Water erosion governs soil carbon reserves and distribution across the watershed or ecosystem. The dynamics of dissolved organic carbon (DOC) under water erosion in red agricultural soil is not ...clear. To determine the effect of tillage management and water erosion on vertical and lateral transportation of soil organic carbon (SOC) and DOC production under distinct rainfall intensities in the hilly red soil region of southern China, a chisel tillage plot with low rainfall intensity (CT-L) and two no-tillage plots with high (NT-H) and low rainfall intensity (NT-L) studies were conducted. Soil samples were collected from 0–5, 5–10, 10–20, and 20–40cm soil layers from triplicate soil blocks pre- and post-rainfall for determining concentration of SOC and DOC. Runoff samples were collected at every 6min for determining concentration of DOC and sediments during rainfall simulations on runoff plots (2m×5m) with various intensities. No fertilizer was applied in any plots. Results clearly show that runoff volumes, sediments and SOC entrained with sediment, and laterally mobilized DOC were significantly larger on NT-H compared to other plots, coinciding with changes in rainfall intensity; and the extent of roughness of the plot surface (CT vs. NT) was the variation in runoff DOC concentration. During the simulated rainfall events, DOC exports average 0.76, 0.64, and 0.27gCm−2h−1; SOC exports average 3.52, 1.08, and 0.07gm−2h−1 in the NT-H, NT-L, and CT-L soils, respectively. The maximum export of DOC was obtained under a high intensity rainfall plot, which lagged behind maximum runoff volumes, sediments, and SOC losses with sediment. Export of DOC was proportional to SOC content of soil loss. The least DOC losses in surface runoff and SOC losses with sediment were observed in CT-L plots. Vertical DOC mobilization achieved its maximum with low intensity rainfall under CT treatment. The DOC did not accumulate at the soil surface and was distributed mainly in the second and third soil horizons. The distribution of DOC content down the soil profile increased compared to pre-rainfall, except for subplots E at NT-H and NT-L. Results indicate that rainfall significantly increased DOC content in experimental plots. The SOC content of sediment leaving the erosion zone was significantly correlated with overland flow volume and soil loss. These observations lead to the conclusion that soil erosion is an important factor controlling the export of dissolved organic carbon.
•Lateral transport of DOC was affected by rainfall intensity in no tillage.•Content of DOC down the soil profile increases after rainfall simulation.•Losses of DOC with runoff and SOC with sediment decline due to chisel till plots.
Afforestation has the potential to elevate soil organic carbon (SOC) stocks, but water erosion would negatively impact such SOC increase. To evaluate the dynamics of SOC and total soil nitrogen (TSN) ...stocks in planted forest catchment in a subtropical region with mean annual precipitation of 1398mm, ranging from 1200 to 1500mm, we measured the inventories of 137Cs, SOC and TSN in five planted forest stands with slope gradients of 10–30%. Results showed that the afforestation systems have experienced appreciable net erosion, while different tree species exerted distinct effects on water erosion intensity and the stocks of SOC and TSN. Masson pine plantations were most susceptible to erosion with the highest average soil losses of 4.15±1.25Mgha−1yr−1. Although erosion occurred under afforestation, the soil illustrated large and significant gains of SOC and TSN stocks in the upper 0–10cm of soil depth (P<0.05). In contrary, soil in the deposition site had the highest SOC and TSN stocks (P<0.05) in layers below 10cm of soil depth. Under Masson pine stands, the lowest accretions of SOC and TSN stocks were observed in the upper 10cm of soil depth with average gains of 0.3MgCha−1 and 0.6MgNha−1, respectively. In the upper 20cm of soil, C:N ratio was significantly greater (P<0.05) in forest stands than that in the deposition site. In conclusion, afforestation had a crucial effect on elevating SOC and TSN stocks in the study watershed, but planting of Masson pine is not an optimal choice in terms of soil loss and carbon sequestration. To maximize the net carbon sequestration and effectively control water erosion, terracing or straw mulching in forest plantations should be implemented.
Abstract
While secondary mass inferences based on single-lined spectroscopic binary (SB1) solutions are subject to
sin
i
degeneracies, this degeneracy can be lifted through the observations of ...eclipses. We combine the subset of Gaia Data Release 3 SB1 solutions consistent with brown dwarf-mass secondaries with the Transiting Exoplanet Survey Satellite (TESS) Object of Interest (TOI) list to identify three candidate transiting brown dwarf systems. Ground-based precision radial velocity follow-up observations confirm that TOI-2533.01 is a transiting brown dwarf with
M
=
72
−
3
+
3
M
Jup
=
0.069
−
0.003
+
0.003
M
⊙
orbiting TYC 2010-124-1 and that TOI-5427.01 is a transiting very low-mass star with
M
=
93
−
2
+
2
M
Jup
=
0.088
−
0.002
+
0.002
M
⊙
orbiting UCAC4 515-012898. We validate TOI-1712.01 as a very low-mass star with
M
=
82
−
7
+
7
M
Jup
=
0.079
−
0.007
+
0.007
M
⊙
transiting the primary in the hierarchical triple system BD+45 1593. Even after accounting for third light, TOI-1712.01 has a radius nearly a factor of 2 larger than predicted for isolated stars with similar properties. We propose that the intense instellation experienced by TOI-1712.01 diminishes the temperature gradient near its surface, suppresses convection, and leads to its inflated radius. Our analyses verify Gaia DR3 SB1 solutions in the low Doppler semiamplitude limit, thereby providing the foundation for future joint analyses of Gaia radial velocities and Kepler, K2, TESS, and PLAnetary Transits and Oscillations light curves for the characterization of transiting massive brown dwarfs and very low-mass stars.
Background
Misinformation about COVID-19 on social media has presented challenges to public health authorities during the pandemic. This paper leverages qualitative and quantitative content analysis ...on cross-platform, cross-national discourse and misinformation in the context of COVID-19. Specifically, we investigated COVID-19-related content on Twitter and Sina Weibo—the largest microblogging sites in the United States and China, respectively.
Objective
Using data from 2 prominent microblogging platform, Twitter, based in the United States, and Sina Weibo, based in China, we compared the content and relative prevalence of misinformation to better understand public discourse of public health issues across social media and cultural contexts.
Methods
A total of 3,579,575 posts were scraped from both Sina Weibo and Twitter, focusing on content from January 30, 2020, within 24 hours of when WHO declared COVID-19 a “public health emergency of international concern,” and a week later, on February 6, 2020. We examined how the use and engagement measured by keyword frequencies and hashtags differ across the 2 platforms. A 1% random sample of tweets that contained both the English keywords “coronavirus” and “covid-19” and the equivalent Chinese characters was extracted and analyzed based on changes in the frequencies of keywords and hashtags and the Viterbi algorithm. We manually coded a random selection of 5%-7% of the content to identify misinformation on each platform and compared posts using the WHO fact-check page to adjudicate accuracy of content.
Results
Both platforms posted about the outbreak and transmission, but posts on Sina Weibo were less likely to reference topics such as WHO, Hong Kong, and death and more likely to cite themes of resisting, fighting, and cheering against coronavirus. Misinformation constituted 1.1% of Twitter content and 0.3% of Sina Weibo content—almost 4 times as much on Twitter compared to Sina Weibo.
Conclusions
Quantitative and qualitative analysis of content on both platforms points to lower degrees of misinformation, more content designed to bolster morale, and less reference to topics such as WHO, death, and Hong Kong on Sina Weibo than on Twitter.
•Yak grazing exerted a negative effect on soil C, N, P and a positive on K stocks.•P and K may limit for soil carbon and nitrogen sequestrations in the alpine meadow.•SOC losses based on the ...conventional method in grazed soils might be overestimated.•Fencing led to soil particles heterogeneity and those silts may sequester nutrients.•Fencing as a restoration tool for alpine meadows to sustain high SOC and TN stocks.
The effects of yak grazing on C and N below-ground pools were evaluated by comparing five grazing-excluded sample site pairs (5 years of grazing exclusion) at the Eastern edge of the Qinghai–Tibetan Plateau. Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), bulk density, pH and soil particle size fractions were analyzed in these samples taken at a depth of 10cm. Our results showed TK stock and bulk density had increasing trends with grazing activity. pH presented a slight increase, but the differences were not significant. On the contrary, SOC, TSN and TP stocks declined in grazing plots (P<0.05) and respectively decreased by 32.9%, 27.4%, and 10.5%, while TK stocks increased by 6.8%. P may become limited elements over time owing to an imbalance of inputs and outputs. Elemental stocks calculated by the equivalent mass method indicated the reported SOC losses based on the conventional method might be overestimated and that sampling depth of 7.64cm rather than same with sampling depth for grazing-excluded site (10cm) should be applied for grazing site if conventional method is used to calculate carbon stock. The soil silt content in grazing-excluded sites was greater than that in grazed zones (P<0.05), whilst greater soil specific surface areas were also found in the grazing-excluded sites, indicating that manual fencing led to heterogeneous distribution of soil particles and those silts may play a primary role in nutrient stocks in this region.
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Dopamine (DA), a simplified mimic of mussel proteins, can be employed as a reductant in the preparation of Au nanoparticles (AuNPs) due to its inherent catechol building block. The ...widely accepted mechanism of AuNP formation using DA as the reductant assumes that the reduction of Au(III) ions involves the two-electron oxidation of DA, where the corresponding phenol and phenolates serve as the reductive species to yield quinone. We herein report a novel insight into the mechanism of formation of AuNPs using DA as the reductant. We demonstrate that the synthesis of AuNPs requires the prior oxidation of the DA to form quinone units, which then catalyze the formation of semiquinones. These semiquinone radicals (SMQs) reduce the Au(III) ions to form the initial AuNPs, and further growth is then catalyzed by the first AuNPs, with nucleation occurring where the SMQs, phenols, and phenolates can serve as reductive species. In addition, DA oxidizes and polymerizes to form a polydopamine capping layer on the AuNPs. We therefore expect that the novel mechanism proposed herein may promote us to furthermore explore the production of noble metal NPs using other polyphenols.
The vertical and horizontal movement of water extractable organic carbon (WEOC) has a significant influence on soil organic carbon (SOC) storage and water quality. However, how the amount, components ...and chemical qualities of WEOC change at horizontal and vertical levels, as well as desorption in the cascade model in subtropical red soils, are not fully understood. We sampled soils from four types of land (Elaeocarpus, Masson Pine, Crape‐Myrtle and a deposition site) in a subtropical catchment as replicated cores (n = 96) and investigated changes in the molecular and structural constituents of WEOC using excitation‐emission matrix fluorescence and UV–visible absorbance spectroscopy. Our results showed that WEOC concentration changed remarkably in all four plots, and that the concentration coupled with the relative abundance of aromatic compounds decreased with increasing soil depth, whereas low‐molecular‐weight materials increased with increasing soil depth. Five fluorescent components were identified by parallel factor analysis (i.e., tryptophan‐like, tyrosine‐like and three humic‐substance‐like components). The relative abundance of these components suggested that WEOC composition shifted along vertical soil layers. Dynamic variations in fluorescent indices indicated that WEOC from the subsoil has strong biological characteristics. Additionally, there was no significant correlation between WEOC and SOC in subsoil, indicating that much of the WEOC within mineral soils is of local microbial origin rather than from local soil organic matter. Sorption processes alone or stepwise exchange processes of WEOC on the soil minerals do not readily occur, as the red soil in a subtropical area is typically unsaturated and potentially has a large sorption capacity. Once soil carbon is adsorbed, it is difficult to release it into soil water by microbial processing. Data from the deposition site suggest that components of hydrophilic WEOC with low molecular weight are preferentially transported.
