Isotope fractionation effect of organic pollutant transformation facilitates a deep understanding of reaction mechanism, and potentially contributes to risk assessment and remediation of contaminated environments. Hexachlorocyclohexanes (HCHs) had been used as pesticides for a long time. They have been classified as persistent organic pollutants (POPs) due to their stability in chemical properties and long half-life in the environment. In recent decades, significant advances were achieved in the isotope fractionation research of HCH transformation and in the isotopic analysis of environmental HCHs, reflecting the state-of-the-art theories and applications in this field. In this review, following a brief introduction to the phenomenon of isotopic fractionation and the compound specific isotope analysis (CSIA) technique, the isotopic effects of HCH transformation were discussed, with an emphasis on the applications of novel technologies, such as dual-element isotope analysis and enatioselectivity analysis. Subsequently, the uses of isotope fractionation in pollutant traceability, food chain transmission, transformation in soil-plant systems and natural attenuation assessment were presented. These progresses demonstrate the potential applications of isotope fractionation in risk assessment and clean-up of environmental organic pollutants.

China has a large area of sewage irrigation farmland which has partly caused heavy metal pollution, especially cadmium pollution. Aimed to understand the present advances of soil cadmium pollution in sewage irrigated farmland, based on the results of literature analysis software, the research progress at home and abroad from the overall perspective of soil-crop ecosystem has been summarized; the content characteristics, transport mechanism and pollution remediation of heavy metal of cadmium pollution in soil-crop ecosystem of sewage irrigated farmland have been reviewed. Highlights show that the cadmium in sewage irrigated farmland soil has the character of surface aggregation, but long-term sewage irrigation may lead to the migration of heavy metals to deeper soil layers. The enrichment degree of cadmium is different in different organs of the same crop and different crops, and there was no significant correlation between cadmium content in soil and crops in field experiment, so that it is urgent to carry out researches on safe utilization of farmland. Although several mathematical models have been used in the study of heavy metal cadmium transport in soil-crop ecosystem, a systematic and widely used model has not yet been formed due to the different conditions of irrigation time, irrigation amount and irrigation frequency. The prominent problems in the study on heavy metal cadmium in sewage irrigation farmland include unclear vertical distribution of cadmium pollution, unclear morphological changes during soil to crop migration, immature practical remediation technology, etc. In the future, researches should be focued on the quantification of the influencing factors of heavy metal cadmium accumulation in farmland soil-crop ecosystem, strengthening of investigation and monitoring of heavy metal cadmium in farmland deep soil, and exploring technologies for remediation and safe utilization of cadmium polluted sewage irrigated farmland.

Clarifying the relationship and interaction mechanisms of multiple ecosystem services can effectively improve the sustainable supply capacity of ecosystems. In this paper, 6 typical ecosystem services of Nanning City were estimated by InVEST model, the ecological service trade-off and synergy were analyzed by Moran's I index, and the different ecosystem service clusters were recognized by principal component factor analysis and clustering method. The results show that: (1) The patterns of 6 typical ecosystem services in Nanning present significant spatial heterogeneity and is high in suburban area but low in urban area, except for water yield. (2) There is synergy relationship between support and adjustment services, but both synergy and trade-off relationship are existing between supply and other services. (3) The ecosystem services are affected by common driving factors revealed by principal component factor 1 and 3, and its mutual inhibition are represented by principal component factor 2. (4) The following 5 typical ecosystem service clusters were discovered in Nanning by employing cluster analysis: the mountain ecological balance area, forest ecological conservation area, urban ecological fragile area, hilly cultivated area, and valley cultivated area. This research results can provide scientific basis for the land use optimization and the ecological health and sustainable development in Nanning City.

Rural settlement is the main habitation of rural population and the central place for social activities such as life and production. With the comprehensive promotion of rural revitalization, urban-rural integration development and migration and relocation in Qinling-Bashan Mountains, the spatial pattern of rural settlements has changed greatly. Taking Danfeng County of Shangluo City in Shaanxi Province in the east of Qinling Mountains as the research object in this paper. The settlement patches data of Danfeng County in 2010, 2015 and 2019 were extracted based on Google Earth historical images. Then the spatial-temporal dynamics of rural settlements spatial distribution pattern in Danfeng County were analyzed using the methods of landscape pattern spatial analysis, ArcGIS spatial analysis and kernel density, and the influencing factors of spatial distribution pattern of rural settlements in Danfeng County were further studied by using Geodetector models. The study results show that: (1) The numbers and the density of rural settlements in Danfeng County decreased from 2010 to 2019, but the area increased continuously, which indicate that the spatial expansion of rural settlements was obvious. (2) The spatial distribution density was high in the southwest and low in the northeast. The distribution of high-density core in the county was characterized by dispersion, diversity and weak continuity, the scope of high-density kernel gradually shrank and moved to the centers of the townships. The directivity of rural settlements along the gentle slopes of lowland and on both sides of river and roads was strengthened. (3)Terrain and other natural factors shaped the basic spatial pattern of rural settlements in the County, and the impact on the spatial evolution of rural settlements continued to strengthen. Location factors such as distance to traffic and river and social and economic factors such as population density are important driving forces to promote the spatial evolution speed and spatial distribution pattern of rural settlements. The study results may provide a theoretical basis for rural revitalization and optimal layout of settlement space in Danfeng County.

Based on survey data from 1 004 households in rural area of five cities in Hubei Province, the Ordered Probit Model was employed to explore the impact of social interaction on farmers' adoption of green technologies. With instrumental variable conditional mixed process estimation (CMP) to solve endogenous problems, conclusions have been drawn that: (1) Social interaction influences farmers' adoption of green technologies through endogenous interaction and situational interaction. By endogenous interaction, farmers could obtain relevant information and learn new knowledge, thus improving the confidence and skills of green technologies adoption. Situational interaction can improve farmers' enthusiasm to adopt green technologies through the demonstration effect. (2) In terms of technology heterogeneity, endogenous interaction extensively influences farmers' adoption of various green technologies, while situational interaction mainly affects their adoption of green farming and green pesticide application technology. (3) Rural households in hilly areas are more affected by social interaction than those in plain areas. Therefore, in promoting agricultural green technologies, full play should be given to the role of social interaction, the channels for farmers to obtain information should be broadened, and more attention should be paid to the radiation and driving role of science and technology demonstration households. Meanwhile, measures should be taken to create a good atmosphere and establish a social trust system.

To study the population structure and distribution pattern of Emmenopterys henryi in Ta-pieh Mountain at the south of Henan Province, a typical sample method was used to investigate the E. henryi population in Liankang Mountain Natural Reserve. The results show that: (1) The age structure of the E. henryi population showed a certain degree of skewness distribution, and the population structures in different plots were different. The population presented the common characteristics of small number of young individuals, concentrated number of middle aged individuals and lacking of big individuals. (2) The survival curve was close to the DeeveyⅠtype, such as low mortality and very few individuals at age Ⅰ and Ⅱ, but the mortality rates at age Ⅶ and Ⅷ were high resulting in the concave and breakpoint of the survival curve. Both individual survival number (a_x) and life expectancy (e_x) decreased with the increasing of diameter-class after age Ⅱ, e_x showed a certain fluctuation change with the increasing of diameter-class, suggesting a poor stability of the population. (3) The results of the analyses by using various coefficients and indices that the spatial pattern of the E. henryi population showed clumped distribution, while there were some differences in the clustering degree among different populations. (4) The E. henryi population in Liankang Mountain was generally in a disadvantageous habitat, and its ability to occupy ecological space in ecosystems was poor, so that, it is suggested to carry out seedling breeding and ex situ conservation to promote effective protection and healthy continuation of the endangered population.

Mangrove wetland is among the wetland ecosystems with the highest biodiversity and production. However, mangrove wetlands are facing serious ecological problems due to human activities and climate change, causing the loss of extend, degradation of ecosystem functions and decline in biodiversity. In this study, mangrove ecosystem health indicators were developed based on the vigor-organization-resilience (VOR) framework, and the health assessment of mangrove wetlands in Jiulong River Estuary (JRE) in South Fujian was performed. The reference standard for each indicator was determined by referring to current standards, history site conditions or range of indicator values within the study area. The weight of each indicator was determined by using expert consultation and the analytic hierarchy process (AHP), and the mangrove health comprehensive index (MHI) was then calculated. The overall MHI value of the JRE mangrove ecosystem was 0.72, indicating a sub-health state. The MHI value showed a spatial variation in the JRE mangrove. The highest MHI value was estimated in Datu Island, followed by Fugong and Haimen Island, and the lowest value was in Zini. The spatial variation in MHI was closely related to the differences in environmental characteristics, human disturbance, invasion degree of Spartina alterniflora, ecological protection and management efforts. Among the VOR components, the resilience value was higher than the organization and vigor values in JRE mangrove, and the mangrove was mainly characterized by low production and reproductive potential, high community diversity and resilience from disturbance, and high vegetation maturity and habitat suitability. At present, the invasion of S. alterniflora is the key threat to the health of the JRE mangrove ecosystem, which has directly or indirectly impacts on ecosystem production, structure and resilience. Therefore, the efforts on S. alterniflora clearance and control should be strengthened in JRE mangrove, to recover the mangrove and tidal flat habitats, to restore wetland bird habitats, to promote the natural restoration of biodiversity and the integrity and stability of the ecosystem as well.

Understanding the wintering habitat of waterbirds is important for their conservation. Eurasian Spoonbill (Platalea leucorodia) is a national gradeⅡ prorected wildlife species in China, few studies on distribution and protection of Eurasian Spoonbill (Platalea leucorodia) have been carried out recently in wintering grounds. The wintering habitat and suitable distribution habitat of Platalea leucorodia had been predicted by using MaxEnt model and ArcGIS software, with 13 environmental factors and 87 encountered sites recorded during the National Waterbird Simultaneous Survey of China in 2016. The results show that the total area for wintering habitat of Platalea leucorodia in China was estimated to be 106 621 km², including 22 197 km² of highly suitable, 30 185 km² of medium suitable, and 54 239 km² of low suitable habitats. Most of the habitats were concentrated in the middle and lower reaches of the Yangtze River, while few of these habitats were scattered in other regions. The distance to the water source, the precipitation of the driest quarter, the altitude, and the mean temperature of the driest quarter were the main factors affecting the wintering habitat selection of Platalea leucorodia. These four factors were found to contribute 85% of the impact on the habitat selection of the species. 245 nature reserves have been designated as the wintering habitats of the species which covering 27% of highly suitable habitats, 13% of medium suitable habitats and 8% of low suitable habitats. However there are still some conservation gaps that need a quality management perspective.

Amphibians are among the world's most threatened species, and the amphibian monitoring could provide the basic information for their protection. To find out the temporal and spatial pattern of amphibian diversity in Fujian Junzifeng National Nature Reserve, 12 line transects that distributing in three different habitats (stream, paddy field and artificial water channel) were selected, for the investigation of environmental data, species and number of amphibians in April, June and August 2018. Then nine diversity indexes were calculated to examine the difference of amphibian diversity in different habitats and different seasons. The results show that: (1) a total of 2 124 amphibians belonging to 22 species, 17 genera, 7 families and 1 order were observed; (2) Fejervarya multistriata, Microhyla heymonsi, Nidirana adenopleura, and Odorrana huanggangensis were the dominant species in all the line transects, and Hoplobatrachus chinensis, the national class Ⅱ protected animal, had been recorded in all seasons; (3) the Pearson correlation analysis show that air temperature, water temperature and humidity positively affected species richness, relative species abundance, and Shannon-Wiener index; (4) species richness, relative abundance, Shannon-Wiener index, Margalef index, F index, and G index in June were significantly higher than those in April, but only species richness, relative abundance, and G index were higher in August than those in April; (5) the G-F index was not influenced by habitat type and observation time.

In order to reveal the responses of bacterial community structure in coastal saline-alkali soil to the addition of different organic materials, field experiments were conducted to study the influences of the amendment of organic materials (straw, biochar and compost of cow manure) on bacterial community in coastal saline-alkali soil by high-throughput sequencing. The results show that compared with the control treatment, the contents of soil organic carbon, total nitrogen, available phosphorus and available potassium were all increased in the soil with the addition of organic materials. The α diversity analysis show that the addition of organic materials increased soil bacteria abundance and community diversity, and the highest bacterial abundance and community diversity were in the cow manure compost treatment and biochar treatments, respectively. Three months after the addition of organic materials, the dominant bacteria phyla were the same in the soil with or without organic materials, but the order and relative abundance of the dominant bacteria phyla were different obviously, especially for the top three dominant bacteria phyla. The dominant bacteria phyla in control treatment was Proteobacteria (29.23%)> Acidobacteria (22.52%)> Planctomycetes (13.62%)> Chloroflexi (9.7%). Compared with the control treatment, the soil with biochar significantly increased the relative abundance of Planctomycetes, which was 25.1%, while significantly reduced the relative abundance of Proteobacteria, which was 23.3%. The relative abundance of Chloroflexi in the soil with cow manure compost was the highest among all treatments and it was up to 10.27%, which was significantly higher than that in the soil with straw (7.55%). The relative abundance of Planctomycetes in the soil with straw was 22.86%, which was significantly higher than that of the cow manure compost treatment (13.82%) and the control treatment (13.62%). The distribution characteristics of dominant bacteria in genus level were similar to those in phyla level, that was due to the similarity of the dominant bacteria genus for different treatments, but the relative abundances were different among the different treatments. The dominant bacteria genus of the control treatment were in the order of uncultured bacterium RB41 (3.43%)=Sphingomonas (3.43%)> Lysobacter (2.47%)> Subgroup_10 (1.28%)> Pirellula (1%). The relative abundance of Sphingomonas in the soil with biochar (2.57%) and uncultured bacterium RB41 in the soil with straw (2.03%) were significantly lower than those of the other treatments; The relative abundance of Pirellula in the soil with cow manure compost and control treatment was significantly lower than that of the biochar treatment (2.11%). The differential species in soils with or without organic materials were as follows: for straw treatment, the main differential species were Proteobacteria α-Proteobacteria (Caulobacterales, Altererythrobacter, Hyphomonadaceae), Delta Proteobacteria Myxococcus (Sorangiineae_bacterium_NIC37A_2, Haliangium, 0319_6G20, Haliangiaceae, BIrii41) and γ-Proteobacteria (R7C24, CCD24); for cow manure compost treatment, the differential species were Proteobacteria α-Proteobacteria (Rhizobiales, Tagaea_marina) and Firmicutes (Halobacillus); and for control treatment, it was AKAU4049 of an uncertain class of Blastomonas. Statistical results show that there existed significant difference of microbial community structure in coastal saline-alkaline soil applied with different organic materials, moreover, the distribution of bacterial community was mainly influenced by soil pH, total organic carbon and electric conductivity.

In this study, we aimed to analyze the effects of different straws on soil organic carbon (SOC), total nitrogen (TN), mineral nitrogen, and activated carbon and nitrogen including dissolve organic carbon (DOC), microbial biomass carbon (MBC), easily oxidized organic carbon (EOC), dissolve organic nitrogen (DON) and microbial biomass nitrogen (MBN). An incubation experiment lasting for 80 days under continuous flooding was conducted. Four treatments including exogenous addition of astragalussinicus straw (ZYY), exogenous addition of wheat straw (XM), exogenous addition of rape straw (YC) and no exogenous additions (CK) were set. The results indicate that the addition of straw (ZYY, XM, and YC) significantly increased the SOC content, and the largest increase range was observed in the YC treatment. The addition of straw had no significant effect on the TN. The mineral nitrogen content in the soil decreased significantly under the XM and YC treatment, and it was increased by 3.29% under the ZYY treatment. Additionally, the straw addition increased significantly the DOC content relative to the CK treatment. The DOC concentration in the XM and YC treatment were significantly higher than that in ZYY treatment. All treatments with straw addition significantly increased the MBC and MBN content relative to the CK treatment, and the content of MBC and MBN in ZYY and YC treatment were significantly higher than that of XM treatment. Compared with the CK treatment, the EOC content was significantly increased by 20.34% in the ZYY treatment, while it was increased by 9.36% and 10.53% in the XM and YC treatment, respectively, with no significant difference to the CK. The ZYY treatment significantly increased the DON content, while XM and YC treatment had no significant effect on the improvement of DON. In conclusion, the addition of straw especially rape straw can significantly improve soil SOC content. Astragalus sinicus straw had the best effect on soil active carbon and nitrogen, followed by rape straw and wheat straw.

In order to study the changes of aquatic vegetation and water quality after removal of pen aquaculture in Lake East Taihu, the landsat-8 (OLI) data with 30 m resolution was selected as the data source to perform the supervised classification of aquatic vegetation. In addition, the field survey data of aquatic plants, as the basis for the classified evaluation of aquatic vegetation, was used to interprete the changes of typical aquatic vegetation in Lake East Taihu before and after the removal of net-pen aquaculture, and to analyze the changes of main water quality indexes and algal biomass from 2018 to 2020. Results show that, after the net-pen aquaculture of Lake East Taihu being completely removed in the end of 2019, the distribution area of floating-leaf plants in 2020 increased by 25.9% compared with that in 2018, and the distribution area of emerged plants and submerged plants reduced by 11.8% and 17.0%, respectively. The dominant species of submerged plants changed from erect species to canopy species. The biomass of floating-leaf plant, Trapha maximowiczii, and the canopy submerged plant, Ceratophyllum demersum, increased explosively to 6.84 and 9.90 kg·m^-2, respectively. From July to November 2020, the water transparency in the former net-pen aquaculture area was only 25.9 cm, which decreased significantly compared with the same period in 2018. The decline of transparency is not conducive to the growth of submerged plants and the maintenance of macrophyte-dominated clear state. The concentrations of chlorophyll-a and ammonia nitrogen increased significantly, implying that there is a risk of transformation to algae-dominated turbidity state in Lake East Taihu. After the removal of pen aquaculture in Lake East Taihu, the lake ecosystem has changed greatly. Therefore, it is necessary to strengthen the ecological research and management of the lake, and artificially assist the lake ecosystem to succeed to the macrophyte-dominated clear state.

Collaborative samples of soil and rice were collected to assess the characteristics of mercury pollution and its environmental risk in paddy fields around Wanshan Mercury Mine. The potential ecological risks and human health risks of Hg were evaluated, and the extraction efficiency of available Hg in soils were compared among different extracting agents. Results show that the concentrations of total Hg and MeHg in paddy soils was 0.95-16.27 mg·kg^-1 and 2.06-3.99 μg·kg^-1, respectively. The Hg content in soils exceeded the risk screening values for soil contamination of agricultural land, being moderate and serious level of pollution. Most proportion of soil Hg were in the residue fraction (92.9%-94.6%), and the contents of MeHg only accounted for 0.016%-0.285% of total Hg. The amount of total Hg in rice grain was 27.38-74.29 μg·kg^-1, and exceeded the Chinese national standard limit of 20 μg·kg^-1, but the potential health risk of Hg was low according to the values of probable daily intake (PDI) and target hazard quotients (THQ). The contents of MeHg in rice grain were 27.38-74.29 μg·kg^-1, and the PDI of some sampling sites exceeded the USEPA recommended limit of 0.1 μg·kg^-1·d^-1, suggesting the potential exposure risk of MeHg. Pearson correlation results indicate that the available Hg extracted by 0.01 mol·L^-1 Na₂S₂O₃ and 0.1 mol·L^-1 HCl had significant positive correlations with total Hg and MeHg in soil and rice grain (P < 0.01), suggesting the two agents could be used to estimate Hg availability in paddy soils.

In order to investigate the state of residuals and the degradation dynamics of butachlor and bensulfuron methyl in farmlands, soils and crops were sampled from two representative plantation areas in the suburbs of Nanjing in June and November 2019, respectively. Then, an analysis was conducted for the butachlor and bensulfuron methyl residues contained in the collected samples through high-performance liquid chromatography (HPLC-UV). The degradation dynamics of the herbicides were explored through the simulation performed under laboratory conditions. The detection rate of butachlor and bensulfuron methyl reached to 54.55% and 63.64%, respectively, while the maximum concentration of butachlor and bensulfuron methyl residues reached to 1.578 and 0.102 mg·kg^-1, respectively. Besides, there was a significant difference found in the content of butachlor residue between the two sampling areas(P < 0.01). Bensulfuron methyl residue was found to be negatively correlated with soil organic matter, but positively related to pH value. While butachlor residue was revealed to be negatively correlated with soil organic matter, but irrelevant to pH value in acidic environment. According to the results of simulation test conducted in the laboratory, the degradation dynamics of bensulfuron methyl and butachlor conformed to the first-order kinetic equation. Moreover, their half-lives reached to 7.94 and 13.08 d, respectively, while their dissipation rate was 0.087 and 0.053 d^-1, respectively. The amount of herbicide residue in farmland soil was related to the characteristics of its degradation.

The experimental method of choice is an important method used internationally to evaluate the value of resources and environmental products. Based on the data of 412 questionnaires on Wuyi Mountain National Park and the status of recreational resources, this paper conducted the experiment using random utility models (M-Logit model and C-Logit model Ⅰ, Ⅱ), natural elements (forest coverage, visibility of streams), management elements (crowding degree, garbage quantity) and economic element (ticket price). The results of the model analysis show that most of the five attribute indicators are significantly influential, the overall results are fitting well, and the experimental model has certain applicability. The results of Model Ⅰ show that the forest coverage rate (Plant indicator) and stream visibility (Water indicator) are positively correlated to the interest of tourists. For tourists, they are more concerned about tour experience than ticket price (insignificant). The results of Model Ⅱ show that the garbage quantity has the largest negative effect with the Garbage3 coefficient value reached to -1.160, and crowding degree (Crowd index) is negatively correlated with tourist experience degree. 10 people per 100 m² is the most suitable tourist density. Stream visibility (Water index) has a significant diminishing trend with water quality. The calculation results on Wuyi Mountain National Park tourist welfare value show that Model Ⅰ is 3.243 billion yuan, and Model Ⅱ's current state, best state and worst state are 2.862 billion, 5.135 billion and -5.533 billion yuan, respectively. Income and education are the two main factors causing heterogeneity of tourists' interest.