Flow–plant interactions at leaf,stem and shoot scales: drag,turbulence, and biomechanics

Flow–plant interactions are experimentally investigated at leaf, stem, and shoot scales in an open-channel flume at a range of Reynolds numbers. The experiments included measurements of instantaneous drag forces acting on leaves, stems, and shoots of the common freshwater plant species Glyceria fluitans, complemented with velocity measurements, high-resolution video recordings, and biomechanical tests of leaf and stem properties. The analyses of bulk statistics, power spectral densities, transfer functions, and cross-correlations of measured velocities and drag forces revealed that flow characteristics, drag force, and plant biomechanical and morphological properties are strongly interconnected and scale-dependent. The plant element–flow interactions can be subdivided into two classes: (I) passive interactions when the drag variability is due to the time variability of the wetted and frontal areas and squared approach velocity (due to the large-scale turbulence); and (II) active interactions representing a range of element-specific instabilities that depend on the element flexural rigidity and morphology. Implications of experimental findings for plant biophysics and ecology are briefly discussed.     

Using data assimilation method to calibrate a heterogeneous conductivity field conditioning on transient flow test data

A data assimilation method is developed to calibrate a heterogeneous hydraulic conductivity field conditioning on transient pumping test data. The ensemble Kalman filter (EnKF) approach is used to update model parameters such as hydraulic conductivity and model variables such as hydraulic head using available data. A synthetical two-dimensional flow case is used to assess the capability of the EnKF method to calibrate a heterogeneous conductivity field by assimilating transient flow data from observation wells under different hydraulic boundary conditions. The study results indicate that the EnKF method will significantly improve the estimation of the hydraulic conductivity field by assimilating continuous hydraulic head measurements and the hydraulic boundary condition will significantly affect the simulation results. For our cases, after a few data assimilation steps, the assimilated conductivity field with four Neumann boundaries matches the real field well while the assimilated conductivity field with mixed Dirichlet and Neumann boundaries does not. We found in our cases that the ensemble size should be 300 or larger for the numerical simulation. The number and the locations of the observation wells will significantly affect the hydraulic conductivity field calibration.     

Improved edge detection mapping through stacking and integration: a case study in the Bathurst Mining Camp

Airborne geophysical surveys provide spatially continuous regional data coverage, which directly reflects subsurface petrophysical differences and thus the underlying geology. A modern geologic mapping exercise requires the fusion of this information to complement what is typically limited regional outcrop. Often, interpretation of the geophysical data in a geological context is done qualitatively using total field and derivative maps. With a qualitative approach, the resulting map product may reflect the interpreter's bias. Source edge detection provides a quantitative means to map lateral physical property changes in potential and non‐potential field data. There are a number of Source edge detection algorithms, all of which apply a transformation to convert local signal inflections associated with source edges into local maxima. As a consequence of differences in their computation, the various algorithms generate slightly different results for any given source depth, geometry, contrast, and noise levels. To enhance the viability of any detected edge, it is recommended that one combines the output of several Source edge detection algorithms. Here we introduce a simple data compilation method, deemed edge stacking, which improves the interpretable product of Source edge detection through direct gridding, grid addition, and amplitude thresholding. In two examples, i.e., a synthetic example and a real‐world example from the Bathurst Mining Camp, New Brunswick, Canada, a number of transformation algorithms are applied to gridded geophysical data sets and the resulting Source edge detection solutions combined. Edge stacking combines the benefits and nuances of each Source edge detection algorithm; coincident or overlapping and laterally continuous solutions are considered more indicative of a true edge, whereas isolated points are taken as being indicative of random noise or false solutions. When additional data types are available, as in our example, they may also be integrated to create a more complete geologic model. The effectiveness of this method is limited only by the resolution of each survey data set and the necessity of lateral physical property contrasts. The end product aims at creating a petrophysical contact map, which, when integrated with known lithological outcrop information, can be led to an improved geological map.     

Rhyolitic ignimbrites in the Rogerson Graben,southern Snake River Plain volcanic province: volcanic stratigraphy,eruption history and basin evolution

The 80 km long NNE-trending Rogerson Graben on the southern margin of the central Snake River Plain, Idaho, USA, hosts a rhyolitic pyroclastic succession, 200 m thick, that records a period of successive, late-Miocene, large-volume explosive eruptions from the Yellowstone–Snake River Plain volcanic province, and contemporaneous extension. The succession, here termed the Rogerson Formation, comprises seven members (defined herein) and records at least eight large explosive eruptions with numerous repose periods. Five high-grade and extremely high-grade ignimbrites are intercalated with three non-welded ignimbrites and two volcaniclastic deposits, with numerous repose periods (palaeosols) throughout. Two of the ignimbrites are dominantly rheomorphic and lava-like but contain subordinate non-welded pyroclastic layers. The ignimbrites are typical Snake River Plain high-silica rhyolites, with anhydrous crystal assemblages and high inferred magmatic temperatures (≤ 1,025°C). We tentatively infer that the Jackpot and Rabbit Springs Members may have been emplaced from the Bruneau–Jarbidge eruptive centre on the basis of: (1) flow lineation trends, (2) crystal assemblage, and (3) radiometric age. We infer that the overlying Brown’s View, Grey’s Landing, and Sand Springs Members may have been emplaced from the Twin Falls eruptive centre on the basis of: (1) kinematic indicators (from the east), and (2) crystal assemblage. Furthermore, we have established the contemporaneous evolution of the Rogerson Graben from the emplacement of the Jackpot Member onwards, and infer that it is similar to younger half-graben along the southern margin of the Snake River Plain, formed by local reactivation of Basin and Range structures by the northeastwardly migration of the Yellowstone hot-spot. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nature of sedimentary deposits in the western Makgadikgadi basin, Botswana

Quaternary sedimentation in the western Makgadikgadi basin of north central Botswana is evaluated on the basis of new evidence from satellite imagery and sedimentological analyses. Thematic Mapper imagery interpretation, combined with field evidence, has led to the identification of geomorphological features which are mainly composed of light grey calcareous sandstones (formerly calcretes) overlain by dark grey sands. The literature suggests that palaeolake Makgadikgadi I formed and developed intermittently after initial downwarping in the early–mid Pleistocene. The calcareous sandstones were formed when calcium carbonate precipitation took place in pre-existing Kalahari sands along the western shoreline of Makgadikgadi I. Field evidence, supported by X-ray diffraction and SEM analyses, indicates that CaCO₃precipitated mainly in marshy conditions around plant roots and stems and in association with bacteria in embayments along the lakeshore. The sandstones thickened and became partially indurated as a result of increasing palaeolake levels. Deposition was terminated by renewed tectonism which uplifted the shoreline zone relative to the lake basin, leading to falling palaeolake levels. Post-uplift reworking led to case hardening and pedogenic calcrete formation in the upper sections of the calcareous sandstones. Sedimentary conditions altered during the late Pleistocene. Extensive distributaries from the proto-Okavango system incised the shoreline ridge contributing to the filling of Makgadikgadi II. Satellite data suggest that the proto-Okavango rivers formed a series of fan deltas at this time along the western Makgadikgadi basin. Widespread dispersal of fluvial grey sands took place as a result of basin tilting which led to anastomosing channels flowing southward possibly around 18,000 B.P. These results, although preliminary in nature, augment previous geomorphological analyses by adding some detail in terms of depositional environments and by providing a tentative age and origin for the ubiquitous grey sands.     

Multi-gas Emissions Pathways to Meet Climate Targets

So far, climate change mitigation pathways focus mostly on CO₂ and a limited number of climate targets. Comprehensive studies of emission implications have been hindered by the absence of a flexible method to generate multi-gas emissions pathways, user-definable in shape and the climate target. The presented method ‘Equal Quantile Walk’ (EQW) is intended to fill this gap, building upon and complementing existing multi-gas emission scenarios. The EQW method generates new mitigation pathways by ‘walking along equal quantile paths’ of the emission distributions derived from existing multi-gas IPCC baseline and stabilization scenarios. Considered emissions include those of CO₂ and all other major radiative forcing agents (greenhouse gases, ozone precursors and sulphur aerosols). Sample EQW pathways are derived for stabilization at 350 ppm to 750 ppm CO₂ concentrations and compared to WRE profiles. Furthermore, the ability of the method to analyze emission implications in a probabilistic multi-gas framework is demonstrated. The probability of overshooting a 2 ^∘C climate target is derived by using different sets of EQW radiative forcing peaking pathways. If the probability shall not be increased above 30%, it seems necessary to peak CO₂ equivalence concentrations around 475 ppm and return to lower levels after peaking (below 400 ppm). EQW emissions pathways can be applied in studies relating to Article 2 of the UNFCCC, for the analysis of climate impacts, adaptation and emission control implications associated with certain climate targets. See for EQW-software and data.     

Changing climate and human response: The impact of recent events on climatology

Over the last decade climate has become an increasingly significant factor in world affairs because of its effect on food supplies, energy consumption and environmental quality. At the same time the scientific community has had to re-appraise the nature and scope of climatology, increasing political relevance, leading to a growth in interdisciplinary activity involving both natural and social scientists. The 1980s promise to continue this broadening of scope as the two-way interaction of human societies and the atmospheric system are further explored and evaluated. This paper examines these trends, paying particular reference to the main climate-based environmental concerns currently being debated: the effect of halocarbons on the ozone shield, climate and food production, desertification, the CO₂ ‘greenhouse’ effect, acid rain and the significance of teleconnections.