Novel shape indices for vector landscape pattern analysis

The formation of an anisotropic landscape is influenced by natural and/or human processes, which can then be inferred on the basis of geometric indices. In this study, two minimal bounding rectangles in consideration of the principles of mechanics (i.e. minimal width bounding (MWB) box and moment bounding (MB) box) were introduced. Based on these boxes, four novel shape indices, namely MBLW (the length-to-width ratio of MB box), PAMBA (area ratio between patch and MB box), PPMBP (perimeter ratio between patch and MB box) and ODI (orientation difference index between MB and MWB boxes), were introduced to capture multiple aspects of landscape features including patch elongation, patch compactness, patch roughness and patch symmetry. Landscape pattern was, thus, quantified by considering both patch directionality and patch shape simultaneously, which is especially suitable for anisotropic landscape analysis. The effectiveness of the new indices were tested with real landscape data consisting of three kinds of saline soil patches (i.e. the elongated shaped slightly saline soil class, the circular or half-moon shaped moderately saline soil, and the large and complex severely saline soil patches). The resulting classification was found to be more accurate and robust than that based on traditional shape complexity indices.     

Festigkeit, verformbarkeit und gefügeregelung von anhydrit — experimentelle stauchverformung unter manteldrucken bis 5 kbar bei temperaturen bis 300°C

The dependence of strength, ductility, and preferred orientation of polycrystalline anhydrite upon confining pressure (up to 5 kbar), temperature (up to 300° C), and strain (up to 30%) has been evaluated by compression tests.Strength and ductility increase at room temperature with increasing mantle pressure. Up to 1 kbar mantle pressure anhydrite is brittle and failure occurs by tension and shear fractures. Homogeneous flow between 1 and 3 kbar mantle pressure is mostly due to intercrystalline slip which is sensitive to pressure. Beyond the elastic limit the stress—strain curves are nearly horizontal. No preferred orientation develops. Between 3 and 4 kbar mantle pressure the intracrystalline mechanisms become noticeable. The stress—strain curves show weak strain hardening. The (210)-planes reveal a weak preferred orientation perpendicular to the axis of compression.With increasing temperature the strength decreases at low strains (< 5%). Intracrystalline mechanisms become more dominant, because the critical resolved shear stresses are lower with increasing temperature. At high strains (> 15%) both strength and ductility increase at higher temperatures. At even higher strains, strain hardening ceases once again and the stress—strain curves become nearly horizontal. From that point on preferred orientation is no longer increased. The stress—strain curves differ with the orientation of the specimen axis to the original fabric.

Zusammenfassung

In Stauchversuchen an polykristallinem Anhydrit wurde die Abhängigkeit der Festigkeit, der Verformbarkeit und der Gefügeregelung vom Manteldruck (bis 5 kbar), von der Temperatur (bis 300°C) und vom Verformungsgrad (bis 30%) untersucht.Festigkeit und Verformbarkeit nehmen bei Raumtemperatur mit steigenden Mantel-drucken zu. Bis etwa l kbar Manteldruck verhält sich der Anhydrit spröde und es treten Trenn und Verschiebungsbrüche auf. Die gleichmässige Fliessverformung bei Manteldrucken über 1 kbar erfolgt durch überwiegend interkristalline, manteldruckempfindliche Verformungsmechanismen. Die Spannungs—Verformungskurven verlaufen nach Überschreiten der elastischen Verformung nahezu horizontal. Eine Regelung tritt nicht ein. Ab 3 kbar bis 4 kbar Manteldruck beginnen sich intrakristalline Mechanismen bemerkbar zu machen. Die Spannungs—Verformungskurven weisen eine schwache Verfestigung auf. Durch die eintretende schwache Regelung stellt sich eine (210)-Ebene bevorzugt senkrecht zur Stauchachse ein.Mit steigender Temperatur bei sonst gleichen Bedingungen nimmt die Festigkeit bei geringen Verformungsgraden (< 5%) ab. Die Verformung erfolgt überwiegend durch intrakristalline Mechanismen, deren kritische Schubspannungen mit zunehmender Temperatur geringer werden. Die Spannungs—Verformungskurven steigen nach Überschreiten des elastischen Bereichs stärker an als zuvor. Es tritt mit zunehmender Temperatur eine stärkere Verfestigung und eine intensivere Einregelung von (210) senkrecht zur Stauchachse ein. Im Bereich hoher Verformungsgrade (> 15%) liegen die Festigkeiten bei höheren Temperaturen höher als bei niedrigen Temperaturen. Bei sehr hohen Verformungsgraden wird die Verfestigung so gross, dass interkristalline Mechanismen die intrakristallinen wieder ablösen. Die Spannungs—Verformungskurven werden wieder flacher und die Zunahme in der Regelung hört auf.Je nach der Orientierung der Stauchachse zum Ausgangsgefüge verlaufen die Spannungs—Verformungskurven unterschiedlich.Die Abhängigkeit der Verformungsmechanismen vom Manteldruck, Verformungsgrad und der Temperatur wird in einem dreidimensionalen Modell vorgestellt.     

Evaluating river morphology change with a geomorphic form variation approach

Geomorphic river design strives for natural resilience by encouraging geomorphic form complexity and morphological processes linked to greater habitat diversity. Increasing availability of high-resolution topographic data and spatial feature mapping methods provide advantages for morphological analysis and river restoration planning. We propose and evaluate an approach to quantifying topographic variability of geomorphic form and pixel-level surface roughness resulting from channel planform geometry differences using spatially continuous variety computation applied to component metrics including flow direction, aspect and planform curvature. We define this as the geomorphic form variation (GFV) approach and found it scalable, repeatable and a multi-stage analytical metric for quantifying physical aspects of river-bed topographic variability. GFV may complement process-based morphological feature mapping applications, hydraulic assessment indices and spatial habitat heterogeneity metrics commonly used for ecological quality evaluation and river restoration. The GFV was tested on controlled synthetic channels derived from River Builder software and quasi-controlled sinuous planform flume experiment channels. Component variety metrics respond independently to specific geometric surface changes and are sensitive to multi-scaled morphology change, including coarser-grained sediment distributions of pixel-level surface roughness. GFV showed systematic patterns of change related to the effects of channel geometry, vertical bed feature (pool-bar) frequency and amplitude, and bar size, shape and orientation. Hotspot analysis found that bar margins were major components of topographic complexity, whereas grain-scale variety class maps further supported the multi-stage analytical capability and scalability of the GFV approach. The GFV can provide an overall variety value that may support river restoration decision-making and planning, particularly when geomorphic complexity enhancement is a design objective. Analysing metric variety values with statistically significant hotspot cluster maps and complementary process-based software and mapping applications allows variety correspondence to systematic feature changes to be assessed, providing an analytical approach for river morphology change comparison, channel design and geomorphic process restoration.     

Transient sediment supply in a high‐altitude Alpine environment evidenced through a 10Be budget of the Etages catchment (French Western Alps)

Although beryllium‐10 (¹⁰Be) concentrations in stream sediments provide useful synoptic views of catchment‐wide erosion rates, little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters. Here we address this issue by conducting a ¹⁰Be‐budget of detrital materials that characterize the morphogenetic domains representative of high‐altitude environments of the European Alps. We focus on the Etages catchment, located in the Ecrins‐Pelvoux massif (southeast France), and illustrate how in situ ¹⁰Be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream. The landscape of the Etages catchment is characterized by a geomorphic transient state, high topographic gradients, and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains. Beryllium‐10 concentrations measured in the Etages catchment vary from ~1 × 10⁴ to 4.5 × 10⁵ atoms per gram quartz, while displaying consistent ¹⁰Be signatures within each representative morphogenetic unit. We show that the basic requirements for inferring catchment‐wide denudation from ¹⁰Be concentration measurements are not satisfied in this small, dynamic catchment. However, the distinct ¹⁰Be signature observed for the geomorphic domains can be used as a tracer. We suggest that a terrestrial cosmogenic nuclide (TCN) budget approach provides a valuable tool for the tracing of material origin in basins where the ‘let nature do the averaging’ principles may be violated. Copyright © 2013 John Wiley & Sons, Ltd.     

Paleomagnetic results from the Late Carboniferous/Early Permian Casper Formation: implications for northern Appalachian tectonics

Paleomagnetic samples were collected from 190 m of the Late Carboniferous/Early Permian Casper Formation in southeastern Wyoming. A total of 549 samples was drilled near the vicinity of Horse Creek Station at an average stratigraphic interval of 33 cm. All samples were reversely magnetized. Rock magnetic analyses indicate that the primary carrier of remanence in the formation is hematite. A selection criterion applied to the partial demagnetized data restricted the sample population to 233, resulting in a paleomagnetic North Pole located at 47.4°N, 127.4°E (δ_p=0.7;δ_m=1.4). The Casper pole agrees well with other Late Carboniferous/Early Permian poles for cratonic North America. The tight clustering of these paleomagnetic poles suggests that little apparent polar motion with respect to North America occurred during this time. Comparing the stable North American poles with paleomagnetic poles from Late Carboniferous/Early Permian strata of the New England-Canadian Maritime region (Acadia) indicates that this region did not reach its present position relative to North America until at least the Early Permian.     

Evaluation of a simple,inexpensive, in situ sampler for measuring time‐weighted average concentrations of suspended sediment in rivers and streams

The accurate measurement of suspended sediment (<200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.     

Arsenic mobility in the ambient sulfidic environment: Sorption of arsenic(V) and arsenic(III) onto disordered mackinawite

Arsenate, As(V), sorption onto synthetic iron(II) monosulfide, disordered mackinawite (FeS), is fast. As(V) sorption decreases above the point of zero surface charge of FeS and follows the pH-dependent concentration of positively charged surface species. No redox reaction is observed between the As(V) ions and the mineral surface over the time span of the experiments. This observation shows that As(V) dominantly forms an outer-sphere complex at the surface of mackinawite. Arsenite, As(III), sorption is not strongly pH-dependent and can be expressed by a Freundlich isotherm. Sorption is fast, although slower than that of As(V). As(III) also forms an outer-sphere complex at the surface of mackinawite. In agreement with previous spectroscopic studies, complexation at low As(V) and As(III) concentration occurs preferentially at the mono-coordinated sulfide edge sites. The K_d (L g⁻¹) values obtained from linear fits to the isotherm data are ∼9 for As(V) and ∼2 for As(III). Stronger sorption of As(V) than As(III), and thus a higher As(III) mobility, may be reflected in natural anoxic sulfidic waters when disordered mackinawite controls arsenic mobility.     

Satellite-Based Assessment of the Extent and Changes in the Mangrove Ecosystem of the Niger Delta

This study was carried out with the primary aim of understanding how the mangrove ecosystem in the Niger Delta has been altered recently. Specifically, we determined the spatial extent of the mangrove forest in the Niger Delta using remotely sensed satellite data and estimated changes in the spatial extent of the forest from the mid-1980s through 2003. Overall, about 21,340 hectares of Mangrove forest was lost over the study period. Fieldwork confirmed that these losses were primarily due to urbanization, dredging activities, activities of the oil and gas industries, and the spread of Nypa Palm (Nypa frutican) plant species.