates appeared to be more sensitive to treated AMD shown by their decline in diversity. This observation leads to dramatic changes in understanding https://doi.org/10.1016/j.jenvman.2019.01.051 Received 23 March 2018; Received in revised form 10 January 2019; Accepted 16 January 2019 * Corresponding author. Council for Scientific and Industrial Research (CSIR), Natural Resources and the Environment, P.O. Box 320, Stellenbosch, D Block, Room D119, Western Cape, South Africa. E-mail address: msteyn@csir.co.za (M. Steyn). Journal of Environmental Management 235 (2019) 377–388 0301-4797/ © 2019 Elsevier Ltd. All rights reserved. T