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A longitudinal analysis of collapsibility with predictions over the southeastern Loess Plateau in China.

ABSTRACT: Loess presents very unique collapsible behaviour due to its special under-compactness, weak cementation and porousness. Many environmental issues and geological hazards including subgrade subsidences, slope collapses or failures, building cracking and so on are directly caused by the collapsible deformation of loess. Such collapsible behaviour may also severe accidents due to sinkholes, underground caves or loess gullies. Moreover, with the increasing demand of construction and development in the loess areas, an in-depth research towards effective evaluation of loess collapsibility is urged. Currently no studies have made attempts to explore a rather complete and representative area of Loess Plateau. This paper thus provides a novel approach on spatial modelling over Jin-Shan Loess Plateau as an extension to experimental studies. The in-lab experiment results have shown that shown that the porosity ratio and collapsibility follow a Gaussian distribution and a Gamma distribution respectively for both sampling areas: Yan'an and Lv Liang. This establishes the prior intuition towards spatial modelling which provides insights of potential influential factors on loess collapsibility and further sets a potential direction of the loess studies by considering an extra dimension of spatial correlation. Such modelling allows robust predictions taken into account of longitudinal information as well as structural parameters and basic physical properties. Water contents, dry densities, pressure levels and elevations of samples are determined to be statistically significant factors which affect the loess collapsibility. All regions in Lv Liang area are at risk of high collapsibility with average around 0.03, out of which roughly a third of them are predicted to be at high risk. Clear spatial patterns of higher expected collapsibility in the southwest comparing to the northeast are shown adjusting for influential covariates. On reference guidelines for potential policy makings, county-level regions with the highest expected loess collapsibility are also identified.

SUBMITTER: Zheng Z

PROVIDER: S-EPMC8664886 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSoil compaction can be mitigated by deep tillage and subsoiling practices following a long period of no-tillage. Fallow tillage rotation methods are frequently used to improve water availability in the soils of the southeastern Loess Plateau region of China. Rhizosphere soil bacteria are ecologically important for the transformation of matter and energy in the plant root system and can be influenced by tillage rotation treatments. However, the effect of tillage rotations on the bacterial community and structure of rhizosphere soil is not well understood.MethodsA two-year field experiment was conducted with four tillage rotation treatments, including subsoil-subsoil (SS-SS), subsoil-deep tillage (SS-DT), deep tillage-deep tillage (DT-DT), and the control treatment of no-tillage-no-tillage (NT-NT). Our study was conducted during wheat's fallow period to investigate the abundance, diversity, and functions of rhizosphere soil bacteria using high-throughput sequencing technology.ResultsOur results showed that tillage rotation methods significantly influenced the bacterial diversity and composition of the rhizosphere soil in the plough layer (20-40 cm depth) by altering the moisture content of the soil. The metabolism, environmental information processing, and genetic information processing of the bacteria in the rhizosphere soil were affected. The most abundant phyla across all samples were Proteobacteria, Actinobacteria, Acidobacteria, Planctomycetes, Bacteroidetes, Gemmatimonadetes, Frimicutes, Chloroflexi, Nitrospirae, and Verrucomicrobia, which are classic bacterial decomposers in soil. The bacterial diversity and composition was similar for treatments causing higher soil perturbation (SS-DT and DT-DT), which disrupted the balance between aerobic and anaerobic bacteria. The less disruptive tillage methods (SS-SS and NT-NT), preserved the integrity of the soil bacteria. However, the NT-NT treatment may have led to soil compaction, particularly in the 20-40 cm layer. These results suggested that SS-SS was the most effective tillage rotation practice to accumulate soil moisture, maintain the balance between aerobic and anaerobic bacteria, and to enhance the metabolic capacity of rhizosphere soil bacteria. This method may have a significant impact on the sustainable development and farming practices of dryland agriculture.

Project description:BACKGROUND:Visceral leishmaniasis (VL) was one of the most important parasitic diseases in China, caused by Leishmania protozoans and transmitted by sand flies. Recently VL cases have reappeared in China, including the extension region of the Loess Plateau. The purpose of this study was to collect fundamental data on the host-vector VL system in the Loess Plateau to assist in the development of prevention and control measures. METHODS:Sand flies were collected by light traps from rural areas in Shanxian, Henan, China in 2015, as well as in Wuxiang and Yangquan, Shanxi, China in 2017. The blood sources of sand flies were analyzed by PCR detecting the host-specific mitochondrial cytochrome b (mtDNA cyt b) gene fragments. Leishmania infection in sand flies was detected by amplifying and sequencing ribosomal DNA internal transcribed spacer 1 (ITS1). The Leishmania specific antibodies in the sera of local dogs were detected by ELISA kit. RESULTS:Blood sources showed diversity in the extension region of the Loess Plateau, including human, chicken, dog, cattle, pig and goat. Multiple blood sources within a sand fly were observed in samples from Yangquan (17/118, 14.4%) and Wuxiang (12/108, 11.1%). Leishmania DNA was detected in sand flies collected from Yangquan with minimum infection rate of 1.00%. The ITS1 sequences were conserved with the Leishmania donovani complex. The positive rate of Leishmania specific antibodies in dogs was 5.97%. CONCLUSIONS:This study detected the blood sources and Leishmania parasites infection of sand flies by molecular methods in the extension region of Loess Plateau, China. A high epidemic risk of leishmaniasis is currently indicated by the results as the infection of Leishmania in sand flies, the extensive blood sources of sand flies including humans, and positive antibody of Leishmania in local dog sera. Given the recent increase of VL cases, asymptomatic patients, dogs and other potential infected animals should be screened and treated. Furthermore, the density of sand flies needs to be controlled and personal protection should be strengthened.

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A longitudinal analysis of collapsibility with predictions over the southeastern Loess Plateau in China.

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