Spatial-temporal Distribution Characteristics Research Articles

Relationship between the Spatial and Temporal Distribution of Squid-Jigging Vessels Operations and Marine Environment in the North Pacific Ocean

Information and understanding of fishing activities at sea is important to fisheries science, public authorities and policy-makers. To understand the spatial–temporal distribution characteristics of squid-jigging vessels and how the marine environment affects the distribution of squid-jigging vessels in the North Pacific Ocean, operation behavior of the squid-jigging vessels was analysed by using spatial–temporal factors and marine environmental factors. The fishing effort (FE) information was calculated based on automatic identification system (AIS) data of squid-jigging fishing vessels in the North Pacific Ocean from July to November in 2017 to 2020, and the overlay maps of the spatial distribution of environmental factors and fishing effort were plotted together with four environmental variables (sea surface temperature (SST), sea surface height (SSH), sea surface salinity (SSS), and concentration of chlorophyll-a (Chla)). A generalized additive model (GAM) was used to investigate the nonlinear influence of the marine environment on squid-jigging fishing vessel activity in the North Pacific Ocean. The results show that fishing effort increased from July to August and then decreased from September to November. The fishing effort was highest in August. The intensity of the fishing effort suggests squid-jigging vessel operations had significant seasonal variations. The overlay maps suggest that the fishing effort of squid-jigging vessels was mainly located in areas where SST was between 10∘C and 20∘C, SSH was between −0.3m and 0.2m, SSS was between 32×10−3 and 34×10−3, and Chla was between 0.1mg·m−3 and 0.4mg·m−3. The generalized additive model indicated evidence of nonlinear relationships between fishing effort and the three environmental factors. The favorable ranges of SST, SSH, SSS and Chla for fishing effort were 15∘C∼18∘C, 0∼0.2m, 33×10−3∼34×10−3 and 0.2mg·m−3∼0.4mg·m−3, respectively. Moreover, the area beneficial to fishing effort was in 41∘N∼44∘N, 152∘E∼165∘E.

A synthesis of geochemistry of Mesozoic igneous rocks in NE China and tectonic superposition and transformation of the easternmost Central Asian Orogenic Belt

As the product of the amalgamation of multiple microcontinental massifs, Northeast China is located in the easternmost segment of the Central Asian Orogenic Belt (CAOB), which underwent multi-stage tectonic superposition in Mesozoic. Extensive and intensive igneous activities occurred throughout northeast China and the related igneous rocks can be considered as an effective probe for constraining tectonic evolution. In this study, numerous available ages and geochemical data are collected from published literature. The spatial-temporal distribution, rock assemblage, and geochemical characteristics of Mesozoic igneous rocks are systematically reassessed and summarized. A conclusion is drawn that NE China experienced the superposition and transformation of the Paleo-Asian Ocean (PAO) domain, the Mongol-Okhotsk Ocean (MOO) domain, and the Paleo-Pacific Ocean (PPO) domain in Mesozoic and detailed tectonic evolution is presented as follows. Firstly, NE China was under the joint effect of the MOO and the PAO during Early-Middle Triassic (ca. 252–237 Ma). Arc-type igneous rocks in the Erguna-Xing’an Block were induced by the southward subduction of the MOO Plate and adakites with high Sr/Y and (La/Yb)N ratios in the south segment of NE China were emplaced in the post-collision orogenic environment related to the closure of the PAO. Secondly, during Late Triassic, the influence of the PAO domain was gradually weakened, and igneous activities developed sporadically along the Solonker-Xar Moron-Changchun-Yanji suture zone. The MOO continued to subduct south until the Early Jurassic (ca. 220–190 Ma), and continental igneous rocks with arc-like features were widely distributed in the Erguna-Xing’an Block. During ca. 220–200 Ma, the Jiamusi-Khanka Massif was slipped away from the Songnen-Zhangguangcai Range Massif and this progress may be related to the PPO domain. Thirdly, in the Early Jurassic-Early Cretaceous (ca. 200–120 Ma), NE China came under the joint influence of the MOO and PPO tectonic domains. The subduction and closure of the MOO Plate and corresponding thickening of the lower crust resulted in widespread and intensive igneous activities in the Erguna and the Great Xing’an Range (GXAR). Two-stage subduction of the PPO and between which a period of change of subduction direction, induced the two-stage arc igneous activities of ca. 185–164 Ma and ca. 135–120 Ma, and the magmatic hiatus between ca. 163.5–135 Ma in the Zhangguangcai Range (ZGCR) and its east. Fourthly, the influence of the MOO domain was completed at ca. 120 Ma and numerous volcanic rocks corresponding chemically to A-type granite began to erupt violently, due to the rollback of the Paleo-Pacific oceanic slab. Since then, NE China has been completely under the control of the PPO domain.

Spatial-temporal distribution, cancer risk, and disease burden attributed to the dietary dioxins exposure of Chinese residents

This study analyzed the characteristics of dioxins represented by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) as well as dioxin-like polychlorinated biphenyls (dl-PCBs) in food from China. The spatial-temporal distribution characteristics of dioxins dietary intake, cancer risk, and disease burden were evaluated among the Chinese population. In the temporal dimension, descending trends in animal-origin-food were found both in dietary intake PCDD/Fs and dl-PCBs, with the reverse for plant-origin-food. The probability assessments of dietary intakes showed that after 2007, the exposure level of PCDD/Fs through diets of urban and rural residents in China was significantly lower than that before 2007 (p < 0.05). The spatial distribution results showed that the southern coastal regions were high exposure regions of dietary intakes of PCDD/Fs and dl-PCBs. Cancer risk and disease burden of dietary dioxins showed downward trends after 2007 both under an average exposure scenario and an extreme exposure scenario. After 2007, the disease burden resulting from exposure to dl-PCBs became higher and approached the median of values reported by the WHO, while the disease burden resulting from exposure to PCDD/Fs approached the lower level of 95% CI reported by the WHO. The results indicate that accompanying the National Implementation Plan and a series of subsequent scientific guidance documents launched for reducing dioxins pollution in 2007, the health benefits and the health risks caused by dl-PCBs should be given further attention and evaluation in future studies.

Dust Radiative Effect Characteristics during a Typical Springtime Dust Storm with Persistent Floating Dust in the Tarim Basin, Northwest China

A special topography and ultra-high atmospheric boundary layer conditions in the Tarim Basin (TB) lead to the unique spatial–temporal distribution characteristics of dust aerosols. A typical dust storm with persistent floating dust over the TB from 27 April to 1 May 2015 was used to investigate the characteristics of the dust radiative effect using the Weather Research and Forecasting Model with Chemistry (WRF-Chem). Based on reasonable evaluations involving in situ sounding observations, as well as remotely sensed MODIS observations of meteorology, dust aerosols, and the ultra-high atmospheric boundary layer, the simulation characterized the complete characteristics of the dust direct radiative effect (DDRE) during the dust storm outbreak stage and persistent floating dust stage over the TB. During the daytime, the shortwave (SW) radiative effect heated the atmosphere and cooled the land surface (SUR), whereas the longwave (LW) radiative effect had the opposite effect on the TB. Regarding low-level dust, the LW radiative effect was greater than the SW DDRE in the atmosphere, while for high-level dust the situation was reversed. During the nighttime, the LW DDRE at the top of the atmosphere (TOA), at the SUR, and in the atmosphere was less than that during the daytime, when the DDRE at the SUR was the most significant. In contrast to the daytime, the near-surface dust aerosols exerted an LW warming effect in the atmosphere during the nighttime; however, the dust LW radiative effect had a cooling effect from above a 100 m altitude until the top of the dust layer. In contrast, the DDRE heating rate peaked at the top of the dust layer within the TB. The event-averaged net DDRE was 0.53, −5.90, and 6.43 W m−2 at the TOA, at the SUR, and in the atmosphere over the TB, respectively. The dust SW radiative effect was stronger than the dust L4W radiative effect over the TB at the SUR and in the atmosphere. Moreover, the DDRE at the TOA was weaker than that at the SUR. Overall, the study revealed noteworthy radiative effect features of dust aerosols during typical dust storms with persistent floating dust over the TB.

Comparing spatial-temporal characteristics of dissolved nitrogen and phosphorus in water of sea cucumber Apostichopus japonicas culture ponds between sandy and muddy sediments

Apostichopus japonicas culture ponds have been invaded by Chaetomorpha valida in recent years in northern China, where the algae may be regionally distribute and the sizes of blooms vary with pond sediments. In this study, the spatial-temporal distribution characteristics of the DIN and SRP in the water of A. japonicas aquaculture ponds with sandy and muddy sediments from March to November 2016 were monitored to analyze whether the overgrowth of C. valida was correlated with the sediments in aquaculture ponds. The surface and bottom water were collected at 6 sampling sites in each aquaculture pond in the field and transported to the laboratory in low temperature incubators for analysis. The results showed that there were no significant differences in the concentrations of the NO3−-N, NH4+-N, NO2−-N and SRP between surface water and bottom water at the same sampling time and site. The relative position of the sampling sites in horizontal direction had no effect on the DIN and SRP concentrations. The variation of the DIN and SRP concentrations over time may be influenced by the biomass of phytoplankton and C. valida. The sediments in the aquaculture ponds had a significant influence on the concentrations of the DIN and SRP in the water. The total DIN concentrations, including all three forms, were slightly higher in muddy ponds than in sandy ponds. Compared with muddy ponds, the SRP concentration in sandy ponds fluctuated greatly with time due to differences in the sediment particle size and adsorption capacity. The biomass of C. valida had the strongest correlation with the NO3−-N concentration in sandy ponds and with the SRP concentration in muddy ponds. Therefore, it is more important to monitor the SRP and NO3−-N concentrations in aquaculture processes. This investigation provided important insight into eutrophication in sea cucumber ponds with different sediments.

Arsenic (As) contamination in sediments from coastal areas of China

Arsenic (As) from various anthropogenic sources has accumulated in estuarine and coastal sediments of China in the past decade, but we know little about the overall situation of As pollution at a national scale. Here, we analysed the spatial-temporal distribution characteristics, source, fate, and potential risks of As from 11 provincial-level regions across coastal China based on reviewed data extracted from previous studies published in the past 20 years. The anthropogenic contribution to As load was evident in 8 out of 11 provinces, especially in developed areas such as Tianjin, Zhejiang, and Guangdong. The weighted mean concentration of As in coastal sediments was 9.75 mg kg−1, which was close to national agricultural land (10.7 mg kg−1) and mixed land (12.1 mg kg−1) soil values, and this indicated the likely terrestrial influences and homogenization of As distribution at the interface between land and sea. The accumulation has decreased significantly since 2005, which might be due to continuously reduced emissions from farming and animal husbandry and household consumption in the catchment of coastal areas. The geoaccumulation index indicated that the proportions of unpolluted, unpolluted to moderately polluted, and moderately polluted cases were 48%, 28%, and 8%, respectively. This study provides a comprehensive and quantitative review on As contamination in coastal sediments on a national scale. The results could be used in coastal sediment quality assessment and decision-making by authorities to meet the regulatory requirements linked to coastal environmental protection and management.

Characteristics and Cause Analysis of the 1954 Yangtze Precipitation Anomalies

In 1954, the Yangtze River valley was hit by heavy precipitation anomalies, which caused large casualties and economic losses; however, systematic analyses of the causes are lacking. Adopting the latest national historical precipitation data collected by the China Meteorological Administration (CMA) and global sea surface temperature (SST) records, this retrospective study determined the spatial–temporal distribution characteristics of the precipitation in 1954 in Wuhan, a city situated in the Yangtze River valley. The results confirmed that the 1954 precipitation anomalies were characterized by a high volume and a long period of rainfall, plus numerous cloudbursts, with most of the precipitation concentrated during June and July at the mid- and low-Yangtze areas along the Yangtze. An El Niño event caused the West Pacific subtropical highs to continually move southward during the summer, creating a long-term rainband in the drainage basin. Moreover, the continued low SSTs in the Sea of Okhotsk generated an active blocking high that continuously brought high-latitude cold air into the south, boosting precipitation over the drainage basin. This study proposed a new causal model of summertime precipitation across the Yangtze River valley in 1954, whereby the unusual SST changes initially triggered atmospheric circulation anomalies, which caused the precipitation anomalies of 1954.

珊瑚礁生态系统病毒研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 珊瑚礁生态系统病毒研究进展 DOI: 10.5846/stxb202005021086 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重大项目（42090041）；国家自然科学基金重点项目（42030502）；广西南海珊瑚礁研究重点实验室自主基金项目（GXLSCRSCS2021103） A review of recent researches on viruses in coral reef ecosystem Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:病毒对珊瑚礁生态系统中的生物进化、生物地球化学循环、珊瑚疾病等方面具有重要的生态影响。随着珊瑚礁的全球性退化，病毒在珊瑚礁生态系统中的功能与危害日益显现。综述了珊瑚礁生态系统中病毒的研究现状与进展，包括：（1）珊瑚礁病毒的多样性与分布特征（水体、宿主、核心病毒组）；（2）珊瑚礁病毒的生态功能（感染方式、促进生物进化、生物地球化学循环）；（3）珊瑚礁病毒对全球气候变化的响应（热压力、珊瑚疾病）。总体而言，珊瑚礁生态系统具有极高的病毒多样性，所发现的60个科占已知所有病毒科数量的58%。珊瑚的核心病毒组主要由双链DNA病毒、单链DNA病毒、单链逆转录病毒所组成，珊瑚黏液层对病毒具有富集作用。"Piggyback-the-Winner"（依附-胜利）是病毒在珊瑚礁中主要的生物动力学模式，其可通过水平基因迁移的方式促进礁区生物进化。病毒可通过裂解细菌与浮游藻类的途径参与珊瑚礁的生物地球化学循环，尤其是碳循环与氮循环过程。此外，病毒还具有介导珊瑚热白化与直接引发珊瑚疾病的能力，这会影响珊瑚礁生态系统应对气候变化的适应性与恢复力。基于国际上的研究进展综述，结合南海珊瑚礁生态现状提出以下研究方向，以期促进我国珊瑚礁病毒学的发展：（1）开展南海珊瑚礁中病毒多样性的识别及其时-空分布特征研究；（2）探索病毒对南海珊瑚热白化、珊瑚疾病的介导作用及其与气候变化的关系；（3）揭示病毒对南海珊瑚礁生物地球化学循环的贡献。 Abstract:Viruses have an important ecological impact on the biological evolution, biogeochemical cycle, and coral diseases in coral reef ecosystems. With the global degradation of coral reefs, the functions and hazards of viruses in coral reef regions have become increasingly prominent. In this article, recent researches on viruses in coral reef ecosystems were reviewed, which included:(1) The diversity and distribution characteristics of viruses in coral reef ecosystem (sea water, host and core coral virome); (2) Ecological function of viruses in coral reef ecosystem (infection pattern, promoting biological evolution, and biogeochemical cycle); (3) Viruses response to global climate change in coral reef ecosystem (thermal stress and coral diseases). Accordingly, coral reef ecosystems have an extremely high viral richness and diversity. About 60 virus families are reported in coral reef ecosystems around the world, which account for 58% of all known viral families. Also, the core coral virome is manly composed of double-stranded DNA virus (dsDNA virus), single-stranded DNA virus (ssDNA virus) and retrovirus. The viruses in coral surface mucus layer are more abundant and diverse, due to enrichment with viruses from around environment in coral reef ecosystem. "Piggyback-the-Winner" is the main biodynamic mode of viruses in coral reefs, which indicates that viruses can promote the evolution of organisms by horizontal gene transduction in reef regions. In addition, viruses can participate in the carbon and nitrogen cycles of coral reefs by lysing bacteria and planktonic algae, respectively, which plays an important role in biogeochemical cycles of coral reef ecosystem. It's worth noting that viruses have ability to mediate coral thermal bleaching, which has closely associations with Phycodnaviridae and Herpesviridae. Moreover, viruses can also lead to coral diseases (e.g., white plague, white band disease and yellow blotch), which can affect the adaptability and resilience of coral reefs to global climate change. Herein, based on a systematic review of international research progress and current ecological status of coral reefs in the South China Sea, this article proposes the following research directions, in order to promote the development of coral reef virology:(1) The diversity and spatial-temporal distribution characteristics of viruses in coral reefs from the South China Sea; (2) The mediation effect of viruses on coral thermal bleaching and diseases in the South China Sea, and their relationship with intensified global climate change; (3) The contribution of viruses in biogeochemical cycles (e.g., carbon and nitrogen cycles) of coral reef ecosystems in the South China Sea. 参考文献 相似文献 引证文献

The Relationship between Urban Population Density Distribution and Land Use in Guangzhou, China: A Spatial Spillover Perspective.

Urban population density distribution contributes towards a deeper understanding of peoples’ activities patterns and urban vibrancy. The associations between the distribution of urban population density and land use are crucial to improve urban spatial structure. Despite numerous studies on population density distribution and land use, the significance of spatial dependence has attained less attention. Based on the Baidu heat map data and points of interests data in the main urban zone of Guangzhou, China, the current paper first investigated the spatial evolution and temporal distribution characteristics of urban population density and examined the spatial spillover influence of land use on it through spatial correlation analysis methods and the spatial Durbin model. The results show that the urban population density distribution is characterized by aggregation in general and varies on weekends and weekdays. The changes in population density within a day present a trend of “rapid growth-gentle decline-rapid growth-rapid decline”. Furthermore, the spatial spillover effects of land use exist and play the same important roles in population density distribution as the direct effects. Additionally, different types of land use show diverse direct effects and spatial spillover effects at various times. These findings suggest that balancing the population density distribution should consider the indirect effect from neighboring areas, which hopefully provide implications for urban planners and policy makers in utilizing the rational allocation of public resources and regarding optimization of urban spatial structure.

Research on numerical simulation for partial discharge of epoxy interface excited by high‐frequency sinusoidal voltage

High-frequency sinusoidal voltage excitation is proposed as a feasible method to solve the difficulty of partial discharge detection at the epoxy interface. In order to study the development process of partial discharge under high-frequency stress, a two-dimensional plasma simulation model of partial discharge for a needle-plate electrode structure is established by coupling particle transport equation, Poisson equation and plasma chemical reaction. The model adopts a reaction set to reduce the difficulty of modelling generation, transport and disappearance of charged particles. It realises dynamic simulation of the partial discharge at the epoxy interface. The spatial–temporal distribution characteristics of microscopic parameters such as electron density, electron temperature and surface charge are obtained. Based on this simulation model, the partial discharge characteristics of the epoxy interface at different frequencies are further studied in this work. The results show that with the increase of applied voltage frequency, the electron temperature shows an increasing trend, but its increasing rate gradually slows down; while surface charge accumulation decreases uniformly with the increase of applied voltage frequency. These two factors make the partial discharge severest under the frequency of 10 kHz. The results of the model are verified from two aspects of discharge form and discharge intensity by experimental means.

Research on the Temperature Field Distribution Characteristics for Thermal Management of Coilgun

Ohmic heating has become one of the main factors restricting their efficiency and longevity of the synchronous induction coilgun (SICG) operating in a complex electromagnetic environment. Therefore, further exploration on the temperature spatial–temporal distribution characteristics of the SICG is of great practical significance to ensure its reliable and efficient operation. The single-stage SICG is taken as the research object to simplify the solving process. First, the effectiveness and accuracy of the numerical simulation models in terms of kinetic and thermodynamic properties are compared and verified. Then, the influence of different structural parameters on temperature rise and acceleration is investigated in detail. The conclusions can not only provide theoretical reference for the long-term service of the SICG but also guide the related research of continuous emission.

Impacts of Climate Change on Blue and Green Water Resources in the Middle and Upper Yarlung Zangbo River, China

The Yarlung Zangbo River is the largest river on the Tibetan Plateau and a major international river in South Asia. Changes in the blue and green water resources in its basin are of great importance to the surrounding local and Asian regions in the context of global warming. This research used the Soil and Water Assessment Tool model to estimate blue and green flows (BWF and GWF) and analyze the spatial-temporal distribution characteristics under different hypothetical climate change scenarios. The results show that (1) the multi-year average BWF in the middle and upper reaches of the Yarlung Zangbo River Basin is 176.2 mm, the GWF is 213.1 mm, and the difference between precipitation and total water resources is only 5.4 mm; (2) both BWF and GWF in this basin showed a slightly increasing trend from 1980 to 2010, but the distribution of subbasins from upstream to downstream is decreasing; and (3) GWF has a positive correlation with both precipitation and temperature, but BWF only increases with precipitation and decreases with increasing temperature. Moreover, the change in blue and green water resources is more sensitive to the changes in precipitation than to changes in the temperature.

Numerical study on transient aerodynamic behaviors in a subway tunnel caused by a metro train running between adjacent platforms

Aerodynamic effects, including slipstream, piston wind, drag, and pressure wave, in the tunnel caused by a metro train running between two adjacent platforms were simulated using a metro train model with six cars, an RNG ᴋ–ε turbulence model, and the sliding mesh technology, and they were verified through some full-scale tests and scale model experiments. Theoretical analysis and computational fluid dynamics (CFD) were used to investigate the formation and spatial–temporal distribution characteristics of the wind environment in a tunnel. The effect of uniform speed on the transient aerodynamic behaviors in the tunnel was analyzed. The results show that there are differences in aerodynamic behaviors in a subway tunnel when a train is in the acceleration and deceleration stages. Piston wind is a kind of high-quality wind resource, and it is better to arrange the wind turbines close to the destination platform. Some results can provide theoretical support for the recovery of wind energy resources and the layout of fans in the tunnel. Further, they can increase the development and utilization of urban underground space.

Spatial-temporal distribution and evolutionary characteristics of water environment sudden pollution incidents in China from 2006 to 2018

Sudden water pollution incidents (SWPI) are random and harmful, which is a problem that cannot be ignored in ecological environment governance and economic development. Identifying spatial-temporal distribution characteristics of SWPI is essential for the disaster prevention and the early warning of water environment. The Kernel Density (DE) and spatial mean center of SWPI transfer curve were used to explore the characteristics with the dataset of 1174 cases from 2006 to 2018 in China. Results showed that: (1) From the time point of view, there was an overall upward trend in the overall number of SWPI. (2) At a regional scale, Eastern China, Southwest China, and Southern China underwent a high frequency with 69.93% of SWPI. The Fujian, Guangdong and Chongqing provinces were specified as the top 3 provinces with incident frequencies. The Yangtze River Basin and the Pearl River Basin were two regions where water pollution incidents occur more often, more than 50% of incidents among basins in China every year. (3) In general, SWPI presents a northeast-southwest distribution pattern and center of SWPI moves in the direction of west by south. (4) More than half of the incidents (57.24% of the total) were induced by illegal pollutant discharge and production safety accidents.

Spatiotemporal Inversion and Mechanism Analysis of Surface Subsidence in Shanghai Area Based on Time-Series InSAR

Abnormal surface subsidence has become a widespread geological problem being faced by cities. As a first-tier city in the world, there are problems such as unclear analysis of subsidence mechanism. Therefore, the monitoring of the Shanghai surface is particularly important. In this paper, the Sentinel-1A satellite SAR image data of 36 scenes covering Shanghai area from January 2018 to March 2020 were processed on the basis of time-series interferometry synthetic aperture radar technique. The subsidence rate field and accumulated surface subsidence in Shanghai area during the study period were obtained, and the spatial–temporal distribution characteristics of subsidence in the study area were discussed and analyzed from many different aspects. Moreover, the correlation between regional subsidence and geological structure, precipitation, urbanization, and other influencing factors were analyzed and established. Results show that the non-uniform subsidence in Shanghai area is clear, and those of the districts of eastern Songjiang, southern Jinshan, and Fengxian are more serious with a maximum subsidence rate of −26.2 mm/year. After analyzing the causes of subsidence, the special foundation of soft soil in Shanghai area is determined as the main reason for the subsidence, and the uneven subsidence is mainly caused by the over-exploitation of groundwater, human activities, and the subsidence of soil layer. Through comparative analysis, factors, such as rainfall, groundwater, and urbanization process, have high correlation with surface subsidence.

Identifying nitrogen source and transport characteristics of the urban estuaries and gate-controlled rivers in northern Taihu Lake, China

Revealing nitrogen source and transport mechanisms are essential to achieving optimal nitrogen management in urban estuaries and gate-controlled rivers. However, in plains river networks, gate and/or dam construction make the nitrogen sources difficult to trace. In this study, seasonal water samples from typical urban estuaries and gate-controlled rivers in northern Taihu Lake were analyzed using statistical analysis and stable isotope analysis in R (SIAR). The results show that the concentrations of various nitrogen forms showed obvious spatial–temporal distribution characteristics by multiple sources. Specifically, the nitrogen concentration was lower during the wet season than the dry season (T = 6.02, p < 0.01). Gate construction had a dual effect on the water environment, because it changed both the nitrogen transport processes and the nitrogen enrichment risk between the river side and lake side. The δ18O-NO3- and δ15N-NO3- values were sensitive to anthropogenic activity intensity and urbanization process, showing the following order of δ15N-NO3- values: Countryside > Suburbs > Downtown, and Construction Land > Forest-grassland > Farmland. While, a contrary trend was observed among the variations in δ18O-NO3- values. According to the SIAR model, sewage/manure, fertilizer, and sediment nitrogen (sediment N) were the main nitrate sources, accounting for 42.68%, 23.79%, and 23.71%, respectively. The proportion of urban nitrogen discharge has surpassed that of agricultural sources, becoming the largest nitrogen source in the waterbody. Under the coupling of meteorological conditions and estuary shape, the endogenous nitrogen released from sediment became the second largest contributor in some estuaries. These findings suggest that it is necessary to strengthen the control of urban exogenous nitrogen input and sediment nitrogen endogenous release to enable future estuarine nitrogen management and habitat restoration.

Spatial-temporal distribution characteristics and evolution mechanism of urban parks in Beijing, China

Urban parks are vital ecological recreational places, and their spatial evolution has a certain influence on the ecological environment and quality of citizens’ daily life. Taking Beijing as an example, this paper firstly explores the dynamic evolution of urban parks in Beijing by comparing spatial distribution characteristics in three time points of 2005, 2010, and 2017. Besides changes in number and area, the spatial structure and accessibility are examined by the methods of directional distribution, kernel density estimation and network analysis. Then three-factor analysis method is used to explain the evolution mechanism. The results reveal that there exist obvious and continuous growths in urban parks regardless of quantity, area or accessibility. According to the core-periphery spatial distribution pattern, Beijing has gradually formed a systematic green recreational network, and the service area of urban parks by walking within 30 min is 58.6 % of total area. Stability factors, dynamic factors and random factors play important roles during the spatial evolution of urban parks through restraint mechanism, supply-demand mechanism and triggering mechanism respectively. The findings offer both theoretical construct and policy recommendations for the development and sustainability of urban parks in Beijing and other rapidly urbanizing cities with high population densities.

Temporal-spatial distribution characteristics and its influencing factors of tuberculosis epidemic in the Chinese mainland from 2014 to 2018

Objective The number of beds per thousand, gross domestic product (GDP) per capita, population density and annual sunshine hours were investigated to analyze the spatio-temporal characteristics of tuberculosis incidence of 31 provinces in the Chinese mainland from 2014 to 2018, so as to provide a theoretical basis for the prevention and control of the spread of tuberculosis in the future. Methods The spatial autocorrelation analysis was performed to explore the spatio-temporal agglomeration of the incidence of tuberculosis in the Chinese mainland in each year. A geographically and temporally weighted Logistic regression analysis model was established to reveal the spatio-temporal non-stationarity of tuberculosis incidence, and to compare the fitting results with the classic Logistic regression analysis model. Results The global spatial Moran's I index of tuberculosis incidence in the Chinese mainland from 2014 to 2018 were 0.43, 0.44, 0.47, 0.49, 0.37, showing a certain spatiotemporal correlation. The coefficient function of the geographically and temporally weighted Logistic regression analysis model fluctuated in the interval (-1, 1), and could reflect the spatio-temporal heterogeneity of tuberculosis well. The confidence interval of each coefficient function did not contain 0, which had spatio-temporal non-stationarity. The results of the goodness of fit test were better than the classic Logistic regression analysis model. Conclusions The incidence of tuberculosis in 31 provinces in the Chinese mainland was closely related to four macro factors, and appropriate strategies should be formulated for tuberculosis prevention and control according to the difference of regional social macro factors.

Dustfall-bound polycyclic aromatic hydrocarbons (PAHs) over the fifth largest Chinese lake: residual levels, source apportionment, and correlations with suspended particulate matter (SPM)-bound PAHs in water

Residual levels and temporal-spatial distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) in dustfall were studied at the seasonal scale between June 2010 and May 2011 in the fifth largest shallow lake in China. PAHs flux of atmospheric deposition and the impact on the PAHs in the lake water column were estimated. The major sources of PAHs were identified by multiple methods. We found that (1) the seasonal residual levels of 16 priority controlled PAHs (PAH16) were spring (8.89 ± 3.93 μg g-1) > summer (6.68 ± 4.31 μg g-1) > winter (6.06 ± 2.95 μg g-1) > autumn (3.55 ± 2.21 μg g-1). (2) Significant positive correlations were found between the PAH levels in the dustfall and the suspended particle material (SPM) content, as well as between the deposition flux and the PAH content in the water in all four seasons. (3) Vehicle emissions, coal combustion, biomass combustion, and coke ovens were the four major sources in Lake Chaohu, accounting for 12.7%, 40.9%, 14.5%, and 31.9% of the total PAHs, respectively. (4) Compared to long-distance trajectories, short-distance trajectories played a more important role in the external sources of atmospheric PAHs in the region of Lake Chaohu.

The spatial-temporal distribution characteristics of atmospheric chloromethane according to data from the CARE-China network

The spatial and temporal distribution of atmospheric chloromethane (CH3Cl) in China was investigated between 2012 and 2014, and the sources of CH3Cl were evaluated by positive matrix factorization (PMF) according to PMF 5.0 (USEPA). Various concentrations of CH3Cl were found throughout China, ranging from 506.4 ± 110.5 to 1132.1 ± 523.3 pptv, showing the characteristics of high in the southeast and low in the northwest. The correlation between CH3Cl and chlorofluorocarbon-12 (CFC-12) at most sites was greater than 0.5 and presented regional characteristics. The distribution of CH3Cl in China is related to the degree of economic development, the high-concentration sites were located in the economically developed eastern region. The CH3Cl concentrations at western sites were similar to the global average and increased with latitude and altitude, indicating that this region was least affected by anthropogenic activities. The annual average concentrations of atmospheric CH3Cl in the northeastern region were below 730 pptv but had strong seasonal fluctuations. Chemical production was the main CH3Cl source in the northeast background areas (46%), while industrial combustion contributed 42% of the CH3Cl in the northeast urban areas. Large seasonal variations combined with a high relative standard deviation were observed in the southern region. Relative to the southwest, in the southeast, the onset of lower concentrations was delayed until September–October, and higher concentrations persisted for longer. Chemical production and biomass burning were the main sources in the southwest, while Chemical production and solvent use were the main contributors in the southeast. The Beijing area is discussed separately as a super megacity. No obvious seasonal fluctuations were observed in the Beijing area. According to the source analysis, chemical production contributed approximately 60% of the atmospheric CH3Cl in the Beijing area, while 15–24% was from solvent release.