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Slope units (SUs) are sub-watersheds bounded by ridge and valley lines. A slope unit reflects the physical relationship between landslides and geomorphological features and is especially useful for landslide sensitivity modeling. There have been significant algorithmic advances in the automatic delineation of SUs. But the intrinsic difficulties of determining input parameters and correcting for unreasonable SUs have hindered their wide application. An improved method of the evaluation and local multi-scale optimization for the automatic extraction of SUs is proposed. The Sus' groups more consistent with the topographic features were achieved through a stepwise approach from a global optimum to a local refining. First, the preliminary subdivisions of multiple SUs were obtained based on the r.slopeunit software. The optimal subdivision scale was obtained by a collaborative evaluation approach capable of simultaneously measuring objective minimum discrepancies and seeking a global optimum. Second, under the selected optimal scale, unreasonable SUs such as over-subdivided slope units (OSSUs) and under-subdivided slope units (USSUs) were further distinguished. The local average similarity (LS) metric for each SU was designed based on calculating the SU's area, common boundary and neighborhood variability. The inflection points of the cumulative frequency curve of LS were calculated as the distinguishing intervals for those unrealistic SUs by maximum interclass variance threshold. Third, a new effective optimization mechanism containing the re-subdivision of USSUs and merging of OSSUs was put into effect. We thus obtained SUs composed of terrain subdivisions with multiple scales, which is currently one of the few available methods for non-single scales. The statistical distributions of density, size and shapes demonstrate the excellent performance of the refined SUs in capturing the variability of complex terrains. Benefiting from the sufficient integrating approach of diverse features for each object, it is a significant advantage that the processing object can be transferred from general entirety to each precise individual. [ABSTRACT FROM AUTHOR]

Outburst floods resulting from giant landslide dams can cause devastating damage to hundreds or thousands of kilometres of a river. Accurate and timely delineation of flood inundated areas is essential for disaster assessment and mitigation. There have been significant advances in flood mapping using remote sensing images in recent years, but little attention has been devoted to outburst flood mapping. The short-duration nature of these events and observation constraints from cloud cover have significantly challenged outburst flood mapping. This study used the outburst flood of the Baige landslide dam on the Jinsha River on 3 November 2018 as an example to propose a new flood mapping method that combines optical images from Sentinel-2, synthetic aperture radar (SAR) images from Sentinel-1 and a Digital Elevation Model (DEM). First, in the cloud-free region, a comparison of four spectral indexes calculated from time series of Sentinel-2 images indicated that the normalized difference vegetation index (NDVI) with the threshold of 0.15 provided the best separation flooded area. Subsequently, in the cloud-covered region, an analysis of dual-polarization RGB false color composites images and backscattering coefficient differences of Sentinel-1 SAR data were found an apparent response to ground roughness's changes caused by the flood. We carried out the flood range prediction model based on the random forest algorithm. Training samples consisted of 13 feature vectors obtained from the Hue-Saturation-Value color space, backscattering coefficient differences/ratio, DEM data, and a label set from the flood range prepared from Sentinel-2 images. Finally, a field investigation and confusion matrix tested the prediction accuracy of the end-of-flood map. The overall accuracy and Kappa coefficient were 92.3%, 0.89 respectively. The full extent of the outburst floods was successfully obtained within five days of its occurrence. The multi-source data merging framework and the massive sample preparation method with SAR images proposed in this paper, provide a practical demonstration for similar machine learning applications using remote sensing. [ABSTRACT FROM AUTHOR]

The El Niño-Southern Oscillation (ENSO) is the principal climatic system in the modern Pacific Ocean, and it potentially influences the global climate. The South China Sea (SCS), in the western tropical Pacific, is significantly affected by ENSO activity. We have conducted a high-resolution oxygen isotope study of the shells of one modern and four fossil Tridacna from the Xisha Islands in the SCS. The results for the modern sample reveal that the shells of Tridacna are a good proxy of ENSO variability. We used the results of the oxygen isotope composition of four fossil Tridacna to produce high-resolution records of ENSO activity during four time slices in the Holocene. The results indicate that ENSO variability in the early Holocene was comparable to that of today, and that a minimum in the frequency and intensity of ENSO activity occurred in the mid Holocene. These findings are consistent with paleoclimatic results from corals, mollusks and sedimentary records. However, the observed extremely low frequency and moderate ENSO intensity at 4.7 ka indicate an anomalous pattern of ENSO changes within this interval of climatic transition. In addition, seasonal temperature variations during the Holocene were different from those of today and extreme seasonality may also occur during warmer periods. [ABSTRACT FROM AUTHOR]

As an emerging environmental contaminant, di (2-ethylhexyl) phthalate (DEHP) is widely present in the aquatic environment, however, the effects and underlying mechanisms of DEHP on the aquatic organisms are poorly understood. This study systematically investigated the ecotoxicity induced by chronic exposure to environmental relevant concentrations of DEHP (0.03 mg/L, 0.1 mg/L, and 0.3 mg/L) on zebrafish brain. Results indicated that DEHP exposure significantly increased the levels of ROS and disturbance of the antioxidant enzymes activities in the brain, which may further enhance lipid peroxidation and DNA damage. Furthermore, acetylcholinesterase activity was first stimulated and inhibited by exposure to DEHP, and the antioxidant and apoptosis related genes were mainly upregulated. Risk assessment indicated that the ecotoxicity of DEHP on the zebrafish showed an "enhancement-reduction" trend as the exposure time was prolonged. Overall, these results provided new insights and useful information to ecological risk assessment and environmental management of DEHP pollution. • DEHP elevated the ROS levels and disturbed antioxidant homeostasis in zebrafish brain. • DEHP induced lipid peroxidation and DNA damage in brain of zebrafish. • DEHP caused hazardous effects on brain at the neural and genetic levels. • The ecotoxicological risk of DEHP to zebrafish brain first increased and then decreased with the increase of exposure time. [ABSTRACT FROM AUTHOR]

On Oct. 10 and Nov. 3, 2018, two landslides, i.e., the "10.10" and "11.3" rockslides, occurred successively at Baige Village, Jiangda County, Tibetan Autonomous Region, P. R. China. The two landslides are located in the upper reaches of the Jinsha River and both dammed the river. Immediately since the slides, the authors have been working on the slides and help disaster reduction. Based on the data collected by April 2020, this paper is aimed at clarifying the geological condition of the slides and at explaining why the slides occurred and what the whole sliding process was. Conclusions are summarized as follows. First, the two landslides occurred in the suture belt of the Jinsha River and the rocks are composed of tectonic mélange slices of mainly gneiss intermingled with carboniferous slate and marble and with intruded serpentine and granite porphyry. The gneiss generally bears a schistosity plane with an averaged attitude of N47° W/47°, dipping into the slope. Secondly, long-term geomorphological evolution of the bank slope due to river incision contributed to the progressive slope deformation for the development of the "10.10" rockslide. No preferential joints exist in the slope, but alteration and weathering played important roles in its occurrences. Rainfall and earthquakes may also accelerate its deformation. Thirdly, the "10.10" rockslide is of high-speed wedge-like slope failure with a high-position and a high-shear outlet. Its sliding and deposition process demonstrate special features as initial speed, collision between debris, surging waterjet, and second slipping. Fourthly, the whole process of the "10.10" rockslide can be divided into 6 steps, i.e., startup of the major sliding and sliding resistance zones, sliding initiation of the trailing zone, formation of debris-eroded zones, collision of debris and triggering waterjet and mist, secondary slip of the landslide dam, and surface flush in the deposition area. The estimated speed may reach as high as 67 m/s. Fifthly, the "11.3" rockslide follows a different mode, i.e., wedge cleaving effect. And finally, the cracked zones still have the risk to constitute a potential landslide and to dam the river again. [ABSTRACT FROM AUTHOR]

Lanzhou New District is the first and largest national-level new district in the Loess Plateau region of China. Large-scale land creation and rapid utilization of the land surface for construction has induced various magnitudes of land subsidence in the region, which is posing an increasing threat to the built environment and quality of life. In this study, the spatial and temporal evolution of surface subsidence in Lanzhou New District was assessed using Persistent Scatterer Interferometric Synthetic Aperture radar (PSInSAR) to process the ENVISAT SAR images from 2003-2010, and the Small Baseline Subset (SBAS) InSAR to process the Sentinel-1A images from 2015-2016. We found that the land subsidence exhibits distinct spatiotemporal patterns in the study region. The spatial pattern of land subsidence has evidently extended from the major urban zone to the land creation region. Significant subsidence of 0-55 mm/year was detected between 2015 and 2016 in the land creation and urbanization area where either zero or minor subsidence of 0-17.2 mm/year was recorded between 2003 and 2010. The change in the spatiotemporal pattern appears to be dominated mainly by the spatial heterogeneity of land creation and urban expansion. The spatial associations of subsidence suggest a clear geological control, in terms of the presence of compressible sedimentary deposits; however, subsidence and groundwater fluctuations are weakly correlated. We infer that the processes of land creation and rapid urban construction are responsible for determining subsidence over the region, and the local geological conditions, including lithology and the thickness of the compressible layer, control the magnitude of the subsidence process. However, anthropogenic activities, especially related to land creation, have more significant impacts on the detected subsidence than other factors. In addition, the higher collapsibility and compressibility of the loess deposits in the land creation region may be the underlying mechanism of macro-subsidence in Lanzhou New District. Our results provide a useful reference for land creation, urban planning and subsidence mitigation in the Loess Plateau region, where the large-scale process of bulldozing mountains and valley infilling to create level areas for city construction is either underway or forthcoming. [ABSTRACT FROM AUTHOR]

Air quality is a vital environment variable which determines spatial accumulation of soil heavy metals. It is very important to estimate the contribution of air quality for soil heavy metals in oil mining area. For the end, we collected 116 samples from surface soil of oil mining in the Yellow River Delta (YRD) of China, and analyzed the content of As, Cr, Ni, Pb, and Zn. Furthermore, 40 monitoring stations data of air quality were collected in study area, including CO, NO 2 , SO 2 , O 3 , PM 2.5 , and PM 10. Spatial estimation and mapping of heavy metals in soil were carried out by hybrid geostatistical models, including multiple linear regression-ordinary kriging (MLROK), support vector machine-ordinary kriging (SVMOK) and random forest-ordinary kriging (RFOK). RFOK exhibited the highest estimation accuracy (R2) for As (65.76%), Cr (77.85%), Ni (61.47%), Pb (74.64%), and Zn (71.35%) in comparison with other models. And relative R2 of RFOK improved 30%, while MLROK and SVMOK increased over 100% for Zn (RI o = 121.90% and RI o = 121.64%) based on their original R2 of machine learning models. In addition, mapping results by RFOK showed the high concentrations of heavy metals were focused in the central and northeastern (As), northern (Cr), northeastern and northwestern (Ni), central and eastern (Pb), and northern (Zn). Especially, compared with vegetation index and topographic factors, PM 2.5 is the highest driving variable for As (18.34%) and Zn (12.91%), and CO is the most important variable for Cr (18.22%), Ni (14.28%). The above results indicated that there is a mechanism of sources-receptor relationship between air quality and soil heavy metals, that is, oil well and factory in study area discharge heavy metal particles into the atmosphere, and then enter the soil through atmospheric deposition and precipitation. Enlightened by this study, variable selection should be focused on important sources for the accumulation of heavy metals in study area, who must take decisions to prevent and to early warn heavy metals pollution in mine soil. [Display omitted] • Air quality data are used to predict the content of heavy metals in oil mining soils. • Random forest-ordinary kriging has the best predicted performance for soil heavy metals. • The high concentrations of soil heavy metals are the northern of study area. • Air quality variables have effective feasibility for predicting soil heavy metals. • PM (for As and Zn) and CO (for Cr and Ni) is the highest driving variable. [ABSTRACT FROM AUTHOR]

• DEHP presented low acute toxicity to adult zebrafish (Danio rerio) • DEHP induced oxidative stress, lipid peroxidation and DNA damage in zebrafish hepatic tissue. • Acetylcholinesterase (AChE) activity of zebrafish liver was significantly inhibited after DEHP exposure. • The ecotoxicological risk of adult zebrafish increased with increasing DEHP concentrations. Di-(2-ethylhexyl) phthalate (DEHP) has become a ubiquitous contaminant in aquatic environments due to its increasing utilization in recent years. Although its environmental risks to aquatic organisms have attracted widespread attention, the ecotoxicological effects and toxic mechanism of DEHP on zebrafish (Danio rerio) liver remain poorly understood. Herein, this study investigated the acute toxicity, oxidative damage, neurotoxicity, and DNA damage of DEHP on zebrafish at the individual, tissue, physiological and biochemical levels. Results showed that no evident lethal effects of DEHP on zebrafish were observed in all testing concentrations. But in the chronic toxicity test (28 days), superoxide dismutase (SOD) and catalase (CAT) activities in zebrafish liver mainly increased during the pre-and mid-exposure experiment and subsequently decreased after 28 days exposure, whereas the acetylcholinesterase (AChE) activities were always inhibited. By comparison, reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione S-transferase (GST) levels generally increased throughout the experiment, indicating that DEHP enhanced oxidative stress lipid peroxidation, and cytotoxicity of zebrafish liver. DEHP induced DNA damage in hepatocyte, which was positively correlated with changes in ROS levels (0.9874 ≥ R2 ≥ 0.7374). Based on the risk assessment results, the integrated biomarker response (IBR) values were positively correlated with the DHEP concentrations, suggesting that higher DHEP concentrations may cause much more serious detrimental effects to zebrafish liver. Overall, this study is of great significance for understanding the ecotoxicity and mechanism of DEHP on zebrafish. [ABSTRACT FROM AUTHOR]