Invertebrate drift plays an important role in river ecosystems. Although drift has been studied extensively, the relative importance of the various factors that initiate drift during disturbances remains unclear. Instream gravel mining releases fine sediment and so provides an opportunity to assess the influence of suspended sediment on drift, without the confounding effects of hydraulic changes and bed-material entrainment associated with floods. This paper examines invertebrate drift responses to increases in suspended sediment during an episode of mining in a Pyrenean river. During short periods of mining activity, suspended sediment concentrations and thus suspended sediment loads (SSLs) increased one order of magnitude at downstream monitoring sections, with maxima similar to those observed during natural floods in the river. Maximum SSLs were recorded at the sections closest to the mining, with downstream transport patterns suggesting that the majority of suspended material was deposited within 1.5 km. Invertebrate drift rates, the number of taxa drifting and the taxonomic structure of the drift changed at sections close to the mining when suspended sediment concentrations and SSLs were high; such changes were not observed at the section 1.5 km downstream. There were significant relationships between SSL and drift, positive for some groups (Ephemeroptera, Plecoptera and Trichoptera) and negative for others (Chironomidae). Our work shows that increases in suspended sediment alone are sufficient to trigger changes in drift, although further studies are needed to elucidate the underlying mechanisms, and especially to explain the varying responses shown by different taxonomic groups. Figure 7. Response of invertebrate drift in the River Cinca to increasing sediment loads: (A) drift rate response to sediment load. (B) Taxon richness response to sediment load. (C) Relative abundance of Ephemeroptera, Plecoptera, Tricoptera taxa response to sediment load. (D) Relative abundance of Chironomidae taxa response to sediment load. The relationships were modelled using generalized estimating equations. Dotted lines show 95% confidence limits. For brevity, only relative abundance is shown. [Colour figure can be viewed at wileyonlinelibrary.com] M. BÉJAR ET AL.

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This work describes the coseismic ceiling block collapse within Benis Cave (2213 m; Murcia, SE Spain), associated with the 1999 Mula earthquake (m b ¼ 4.8, MSK VII). The collapse occurred at 2156 m into the Earthquake Hall, and as a consequence one small gallery became blind. We studied the geology, topography and active tectonic structures relevant to the cave. In addition, we carried out a seismotectonic analysis of the focal mechanism solutions, and also a fault population analysis on slickensides measured in fault planes in the cave. The stress and strain regime is interpreted as being congruent with the palaeoseismic evidence, and agrees with the fault kinematics established for cave galleries developed within fault planes and growth anomalies of coral flowstone. Our analysis suggests that one active segment (NNE-SSW) determined the morphology and topography of the Benis Cave, where strong to moderate palaeoearthquakes (6 M 7) took place. As a consequence of this intense seismic activity a small gallery collapsed. A new palaeoseismic structure, or seismothem, has been recognized, namely the effect of palaeoearthquakes affecting the pattern of development of the spatial coral flowstone distribution located at the bottom of the cave. Endokarsticterrains represent favourable environments for the preservation of palaeoseismic evidence associated with shaking and faulting produced by earthquakes (Postpischl et al. 1991;Gilli et al. 1999;Cadorin et al. 2001;Kagan et al. 2005). This terrain results from a delicate equilibrium between dissolution-precipitation processes affecting soluble rocks (carbonates, evaporites, lime sandstones, etc.). The equilibrium reflects the climatic conditions of the area (atmospheric content of CO 2 , temperature, humidity, etc.), the tectonic setting of the rock mass (fault and joint geometry), the hydrogeologic constraint (phreatic level) and the chemical composition of the source area (water and rock).A rhythmic and constant velocity of the dissolution-precipitation rate controls the genesis of the endokarst (Bauer et al. 2003). This fact implicates quiet periods, slow variations of the phreatic level and the presence of permanent water-sheets and pools. In this context, the occurrence of earthquakes perturbs the short-term dynamic of the karst, for example causing broken and tilted speleothems, growth anomalies in carbonate layers and block collapses (Gilli 2005).Speleoseismology represents a new branch of the palaeoseismology that analyses the earthquake record in caves (Kagan et al. 2005;Becker et al. 2006). Earthquake shaking and faulting in caves can be deduced from two different features. (A) Destructive features: broken speleothems, fallen stalactites, severed stalagmites (Kagan et al. 2005), block collapse (incasion), blind galleries, deformed cave sediment structures and coseismic fault displacement affecting cave deposits. These types of features are classified as seismothems (Delaby 2001).

The tectonic field on Deception Island (South Shetlands, West Antarctica) is determined from structural and fractal analyses. Three different analyses are applied to the study of the strain and stress fields in the area: (1) field measurements of faults (strain analysis), (2) fractal geometry of the spatial distribution of lineaments and (3) the caldera shape (stress analyses). In this work, the identified strain field is extensional with the maximum horizontal shortening trending NE-SW and NW-SE. The fractal technique applied to the spatial distribution of lineaments indicates a stress field with S HMAX oriented NE-SW. The elliptical caldera of Deception Island, determined from field mapping, satellite imagery, vents and fissure eruptions, has an elongate shape and a stress field with S HMAX trending NE-SW.

Maintaining or restoring physical habitat diversity is a central tenet of sustainable river management, yet a link between habitat and ecological diversity in fluvial systems has long remained equivocal. The lack of consistent evidence partly reflects the problems of characterizing habitat in ways that are ecologically meaningful. This paper assesses the influence of habitat heterogeneity and complexity on macroinvertebrate assemblages in a mountain gravel‐bed river. With the use of 0.1‐m resolution data obtained from an acoustic Doppler current profiler, heterogeneity and complexity in hydraulic conditions and bed topography were characterized using 13 metrics applied to 30 areas, each 1 m2, with an invertebrate sample collected from each area. Turnover of invertebrate taxa (i.e., β‐diversity) between sampled areas was rather limited, but observed differences in diversity were related significantly to several metrics of habitat heterogeneity. Invertebrate abundance was related to habitat diversity, patch size coefficient of variation, and patch size, whereas the Shannon diversity was related to the number of patches and patch size. None of the habitat complexity metrics accounted for a significant amount of observed variation in invertebrate communities between sampled areas. The paper demonstrates that high‐resolution data can help reveal relationships between habitat and benthic invertebrate diversity.

This paper examines the effects of gravel mining on the suspended sediment transport in the Upper River Cinca (Central Pyrenees). Discharge, sediment transport and sediment grain-size distribution were measured, sampled and further determined in five monitoring sections along a 5-km river reach. Samples were taken at a section upstream from the mined area (i.e. reference section) and in four sections downstream (0, 200, 500 and 1500 meters). The results show that sediment concentrations downstream from the target site were up to one order of magnitude higher than in the reference section. Average concentrations during the impact were similar to those observed during floods, with maximum values attaining 6 g/l. Total load ranged from 2.2 to 17 Mg/day between sections; these values include the effects of the earth-moving works performed before the mining started. Concentrations at the lowermost section of the study reach were similar to those observed at the upstream reference section, suggesting that most of the suspended material was deposited in the channel. The transported material was coarse than that sampled under reference conditions; nevertheless, largest particles settled quickly, suggesting a selective transport downstream. This study constitutes a first step towards a better understanding of local sediment dynamics in rivers affected by maintenance works and related activities, such as gravel mining, and, overall, supports the comprehensive assessment of the effects of human actions on channel morphodynamics and the ecological functioning of mountain fluvial systems.

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