Comparing the spectral settings of the new generation broad and narrow band sensors in estimating biomass of native grasses grown under different management practices

The challenge of assessing and monitoring the influence of rangeland management practices on grassland productivity has been hampered in southern Africa, due to the lack of cheap earth observation facilities. This study, therefore, sought to evaluate the capability of the newly launched Sentinel 2 multispectral imager (MSI) data, in relation to Hyperspectral infrared imager (HyspIRI) data in estimating grass biomass subjected to different management practices, namely, burning, mowing and fertilizer application. Using sparse partial least squares regression (SPLSR), results showed that HyspIRI data exhibited slightly higher grass biomass estimation accuracies (RMSE = 6.65 g/m², R² = 0.69) than Sentinel 2 MSI (RMSE = 6.79 g/m², R² = 0.58) across all rangeland management practices. Student t-test results then showed that Sentinel 2 MSI exhibited a comparable performance to HyspIRI in estimating the biomass of grasslands under burning, mowing and fertilizer application. In comparing the RMSEs derived using wave bands and vegetation indices of HyspIRI and Sentinel, no statistically significant differences were exhibited (α = 0.05). Sentinel (Bands 5, 6 and 7) and HyspIRI (Bands 730 nm, 740 nm, 750 nm, 710 nm), as well as their derived vegetation indices, yielded the highest predictive accuracies. These findings illustrate that the accuracy of Sentinel 2 MSI data in estimating grass biomass is acceptable when compared with HyspIRI. The findings of this work provide an insight into the prospects of large-scale grass biomass modeling and prediction, using cheap and readily available multispectral data.     

Metamorphic sole formation,emplacement and blueschist facies overprint: early subduction dynamics witnessed by western Turkey ophiolites

The largest ophiolite on Earth, in western Turkey, is a key place to study obduction and early subduction dynamics. Ophiolite remnants derived from the same Neotethyan branch (preserved as a result of long‐lived Late Cretaceous continental subduction and later obduction) are underlain by hundred‐metre‐thick extensive metamorphic soles. These soles formed synchronously, at c. 93 Ma, and were welded to the base of the ophiolite, thereby dating the start of intra‐oceanic subduction. This contribution focuses on the structure, petrology and pressure–temperature evolution of the soles and other subduction‐derived units. Peak pressure–temperature conditions were estimated at 10.5 ± 2 kbar and 800 ± 50 °C for the sole by means of pseudosection calculations using Theriak/Domino and at 12 kbar and 425 °C for the unique, enigmatic blueschist facies overprint of the sole. This study provides clues to the mechanisms of sole underplating during early subduction, later cooling, and the nature of the western Turkey ophiolite.     

A regional Bayesian POT model for flood frequency analysis

Flood frequency analysis is usually based on the fitting of an extreme value distribution to the local streamflow series. However, when the local data series is short, frequency analysis results become unreliable. Regional frequency analysis is a convenient way to reduce the estimation uncertainty. In this work, we propose a regional Bayesian model for short record length sites. This model is less restrictive than the index flood model while preserving the formalism of “homogeneous regions”. The performance of the proposed model is assessed on a set of gauging stations in France. The accuracy of quantile estimates as a function of the degree of homogeneity of the pooling group is also analysed. The results indicate that the regional Bayesian model outperforms the index flood model and local estimators. Furthermore, it seems that working with relatively large and homogeneous regions may lead to more accurate results than working with smaller and highly homogeneous regions.     

http://dx.doi.org/10.1016/j.gsf.2016.10.001

The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.This study reports new zircon data obtained from Chaillu massif and N'goutou complex,which constrain the protolith age of the basement orthogneisses and the igneous age of an intrusive granite,respectively.Most zircons from the orthogneisses are blue and exhibit oscillatory zoning in cathode-luminescence images.Zircons with lower common lead abundances tend to be distributed close to the concordia curve.Two age clusters around 2860 Ma and 2910 Ma are found in zircons plotted on the concordia curve.Based on the Th/U ratios of zircons,these ages correspond to the protolith ages of the orthogneisses,and the zircons are not metamorphic in origin.Syenites and granites were collected from the N'goutou complex that intrudes into the FA and FB units of the Francevillian Group.The granitoids exhibit chemical composition of A-type granite affinity.Half of zircons separated from the granite are non-luminous,and the remaining half exhibit obscure internal textures under cathode-luminescence observation.All zircon grains contain significant amounts of common lead;the lead isotopic variability is probably attributed to the mixing of two components in the zircons.The zircon radiogenic ~(207)Pb/~(206)Pb ratio is 0.13707 ± 0.0010.corresponding to a ~(207)Pb/~(206)Pb age of 2191 ± 13 Ma.This constrains the minimum depositional age of the FA and FB units.Furthermore,the FB unit consists of manganese-rich carbonate rocks and organic carbon-rich black shales with macroscopic fossils.Based on our age constraints,these organisms appeared in the study area just after the last Paleoproterozoic Snowball Earth event,in concert with global scale oxidation event encompassing the Snowball Earth.     

From kinematics to dynamics in thin galactic discs

We present a method for recovering the distribution functions of edge-on thin axisymmetric discs directly from their observable kinematic properties. The most generally observable properties of such a stellar system are the line-of-sight velocity distributions of the stars at different projected radii along the galaxy. If the gravitational potential is known, then the general two-integral distribution function can be reconstructed using the shapes of the high-velocity tails of these line-of-sight distributions. If the wrong gravitational potential is adopted, then a distribution function can still be constructed using this technique, but the low-velocity parts of the observed velocity distributions will not be reproduced by the derived dynamical model. Thus, the gravitational potential is also tightly constrained by the observed kinematics.     

Methane sources,sinks and fluxes in a temperate tidal Lagoon: The Arcachon lagoon (SW France)

The Arcachon lagoon is a 156 km² temperate mesotidal lagoon dominated by tidal flats (66% of the surface area). The methane (CH₄) sources, sinks and fluxes were estimated from water and pore water concentrations, from chamber flux measurements at the sediment–air (low tide), sediment–water and water–air (high tide) interfaces, and from potential oxidation and production rate measurements in sediments. CH₄ concentrations in waters were maximal (500–1000 nmol l⁻¹) in river waters and in tidal creeks at low tide, and minimal in the lagoon at high tide (<50 nmol l⁻¹). The major CH₄ sources are continental waters and the tidal pumping of sediment pore waters at low tide. Methanogenesis occurred in the tidal flat sediments, in which pore water concentrations were relatively high (2.5–8.0 μmol l⁻¹). Nevertheless, the sediment was a minor CH₄ source for the water column and the atmosphere because of a high degree of anaerobic and aerobic CH₄ oxidation in sediments. Atmospheric CH₄ fluxes at high and low tide were low compared to freshwater wetlands. Temperate tidal lagoons appear to be very minor contributor of CH₄ to global atmosphere and to open ocean.     

Impact of the Phaeocystis globosa spring bloom on the intertidal benthic compartment in the eastern English Channel: a synthesis

From 1999 to 2005, studies carried out in the frame of regional and national French programs aimed to determine whether the Phaeocystisglobosa bloom affected the intertidal benthic communities of the French coast of the eastern English Channel in terms of composition and/or functioning. Study sites were chosen to cover most of the typical shore types encountered on this coast (a rocky shore, an exposed sandy beach and a small estuary). Both the presence of active Phaeocystis cells and their degradation product (foam) did have a significant impact on the studied shores. The primary production and growth rates of the kelp Saccharina latissima decreased during the bloom because of a shortage of light and nutrient for the macroalgae. On sandy sediments, the benthic metabolism (community respiration and community primary production), as well as the nitrification rate, were enhanced during foam deposits, in relation with the presence of bacteria and active pelagic cells within the decaying colonies. In estuarine sediments, the most impressive impact was the formation of a crust at the sediment surface due to drying foam. This led to anoxic conditions in the surface sediment and resulted in a high mortality among the benthic community. Some organisms also tended to migrate upward and were then directly accessible to the higher trophic level represented by birds. Phaeocystis then created a shortcut in the estuarine trophic network. Most of these modifications lasted shortly and all the systems considered came back to their regular properties and activities a few weeks after the end of the bloom, except for the most impacted estuarine area.     

Edifice and substrata deformation induced by intrusive complexes and gravitational loading in the Mull volcano (Scotland)

It is likely that the structure of a volcanic edifice can be significantly modified by deformation caused by large, shallow intrusions. Such deformation may interact with that caused by volcano loading. We explore such intrusion-related and loading-related deformation with field evidence and analogue models. To do this we have chosen the eroded Palaeogene Mull volcano (Scotland) that had a major edifice, has well exposed intrusions and significant deformation. There are thin Mesozoic sedimentary rocks forming ductile layers below the volcano, but their thickness is insufficient to allow the gravitational spreading of the volcanic edifice, especially when considering that a thick lava pile covers them. Thus intrusive push may have been the driving force for deformation. The Mull activity migrated toward the northwest, forming three successive intrusive complexes (Centres 1, 2 and 3). Our detailed fieldwork reveals that deformation due to these was accommodated on three levels; along thrust planes in lava sequences, along a décollement located in a thin clay-rich sediment succession and in basement schists. A relative chronology has been established between different groups of structures using dyke and sill cross-cutting relationships. Centre 1 is surrounded by a fold and thrust belt leading to radial expansion. In contrast, Centre 2 and 3 are connected to thrusts located to the south and east, bounded by strike-slip faults, leading to expansion to the southeast. The migration of centres and the directed sliding of the edifice may be related to the presence to the southeast of low-resistance Dalradian basement that failed significantly during growth of Centres 2 and 3. To study the observed relationships we have carried out scaled analogue models. Models are made with fine powder intruded by a viscous magma analogue. The models show an intimate relationship between intrusion growth, uplift of the volcano and subsequent flank sliding. The structures produced can be compared with Mull and suggest that the Centre 1 thrust belt probably formed following edifice gravitational sliding as a consequence of the uplift associated with Centre 1 formation. Centre 2 and 3 are responsible for the sector sliding of the edifice flank toward the southeast as the magmatic complex became more asymmetric. The features observed at Mull and in the models are similar to those seen on active volcanoes, such as Etna, providing a structural framework for their deformation and evolution.     

What indicators can capture runoff-relevant connectivity properties of the micro-topography at the plot scale?

Although connectivity is acknowledged as a key factor of a catchment hydrological behaviour, it still misses reference evaluation methodologies. Therefore the objective of the paper is to evaluate different quantitative indicators of hydrological connectivity, using the concepts of structural and functional connectivity commonly used in ecology. The indicators were tested on contrasted numerical fields of micro-topography that present distinct hydrological responses.     

Using Causal Inference in Field Development Optimization: Application to Unconventional Plays

Mathematical Geosciences - In the current era of big data and machine learning, a strong focus exists on prediction and classification. In industrial applications, however, many important questions...