Coalescent angiogenesis—evidence for a novel concept of vascular network maturation

Angiogenesis describes the formation of new blood vessels from pre-existing vascular structures. While the most studied mode of angiogenesis is vascular sprouting, specific conditions or organs favor intussusception, i.e., the division or splitting of an existing vessel, as preferential mode of new vessel formation. In the present study, sustained (33-h) intravital microscopy of the vasculature in the chick chorioallantoic membrane (CAM) led to the hypothesis of a novel non-sprouting mode for vessel generation, which we termed “coalescent angiogenesis.” In this process, preferential flow pathways evolve from isotropic capillary meshes enclosing tissue islands. These preferential flow pathways progressively enlarge by coalescence of capillaries and elimination of internal tissue pillars, in a process that is the reverse of intussusception. Concomitantly, less perfused segments regress. In this way, an initially mesh-like capillary network is remodeled into a tree structure, while conserving vascular wall components and maintaining blood flow. Coalescent angiogenesis, thus, describes the remodeling of an initial, hemodynamically inefficient mesh structure, into a hierarchical tree structure that provides efficient convective transport, allowing for the rapid expansion of the vasculature with maintained blood supply and function during development.

Changes in soil hydraulic conductivity and preferential flow pathways after assisted forest restoration on degraded land in the Khasi Hills (Meghalaya, NE India)

<p>As in other parts of the Indian subcontinent, the forests of Meghalaya (NE India) provide an array of environmental services but the prevalence of traditional slash-and-burn agriculture (locally called jhum) plus mining has led to severely degraded hillsides and a critical loss of soil water storage opportunity and groundwater recharge. As a result, despite receiving some of the highest rainfall totals in the world (MAP up to 11 m, 75% received between May and September), the Meghalaya plateau faces severe water scarcity during the five-month long dry season. In response to such problems, initiatives have been taken towards restoring hydrological functioning through reforestation and assisted natural regeneration (ANR) programmes. As a first step towards assessing the possible improvement of soil physical characteristics and associated hydrological functioning after several years of ANR we measured topsoil (0–10 cm) saturated hydraulic conductivity (K<sub>sat</sub>) using double-ring infiltrometry at 12 sites in the Khasi Hills that represented three contrasting vegetation covers: (i) sacred forest (n = 6, natural baseline), (ii) 2–10-year-old ANR (n = 3), and (iii) degraded Imperata grassland (n = 3, degraded reference). At each site, nine K<sub>sat</sub>-measurements were taken along the hillslope gradient. In addition, at three sites, blue dye infiltration experiments (n = 2 per site) were carried out to examine the dominant percolation pathways associated with each land-cover type. The median K<sub>sat</sub> value for the sacred forest sites was highest (373 mm h<sup>-1</sup>), reflecting the abundance of biologically mediated macropores arising from the decomposing activity of soil microflora and fauna at these relatively undisturbed sites. The corresponding value for the ANR sites (160 mm h<sup>-1</sup>) was much higher than the median K<sub>sat</sub> for the degraded grasslands (71 mm h<sup>-1</sup>) but still considerably below the forest reference. Limited observations of topsoil bulk density and carbon content (n = 5 samples in each of three plots) showed increasing bulk density and decreasing carbon content from forest via ANR to grassland, thereby reflecting the observed trend in K<sub>sat</sub>. The blue dye experiments suggested infiltration in the sacred forest was dominated by flow along roots and other preferential flow pathways whereas the degraded grassland was mostly characterized by matrix flow. The ANR site showed intermediate behaviour with macropore flow exhibiting high matrix interaction. Comparison of observed median topsoil K<sub>sat</sub> in top-layer with prevailing (maximum) hourly rainfall intensities for Cherrapunji suggested infiltration-excess overland flow (IOF) must be considered a rare phenomenon in the sacred forest. Conversely, the K<sub>sat</sub>-values for the ANR and degraded grassland sites indicated the occurrence of IOF at high-intensity rainfall events. Despite the observed improvement in surface K<sub>sat</sub> it cannot be excluded that the generally shallow nature and high stoniness of the soils pose serious limitations to rebuilding soil water storage capacity through ANR/reforestation. Furthermore, frequent occurrence of saturation-excess OF at the height of the monsoon and associated surface erosion cannot be excluded.</p>

Remediation of intrinsic preferential flow pathways in water repellent soils' profile using surfactant

<p>Preferential flow pathways and uneven soil water and chemical distribution are intrinsic phenomena in water repellent soils. These uneven water and chemical distribution reduce water uptake by the plant roots on one hand and enhance deep percolation and chemical leaching, on the other hand, thereby enhancing soil and groundwater pollution. The results of attempts to remediate soil water repellency and heterogeneous spatial distribution of soil moisture and chemicals within the root zone by surfactant application will be addressed.  </p><p>This study was conducted in a commercial citrus orchard in central Israel that is irrigated with treated wastewater. Previous studies have revealed that prolonged irrigation using treated wastewater renders the soil water repellent with its associated adverse effects. The soil water distribution within the soil profile was monitored by frequent electrical resistance tomography (ERT) scans. The spatial distribution of different chemicals within the soil profile was obtained by chemical analysis of disturbed soil samples taken manually along a line transects. Two methods of surfactant application were used and compared: 1) on soil surface spraying (area source), 2) via drippers application (point source).</p><p>Surfactant spraying onto the water repellent soil's surface succeeded in turning the soil wettable, diminishing the preferential flow pathways, and renders the soil water and dissolved chemicals uniformly distributed. In contrast, drip applied surfactant exacerbated the incidence of preferential flow pathways and the leaching of solutes from the soil. Moreover, the overall average water content in the 0-40 cm soil layer significantly increased with surfactant spraying than with drip application even though both were higher than the control plots. These results substantiate previous laboratory-scale studies in which surfactant was applied to water repellent soils packed in a transparent flow chamber by these two methods. Additionally, the yield from the on-surface surfactant sprayed plots show a slight continuous increase compared to the untreated plots.</p>

Quantifying the Importance of Preferential Flow in a Riparian Buffer

HighlightsRiparian buffers and vegetative filter strips are uniquely susceptible to preferential flow.An innovative method is proposed to partition infiltration into matrix and macropore domains.Riparian buffer matrix and plot-scale infiltration experiments were simulated with HYDRUS-1D and VFSMOD.Preferential flow accounted for 32% to 47% of infiltration depending on hydrologic conditions.Preferential flow mechanisms should be incorporated into riparian buffer design tools and models.Abstract. Riparian buffers are uniquely susceptible to preferential flow due to the abundance of root channels, biological activity, and frequent wetting and drying cycles. Previous research has indicated such susceptibility and even measured the connectivity of preferential flow pathways with adjacent streams and rivers. However, limited research has attempted to partition the riparian buffer infiltration between matrix and preferential flow domains. The objectives of this research were to develop an innovative method to quantify soil matrix infiltration at the plot scale, develop a method to partition infiltration into matrix and macropore infiltration at the plot scale, and then use these methods to quantify the significance of macropore infiltration at a riparian buffer site. This research further demonstrated the importance of considering preferential flow processes in design tools and models to evaluate riparian buffer effectiveness. Sprinkler and runon field experiments were conducted at an established riparian buffer site with sandy loam soil. Trenches were installed and instrumented with soil moisture sensors along the width of the riparian buffer (i.e., along the flow path toward the stream) for detecting non-uniform flow patterns due to preferential flow. Riparian buffer parameters, including soil hydraulic parameters, were estimated using HYDRUS-1D for the sprinkler experiments and VFSMOD for the runon experiments. This research partitioned the infiltration into matrix and preferential flow domains by assuming negligible exchange of water between the soil matrix and preferential flow pathways in comparison to the magnitude of soil matrix flow. For these experimental conditions with 0.20 to 0.48 L s-1 of runon and initial soil water contents of 0.29 to 0.32 cm3 cm-3, preferential flow accounted for at least 27% to 32% of the total runon water entering the riparian buffer. This corresponded to approximately 32% to 47% of the total infiltration. While increasing the riparian buffer plot soil hydraulic conductivity in single-porosity models can adequately predict the total infiltration and therefore the surface outflow from the buffer, design tools and models should specifically consider preferential flow processes to improve predictive power regarding the actual infiltration processes and correspondingly the non-equilibrium flow and solute transport mechanisms. Keywords: Flow partitioning, HYDRUS, Matrix flow, Preferential flow, Riparian buffer, VFSMOD.

Stratigraphic Identification with Airborne Electromagnetic Methods at the Hanford Site, Washington

Stratigraphic units can influence the fate and transport of subsurface contaminants within groundwater. Units having coarse-grained sediments act as preferential flow pathways, and therefore can accelerate the transport of contaminants to reach human and ecological receptors. At legacy waste sites, detailed knowledge of subsurface stratigraphy can be used for effective monitoring and remediation planning to help minimize risk to human health and the environment. Airborne electromagnetic (AEM) methods can non-invasively provide information on kilometer-scale or larger subsurface stratigraphic features and fill informational gaps in directly sampled data from sparsely located boreholes. In this paper, we present inversion results of a 412 line-km frequency-domain AEM survey to delineate subsurface stratigraphic features at the Hanford Site, located in southeastern Washington State. The inversion was performed using a massively parallel 3D electromagnetic modeling and inversion code, where the modeling is based on solving frequency-domain Maxwell’s equations using an unstructured-mesh finite-element method and the inversion employs a Gauss-Newton optimization scheme. The results are compared to an underlying geologic framework model (GFM), built by interpolating contact depths of stratigraphic units interpreted from site borehole datasets. In areas with good borehole coverage, the inversion results show a good match with the GFM to a depth of about 60 m. Outside of these areas, the inversion results exhibit inconsistencies from the assumptions made to create the GFM, demonstrating that the AEM survey results can be used to improve the understanding of the geological conceptual model.

Distribution of preferential flow pathways and solute transfer along the Hailuogou Glacier Chronosequence on the Eastern Tibetan Plateau

<p>Preferential flow pathways (PFPs) are key contributors for the ecological status of the hydrosphere in high mountain environments, as the precipitation will transfer to PFPs with rapid solute transport from soil to groundwater. This particularly refers to nutrient allocation from soils to groundwater and surface waters.</p><p>To understand the effects of the pedogenesis and forest types on the soil PFPs, the soil preferential flow was studied by <em>in situ</em> dye tracing image analysis and elemental chemical analysis at the Hailuogou glacier chronosequence, Gongga Mountain on the eastern Tibetan Plateau. A soil chronosequence and a vegetation primary succession following the retreat of the Hailuogou glacier has been forming since ~1890. Three sites representing different exposure age (45, 85 and 125 years) in the Hailuogou glacier retreat area chronosequence and two sites typical forest lands (deciduous broadleaf forest and coniferous forest) were selected to carry out a brilliant blue dyeing experiment to visualize the distribution of water infiltration in soil.</p><p>The tracer-infiltration patterns were parameterized by dye coverage (DC), preferential flow fraction (PF), length index (L<sub>i</sub>) and the variation coefficient of DC in the PFPs (C<sub>V</sub>). Furthermore, the distribution of PFPs, transported solute of soil PFPs was analyzed including Hailuogou glacier chronosequence and vegetation succession.</p><p>According to the comparison of PFPs parameters, soil PFPs at the 125-year-old site extremely more developed than that at the younger site due to the fracture development between rock and soil on the process of soil development. The soil PFPs under broadleaf forest is more pronounced than that in coniferous forest soils, largely depending on the different root system.</p><p>In general, PFPs in Gongga Mountain were important contributors to the potential translocation of bioavailable inorganic P (PBPi) and organic P translocation to the hydrosphere. The elements transported with PFPs could be divided into three categories, reactive, conservative, and both reacted and conservative elements for the concentration of the elements remain in the PFPs. The results indicated that Mg and Al are the reactive elements, while Na, K, Ca and Mn are the conservative elements in the PFPs. Iron is both reacted and conservative element in the PFPs. Zn, Na, K, Mg, PBPi, had a significant correlation with the variation coefficient of DC in the PFPs (C<sub>V</sub>).</p><p>The results highlight the effects of the pedogenesis and forest types on the distribution of PFPs and solute transfer. Preferential flow contributes largely to elements flow at the Hailuogou glacier chronosequence and vegetation succession, Gongga Mountain.</p><p>The financial support of this work was obtained from National Natural Science Foundation of China (Grant No. 41272220) and Natural Scientifc Foundation for Young Scientists of Guangxi Zhuang Autonomous Region of China (Grant No. 2017GXNSFBA198162). The first author was financially supported by the Sino-German (CSC-DAAD) Postdoc Scholarship Program funded by China Scholarship Council (CSC) and Deutscher Akademischer Austausch Dienst (DAAD).</p>