RESPONSE OF MACROINVERTEBRATE AND DIATOM COMMUNITIES TO HUMAN-INDUCED PHYSICAL ALTERATION IN MOUNTAIN STREAMS FRANCESCA BONA, a * ELISA FALASCO, a STEFANO FENOGLIO, b LUCA IORIO a and GUIDO BADINO a a DBAU, Universita ` degli Studi di Torino, Via Accademia Albertina 13, 10123 Torino, Italy b DiSAV, Universita ` del Piemonte Orientale, Via Bellini 25, I-15100 Alessandria, Italy ABSTRACT It is generally argued that epilithic diatoms and macroinvertebrates are highly sensitive to changes in water quality, while only a few studies have been conducted on their response to physical disturbance. The main purpose of this research is to investigate whether these two communities respond to physical river disturbance like banks, substrate and flux alteration induced by human action. We sampled 12 high-altitude streams in the Gran Paradiso National Park, a protected area where the main human activities are limited to hiking and high-altitude pasture. The sampled stretches of the rivers were characterized with respect to their geomorphological features and possible human modifications. Water uptake for power supply, riverbed and bank modifications represented the main human activities which could determinate alterations in community structure and composition. Habitat structure was evaluated using the Southern European River Habitat (RHS–SE), while the biological status of the river has been estimated by means of the following biotic and diatomic indices: IBE, BMWP, ASPT, Ephemeroptera, Plecoptera and Trichoptera families (EPT) for macroinvertebrates, EPI-D, IBD and IPS for diatoms. A general concordance between chemical parameters and structure of biological communities was observed. On the other hand, the RHS–SE highlighted the main geomorphological features and detected some slight physical alterations, as quantified by the indices Habitat Modification Score (HMS) and Habitat Quality Assessment (HQA). In short, our findings demonstrate that morphological alterations, even if slight, affect biological diversity and the presence of some specific taxa, while biological indices are independent of the level of physical modifications. Copyright # 2008 John Wiley & Sons, Ltd. key words: RHS; biotic indices; western Alps; river habitat modification; macroinvertebrates; diatoms Received 25 September 2007; Revised 27 December 2007; Accepted 3 January 2008 INTRODUCTION Perhaps no other ecosystems have been as significantly modified by human activity as have streams and rivers (Allan, 1997): lotic environments are one of the most vulnerable and, at the same time, most exploited ecological systems in our planet. In the recent past river modification for human convenience has been both widespread and intensive. The combined effects of pollution, channelization and river regulation are a serious threat to river integrity. Changes in water quality and the physical structure of rivers have caused changes in the composition of the biotic community inhabiting the river usually with a reduction in the biological diversity of the aquatic ecosystem (Maddock, 1999). These impacts were historically confined to areas with major anthropic presence, but in recent times the influence of human activities has come to also constitute a serious threat for mountainous and alpine lotic systems. Alpine streams are unique environments, due to their harshness with respect to low temperatures and trophic levels (Giller and Malmqvist, 1998). The main ecological peculiarities of these environments are the presence of cold water, conspicuous seasonal and daily variations in flow, high turbidity, oligosalinity and particular hydrological and morphological conditions (Milner and Petts, 1994). With regard to these parameters, recent studies have underlined the importance of a particular key driver that strongly influences alpine fluvial ecosystems: the physical instability of channels and riverbeds, due to high energy of waters, high transports of solids and high erosion (Petts et al., 2000; Smith et al., 2001). This widespread instability, although RIVER RESEARCH AND APPLICATIONS River. Res. Applic. 24: 1068–1081 (2008) Published online 29 April 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rra.1110 *Correspondence to: Francesca Bona, DBAU, Universita ` degli Studi di Torino, Via Accademia Albertina 13, 10123 Torino, Italy. E-mail: francesca.bona@unito.it Copyright # 2008 John Wiley & Sons, Ltd.