A first-principles study of the structural, electronic and elastic properties of the FeO2-FeO2He system under high pressure.

The origin of the wave velocity anomalies at the core-mantle boundary (CMB) has been controversial. The primordial helium reservoir in the deep lower mantle remains elusive even with geochemical evidence for its existence. Here, we calculated the density and wave velocity of the FeO2-FeO2He system under the CMB conditions using first principles. The FeO2 and FeO2He of pyrite-type can exist stably under the CMB conditions without melting, and the incorporated helium increases the stability of the system. The electrical properties of FeO2 and FeO2He are not related to pressure. Doped helium reduces the density of the system but increases the elastic modulus. Our results suggest that FeO2 can be used as a viable material composition of ultra-low velocity zones (ULVZs), and FeO2He can explain the D'' seismic discontinuity instead of ULVZs. The primordial helium reservoir possibly formed by the accumulation of FeO2He, the only stable solid helium-bearing compound under the CMB conditions, may coincide with the location of the D'' layer.

[Mangrove forest fragmentation and its ecological service value in Tongming Sea of Zhanjiang, Guangdong, China during 2000-2018]. / 2000­2018å¹´æ¹›æ±Ÿé€šæ˜Žæµ·çº¢æ ‘æž—ç ´ç¢ŽåŒ–åŠç”Ÿæ€æœåŠ¡ä»·å€¼.

Mangrove forest has high ecological service value. Due to the destruction of human activities, mangrove forest has been greatly reduced and seriously fragmented, resulting in huge losses in the ecological service value. In this study, taking the mangrove forest in Tongming Sea of Zhanjiang as an example, we analyzed the characteristics of mangrove forest fragmentation and its ecological service value based on high-resolution distribution data from 2000 to 2018, and put forward suggestions for mangrove restoration. The results showed that the area of mangrove forest decreased by 1415.33 hm2 from 2000 to 2018, and the reduction rate (78.63 hm2·a-1) ranked the first among mangrove forests in China. The patch number and average patch size of mangrove forest changed from 283 and 1002 hm2 in 2000 to 418 and 341 hm2 in 2018, respectively. The largest patch in 2000 became twenty-nine small patches in 2018, with obvious fragmentation and poor connectivity. The total edge, edge density and mean patch size of mangrove forest were the main influencing factors for its service value. The landscape ecological risk of mangrove forest increased, the fragmentation rate in Huguang Town Region and the middle of the west coast of Donghai Island was faster than that in the other regions. During the study, the mangrove itself sevice value decreased by 1.35 billion yuan, and its ecosystem service value decreased by 1.45 billion yuan, especially for the significant reduction of regulation and support services. The mangrove forest in Tongming Sea of Zhanjiang urgently need to be restored and protected. It is necessary to implement protection and regeneration plans for vulnerable mangrove patches (such as 'Island'). The effective methods were to return the pond to forest and beach afforestation. In summary, our results could provide important references for local government to carry out mangrove forest restoration and protection, and realize the sustainable development of mangrove forest.

[Analysis of Heavy Metal Sources in Groundwater and Assessment of Health Risks: An Example from the Southwest Sub-basin of the Shiqi River].

In order to explore the sources of pollution and health risk profile of heavy metal elements in groundwater, 41 sets of representative groundwater samples from the southwest sub-basin of the Shiqi River were examined for 10 heavy metal elements (As, Cr, Cd, Al, Cu, Zn, Ni, Co, Mn, and Hg), and correlation analysis and principal component analysis were used to resolve the possible sources of heavy metal contamination in groundwater in the study area. The concentration characteristics and health risk levels of the 10 heavy metals were assessed using the single-factor contamination index (Pi), the Nemerow comprehensive contamination index (PN), and the health risk model. The results showed that:① the average values of heavy metal elements of the groundwater in the study area all met the limit of the class Ⅲ water standard in the quality standard for groundwater (GB/T 14848-2017); only the maximum value of Al was exceeded, followed by a large variation in the concentrations of Al, Mn, and Cr. The heavy metal element with the largest average contribution was Al (65.74%). ② The results of the single-factor contamination index evaluation showed that only the heavy metal element Al exceeded the cleaning level, and the results of the Nemerow comprehensive contamination index evaluation showed that the study area was basically at low pollution levels, and the quality of groundwater was good. ③ The results of the multivariate statistical analysis showed that Zn, Co, and Mn were from mixed sources consisting of geological formation and domestic waste; Al, As, and Cu were from agricultural sources; Cd, Cr, and Ni were from industrial sources; and Hg came from long-range atmospheric transport. ④ The health risk values for all heavy metals in the study area were within acceptable limits, with higher health risk values for children than for adults from the drinking water route, lower health risk values than in adults from the dermal route, and higher health risk values for heavy metals from the drinking water route than those from the dermal route, indicating that the drinking water route was the main route of exposure to heavy metals.

[Multi-scenario Land Use Optimization and Carbon Storage Assessment in Northwest China].

Land use/cover change (LUCC) is the main factor leading to the change in carbon stock of terrestrial ecosystems. Studying the process of land use and carbon storage change under different scenarios in the future will help to formulate scientific land use policies and increase regional terrestrial ecosystem carbon storage. The GMMOP-PLUS-InVEST model was constructed to analyze the change characteristics of land use and carbon storage in northwest China from 2000 to 2020 through multi-source data and to predict the land use and carbon storage in northwest China in 2030 under the scenarios of natural development (ND), economic development (ED), ecological protection (EP), and comprehensive development (CD). The results showed that:①from 2000 to 2020, the area of grassland decreased by 1680.99×104 hm2, and the area of cultivated land, forest land, water area, wetland, construction land, and unused land increased by 201.19×104, 208.47×104, 91.54×104, 51.30×104, 157.40×104, and 971.09×104 hm2, respectively. ②From 2000 to 2020, soil and underground carbon storage decreased, dead organic matter and aboveground carbon storage increased, and total carbon storage decreased by 677.97×106 t. Grassland degradation was the main reason for the decrease in carbon storage. ③Compared to that in 2020, the total carbon storage in the ND scenario was reduced by 63.12×106 t, and the total carbon storage in the ED, EP, and CD scenarios increased by 759.19×106, 804.57×106, and 817.89×106 t, respectively; the CD scenario was the optimal development model. These results can provide a reference for regional land use planning and the increase of terrestrial ecosystem carbon storage.

Health Risk Assessment Based on Source Identification of Heavy Metal(loid)s: A Case Study of Surface Water in the Lijiang River, China.

In this study, 24 surface water samples were collected from the main trunk/tributary of the Lijiang River during the wet season (April) and the dry season (December) in 2021. The total concentration of 11 heavy metal(loid)s (Al, Cu, Pb, Zn, Cr, Ni, Co, Cd, Mn, As, and Hg) was determined to investigate their physicochemical properties and spatial-temporal distribution characteristics. The heavy metal evaluation index (HEI) and the positive matrix factorization (PMF) model were employed to evaluate water quality and to reveal quantitatively identified pollution sources for further investigation to obtain a health risk assessment using the hazard index (HI) and carcinogenic risk (CR) of various pollution sources. The mean concentrations of heavy metal(loid)s in surface water in the wet and dry seasons were ranked as: Al > Mn > Zn > Ni > Cd > Cr > Cu > As >Hg = Pb > Co, with the mean concentration of Hg being higher than the national Class II surface water environmental quality standard (GB3838-2002). In terms of time scale, the concentration of most heavy metal(loid)s was higher in the wet season; most heavy metal(loid)s were distributed mainly in the midstream area. HEI index indicated that the main water quality status was "slightly affected" in the study area. Five potential sources of pollution were obtained from the PMF model, including industrial activities, traffic sources, agricultural activities, domestic waste emissions, and natural resources. The source-oriented risk assessment indicated that the largest contributions of HI and CR were agricultural sources in the Lijiang River. This study provides a "target" for the precise control of pollution sources, which has a broad impact on improving the fine management of the water environment in the basin.

[Evaluation of Heavy Metal Content, Sources, and Potential Ecological Risks in Soils of Southern Hilly Areas].

In order to explore the characteristics of soil heavy metal pollution and ecological risk status in southern hilly areas, a hilly area of a southern province was selected as the research area, using soil samples collected at 60 points in 2017. The single factor pollution index (Pi), Nemero comprehensive pollution index, and potential ecological risk index (RI) were used to evaluate the content characteristics and potential ecological risks of eight heavy metal elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn), and positive definite matrix factor analysis models (PMF) were used to analyze their sources of pollution. The results were as follows:① the content of eight heavy metal elements in the study area exceeded the standard, and the Nemeiro comprehensive pollution index showed that the proportions of light, moderate, and heavy pollution in the study area were 63%, 8%, and 2%, respectively. Unpolluted and lightly polluted samples accounted for 27% and were thus basically lightly polluted. ②The comprehensive potential ecological risk index showed that the RI of soil heavy metals was 39.58-224.15, the proportions of samples with low and medium ecological risks were 73.33% and 25%, respectively, and the proportion of sites with severe ecological risks was 1.67%. Although this site had the highest ecological risk, the content of heavy metals was lower than the background value of soil elements in the province. ③Six pollution sources were obtained through the PMF model:natural sources, agricultural activity sources, mixed sources composed of copper mining and transportation, industrial activity sources, transportation sources, and domestic waste emission sources. The contribution rates of each source were 24.8%, 17.7%, 17.7%, 17.6%, 12.0%, and 10.2%, respectively.

[Spatial and Temporal Distribution and Pollution Evaluation of Soluble Heavy Metals in Liujiang River Basin].

In the Liujiang River, soluble heavy metals Zn, Al, Co, As, Ni, Cr, Cu, Mn, Pb, Hg, and Cd were monitored day and night to determine their temporal and spatial distribution as well as the sources of this pollution. The Nemerow comprehensive pollution index method was then used to evaluate the environmental quality of the Liujiang River water body. The results showed that: ① For each river section (Lutang and Luowei), the amounts of soluble Al, Co, As, Ni, Cr, Mn, Pb, and Cd all met the Class Ⅲ water quality standard limit, as defined in the National Surface Water Quality Class Ⅲ Standard. The concentration of Zn and Cu was far below the standard limit, while the Hg content slightly exceeded the standard; the concentration of heavy metals in Liujiang River basin was highest in the normal season and lowest in the wet season. In terms of spatial distribution, the Luowei section had a higher heavy metal concentration. ② The single factor pollution indexes for elemental Hg, Cd, and As were higher in the Liujiang River basin. The Nemerow comprehensive pollution index evaluation shows that the risk of heavy metal pollution in the water body exhibits certain seasonal variations (March > November > June), indicating that rainfall in different seasons may result in reduced drinking water safety in the study area. The water of the Lutang and Luowei sections generally exhibited a moderate level of heavy metal pollution. The comprehensive pollution index of the Luowei section was higher than that of the Lutang section, and the pollution level was relatively severe. Therefore, the Luowei section should be listed as a priority control section of the Liujiang River basin by the water environment management department; ③ After assessing the difference in heavy metal pollution between annual and monthly rainfall periods, it was found that the selection of rainy season or conventional season has no significant impact on the assessment of heavy metal pollution in rivers, when the mass concentration of Cu in the river is used. However, the presence of As, Mn, Pb, Al, Cr, and Ni elements in the river will cause significant differences in the evaluation of heavy metal pollution on an interannual scale; ④ Multivariate statistical analysis results show that Cd, Cr, Ni, Co, and Pb in the Liujiang River are mainly derived from industrial production activities; As and Zn are mainly derived from rainwater leaching of domestic pollution waste; Mn, Al, and Cu are mainly derived from the application of pesticides and fertilizers.

Effects of stand age on carbon storage in dragon spruce forest ecosystems in the upper reaches of the Bailongjiang River basin, China.

At an ecosystem level, stand age has a significant influence on carbon storage (CS). Dragon spruce (Picea asperata Mast.) situated along the upper reaches of the Bailongjiang River in northwest China were categorized into three age classes (29-32 years, Y1; 34-39 years, Y2; 40-46 years, Y3), and age-related differences in total carbon storage (TCS) of the forest ecosystem were investigated for the first time. Results showed that TCS for the Y1, Y2, and the Y3 age groups were 323.64, 240.66 and 174.60 Mg ha-1, respectively. The average TCS of the three age groups was 255.65 Mg C ha-1, with above-ground biomass, below-ground biomass, litter, and soil in the top 0.6 m contributing 15.0%, 3.7%, 12.1%, and 69.2%, respectively. CS in soil and TCS of the Y1 age group both significantly exceeded those of the Y3 age group (P < 0.05). Contrary to other recent findings, the present study supports the hypothesis that TCS is likely to decrease as stand age increases. This indicates that natural resource managers should rejuvenate forests by routinely thinning older stands, thereby not only achieving vegetation restoration, but also allowing these stands to create a long-term carbon sink for this important eco-region.