Aquatic Toxicology 127 (2013) 36–45 Contents lists available at SciVerse ScienceDirect Aquatic Toxicology j ourna l ho me p ag e: www.elsevier.com/l ocate/aquatox Drought episode modulates the response of river biofilms to triclosan L. Proia a,∗ , C. Vilches a,b , C. Boninneau a , L. Kantiani c , M. Farré c , A.M. Romaní a , S. Sabater a,d , H. Guasch a a Institute of Aquatic Ecology, University of Girona, Spain b Consejo de Investigaciones Científicas y Técnicas (CONICET), Departamento Ciencias Básicas, Universidad Nacional de Luján, Argentina c Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDAEA), Spanish National Research Council (CSIC), Spain d Catalan Institute for Water Research (ICRA), Spain a r t i c l e i n f o Article history: Received 16 November 2011 Received in revised form 30 December 2011 Accepted 7 January 2012 Keywords: Biofilms Drought Triclosan Recovery River Toxicity a b s t r a c t The consequences of global change on rivers include altered flow regime, and entrance of compounds that may be toxic to biota. When water is scarce, a reduced dilution capacity may amplify the effects of chemical pollution. Therefore, studying the response of natural communities to compromised water flow and to toxicants is critical for assessing how global change may affect river ecosystems. This work aims to investigate how an episode of drought might influence the response of river biofilms to pulses of triclosan (TCS). The objectives were to assess the separate and combined effects of simulated drought (achieved through drastic flow alteration) and of TCS exposure on biofilms growing in artificial chan- nels. Thus, three-week-old biofilms were studied under four conditions: Control (normal water flow); Simulated Drought (1 week reduced flow + 2 days interrupted flow); TCS only (normal water flow plus a 48-h pulse of TCS); and Simulated Drought + TCS. All channels were then left for 2 weeks under steady flow conditions, and their responses and recovery were studied. Several descriptors of biofilms were analyzed before and after each step. Flow reduction and subsequent interruption were found to provoke an increase in extracellular phosphatase activity, bacterial mortality and green algae biomass. The TCS pulses severely affected biofilms: they drastically reduced photosynthetic efficiency, the viability of bac- teria and diatoms, and phosphate uptake. Latent consequences evidenced significant combined effects caused by the two stressors. The biofilms exposed only to TCS recovered far better than those subjected to both altered flow and subsequent TCS exposure: the latter suffered more persistent consequences, indicating that simulated drought amplified the toxicity of this compound. This finding has implications for river ecosystems, as it suggests that the toxicity of pollutants to biofilms may be exacerbated following a drought. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The consequences of global change on rivers include altered flow regime, and entrance of compounds that may be toxic to biota. Based on climate change scenarios, researchers have pre- dicted substantial increases in both the frequency and magnitude of fluctuations in many ecosystems (Acu ˜ na, 2010). Alterations in flow regime, resulting from fewer precipitation days and more heavy rain events (Hirabayashi et al., 2008; Sillman and Roeckner, 2008), are expected to severely affect certain regions (e.g. the Mediterranean), chiefly through more frequent and more intense floods and droughts. Although flooding may strongly affect biogeo- chemical processes, drought implies more persistent consequences (Sabater and Tockner, 2010), e.g. by disrupting hydrological con- nectivity and consequently favoring the extension of lentic habitats. ∗ Corresponding author. E-mail address: lorenzo.proia@udg.edu (L. Proia). During drought periods, shallow sections disappear and the stream becomes a series of fragmented, short-lived pools (Lake, 2003). Flow cessation triggers a cascade of effects on community struc- ture and ecosystem function (Lake, 2003; Sabater and Tockner, 2010). Specifically, the benthic microbial community may respond to changes in water quality during drought (e.g. increased temper- ature, or altered quality of organic matter; Ylla et al., 2010), since it serves as an interface between the water column and the sub- strata (Sabater et al., 2007). Benthic biofilms are complex microbial communities adhered to solid surfaces (Mathuriau and Chauvet, 2002; Findlay et al., 1993; Sabater et al., 2007). They are funda- mental in the trophic web and in the geochemical cycles within aquatic ecosystems (Battin et al., 2003; Lock, 1993). Field stud- ies have shown the consequences of drought and intermittency on biofilm primary production and algal recolonization (Robson and Matthews, 2004; Robson et al., 2008; Stanley et al., 2004; Ryder, 2004). Some benthic autotrophic groups and species are better adapted to drought than others, owing to structural traits (e.g. a higher content of extracellular polymeric substances) and/or 0166-445X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2012.01.006