Method for computing the three-dimensional capacity dimension from two-dimensional projections of fractal aggregates

Disturbance of sedimentary processes in tidal salt marshes invaded by exotic vegetation

In situ moorings were conducted at salt marsh and bare flat to reveal the environmental disturbance of sedimentary processes in the intertidal flat. Spartina alterniflora (Spartina), an invasive species, grew up to 156 cm in the Ganghwa tidal flat from June to November 2019. This rapid growth has resulted in the dense salt marsh, which complicated hydrodynamics and associated sediment processes. Stems and leaves could effectively trap fine-grained sediments (17.24-20.42 μm) at the bed, increasing the differences in bed elevation between the two sites to up to 5.11 cm. The cohesive sediments accumulated in Spartina communities were resuspended differently by stem-scale turbulence generated from the disturbance of stems and leaves, depending on wind forcing and vegetation conditions. The vegetated sediments, under low wind speeds (<4 m s^-1), were hardly resuspended in the water column, compared to those in the bare flat, resulting in sedimentation. Under high wind speeds (>6 m s^-1), stem-scale turbulence was sufficiently strengthened to surpass the sedimentation of suspended sediments; thus, it resuspended additional bed sediments without a loss of the trapped sediment, unlike in the bare flat. The flocculation of suspended sediments in Spartina communities was mainly controlled by stem-scale turbulence. The flocs were confined to a size of 40 μm (settling velocity: 0.17 mm s^-1) and developed an approaching spherical shape. After the cut-off of Spartina, a favorable condition for the flocs to grow by 57 μm (settling velocity: 0.23 mm s^-1) was established with decrease in stem-scale turbulence. These larger flocs were able to develop into a ramified spherical structure. Despite diminishment of stem-scale turbulence, the disturbed sediments were outflowed, resulting in an abrupt decrease in bed elevation (0.12 cm day^-1). The results suggest that the sediment accumulated in Spartina communities remained erodible due to frequent disturbances without sufficient consolidation.

Flocculation Efficiency and Spatial Distribution of Water in Oil Sands Tailings Flocculated with a Partially Hydrophobic Graft Copolymer

This work investigates the effect of partially hydrophobic grafted polymers on flocculation and dewatering of oil sands mature fine tailings. Here, we combine confocal microscopy and rheology to investigate how the graft density of ethylene-propylene-diene grafted with hydrolyzed poly(methyl acrylate) (EPDM-g-HPMA) affects its dispersion in water and flocculation efficiency in terms of sediment solids content and long-term dewatering of oil sands tailings. Increasing the graft density from 30 to 50% makes the flocculant easier to disperse, increases the rate of initial dewatering, and also enhances the viscoelastic response of the flocculated sediments. Conversely, the long-term rheological properties of the flocculated sediments were similar for all flocculants. Tri-dimensional microscopic details of the spatial distribution of water within the flocculated sludge provide novel insights into the performance of the flocculants. Increasing the graft density in EPDM-g-HPMA traps more water within the individual flocs and, consequently, decreases the post-flocculation dewatering rate. Our systematic approach confirms the importance of the spatial distribution of water in the flocculated sediment, which depends on how the flocculant is dispersed and how it retains water in the flocs.

Sinking of microbial-associated microplastics in natural waters

Degraded plastic debris has been found in nearly all waters within and nearby urban developments as well as in the open oceans. Natural removal of suspended microplastics (MPs) by deposition is often limited by their excess buoyancy relative to water, but this can change with the attachment of biological matter. The extent to which the attached biological ballast affects MP dynamics is still not well characterised. Here, we experimentally demonstrate using a novel OMCEC (Optical Measurement of CEll colonisation) system that the biological fraction of MP aggregates has substantial control over their size, shape and, most importantly, their settling velocity. Polyurethane MP aggregates made of 80% biological ballast had an average size almost twice of those containing 5% biological ballast, and sank about two times slower. Based on our experiments, we introduce a settling velocity equation that accounts for different biological content as well as the irregular fractal structure of MP aggregates. This equation can capture the settling velocity of both virgin MPs and microbial-associated MP aggregates in our experiment with 7% error and can be used as a preliminary tool to estimate the vertical transport of MP aggregates made of different polymers and types of microbial ballast.

Living microorganisms change the information (Shannon) content of a geophysical system

The detection of microbial colonization in geophysical systems is becoming of interest in various disciplines of Earth and planetary sciences, including microbial ecology, biogeochemistry, geomicrobiology, and astrobiology. Microorganisms are often observed to colonize mineral surfaces, modify the reactivity of minerals either through the attachment of their own biomass or the glueing of mineral particles with their mucilaginous metabolites, and alter both the physical and chemical components of a geophysical system. Here, we hypothesise that microorganisms engineer their habitat, causing a substantial change to the information content embedded in geophysical measures (e.g., particle size and space-filling capacity). After proving this hypothesis, we introduce and test a systematic method that exploits this change in information content to detect microbial colonization in geophysical systems. Effectiveness and robustness of this method are tested using a mineral sediment suspension as a model geophysical system; tests are carried out against 105 experiments conducted with different suspension types (i.e., pure mineral and microbially-colonized) subject to different abiotic conditions, including various nutrient and mineral concentrations, and different background entropy production rates. Results reveal that this method can systematically detect microbial colonization with less than 10% error in geophysical systems with low-entropy background production rate.

A mesocosm experiment of suspended particulate matter dynamics in nutrient- and biomass-affected waters

An experimental study was conducted to test the hypothesis that the biomass growing after an increase in available nutrient in an aquatic ecosystem affects the flocculation dynamics of suspended particulate matter (SPM). The experiment was carried out in a settling column equipped with a turbulence generating system, a water quality monitoring system, and an automated μPIV system to acquire micro photographs of SPM. Three SPM types were tested combinatorially at five turbulence shear rates, three nutrient concentrations, and three mineral concentrations. Analyses of experimental data showed that nutrient availability together with the presence of biomass increased the SPM size by about 60% at low shear as compared to nutrient- and biomass-free conditions; a lower increase was observed at higher shears. In contrast, only 2% lower fractal (capacity) dimension and nearly invariant settling velocity were observed than in nutrient- and biomass-free conditions. Likewise, SPM size and capacity dimension were found to be insensitive to the SPM concentration. Although limited to nearly homogeneous mineral mixes (kaolinite), these experimental findings not only reject the hypothesis that SPM in natural waters can be dealt with as purely mineral systems in all instances, but also anticipate that SPM dynamics in natural waters increasingly exposed to the threat of anthropogenic nutrient discharge would lead to an increased advective flow of adsorbed chemicals and organic carbon.

Reconstructing the fractal dimension of granular aggregates from light intensity spectra

There has been growing interest in using the fractal dimension to study the hierarchical structures of soft materials after realising that fractality is an important property of natural and engineered materials. This work presents a method to quantify the internal architecture and the space-filling capacity of granular fractal aggregates by reconstructing the three-dimensional capacity dimension from their two-dimensional optical projections. Use is made of the light intensity of the two-dimensional aggregate images to describe the aggregate surface asperities (quantified by the perimeter-based fractal dimension) and the internal architecture (quantified by the capacity dimension) within a mathematical framework. This method was tested on control aggregates of diffusion-limited (DLA), cluster-cluster (CCA) and self-correlated (SCA) types, stereolithographically-fabricated aggregates, and experimentally-acquired natural sedimentary aggregates. Statistics of the reconstructed capacity dimension featured correlation coefficients R ≥ 98%, residuals NRMSE ≤ 10% and percent errors PE ≤ 4% as compared to controls, and improved earlier approaches by up to 50%.

Fractal dimension analysis of MDCT images for quantifying the morphological changes of the pulmonary artery tree in patients with pulmonary hypertension

Objective

The aim of this study was to use fractal dimension (FD) analysis on multidetector CT (MDCT) images for quantifying the morphological changes of the pulmonary artery tree in patients with pulmonary hypertension (PH).

Materials and Methods

Fourteen patients with PH and 17 patients without PH as controls were studied. All of the patients underwent contrast-enhanced helical CT and transthoracic echocardiography. The pulmonary artery trees were generated using post-processing software, and the FD and projected image area of the pulmonary artery trees were determined with ImageJ software in a personal computer. The FD, the projected image area and the pulmonary artery pressure (PAP) were statistically evaluated in the two groups.

Results

The FD, the projected image area and the PAP of the patients with PH were higher than those values of the patients without PH (p < 0.05, t-test). There was a high correlation of FD with the PAP (r = 0.82, p < 0.05, partial correlation analysis). There was a moderate correlation of FD with the projected image area (r = 0.49, p < 0.05, partial correlation analysis). There was a correlation of the PAP with the projected image area (r = 0.65, p < 0.05, Pearson correlation analysis).

Conclusion

The FD of the pulmonary arteries in the PH patients was significantly higher than that of the controls. There is a high correlation of FD with the PAP.