Artificial macrophytes as fish habitat in a Mediterranean reservoir subjected to seasonal water level disturbances

Artificial macrophytes were experimentally deployed in Boadella Reservoir (NE Spain) and assessed for fish use throughout the first 3 months of the 2007 summer drawdown. In total, 1,832 individuals of seven fish species were recorded through visual censuses, with introduced perch Perca fluviatilis being the prevalent species. Fish richness and abundance were significantly higher in artificial macrophytes than in rocky shores and sandy beaches, displaying a unimodal variation through time. P. fluviatilis, Rutilus rutilus and Abramis brama were significantly more abundant in artificial macrophytes than in the other two naturally submersed habitats, where no individuals of these species were recorded. The abundances of Squalius laietanus, Lepomis gibbosus, Micropterus salmoides and Cyprinus carpio were overall greater in artificial macrophytes than in rocky shores but displayed significant habitat × time interactions. A decrease in predation risk was apparently the key-factor of the intensive use of artificial macrophytes by small fish (≤100 mm TL) in Boadella Reservoir, since most species reduced drastically or completely the use of submerged structures when body size increased. This study demonstrates that adding artificial structures mimicking aquatic macrophytes can be an interesting tool to mitigate the adverse effects of water level fluctuations on fish assemblages in structure-less and homogeneous ecosystems, and to understand the mechanisms affecting habitat use and species replacement.     

Glacial and paraglacial history of the Troutbeck Valley,Cumbria, UK: integrating airborne LiDAR,multibeam bathymetry,and geological field mapping

High resolution airborne LiDAR (light detection and ranging) and multibeam bathymetry data, supplemented by geomorphological and geological field mapping are used to derive the glacial and post-glacial history of Troutbeck Valley (English Lake District) at a catchment scale. The results inform wider regional and ice sheet wide glacial reconstructions and demonstrate the effectiveness of an integrated approach combining geomorphological and sedimentological signatures with remote sensing. The holistic catchment approach is used to reconstruct palaeo-ice flow and behaviour of a small part of the last British and Irish Ice Sheet, identifying a series of depositional environments that accompanied both ice advance, ice retreat and post-glacial deposition within the Lake District. Drumlins are mapped in the lower catchment and show multiple regional (wider-extent) ice flow events and a sedimentology consistent with deposition by lodgement processes during the Main Late Devensian Stadial. Other subglacial deposits include till sequences formed under variable basal conditions beneath an advancing ice mass. Retreat features include a suite of recessional moraines formed by still-stands or small readvances of an outlet glacier. Following deglaciation, major sediment redistribution led to formation of a large fan delta via paraglacial and post-glacial fluvial sedimentation. This study indicates that an integrated approach, using geomorphology, sedimentology and remote sensing on a catchment scale, is capable of deriving a more in-depth understanding of regional ice sheet reconstructions and highlights the complexity of palaeo-ice sheet dynamics at a range of spatial scales.     

Olivine or impact melt: Nature of the “Orange” material on Vesta from Dawn

NASA’s Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types: (a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), (b) lobate patches with well-defined edges (nicknamed “pumpkin patches”), and (c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed “Leslie feature” first identified by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Several possible options for the composition of the orange material are investigated including, cumulate eucrite layer exposed during impact, metal delivered by impactor, olivine–orthopyroxene mixture and impact melt. Based on our analysis, the orange material on Vesta is unlikely to be metal or olivine (originally proposed by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157)). Analysis of the elemental composition of Oppia ejecta blanket with GRaND suggests that its orange material has ∼25% cumulate eucrite component in a howarditic mixture, whereas two other craters with orange material in their ejecta, Octavia and Arruntia, show no sign of cumulate eucrites. Morphology and topography of the orange material in Oppia and Octavia ejecta and orange patches suggests an impact melt origin. A majority of the orange patches appear to be related to the formation of the Rheasilvia basin. Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt.     

Factors influencing nitrate within a low-gradient agricultural stream

In low-gradient agricultural streams, the proportion of land use devoted to agriculture, the sinuosity of the stream and the time of year influence the concentration of nitrate in the stream waters. Land use influences the source of nitrate and also the morphology of the stream. Greater agricultural land use weakly correlated (r = 0.67) to higher nitrate concentrations. Streams in agricultural areas have been straightened, which decreases the sinuosity. As a stream meanders and becomes more sinuous, the potential for lateral hyporheic flow increases, which can enhance a stream system’s ability to remove nitrate. Logically, higher sinuous streams should remove more nitrate and likely sulfate as there is a greater potential for lateral hyporheic flows. To test this hypothesis, nitrate and sulfate were monitored. Mass fluxes of nitrate along six stream segments with varying sinuosity values were calculated and statistically analyzed to assess if differences in mass fluxes along the segments existed. Along the segments, there are statistically significant differences in the mass fluxes of nitrate [F(5,174) = 4.777; p = 0.001]. Stream segments with higher sinuosity index values exhibited a loss or lower gain in nitrate and sulfate than lower sinuosity index segments. The data suggest that stream segments with high sinuosity indices provide greater stream distance and increased hyporheic interaction within the streambed. Additionally, the more sinuous segments provide for an increase in lateral hyporheic flow beneath meander lobes. These additional hyporheic flows lead to enhanced denitrification in low-gradient agricultural streams. Seasonal differences were also noted. August through October experienced the lower nitrate concentrations as compared to June and July which exhibited the highest nitrate concentrations.     

Organic and inorganic correlations for Northwest Africa 852 by synchrotron‐based Fourier transform infrared microspectroscopy

Relationships between organic molecules and inorganic minerals are investigated in a single 34 μm diameter grain of the CR2 chondrite Northwest Africa 852 (NWA) 852 with submicron spatial resolution using synchrotron‐based imaging micro‐FTIR spectroscopy. Correlations based on absorption strength for the various constituents are determined using statistical correlation analysis. The silicate band is found to be correlated with the hydration band, and the latter is highly correlated with stretching modes of aliphatic hydrocarbons. Spatial distribution maps show that water+organic combination, silicate, OH, and C‐H distributions overlap, suggesting a possible catalytic role of phyllosilicates in the formation of organics. In contrast, the carbonate band is anticorrelated with water+organic combination, however uncorrelated with any other spectral feature. The average ratio of asymmetric CH₂ and CH₃ band strengths (CH₂/CH₃ = 2.53) for NWA 852 is similar to the average ratio of interplanetary dust particles (~2.40) and Wild 2 cometary dust particles (2.50), but it significantly exceeds that of interstellar medium objects (~1.00) and several aqueously altered carbonaceous chondrites (~1.40). This suggests organics of similar length/branching, and perhaps similar formation regions, for NWA 852, Wild 2 dust particles, and interplanetary dust particles. The heterogeneous spatial distribution of ratio values indicates the presence of a mixture of aliphatic organic material with different length/branching, and thus a wide range of parent body processes, which occurred before the considered grain was formed.     

Wide-angle deep crustal reflections in the northern Appalachians

Summary. Seismic refraction data collected in the northern Appalachians provide an unusual opportunity to use wide-angle reflections to examine the lower crust and upper mantle. The PmP phase, clearly identified on several hundred records, has been used to construct an isopach map of the crust which shows a stepwise regional thickening of the crust beneath the axis of the Appalachians. The data have been examined to times of up to 40 s two-way travel time to investigate the possibility of coherent upper-mantle reflections such as those recently observed by BIRPS on near-vertical data northwest of Britain. Although substantial coherent energy appears after the PmP phase, synthetic seismogram modelling shows that all of these arrivals are explicable by S-phases, converted phases and multiples from within the crust. We conclude that in this region of the northern Appalachians we have not detected any significant regionally extensive reflecting horizons within the upper mantle.