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The groundwater table depth, which is typically shallow in coastal areas, is one of the decisive conditions impacting soil salinization. The influence mechanism of shaollow groundwater table depth change on the evolution of saline-alkali land is still unclear. In this study, Huanghua City, a coastal city of the Bohai Sea in China, was selected as the research area, and four wells with groundwater table depths ranging from shallow to deep were studied. The groundwater table depth was divided into three levels based on the average groundwater table depth over 30 years, namely shallow, medium, and deep. We analyzed the influence of changes in groundwater table depth in each well on the evolution of saline-alkali land within a radius of 2 km. The results showed that changes in groundwater table depth did not cause conversion between saline-alkali land grades in shallow areas, whereas, in medium-depth areas, changes in groundwater table depth caused conversion among saline-alkali land grades. In deep areas, changes in groundwater table depth did not affect the conversion of moderate/heavy saline-alkali land to non-mild saline-alkali land. The lower limit and upper limit of the groundwater table depth response threshold of saline-alkali land were found to be 1.35 and 3.58 m, respectively, in this coastal area. When the groundwater table depth of saline-alkali land remains lower than 1.35 m for a long period, it will become heavily salinized, one appropriate treatment measure in this instance is to plant saline-alkali tolerant plants beacause improving saline-alkali land by reducing the groundwater table depth is a challenge. When the groundwater table depth of saline-alkali land remains greater than 3.58 m for a long period, changes in groundwater table depth will not influence the gradual reduction of salinization, the saline-alkali land should be properly irrigated and drained to avoid secondary salinization caused by the groundwater level rising to the upper limit of the response threshold. When the water depth in saline-alkali land remains between 1.35 and 3.58 m for a long time, the degree of salinization will change with the change in water depth, the underground water depth can be reduced under a subsurface drainage system in order to treat the saline-alkali land. The research results can provide a scientific basis for improvement of saline-alkali land. [ABSTRACT FROM AUTHOR]

Some indicators for evaluating heavy metal pollution have been proposed. However, a threshold is lacking to judge if the heavy metal concentration has reached the extent that is harmful to plant health. In order to get the threshold, aerial hyperspectral images were obtained. The spatial patterns of six soil heavy metals (Cu, Zn, As, Sn, Cr and Cd) were obtained by establishing random forest inversion models. The normalized difference vegetation index (NDVI) under different soil heavy metal concentrations was analysed. Cu, Zn, As, Sn and Cr exhibited that low concentrations stimulated plant growth while high concentrations suppressed it. When the concentrations of Cu, Zn, As, Sn and Cr exceeded 19.960 mg/kg, 49.040 mg/kg, 14.049 mg/kg, 0.193 mg/kg and 89.799 mg/kg, respectively, heavy metals began to inhibit the growth of vegetation. The lower reaches of the river and the downwind area of the mining area were easily to exceed the threshold. [ABSTRACT FROM AUTHOR]

Background : Magnesium (Mg) is an essential element and participates in many metabolic pathways. Many studies have found a certain negative correlation between magnesium and blood glucose parameters, but the dose-response relationship between them is still a relatively narrow research field. We aim to explore the dose-response relationship between plasma and dietary Mg and type 2 diabetes (T2DM) among childbearing women in a nationally representative sample. And we will also initially explore the threshold of dietary and plasma magnesium in the prevention of T2DM and their consistency. Methods : A total of 2912 18-44 year-old childbearing women were recruited from the China Adult Chronic Disease and Nutrition Surveillance (2015). Multivariate logistic regression was used to explore the dose-response relationship between plasma and dietary Mg and glucose parameters. The threshold effect between Mg and T2DM was explored by a restricted cubic spline regression. Results : It was found that when plasma Mg was increased by 0.041 mmol/L, the risk of T2DM, impaired fasting glucose (IFG), and HbA1c-hyperglycemia was reduced by 18%, 19%, and 18%, respectively. The possible threshold value for plasma Mg to prevent the risk of T2DM was 0.87 mmol/L. Through the quality control of the sample dietary survey data, 2469 cases were finally included for dietary analysis. And the possible threshold value for dietary Mg to prevent the risk of T2DM was 408 mg/d. Taking the recommended dietary Mg intake of 330 mg/d as the reference group, when the Mg intake reached 408 mg/d, the risk of T2DM was significantly reduced. And the average plasma Mg level of the people whose dietary intake reached 408 mg/d was 0.87 mmol/L. Conclusions : These results indicate that dietary Mg and plasma Mg have good consistency on the threshold effect of glucose parameters in women of childbearing age.

Many hydrological algorithms have been developed to automatically extract drainage networks from DEM, and the D8 algorithm is widely used worldwide to delineate drainage networks and catchments. The simulation accuracy of the SWAT model depends on characteristics of the watershed, and previous studies of DEM resolution and its impacts on drainage network extraction have not generally considered the effects of resolution and threshold value on uncertainty. In order to assess the influence of different DEM resolutions and drainage threshold values on drainage network extraction using the SWAT model, 10 basic watershed regions in China were chosen as case studies to analyse the relationship between extracted watershed parameters and the threshold value. SRTM DEM data at 3 different resolutions were used in this study, and regression analysis for DEM resolution, threshold value and extraction effects was done. The results show that DEM resolution influences the selected flow accumulation threshold value; the suitable flow accumulation threshold value increases as the DEM resolution increases, and shows greater variability for basins with lower drainage densities. The link between drainage area threshold value and stream network extraction results was also examined, and showed a variation trend of power function y = ax b between the sub-basin counts and threshold value, i.e., the maximum reach length increases while the threshold value increases, and the minimum reach length shows no relation with the threshold value. The stream network extraction resulting from a 250 m DEM resolution and a 50 000 ha threshold value was similar to the real stream network. The drainage network density and the threshold value also shows a trend of power function y = ax b; the value of b is usually 0.5. [ABSTRACT FROM AUTHOR]

• Threshold of WUE with climate variability and land-use changes were analyzed. • Contribution rate of climate variability and land-use changes to WUE variation was quantified. • Precipitation, temperature and LAI are the main driving factors of the regional WUE. • The Grain to Green Program contributed to increase of WUE. • Mixed forest has the highest annual average WUE in water deficient regions. Water use efficiency (WUE) is a measure used for evaluating the trade-off between carbon sequestration and water consumption of terrestrial ecosystems. Much attention has been directed on how and to what extent WUE varies with climate variability and land-use changes. In this study, the Carnegie-Ames-Stanford Approach model and remote sensing data are utilized to analyze the response of WUE to climate variability and land-use changes in the mountainous area of North China from 2000 to 2020. The results show that the annual WUE follows an increasing trend at a rate of 0.012 gC/mm·m2·yr with an average value of 1.027 gC/mm·m2. Spatially, significant heterogeneity was detected in WUE with gradients decreasing from the southeast to the northwest, while significant increases were found in Beijing, Tianjin, and some regions of Hebei. The annual average WUE of different vegetation types decreased following the order of mixed forest > needleleaf forest > broadleaf forest > grassland > shrubland > cropland. Among various meteorologic and vegetation factors, WUE was mainly influenced by temperature, precipitation, and LAI. The cumulative effect of these three factors explained 79.43 % of the variations of WUE. Finally, when precipitation was 490–510 mm, or temperature was 13 ℃, or LAI was 1.27 m2m−2, WUE reached the threshold value, i.e., vegetation had the highest degree of water use. These results have implications for the management of water resources and regional ecosystem optimization in regions with limited water resources. [ABSTRACT FROM AUTHOR]

• Nutrient thresholds increase and then decrease from west to east. • For West Lake TP ≤ 0.05 mg/l, the nutrient load needs to be reduced by over 80 %. • Wide variation in thresholds under different management objectives. • Flow density and wind influence the spatial distribution of nutrient thresholds. Persistent eutrophication frequently causes toxic algal blooms, which is a serious threat to drinking water safety, food security, and public health. Nutrient thresholds, the maximum nutrient load that an aquatic ecosystem can absorb while meeting management objective, are key to avoiding and reducing blooms. The determination of thresholds relies on nutrient load-response curves. The spatial heterogeneity of large shallow lakes in terms of lake characteristics results in different curves shape among areas of the lake, which leads to spatial differences in thresholds. However, the spatial heterogeneity of thresholds is typically neglected; there are few methods to analyse the relationship between river loads and lake-specific area thresholds. Here, we proposed the Area Threshold Analysis Framework to analyse the spatial patterns of nutrient loads and thresholds in lakes. We first quantified the flow and load of the rivers entering the lake. The lake was then zoned and modelled to analyse area thresholds. Finally, an intuitive link between the nutrient loads of specific rivers and the thresholds of specific areas of the lake was established. The results showed a nonlinear without hysteresis response in all areas of Chaohu Lake; the nutrient loads and thresholds were highly variable in space, showing a trend of increasing and then decreasing from west to east. Flow density and wind might be important in influencing the spatial distribution of thresholds. The different effects of the wind and flow density on total phosphorus (TP) and chlorophyll a (Chl-a) lead to large differences in the thresholds with TP and Chl-a as management objectives, respectively. The large gap between nutrient loads and thresholds made it important for management to consider appropriate management goals to deal with unrealistic nutrient reductions. Achieving year-round Chl-a ≤ 30 µg/l in Chaohu Lake was easier than TP ≤ 0.05 mg/l, since for the latter, the Shiwuli, Paihe, and Nanfei river loads needed reductions of >80 %. In addition, for Area 1 and 2, it was more practical to first start meeting TP ≤ 0.05 mg/l for 2 or 3 seasons of the year than for 4 seasons. Overall, we developed a new framework for spatial threshold analysis and established an intuitive link between nutrient loads and thresholds in large shallow lakes. These results are valuable for understanding the threshold properties of spatially heterogeneous ecosystems in general and provide a reference for watershed nutrient management and ecological restoration of lakes. [ABSTRACT FROM AUTHOR]

Forests play a vital role in global carbon (C) cycling. Accordingly, afforestation engineering programs that promote increased terrestrial C stocks are an important means to help gradually decrease atmospheric CO2 emissions. China, however, had increased its afforested area bordering hydroclimatic zones to 275.71 million hm² between 1949 and 2010. Ecosystem water use efficiency (EWUE) and plant water use efficiency (PWUE) provide data on ecosystem sensitivity to water availability across rainfall regimes. The water consumption cost of C sequestration (WCCC) is also an important parameter that gauges the cost of C sequestration under afforestation. However, abrupt changes in EWUE and PWUE (threshold values of 1.5 and 3.6 gC kg-1 H2O, respectively) have been measured within the 400-500mm precipitation climatic isoline boundary situated between semi-humid and arid zones. The threshold value of the corresponding WCCC was 1.0 kg H2O gC-1. Forest ecosystems in China typically generate high EWUE and PWUE values (2.80±0.77 and 4.25±1.02 gC kg-1 H2O, respectively) but low WCCC values (0.52±0.42 kg H2Og-1C), providing proof that afforestation is the best choice in increasing terrestrial C stocks. However, China's major afforestation engineering programs have concentrated efforts toward low EWUE and PWUE and high WCCC in the western region of the 400-500mm precipitation isoline boundary, belonging to the arid and semiarid zones, which introduced potential environmental risks. Therefore, policies related to large-scale C sequestration initiatives under afforestation must first fully consider the statuses of WCCC and WUE. [ABSTRACT FROM AUTHOR]

Short-term hydrodynamic fluctuations caused by extreme weather events are expected to increase worldwide because of global climate change, and such fluctuations can strongly influence cyanobacterial blooms. In this study, the cyanobacterial bloom disappearance and reappearance in Lake Taihu, China, in response to short-term hydrodynamic fluctuations, was investigated by field sampling, long-term ecological records, high-frequency sensors and MODIS satellite images. The horizontal drift caused by the dominant easterly wind during the phytoplankton growth season was mainly responsible for cyanobacterial biomass accumulation in the western and northern regions of the lake and subsequent bloom formation over relatively long time scales. The cyanobacterial bloom changed slowly under calm or gentle wind conditions. In contrast, the short-term bloom events within a day were mainly caused by entrainment and disentrainment of cyanobacterial colonies by wind-induced hydrodynamics. Observation of a westerly event in Lake Taihu revealed that when the 30 min mean wind speed (flow speed) exceeded the threshold value of 6 m/s (5.7 cm/s), cyanobacteria in colonies were entrained by the wind-induced hydrodynamics. Subsequently, the vertical migration of cyanobacterial colonies was controlled by hydrodynamics, resulting in thorough mixing of algal biomass throughout the water depth and the eventual disappearance of surface blooms. Moreover, the intense mixing can also increase the chance for forming larger and more cyanobacterial colonies, namely, aggregation. Subsequently, when the hydrodynamics became weak, the cyanobacterial colonies continuously float upward without effective buoyancy regulation, and cause cyanobacterial bloom explosive expansion after the westerly. Furthermore, the results of this study indicate that the strong wind happening frequently during April and October can be an important cause of the formation and expansion of cyanobacterial blooms in Lake Taihu. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the spatial and temporal variations of sediment accumulation and their impacts on coral communities in four sites at two or three depths (3m, 6m and 9m) at the Sanya Coral Reef Reserve by deploying sediment traps on the sea floor during 2007–2009. Rainfall and typhoon events, which appeared to control sediment accumulation in the sea floor of the coral reef, were positively correlated with total sediment and sand-sized (i.e. 63–2000µm) sediment accumulation. Sediment accumulation rate significantly decreased with the distance far away from the coast in Sanya. The mean sediment accumulation rates in Ximaozhou, Luhuitou and Xiaodonghai during 2007 to 2009 were close to 20mgcm−2 d−1, and they were significantly higher than that in Yalongwan, probably as a result of terrestrial soil erosion caused by strong coast human activities (e.g. coastal construction, dredging and hillside clearing). Correlation analysis revealed that silt-clay-sized sediment accumulation rate was highly negatively correlated with total live coral cover and coral cover in some taxa, such as Montipora and branching Porites. whereas, Diploastrea heliopora was positively correlated with silt-clay-sized sediment accumulation. Correlation analysis also suggested that silt-clay-sized sediment accumulation had a higher efficiency in predicting the spatial variation of total live coral cover in Sanya than did the total sediment accumulation. Based on this investigation, we conclude that high rates of sediment accumulation pose a severe threat to the Sanya Coral Reef Reserve, highlighting the importance of integrated watershed management practices in the Sanya Coral Reef Reserve. [Copyright &y& Elsevier]

Abstract: Objective: The objective of this study is to determine the diagnostic threshold of HbA1c for diabetes and the impact of using it on diabetes prevalence. Methods: A population-based stratified study was conducted in 2010 among community-dwelling adults aged ≥35years in southern China. Participants without previously-diagnosed diabetes (PDD) took oral glucose tolerance test (OGTT) and HbA1c assay. HbA1c diagnostic threshold was determined by receiver operating characteristic curve. Results: A total of 6989 participants with mean age of 52years were recruited. The area under curve of HbA1c was 0.903 (95% CI: 0.883–0.922), with optimal cut-off value at 6.25% (sensitivity 75.6% and specificity 91.9%). There were 449 (6.42%) patients with PDD and 422 (6.04%), 815 (11.66%) and 918 (13.13%) new cases diagnosed by OGTT, HbA1c ≥6.25% or either, respectively. When either HbA1c or OGTT was used, newly-diagnosed diabetes prevalence increased by 117.4%. Conclusions: Diabetes is prevalent in southern China. Near half of the patients go undetected with current diagnostic criteria. HbA1c ≥6.25% may be the diagnostic threshold value but needs further verification. The introduction of HbA1c threshold into diabetes diagnosis in China will cause a substantial increase in diabetes prevalence and great challenge on the public healthcare system. [Copyright &y& Elsevier]

Environmental risk assessment is an essential step in the development of solutions for pollution problems and new environmental regulations. An assessment system for environmental risks has been developed in China in recent decades. However, many of the Chinese technical guidelines, standards, and regulations were directly adapted from those of developed countries, and were not based on the Chinese environmental and socioeconomic context. Although existing environmental regulations for pollutants are usually obtained by extrapolations from high-dose toxicological data to low-dose scenarios using linear-non-threshold (LNT) models, toxicologists have argued that J-shaped or inverse J-shaped curves may dominate the dose-response relationships for environmental pollutants at low doses because low exposures stimulate biological protective mechanisms that are ineffective at higher doses. The costs of regulations based on LNT and J-shaped models could therefore be dramatically different. Since economic factors strongly affect the decision-making process, particularly for developing countries, it is time to strengthen basic research to provide more scientific support for Chinese environmental regulations. In this paper, we summarize current Chinese environmental policies and standards and the application of environmental risk assessment in China, and recommend a more scientific approach to the development of Chinese regulations. [ABSTRACT FROM AUTHOR]

Although considered an effective means to alleviate the urban heat island effect, the cold island effect of urban wetlands and its influencing factors remain unclear, especially in inland basin areas. Chengdu, a typical inland metropolis in Southwest China, was chosen as the case study area to study the cooling effect of wetlands and the impact of the spatial form of wetlands (e.g., size, shape, hydrological connectivity) on the cooling effect, and optimized strategies for the cooling efficiency of urban wetlands were proposed. The results showed that (1) the cooling intensity logarithmically increased with the wetland size and that the threshold value of efficiency (TVoE) was 1.47 ± 0.34 ha. (2) The hydrological connectivity significantly influenced the cooling effect, accounting for 28.2% of the total. (3) The wetlands within the high-density building areas had a relatively high cooling efficiency, while the green space could expand the cooling extent. We propose building a number of small and connected wetlands in densely built-up areas instead of building large and isolated wetlands to improve the cooling efficiency of urban wetlands. • The threshold value of efficiency (TVoE) is 1.47 ± 0.34 ha in the inland megacity. • Building small wetlands is the important and cost-effective way to alleviate UHIs. • Hydrological connected wetlands exert higher cooling intensity than isolated ones. • The cooling efficiency in urban built-up areas is higher than nonurban areas. [ABSTRACT FROM AUTHOR]

• Agricultural labor migrants have a phased impact on rural land transfer in China. • Labor migration will significantly promote rural land transfer if it is less than or equal to 0.125 on the national level. • The thresholds of labor migration scale varied from different regions on the regional level. • Land transfer policies should be targeted to different labor migration phases and regions. Land transfer in rural areas and labor migration from rural areas to cities are both becoming common in China due to the increasing development of the non-agricultural sector resulting from rapid urbanization. Many rural labours who migrated to cities left their land in rural areas, and in most cases, this land was abandoned. To make full use of abandoned land in rural areas, the central government in China has formulated policies to promote rural land transfer, but rural land transfer still lags far behind labor migration in China. Drivers of rural land transfer still need to be explored. In addition, the labor migration scale shows dynamic features as the labor migration of more family members is substituted for that of individuals recent years. Thus, the phased feature of household labor migration should be taken into consideration to examine the phased influence of the labor migration scale on rural land transfer. Considering the probability threshold effect of the impact of labor migration on rural land transfer, a threshold model was used to perform the empirical analysis. Based on the threshold model and CHARLS 2015 data, this study empirically analysed the impact of the labor migration scale on rural land transfer. On the national level, labor migration will significantly promote rural land transfer if it is less than or equal to 0.125, but when it is greater than 0.125, its impact on land transfer is not significant. On the basis of the spatial differentiation of rural land transfer, four regions were divided to do the regional threshold regression analysis. On the regional level, the thresholds of labor migration scale of the central region, the east region and the west region are 0.112, 0.221 and 0.133 respectively, and there is no threshold in the north region. The results show that labor migration have a phased impact on rural land transfer in China and policies should be targeted to different labor migration phases and different regions. [ABSTRACT FROM AUTHOR]

The total arsenic concentrations of the three main drinking water types in China were determined through a systematic literature review. The distribution models of drinking water exposure parameters for different age groups were obtained using the regression method. The carcinogenic and non-carcinogenic risks of different population groups caused by arsenic exposure through different drinking water types were evaluated by a probabilistic risk assessment. The results showed that the geometric mean of total arsenic content in all the drinking water samples in China was (13.0±38.1) μg·L -1 . The highest arsenic content was found in the Inner Mongolia Autonomous Region, followed by Guangxi and Shanxi. Based on the relevant standards for drinking water quality, the probability exceeding the threshold value of groundwater and source water is 23.2% and 18.4%, respectively. According to the results of non-carcinogenic risk assessment, the probability of the residents drinking well water and surface water from the water source area exceeding the daily average exposure dose threshold was 24.0% and 19.5%, respectively. According to the carcinogenic risk assessment, the median of carcinogenic risk caused by arsenic in drinking water in China was 3.22×10 -5 , which is acceptable. The population group of 18-45 years old had the highest risk, and the median LCR was 1.37×10 -5 . There was still a certain probability that the LCR of drinking well water and surface water would exceed the acceptable risk level recommended by the US EPA. In conclusion, the potential health risks caused by arsenic exposure through drinking water intake exist among Chinese residents. Further control of the arsenic concentration in drinking water is required to reduce the health risk and improve the safety of drinking water. Meanwhile, it is suggested to strengthen the research on risk threshold to provide a scientific basis for the residents' health protection.

Aquiclude plays a critical role in the occurrence of mining-induced roof water inrush in underground coal mines. This paper proposes an assessment index for the evaluation of aquiclude stability and a threshold value of water inrush from the roof, based on a case study of roof water inrush accidents in Cuimu coal mine, China. The relation between roof water inrush and water level variation in the aquifer, and the characteristics of aquiclude deformation, were studied in this assessment. Using the developed assessment criteria, the likelihood of roof water inrush was categorized into different risk levels, which were followed by a proposal for roof water inrush control measures. The main findings of this study are: a) in Cuimu coal mine, the waterbody in the bed separation between the upper aquifer and the aquiclude directly causes the inrush, and inrush occurs after the water level declines in the aquifer; b) tension-induced horizontal strains of aquiclude can be regarded as the index to evaluate the stability of aquiclude affected by underground coal mining—roof water inrush occurs when the maximum horizontal strain reaches a threshold of 10mm/m—c) based on the critical mining height for aquiclude instability, and the different thicknesses of barrier layers, high-risk zones are identified and inrush controls are proposed. [ABSTRACT FROM AUTHOR]