Riparian arthropod responses to flow regulation and river channelization.
Alterations to river flow and morphology widely impact riverine habitats. Little is known about the consequences of such alterations on riparian arthropods, although they contribute substantially to riverine biodiversity and play a critical role in linking aquatic and terrestrial food webs. We investigated the interactive effects of flow regulation (hydropeaking) and river channelization on gravel-bar habitat characteristics and riparian arthropods in seven Alpine rivers. Digital elevation models were developed to simulate inundation dynamics of each gravel bar. Channelization significantly increased inundation frequency, and hydropeaking increased substrate embeddedness. The total abundance of riparian arthropods was significantly reduced by hydropeaking, whereas arthropod species richness was reduced by both hydropeaking and channelization. Sites that were affected by both hydrological and morphological modifications together were almost devoid of arthropods. The sensitivity of riparian arthropods to alterations in flow and morphology differed among taxa. Spider abundance and richness were significantly reduced by channelization only. Ground beetles showed no significant response. Rove beetle abundance and richness were negatively affected by hydropeaking whereas channelization had a negative effect only in rivers with hydropeaking. Abundance and richness of all taxa combined, and of spiders independently, were negatively correlated with inundation frequency and substrate embeddedness. Rove beetle abundance and richness were negatively correlated with embeddedness. Spider and rove beetle richness were also correlated with gravel bar area. Synthesis and applications. Our results indicate that the richness and abundance of riparian arthropods were predominantly affected by the availability of exposed gravel above the average high-water level and substrate embeddedness. Restoration of riverbank morphology and mitigation of hydropeaking are likely to benefit riparian arthropods. Riparian arthropods, particularly spiders and rove beetles, appear to be sensitive indicators of the ecological effects of hydromorphological alterations in rivers.