Seasonal and Spatial Variation in Dissolved Heavy Metals in Liaodong Bay, China

Spatial–seasonal variations in dissolved heavy metals in surface seawater were analyzed based on surveys at 87 sampling sites and water samples from six rivers across Liaodong Bay. The concentrations of copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) had ranges of 0.20–40.00 (5.45 ± 5.67), 0.51–33.64 (4.68 ± 3.93), 0.03–13.47 (2.22 ± 2.01), and 0.50–80.09 μg/L (14.22 ± 16.32), respectively, throughout the four seasons of 2020. The trace metal concentration showed a spatial gradient of high to low from river to estuary and from inshore to offshore areas. A combination of pollution levels and marine sensitivity was employed to assess the pollution degree of the heavy metals. As a whole, the single pollution factors of trace metals in Liaodong Bay were ranged in the order Pb > Zn > Cu > Cd. The total pollution degree was relatively high in autumn and summer due to increased riverine inputs after the rainy season, while relatively low in spring and winter. These findings provide baseline data for future targeting policies to protect marine environments in Liaodong Bay.

Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

THE INFLUENCE OF RECREATIONAL IMPACT IN FOREST COMMUNITIES ON THE ALLELOPATHIC REGIME OF TREE EDIFICATORS

The allelopathic regime of the phytogenic field of model middle-aged trees of seven forest formations in the zone of humid subtropics of the Sochi Black Sea region was evaluated with an admissible range of stages of recreational digression. The method of biotesting of water extracts from forest litter, soil and roots was used to determine the spatial gradient of allelopathic activity of the phytogenic field environ-ment. The share of participation of the allelopathic factor in the formation of the phytogenic field at certain stages of recreational digression was established. It was determined that the value of allelopathic intensity of the phytogenic field, depending on the stage of recreational digression, field zones and edifi-cator species, can characterize the degree of resistance to the introduction of new species, recreational resistance and community stability.

Low-Dose Cone-Beam CT Iterative Reconstruction via Total Variation and Gradient Total Variation

The compressed sensing (CS) technique has been utilized to reconstruct Cone-beam computed tomography (CBCT) images via limited projection from under-sampled measurements. However, the condition of limited projection is an ill-posed problem. Since the CBCT image itself doesn’t have sparse features, the total variation (TV) transform has been widely adopted in CBCT reconstruction. This method, which penalizes the weight of each voxel at a constant rate regardless of different spatial gradient, may not recover qualified CBCT images from ill-posed projection data. This work presents a new strategy to deal with the deficits stated above by utilizing non-uniform weighting penalization in CBCT reconstruction. The proposed new strategy combines TV and gradient total variation (GTV) for reconstruction in a hybrid weighting penalization way, where the total variation is penalized by the gradient total variation in advance. The proposed penalty not only retains the benefits of TV, including artifact and noise suppression, but also maintains the structures in regions with gradual gradient intensity transition more effectively. This study tested the proposed method by under-sampled projections of 2 objects and 2 experiments (2 digital phantom). We assessed its performance against the OS-SART method, FDK method, conventional TV method and TV+GTV method in the tissue contrast, reconstruction accuracy, and imaging resolution by comparing the root mean squared error (RMSE), the correlation coefficient (CC), the structural similarity (SSIM), and profiles intensity of the reconstructed images. The proposed method produced the reconstructed image with the lowest RMSEs and the highest CCs and SSIMs for each experiment.

Image Scale-Space Filtering Using Directional Local Variance Controlled Anisotropic Diffusion

The purpose of this paper is to develop an effective edge indicator and propose an image scale-space filter based on anisotropic diffusion equation for image denoising. We first develop an effective edge indicator named directional local variance (DLV) for detecting image features, which is anisotropic and robust and able to indicate the orientations of image features. We then combine two edge indicators (i.e., DLV and local spatial gradient) to formulate the desired image scale-space filter and incorporate the modulus of noise magnitude into the filter to trigger time-varying selective filtering. Moreover, we theoretically show that the proposed filter is robust to the outliers inherently. A series of experiments are conducted to demonstrate that the DLV metric is effective for detecting image features and the proposed filter yields promising results with higher quantitative indexes and better visual performance, which surpass those of some benchmark models.

Multiple anthropogenic stressors have inconsistent cumulative effects across a large spatial gradient

Biodiversity is declining, typically because of multiple anthropogenic stressors. Cumulative effects of multiple stressors are classified as additive, when cumulative effects are as expected from the stressor’s singular effects, synergistic when greater than additive or antagonistic when less than additive. Less attention has been given to the consistency of cumulative effects. We analysed stream insects, Ephemeroptera, Plecoptera and Trichoptera (EPT) data from two habitats spanning a 3,600 km latitudinal (S11◦-S43◦) gradient in eastern Australia. We found that the cumulative effect of salinity and suspended sediments on EPT family richness was inconsistent with additive, synergistic or antagonistic effects, and the reduction EPT family richness from increasing both stressors varied (48-70%) depending on habitat (riffle vs. edge), water temperature and terrain slope. Studies of cumulative effects of multiple stressors at one location risk not describing cumulative effects elsewhere and ecologists should consider the spatial consistency of multiple stressors.

Rabbits use both spectral and temporal cues to discriminate the fundamental frequency of harmonic complexes with missing fundamentals

The pitch of harmonic complex tones (HCT) common in speech, music and animal vocalizations plays a key role in the perceptual organization of sound. Unraveling the neural mechanisms of pitch perception requires animal models but little is known about complex pitch perception by animals, and some species appear to use different pitch mechanisms than humans. Here, we tested rabbits' ability to discriminate the fundamental frequency (F0) of HCTs with missing fundamentals using a behavioral paradigm inspired by foraging behavior in which rabbits learned to harness a spatial gradient in F0 to find the location of a virtual target within a room for a food reward. Rabbits were initially trained to discriminate HCTs with F0s in the range 400-800 Hz and with harmonics covering a wide frequency range (800-16,000 Hz), and then tested with stimuli differing either in spectral composition to test the role of harmonic resolvability (Experiment 1), or in F0 range (Experiment 2), or both F0 and spectral content (Experiment 3). Together, these experiments show that rabbits can discriminate HCTs over a wide F0 range (200-1600 Hz) encompassing the range of conspecific vocalizations, and can use either the spectral pattern of harmonics resolved by the cochlea for higher F0s or temporal envelope cues resulting from interaction between unresolved harmonics for lower F0s. The qualitative similarity of these results to human performance supports using rabbits as an animal model for studies of pitch mechanisms providing species differences in cochlear frequency selectivity and F0 range of vocalizations are taken into account.

Zonal flow generation and toroidal Alfvén eigenmode excitation due to tearing mode induced energetic particle redistribution

Generation of the n = 0 zonal flow and excitation of the n = 1 toroidal Alfvén eigenmode (TAE) due to the redistribution of energetic particles (EPs) by the m/n = 2/1 tearing mode (TM) are systematically studied with the hybrid drift-kinetic magnetohydrodynamic (MHD) simulations (m and n represent the poloidal and toroidal mode number, respectively). In the presence of the m/n = 2/1 TM, the amplitude of the n = 1 TAE shows a slower decay after its first saturation due to the wave-particle nonlinearity and the nonlinear generation of the n = 0 & higher-n (n ≥ 2) sidebands. Meanwhile, a strong n = 0 zonal flow component is nonlinearly generated when both TAE and TM grow to large amplitudes. The redistribution of EPs by the m/n = 2/1 magnetic island results in a continuous drive on the background plasma, and finally produces the zonal flow through the MHD nonlinearity. In addition, the large m/n = 2/1 magnetic island is found to be responsible for the formation of the strong spatial gradient of the EP distribution through the resonance between EPs and TM, which can lead to burst of unstable TAE and destabilization of originally stable TAE.

Variations of the Oxidative Ratio across Ecosystem Components and Seasons in a Managed Temperate Beech Forest (Leinefelde, Germany)

The oxidative ratio (OR) of organic material integrates the ratio of CO2 sequestered in biomass vs. O2 produced over longer timescales, but the temporal and spatial variability within a single ecosystem has received very limited attention. Between October 2017 and October 2019, we repeatedly sampled leaves, twigs, bark, outer stem wood, understorey vegetation and litter in a temperate beech forest close to Leinefelde (Germany) for OR measurements across a seasonal and spatial gradient. Plant component OR ranged from 1.004 ± 0.010 for fine roots to 1.089 ± 0.002 for leaves. Inter- and intra-annual differences for leaf and twig OR exist, but we found no correlation with sampling height within the canopy. Leaf OR had the highest temporal variability (minimum 1.069 ± 0.007, maximum 1.098 ± 0.002). This was expected, since leaf biomass of deciduous trees only represents the signal of the current growing season, while twig, stem and litter layer OR integrate multiple years. The sampling years 2018 and 2019 were unusually hot and dry, with low water availability in the summer, which could especially affect the August leaf OR. Total above-ground OR is dominated by the extremely stable stem OR and shows little variation (1.070 ± 0.02) throughout the two sampling years, even when facing extreme events.

Investigation of heat transfer during evaporation of droplets of Fe3O4 nanofluids from biphilic surfaces

In this work, unique biphilic substrates were prepared with a sharp spatial gradient of the contact angle of wetting. Experimental studies of the process of evaporation of liquid droplets lying on the structured surfaces have been carried out. In the experiment, the dynamics of the temperature of an evaporating droplet was compared depending on its orientation in space. It was found that suspended droplets of 0.1 wt % Fe3O4 nanofluid have a higher evaporation temperature and a higher evaporation rate as compared to sessile droplets.