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Berlin Brandenburg

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  • 1
    Language: English
    In: 2015, Vol.10(4), p.e0127015
    Keywords: Correction
    E-ISSN: 1932-6203
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  • 2
    Language: English
    In: PLoS ONE, 01 January 2015, Vol.10(6), p.e0128914
    Description: We quantify mechanical processes common to soil penetration by earthworms and growing plant roots, including the energetic requirements for soil plastic displacement. The basic mechanical model considers cavity expansion into a plastic wet soil involving wedging by root tips or earthworms via cone-like penetration followed by cavity expansion due to pressurized earthworm hydroskeleton or root radial growth. The mechanical stresses and resulting soil strains determine the mechanical energy required for bioturbation under different soil hydro-mechanical conditions for a realistic range of root/earthworm geometries. Modeling results suggest that higher soil water content and reduced clay content reduce the strain energy required for soil penetration. The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip). The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters. The study provides a quantitative framework for estimating energy requirements for soil penetration work done by earthworms and plant roots, and delineates intrinsic and external mechanical limits for bioturbation processes. Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 3
    In: New Phytologist, September 2015, Vol.207(4), pp.1015-1025
    Description: A general theoretical framework for quantifying the stomatal clustering effects on leaf gaseous diffusive conductance was developed and tested. The theory accounts for stomatal spacing and interactions among ‘gaseous concentration shells’. The theory was tested using the unique measurements of Dow et al. (2014) that have shown lower leaf diffusive conductance for a genotype of Arabidopsis thaliana with clustered stomata relative to uniformly distributed stomata of similar size and density. The model accounts for gaseous diffusion: through stomatal pores; via concentration shells forming at pore apertures that vary with stomata spacing and are thus altered by clustering; and across the adjacent air boundary layer. Analytical approximations were derived and validated using a numerical model for 3D diffusion equation. Stomata clustering increases the interactions among concentration shells resulting in larger diffusive resistance that may reduce fluxes by 5–15%. A similar reduction in conductance was found for clusters formed by networks of veins. The study resolves ambiguities found in the literature concerning stomata end‐corrections and stomatal shape, and provides a new stomata density threshold for diffusive interactions of overlapping vapor shells. The predicted reduction in gaseous exchange due to clustering, suggests that guard cell function is impaired, limiting stomatal aperture opening.
    Keywords: Gas Diffusion ; Leaf Conductance ; Spatial Organization ; Stomata Clustering ; Stomatal Aperture
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 4
    Language: English
    In: Journal of Hydrology, November 2015, Vol.530, pp.103-116
    Description: Bluff-body obstacles interacting with turbulent airflows are common in many natural and engineering applications (from desert pavement and shrubs over natural surfaces to cylindrical elements in compact heat exchangers). Even with obstacles of simple geometry, their interactions within turbulent airflows result in a complex and unsteady flow field that affects surface drag partitioning and transport of scalars from adjacent evaporating surfaces. Observations of spatio-temporal thermal patterns on evaporating porous surfaces adjacent to bluff-body obstacles depict well-defined and persistent zonation of evaporation rates that were used to construct a simple mechanistic model for surface–turbulence interactions. Results from evaporative drying of sand surfaces with isolated cylindrical elements (bluff bodies) subjected to constant turbulent airflows were in good agreement with model predictions for localized exchange rates. Experimental and theoretical results show persistent enhancement of evaporative fluxes from bluff-rough surfaces relative to smooth flat surfaces under similar conditions. The enhancement is attributed to formation of vortices that induce a thinner boundary layer over part of the interacting surface footprint. For a practical range of air velocities (0.5–4.0 m/s), low-aspect ratio cylindrical bluff elements placed on evaporating sand surfaces enhanced evaporative mass losses (relative to a flat surface) by up to 300% for high density of elements and high wind velocity, similar to observations reported in the literature. Concepts from drag partitioning were used to generalize the model and upscale predictions to evaporation from surfaces with multiple obstacles for potential applications to natural bluff-rough surfaces.
    Keywords: Evaporation ; Porous Surface ; Bluff-Body Obstacle ; Turbulent Airflow ; Momentum Partitioning ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    Language: English
    In: Journal of Colloid And Interface Science, 01 July 2012, Vol.377(1), pp.406-415
    Description: ► We quantified pore scale pinning–jumping motions of displacement fluid fronts. ► Interfacial jumps are highly inertial exceeding 50 times mean front velocity. ► Waiting times between jumps influence displacement patterns and pressure fluctuations. ► A model of interacting pair of capillaries captures the observed complex dynamics. The macroscopically regular motion of fluid displacement fronts in porous media often results from numerous pore scale interfacial jumps and associated pressure fluctuations. Such rapid pore scale dynamics defy postulated slow viscous energy dissipation and may shape phase entrapment and subsequent macroscopic transport properties. Certain displacement characteristics are predictable from percolation theory; however, insights into rapid interfacial dynamics require mechanistic models for hydraulically interacting pores such as found along fluid displacement fronts. A model for hydraulically coupled sinusoidal capillaries was used to analyze stick-jump interfacial motions with a significant inertial component absent in Darcy-based description of fluid front displacement. High-speed camera provided measurements of rapid interfacial dynamics in sintered glass beads cell during drainage. Interfacial velocities exceeding 50 times mean front velocity were observed in good agreement with model predictions for a pair of sinusoidal capillaries. In addition to characteristic pinning–jumping behavior, interfacial dynamics were sensitive to initial positions within pores at the onset of a jump. Even for a pair of sinusoidal capillaries, minute variations in pore geometry and boundary conditions yield rich behavior of motions, highlighting challenges and potential new insights offered by consideration of pore scale mechanisms in macroscopic description of fluid displacement fronts in porous media.
    Keywords: Fluid Front Displacement ; Interfacial Jumps ; Jump Velocity ; Inertial Oscillations ; Pressure Fluctuations ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 6
    In: Global Change Biology, January 2018, Vol.24(1), pp.e378-e392
    Description: Changes in soil hydration status affect microbial community dynamics and shape key biogeochemical processes. Evidence suggests that local anoxic conditions may persist and support anaerobic microbial activity in soil aggregates (or in similar hot spots) long after the bulk soil becomes aerated. To facilitate systematic studies of interactions among environmental factors with biogeochemical emissions of , NO and from soil aggregates, we remolded silt soil aggregates to different sizes and incorporated carbon at different configurations (core, mixed, no addition). Assemblies of remolded soil aggregates of three sizes (18, 12, and 6 mm) and equal volumetric proportions were embedded in sand columns at four distinct layers. The water table level in each column varied periodically while obtaining measurements of soil emissions for the different aggregate carbon configurations. Experimental results illustrate that methane production required prolonged inundation and highly anoxic conditions for inducing measurable fluxes. The onset of unsaturated conditions (lowering water table) resulted in a decrease in emissions while temporarily increasing NO fluxes. Interestingly, NO fluxes were about 80% higher form aggregates with carbon placement in center (anoxic) core compared to mixed carbon within aggregates. The fluxes of were comparable for both scenarios of carbon sources. These experimental results highlight the importance of hydration dynamics in activating different production and affecting various transport mechanisms about 80% of total methane emissions during lowering water table level are attributed to physical storage (rather than production), whereas emissions (~80%) are attributed to biological activity. A biophysical model for microbial activity within soil aggregates and profiles provides a means for results interpretation and prediction of trends within natural soils under a wide range of conditions. The study highlights the role of carbon distribution within soil aggregates on anaerobically produced GHGs, with highest NO emissions measured from aggregates with centered carbon source. The results quantify the temporal and spatial scales of variability in local greenhouse gas productions from soil and highlight the role of water table fluctuations (gradual vs. abrupt) as important variable in GHG emissions resembling irrigation or precipitation patterns from the scale of hours to days.
    Keywords: Biogeochemical Gas Fluxes ; Mechanistic Modeling ; Microbial Community ; N 2 O Emissions ; Soil Aggregate ; Soil Structure
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 7
    In: Global Change Biology, September 2016, Vol.22(9), pp.3141-3156
    Description: Microbial communities inhabiting soil aggregates dynamically adjust their activity and composition in response to variations in hydration and other external conditions. These rapid dynamics shape signatures of biogeochemical activity and gas fluxes emitted from soil profiles. Recent mechanistic models of microbial processes in unsaturated aggregate‐like pore networks revealed a highly dynamic interplay between oxic and anoxic microsites jointly shaped by hydration conditions and by aerobic and anaerobic microbial community abundance and self‐organization. The spatial extent of anoxic niches (hotspots) flicker in time (hot moments) and support substantial anaerobic microbial activity even in aerated soil profiles. We employed an individual‐based model for microbial community life in soil aggregate assemblies represented by 3D angular pore networks. Model aggregates of different sizes were subjected to variable water, carbon and oxygen contents that varied with soil depth as boundary conditions. The study integrates microbial activity within aggregates of different sizes and soil depth to obtain estimates of biogeochemical fluxes from the soil profile. The results quantify impacts of dynamic shifts in microbial community composition on and NO production rates in soil profiles in good agreement with experimental data. Aggregate size distribution and the shape of resource profiles in a soil determine how hydration dynamics shape denitrification and carbon utilization rates. Results from the mechanistic model for microbial activity in aggregates of different sizes were used to derive parameters for analytical representation of soil biogeochemical processes across large scales of practical interest for hydrological and climate models.
    Keywords: Biogeochemical Fluxes ; Denitrification ; Hydration ; Individual‐Based Model ; Microbial Community ; Pore Network Modeling ; Soil Aggregates ; Soil Stracture
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 8
    In: Geophysical Research Letters, 16 July 2015, Vol.42(13), pp.5325-5336
    Description: Soil wetness and airflow turbulence are key factors affecting surface energy balance components thereby influencing surface skin temperature. Turbulent eddies interacting with evaporating surfaces often induce localized and intermittent evaporative and sensible heat fluxes that leave distinct thermal signatures. These surface thermal fluctuations observable by infrared thermography (IRT) offer a means for characterization of overlaying turbulent airflows and remote quantification of surface wetness. We developed a theoretical and experimental methodology for using rapid IR surface temperature measurements to deduce surface wetness and evaporative fluxes from smooth bare soils. The mechanistic model provides theoretical links between surface thermal fluctuations, soil, and aerodynamic properties enabling thermal inferences of soil wetness with explicit consideration of soil thermal capacity and airflow turbulence effects. The method potentially improves accuracy of soil wetness assessment by IRT‐based techniques whose performance is strongly influenced by surface‐turbulence interactions and offers new ways for quantifying fluxes directly at their origin. Linking surface hydrothermal properties with turbulence thermal imprints Remote estimation of surface water content from surface thermal fluctuations Surface temperature-based quantification of evaporation from smooth bare soils
    Keywords: Soil Evaporation ; Turbulent Exchange ; Surface Renewal ; Thermal Signatures
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 9
    Language: English
    In: Journal of Hydrology, 27 November 2014, Vol.519, pp.1257-1270
    Description: The dynamics of radiative energy partitioning on drying terrestrial surfaces reflects the strong coupling between evaporation and surface temperature that shapes latent and sensible heat fluxes. We used a new pore-scale analytical model that explicitly links evaporative fluxes with temperature dynamics of drying surfaces. Model predictions were in good agreement with measured evaporation rates and surface temperature variations observed during drying of a homogeneous sand surface. The model was extended to heterogeneous surfaces by considering responses of representative elements of a complex surface and weighing relative contributions to formulate area-averaged fluxes. Notwithstanding the small scale basis of the model, the fully coupled surface energy balance provides a physically-based framework for predicting the Bowen ratio and the Priestley–Taylor (Priestley and Taylor, 1972) for a range of boundary conditions using readily available input variables (radiation, air temperature, etc.). Analyses show that is not constant (typically assumed as = 1.26), it decreases with surface drying and increasing net radiation, and increases with increasing wind speed. The physically-based predictability offers new opportunities for generalization of algorithms that rely on remotely sensed surface temperature to estimate surface fluxes.
    Keywords: Energy Partitioning ; Terrestrial Surfaces ; Evaporative Fluxes ; Heterogeneous Surface ; Bowen Ratio ; Priestley–Taylor Α ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 10
    Language: English
    In: Journal of Hydrology, June 2015, Vol.525, pp.684-693
    Description: The Monin–Obukhov similarity theory (MOST) provides the theoretical basis for many “atmospheric-based” methods (such as eddy covariance and flux-profile methods) that are widely used for quantifying surface–atmosphere exchange processes. The turbulence driven and highly nonlinear profiles of momentum, air temperature, and vapor densities require complex resistance expressions applied to simple gradients deduced from a single or few height measurements. Notwithstanding the success of these atmospheric-based methods, they often leave a gap at the immediate vicinity of terrestrial surfaces where fluxes emanate. A complementary approach for quantifying surface fluxes relies on diffusive interactions across a viscous sublayer next to the surface, referred to as the “surface boundary layer (BL)” approach. This study (for bare soil) establishes formal links between these two approaches thereby offering a physically based lower boundary condition (BC) for flux-profile methods while improving the top BC for surface BL-based formulations to include atmospheric stability. The modified lower BC for flux-profile relationships links characteristics of drying evaporating surfaces considering nonlinearities between wetness and evaporative fluxes and obviates reliance on both profile measurements and empirical surface resistances. The revised top BC for surface BL methods greatly improves the agreement with published field-scale experimental measurements. The proposed reconciliation procedure improves estimation capabilities of both flux-profile and surface BL formulations, and considerably enhances their accuracy of flux estimation when applied theoretically (in the absence of measured profiles) to drying bare soil surfaces.
    Keywords: Evaporation ; Porous Surface ; Flux Reconciliation ; Surface Resistance ; Monin–Obukhov Similarity Theory ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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