Spatial and temporal distribution characteristics and risk assessment of heavy metals in groundwater of Pingshuo mining area.

Groundwater pollution in the Pingshuo mining area is strongly associated with mining activities, with heavy metals (HMs) representing predominant pollutants. To obtain accurate information about the pollution status and health risks of groundwater, 189 groups of samples were collected from four types of groundwater, during three periods of the year, and analyzed for HMs. The results showed that the concentration of HMs in groundwater was higher near the open pit, waste slag pile, riverfront area, and human settlements. Except for Ordovician groundwater, excessive HMs were found in all investigated groundwater of the mining area, as compared with the standard thresholds. Fe exceeded the threshold in 13-75% of the groundwater samples. Three sources of HMs were identified and quantified by Pearson's correlation analysis and the PMF model, including coal mining activities (68.22%), industrial, agricultural, and residential chemicals residue and leakage (16.91%), and natural sources (14.87%). The Nemerow pollution index revealed that 7.58% and 100% of Quaternary groundwater and mine water samples were polluted. The health risk index for HMs in groundwater showed that the non-carcinogenic health risk ranged from 0.18 to 0.42 for adults, indicating an acceptable level. Additionally, high carcinogenic risks were identified in Quaternary groundwater (95.45%), coal series groundwater (91.67%), and Ordovician groundwater (26.67%). Both carcinogenic and non-carcinogenic risks were greater for children than adults, highlighting their increased vulnerability to HMs in groundwater. This study provides a scientific foundation for managing groundwater quality and ensuring drinking water safety in mining areas.

Tracing spatial patterns of lacustrine groundwater discharge in a closed inland lake using stable isotopes.

Tracing lacustrine groundwater discharge (LGD) is essential for understanding the hydrological cycle and water chemistry behaviour of lakes. LGD usually exhibits large spatial variability, but there are few reports on quantitatively revealing the spatial patterns of LGD at the whole lake scale. This study investigated the spatial patterns of LGD in Daihai Lake, a typical closed inland lake in northern China, based on the stable isotopes (δ2H and δ18O) of groundwater, surface water, and sediment pore water (SPW). The results showed that there were significant differences between the δ2H and δ18O values of different water bodies in the Daihai Lake Basin: groundwater < SPW < lake water. The LGD through SPW was found to be an important recharge pathway for the lake. Accordingly, stable isotopes of SPW showed that LGD in the northeastern and northwestern of Daihai Lake was significantly greater both horizontally and vertically than that in the other regions, and the proportions of groundwater in SPW in these two regions were 55.53% and 29.84%, respectively. Additionally, the proportion of groundwater in SPW showed a significant increase with profile depth, and the proportion reached 100% at 50 cm below the sediment surface in the northeastern of the lake where the LGD intensity was strongest. The total LGD to Daihai Lake was 1.47 × 107 m3/a, while the LGD in the northeastern and northwestern of the lake exceeded 1.9 × 106 m3/a. This study provides new insights into assessing the spatial patterns of LGD and water resource management in lakes.

Characterization and drivers of water and carbon fluxes dynamics in dune ecosystems of the Horqin Sandy Land.

Sandy regions constitute pivotal components of terrestrial ecosystems, exerting significant influences on global ecological equilibrium and security. This study meticulously explored water and carbon fluxes dynamics within a dune ecosystem in the Horqin Sandy Land throughout the growing seasons from 2013 to 2022 by employing an advanced eddy covariance system. The dynamic characteristics of these fluxes and their underlying driving forces were extensively analyzed, with a particular focus on the impact of precipitation. The main results are as follows: (1) During the growing seasons of 2015 and 2016, the dune ecosystem acted as a modest carbon source, while in 2013, 2014, and 2017- 2022, it transformed into a net carbon sink. Notably, the annual mean values of water use efficiency (WUE) and evapotranspiration (ET) were 5.16 gC·kg-1H2O and 255.4 mm, respectively. (2) The intensity, frequency, and temporal distribution of precipitation were found to significantly influence the carbon and water fluxes dynamics. Isolated minor precipitation events did not trigger substantial fluctuations, but substantial and prolonged precipitation events spanning multiple days or consecutive minor precipitation events resulted in notable assimilation delays. (3) Air temperature, soil temperature, and fractional vegetation cover (FVC) were found to be key factors influencing the carbon and water fluxes. Specifically, FVC exhibited a negative logarithmic correlation with net ecosystem CO2 exchange (NEE) and a power function relationship with WUE. (4) The interaction between carbon and water fluxes is exhibited by exponential increases in ecosystem respiration (Reco) and gross primary productivity (GPP) with WUE, while NEE displayed an exponential decrease in relation to WUE. These findings are of high significance in predicting the potential ramifications of climate change on the intricate carbon and water cycles, and enhance our understanding of ecosystem dynamics in sandy environments.

Risk assessment and source apportionment of available atmospheric heavy metal in a typical sandy area reservoir in Inner Mongolia, China.

This study evaluated dry and wet deposition of atmospheric heavy metals (HMs) in a sandy area of Inner Mongolia, China, with the Dahekou Reservoir, Xilin Gol League, adopted as the study area. Monthly monitoring of atmospheric HM dry and wet deposition was conducted over one year (2021 to 2022) at 12 monitoring points, producing 144 dry and wet deposition samples, respectively. The sample contents of eight HMs (Cr, Ni, Pb, Cu, Zn, Mn, As, and Cd) were determined to estimate the fluxes of available forms of heavy metal (AHM) in dry and wet deposition. The potential ecological index (Eri), risk assessment coding (RAC), and ratio of secondary phase to primary phase (RSP) were used to evaluate the impact of atmospheric HM dry deposition on ecological security. Correlation analysis, principal component analysis, and the absolute principal component scores-multiple linear regression (APCS-MLR) receptor model were used to quantitatively analyze the sources of AHMs in atmospheric dry and wet deposition. The results showed that the study area experienced annual dry and wet deposition fluxes of AHMs of 1712.59 kg and 534.97 kg, respectively. Atmospheric heavy metal dry deposition over the entire year presented a strong ecological risk, with Cd contributing most to this risk. Risk assessment of HM speciation showed that the greatest risks of migration and transformation were for Cd and Pb. The APCS-MLR receptor model identified five and three sources of dry and wet deposition, respectively, in order of proportion of total contribution of: natural wind and sand > road traffic and coal combustion > mineral mining > other human activities > industrial soot.

Analysis of the distribution across media, migration, and related driving factors of fluoride in cold and arid lakes during the freezing period.

Fluoride pollution in water has become a global challenge. This challenge especially affects China as a country experiencing serious fluoride pollution. While the have been past studies on the spatial distribution of fluoride, there has been less attention on different forms of fluoride. This study collected 176 samples (60, 40, and 76 ice, water, and sediment samples, respectively) from Lake Ulansuhai during the freezing period. The occurrence and spatial distribution characteristics of fluoride in lake ice-water-sediment were explored using Kriging interpolation, Piper three-line diagram, and Gibbs diagram analysis methods. The migration and transformation of fluoride during the freezing period were revealed and the factors influencing fluoride concentration in the water body were discussed considering the hydrochemical characteristics of lake surface water. The results showed that the average fluoride concentrations in the upper ice, middle ice and lower ice were 0.18, 0.09, and 0.12 mg/L, respectively, decreasing from north to south in the lake. The average concentrations of fluoride in surface water and bottom water were 0.63 and 0.83 mg/L, respectively. The concentrations of fluoride in ice and water were within the World Health Organisation drinking water threshold of 1.50 mg/L and the Class III Chinese surface water standard (GB3838-2002). The average sediment total fluorine was 1344.38 ± 200 mg/kg, significantly exceeding the global average (321 mg/kg) and decreasing with depth. The contents of water soluble, exchangeable, Fe/Mn bound, organic bound, and residual fluorides were 40.22-47.18, 13.24-43.23, 49.52-160.48, and 71.59-173.03 mg/kg, respectively. There was a significant positive correlation between fluoride concentration in ice and that in water. The change in fluoride concentration in water was mainly due to specific climatic and geographical conditions, pH, hydrochemical characteristics and ice sealing. This study is of great significance for the management of high-fluorine lakes in arid and semi-arid areas.

Effects of coal mining and climate-environment factors on the evolution of a typical Eurasian grassland.

Coal mining can significantly impact vegetation evolution, yet the limited information on its patterns and driving factors hampers efforts to mitigate these effects and reclaim abandoned mines. This study aimed to 1) examine vegetation evolution in a semiarid steppe watershed in northeast China; and 2) characterize the driving factors behind this evolution. We analyzed the impact of twelve selected driving factors on fractional vegetation coverage (FVC) from 2000 to 2021 using a dimidiate pixel model, Sen's slope analysis, Mann-Kendall trend test, coefficient of variation analysis, and Geodetector model. At a significance level of α = 0.05, our findings revealed a south-to-north decline pattern in FVC, a significant decrease trend in proximity to coal mines, and a notable increase trend adjacent to river channels. Approximately 37% of the watershed exhibited low FVC, while the overall temporal trend across the watershed was deemed insignificant. Areas surrounding the mines experienced a substantial reduction in FVC due to coal mining activities, while FVC variations across the watershed were linked to precipitation, temperature, and soil type. FVC predictions improved notably when interactions between multiple two-way factors were considered. Each driving factors displayed an optimal range (e.g., precipitation = 63-71 mm) for maximizing FVC. Given the study watershed's status as a national energy base, understanding vegetation responses to coal mining and climate-environment changes is crucial for sustaining fragile terrestrial ecosystems and socioeconomic development. Achieving a long-time balance between coal extraction and ecological protection is essential. The study outcomes hold significant promise for advancing ecological conservation, vegetation restoration, and mitigation of environmental degradation in semiarid regions affected by extensive coal mining and climate fluctuations. These findings contribute to the strategic management of such areas, promoting sustainable practices amidst evolving environmental challenges.

[Hydrochemical Characteristics and Control Factors of Groundwater in the Northwest Salt Lake Basin].

Taking the Tugeligaole sub-basin of the Jilantai Salt Lake Basin in Inner Mongolia as the typical study area, the groundwater samples of 22 points were collected, and their main characteristic indexes were tested during the wet season and the dry season separately in 2021. Mathematical statistics, Piper triangular diagrams, a Gibbs plot, ionic relations, and factor analysis were used to analyze and discuss the hydrochemical characteristics and formation mechanism of groundwater in different periods. Based on the evaluation of the groundwater quality using the water quality index(WQI) method, the potential risks of groundwater Cr6+ and F- were evaluated using the health risk evaluation model. The results showed that the groundwater was overall weakly alkaline; the dominant anions and cations during the different periods were Cl- and Na+, and the water chemistry type was mainly Cl--Na+; the groundwater quality was generally good, and the difference in water quality between the wet season and the dry season was not significant; adults and children had higher carcinogenic health risks in the dry season than that in the wet season, and the health risks of children were significantly higher than those in adults. The maximum carcinogenic health risk of drinking water exposure to Cr6+ in adults and children was higher than the maximum acceptable risk level(5×10-5). The chemical evolution of groundwater was mainly affected by evaporative concentration, evaporative salt rock dissolution, and cation exchange, and the main control factors were evaporative concentration(contribution rate of 54.19%), native geological environment factors(contribution rate of 12.99%), and carbonate rock dissolution(contribution rate of 11.66%). The study results have significance to some degree to the sustainable exploitation and utilization of groundwater resources and environmental protection of the salt lake basin.

[Relationship Between Precipitation, River Water, and Groundwater Conversion in the Upper Reaches of Xilin River During the Rainy Season].

To deeply understand the hydrological cycle process and the transformation mechanism of different water bodies in the grassland inland river basin, the atmospheric precipitation, river water, and groundwater in the Xilin River Basin were taken as the research objects, the hydrogen and oxygen stable isotopes were analyzed, and the multi-scale spatio-temporal characteristics were analyzed to explore the quantitative transformation relationship between different water bodies in the basin. The results showed that:① the Xilin River Basin had an obvious inland semi-arid climate, the atmospheric precipitation was the main source of recharge for the river water and groundwater, and the groundwater and river water experienced different degrees of non-equilibrium evaporation at the same time. ② The isotopic composition of the river water showed the characteristics of depletion in spring and autumn and enrichment in summer and showed a trend of increasing from upstream to downstream in space. The variation in δ18O in shallow and deep groundwater during the growing season was basically the same, and the main difference between the two occurred at the end of the growing season, that is, the former tended to be stable, whereas the latter showed an upward trend, which reflected that the deep groundwater had a lagged response to the infiltration and recharge of atmospheric precipitation and surface water, and both of them were depleted gradually from southeast to northwest in space. ③ Based on the estimation results of the endmember mixing model, the average recharge ratio of atmospheric precipitation and shallow groundwater to river water in summer was 52.69% and 47.31%, respectively, indicating that shallow groundwater was an important recharge source of river water in the inland river basin even during the rainy season. The results of this study provide theoretical guidance for water resource regulation and ecological environment protection in a typical semi-arid grassland inland river basin.

[Risk Assessment of Heavy Metals in Dust Fall Around Reservoirs in Typical Ecologically Fragile Areas and Traceability Based on APCS-MLR Model].

To assess the health risk status and pollution sources of heavy metals in the atmosphere of ecologically vulnerable areas, the surrounding area of Dahekou Reservoir in Xilingol League was selected as the study area. From 2021 to 2022, 12 monitoring points for atmospheric dust fall were collected for a period of one year. A total of 144 samples were collected to determine the contents of eight types of heavy metals, namely Cr, Ni, Pb, Cu, Zn, Mn, As, and Cd. The potential ecological index (Eri) and health risk assessment model were used to assess the risk level of atmospheric heavy metals on ecological security and human health. The analysis of enrichment factors, principal components, and the model of absolute principal component multiple linear regression (APCS-MLR) receptor were used to analyze the sources of heavy metal pollution qualitatively in the atmosphere of the study area. The results showed that:① the mean value of the comprehensive potential ecological risk of heavy metals in the annual atmospheric dust fall in the study area was at a high ecological risk, and only the Cd value was at a very high risk level among the heavy metals, whereas the remaining were at a slight risk. ② The results of the health risk showed that intake by hand, mouth, and skin contact were the main exposure routes, which led to non-carcinogenic and carcinogenic risks. Children were under non-carcinogenic and acceptable carcinogenic risks in different months. During those months, the main source of the risks was As. ③ Through enrichment factor analysis, principal component analysis, and APCS-MLR receptor model calculation, the results revealed that the proportion of wind-blown sources was the largest, accounting for 37.82%, and the contribution rates of coal combustion and traffic sources to Cu, Cd, Pb, and Zn were 73.01%, 40.22%, 70.31%, and 32.82%, respectively. The contribution rate of mining activities to As was 42.59%, while that of industrial sources of Cd was 22.01%; the contributions of other human activity sources of Cd, As, Pb, and Zn were 21.12%, 34.40%, 23.04%, and 32.15%, respectively.

Deciphering spatio-seasonal patterns, driving forces, and human health risks of nitrate and fluoride enriched water bodies in the Inner Mongolia Reaches of the Yellow River Basin, China.

The ecology and environment of the Yellow River Basin is threatened by fluoride and nitrate contamination induced by anthropogenic activity and geogenic factors. As a result, deciphering the spatio-temporal variability of fluoride and nitrate contamination in this area remains a challenge. Three hundred eighty-six samples of surface water and groundwater from the Inner Mongolia Reaches of the Yellow River Basin were taken for this investigation. According to the results of the multivariate statistical and geostatistical analyses, the fluoride pollution was primarily discovered in the middle and lower reaches of the study area and was determined to be more severe during the dry season. In contrast, nitrate contamination was found to be more severe during the wet season while being widely distributed in groundwater and concentrated in areas with intensive agricultural activities. The primary mechanisms governing the spatial-seasonal patterns of NO3- and F- pollution were shown by the principal component analysis, isotopic, and hydrochemical diagrams. The water-rock interaction or evaporation was crucial in the enrichment of F-. The human inputs (e.g., fertilizer or sewage) dominated fluoride and nitrate contamination. Additionally, the alkaline environment played a role in the generation of NO3- and F-. The health risk assessment concluded that the threat of fluoride contamination was greater than that of nitrate contamination. Children faced the greatest health risks, followed by females and males. These findings would serve as a guide for water management and pollution control in the Yellow River Basin.

[Water Chemical Isotope Characteristics and Water Transformation Relationship in Mongolian Section of the Yellow River Basin].

The Yellow River in Inner Mongolia was selected as the study area in this study. In July (wet season) and October (dry season) of 2021, the acquisition of seasonal rivers, the Yellow River tributaries and precipitation, the Yellow River, Wuliangsuhai, Lake Hasuhai, Lake Daihai, an irrigation canal system, and underground water and sea water samples were collected to test the water chemical composition and hydrogen and oxygen isotopic values of different water types. Using the Piper triplot, Gibbs plot, ion ratio, and MixSIAR model methods, the evolution of water chemistry in the Mongolian section of the Yellow River Basin was analyzed, and the transformation relationship between precipitation, surface water, and groundwater was revealed. The results showed that both groundwater and surface water in the study area were slightly alkaline; the dominant anion in water was Cl-, and the dominant cation was Na+. The main hydrochemical types of surface water were Cl·SO4-Na·Mg and SO4·HCO3-Na·Mg, whereas those of groundwater were Cl·SO4-Na·Mg and SO4·HCO3-Na·Ca. Groundwater Ca2+ and Mg2+ were primarily derived from the dissolution of silicate and evaporite, and surface water Ca2+ and Mg2+ were primarily derived from carbonate karst dissolution and carbonate and sulfuric acid in water participating in the dissolution process of carbonate and sulfide minerals. Na+ and Cl- in different water bodies were all affected by anthropogenic pollution sources. Owing to the seasonal effect, δD and δ18O of surface water and groundwater were higher in the wet season than in the dry season. The results showed that surface water was affected by evaporative fractionation after receiving precipitation recharge, and the groundwater recharge sources were complex. The MixSIAR model revealed that surface water was the main recharge source of groundwater, accounting for 52.4%-62.2% of the total recharge, and atmospheric precipitation was the main recharge source of surface water, accounting for 85.4%-97.1% of the total recharge.

Spatiotemporal variations of ecosystem security pattern in Horqin sandy dune meadow alternating area, China.

The natural and geographical environment of ecologically fragile areas in northern China is complex. Due to heavy human disturbance and impacts of climate change, the sustainable development of ecosystems is facing serious challenges. Constructing ecological security pattern can provide decision-making basis for ecological environment protection in desertification areas. Based on land use change data of Horqin dune-meadow interphase area from 1985 to 2021, we identified ecological sources with the importance of ecosystem services and ecological sensitivity, and constructed the ecological security pattern using the minimum cumulative resistance model. We further analyzed the ecological security pattern and its development trend in 1985, 1995, 2005, 2015 and 2021, and explored the ecological spatial layout adjustment strategy. The results showed that the proportion of source area in the ecological security pattern of the study area was always small and scattered from 1985 to 2021, the network of ecological corridors was low, and the connectivity between ecological patches was lacking. The ecological security pattern had experienced a trend of deterioration first and then gradually improving. Ecological policies such as returning farmland to forest and grassland and afforestation had significantly improved the environmental security. We optimized the study area by combining the cultivated land suitability evaluation method. The ecological security pattern showed a spatial trend of 'dual-core, scattered and semi-surrounded'. The results could provide references for the construction of county-scale ecological security pattern in ecologically fragile areas and the ecological management of Horqin sands.

Treatment change comparisons between skeletal Class I and II white adolescents with 3 different vertical divergencies-part 1: Frankfort-Mandibular Incisor Angle (FMIA) and soft-tissue profile.

INTRODUCTION: This study investigated the interrelationship between FMIA and soft-tissue profile changes in skeletal Class I and II white adolescents with 3 different vertical skeletal patterns. METHODS: Two hundred seventy cephalometric images were constructed from pretreatment and posttreatment cone-beam computed tomography images of 135 white adolescents (69 females and 66 males with a mean age of 12.8 ± 1.4 years pretreatment and 15.0 ± 1.4 years posttreatment). SNA, SNB, ANB, Frankfort Mandibular Angle [FMA], Incisor Mandibular Plane Angle [IMPA], Frankfort-Mandibular Incisor Angle [FMIA], and Z angle were measured. A mixed-model analysis of variance was performed for patients with an increased posttreatment Z angle to evaluate within-subject and between-subject effects of variables in relation to horizontal and vertical skeletal patterns. Post-hoc tests were conducted to identify statistical significance among the 3 different divergent subgroups. RESULTS: Patients with a skeletal Class I relationship had straighter facial profiles and a larger FMIA than patients with a skeletal Class II relationship before and after treatment. FMA, FMIA, IMPA, and Z angle treatment changes were similar between the skeletal Class I and II groups. The final FMIA means of the 3 divergent subgroups converged at 65° in the skeletal Class I group and 60° in the skeletal Class II group. The mandibular incisors were uprighted during treatment in the hyperdivergent patients whose Z angle values increased after treatment. CONCLUSION: Horizontal skeletal relationships seem more suitable for determining the desired FMIA in Tweed's total space analysis than vertical skeletal divergencies.

Variability in the minimum temperature over two centuries in the overlap region between the fringe of the Asian westerly region and the temperate continental-monsoon climate transition zone.

The overlap region between the eastern fringe of the Asian westerly region and the temperate continental-monsoon climate transition zone is sensitive to climate changes and is characterized by fragile ecosystems. Uncovering the long-term historical climate variability patterns in this region is necessary. A standardized tree-ring width chronology was constructed based on the tree-ring samples collected from four representative tree species in four typical areas in the overlap region, and the 203- to 343-year annual mean minimum temperature series in the overlap region were reconstructed. The reconstructed series overlapped well with extreme climate events and low-temperature periods recorded in historical data. Therefore, the reconstructed model is stable and reliable. As suggested by the reconstructed series, the annual average minimum temperature in the overlap region changes sharply from east to west, and the periodicity change in the overlap region shows a trend of gradually weakening from the east and west ends to the middle. In the nineteenth century, the high-latitude area was in the high-temperature period, and the entire overlap region experienced significant low-temperature periods lasting 20-45 years until the 1950s. The western part had an earlier low-temperature period start time, a longer cooling duration, and a slower cooling rate than the central part. The overlap region experienced a significant warming period in approximately the last half-century, with temperatures increasing faster in the western and eastern parts than in the central part. The temperature variability in the overlap region was more intense in the last two centuries, with shorter periodicities and a larger proportion of cold periods. The central and western parts of the Asian westerly region, the mid- to high-latitude regions of the transition zone, and the overlap region experienced significant low-temperature periods or drastic cooling trends (the Little Ice Age) in the first half of the nineteenth century and significant warming trends afterwards due to global warming. The influences of these changes may have been exacerbated by the westerly circulation. The results of this study provide new insights into the use of dendroclimatology to extract temperature series in the Asian westerly region and the transition zone and a reference for research on global climate change.

Experimental analysis of soil moisture response to rainfall in a typical grassland hillslope under different vegetation treatments.

The responses of soil moisture to rainfall are of great significance for watershed hydrological modeling. However, few studies have been done to investigate these responds on hillslope in a typical semi-arid grassland region. This study used high temporal resolution soil moisture data to explore the soil moisture dynamics, response conditions and its controls of 0-40 cm soil profile in the upslope (14°), midslope (9°), and downslope (4°) of a typical grassland inland river basin under bare ground (BG), stubble (SG), and natural grassland (CK) treatments. The results showed that soil water content and water storage increased in the downslope direction, and all showed as BG > SG > CK. The dry and wet changes in fast-changing layer (5 cm) and active layer (10 cm) were rapid, while soil moisture below 20 cm was relatively stable and fluctuated only in heavy or continuous rainfalls. The soil moisture response process varied greatly under different rainfall, rainfall intensity and antecedent soil moisture conditions, which explained 41.1% of the total difference. The rainfall replenishment threshold and the required initial soil profile water content of soil moisture response in 5 cm, 10 cm and 20 cm soil layers were 5.8 mm, 8.0 mm, 11.4 mm and 8.7 vol%, 9.4 vol%, 10.8 vol%, respectively. Soil properties, vegetation characteristics and topography could explain 38.8%, 14.5% and 5.6% of the soil moisture variation on the hillslope. In addition, under the comprehensive influence of environmental factors, changes in soil moisture of the upslope were significantly affected by soil sand content, the differences in the midslope were mainly due to soil clay content and belowground biomass, whereas the vegetation characteristics were the main factors in the downslope. This study can contribute to the further understanding of slope-scale ecohydrological processes and hydrological simulation of semi-arid grassland watersheds.

Forecasting groundwater level of karst aquifer in a large mining area using partial mutual information and NARX hybrid model.

Predicting the groundwater level of karst aquifers in North China Coalfield is essential for early warning of mine water hazards and regional water resources management. However, the dynamic changes of strata structure and hydrogeological parameters driven by coal mining activity cause challenges to the process-oriented groundwater model. In order to achieve accurate prediction of groundwater level in large mining areas, this study was the first to use the data-driven Nonlinear Autoregressive with External Input (NARX) model to predict the groundwater level of six karst aquifer observation wells in Pingshuo Mining Area. Three variable input scenarios were set up, solely considering meteorological factors, anthropogenic disturbance factors, and considering both meteorological and anthropogenic disturbance factors. The novel partial mutual information (PMI) screening algorithm was adopted to determine optimized input variables in each scenario. The input and feedback delay coefficients of NARX model were determined by using Seasonal-trend Decomposition Procedure Based on Loess (STL) algorithm and auto- and cross-correlation functions. The results showed that PMI algorithm can effectively screen out the optimal input variables for predicting groundwater level, the NSE coefficients of the PMI-NARX models under the three scenarios were 38.81%, 4.26% and 41.46% higher than those of the corresponding control experiments, respectively. In addition, the prediction performance of the PMI-NARX built on the basis of meteorological factors is poor (NSE <0.63). However, in scenarios which solely use anthropogenic disturbance factors and both use meteorological and anthropogenic disturbance factors, the PMI-NARX coupling models exhibit good prediction performance (NSE and R2 are all greater than 0.8). Especially under solely considering anthropogenic disturbance factors scenario, the model still exhibited good prediction accuracy with a negligible number of input variables. The results can provide technical and theoretical support for the prediction of groundwater level in other mining areas.

[Temporal and spatial variations of annual precipitation and meteorological drought in China during 1951-2018]. / 1951­2018年中国年降水量及气象干旱的时空变异.

Exploring the temporal and spatial variations of precipitation and drought is an important topic in hydro-logy. Based on the precipitation data of 619 meteorological stations in China from 1951 to 2018, we used anomaly percentage method and Morlet wavelet analysis to analyze the temporal and spatial variations of annual precipitation and drought. The results showed that annual precipitation in China showed a stepwise decreasing trend from southeast to northwest during the study period, and that the intensity of annual precipitation change was on the contrary. The precipitation near the boundary of the second and third steps showed a downward trend, and the abrupt change of precipitation occurred mainly in the 1960s and 1970s. The rest region was on the rise, with substantial changes in the 1990s. The main period of precipitation was short in the regions with temperate continental climate and temperate monsoon climate. From 1960s to 2010s, the area of arid land in China had decreased, while that of the semi-arid area and semi-humid area had increased gradually, especially in the recent decade. An aridity boundary was found between 30° N and 40° N, with drought frequency in its north being much more than the south. On the whole, the frequency and scope of drought events showed a decreasing trend and its interdecadal shift direction was from the central part of northwest China to the southern part of North China and then to the northern part of North China.

Spatiotemporal hysteresis distribution and decomposition of solar activities and climatic oscillation during 1900-2020.

Solar radiation is the external driving force of the Earth's climate system. In different spatial and temporal scales, meteorological elements have different responses and lag periods to solar activity (SA), climatic oscillation (CO), geographic factors (GF) and other influencing factors. However, such studies are not abundant and in-depth in the world. To further understand the "solar-climate-water resource" system, this study considers China as the study area and investigates the monthly data of temperature (T) and precipitation (P) during 1900-2020 that were obtained from 3836 grid stations. The strong interaction and lag distribution between T or P with SA and CO were studied and influence weights of SA, CO, and geographical factors (GF) of each grid station were calculated. A multivariate hysteretic decomposition model was established to simulate and quantitatively decompose the periodic lag considering the factors of the earth's revolution. It is found that the strong interaction/lag periods obtained in a long-time scale can be decomposed into several periods shorter than the SA period. The distribution of strong interaction/lag periods is nested with topography and echoes with cities. The underlying surface conditions and urbanization are also important factors affecting the T and P lag. There are two distinct dividing lines in the lag period and influencing factor pattern of T and P. The T dividing line moves through valleys where water or mountain ranges meet, where the gap facilitates monsoon movement across regions, while the P dividing line is a zone of dramatic terrain, where tall mountains block water vapor transport. In the lag trend of T, the northern region of China has the longest lag period, and the lag period of surrounding regions tends to converge to the northern region. The lag period caused by SN in southwest China is larger than that in northwest China, while the lag effect of CO is opposite in the above two regions. The lag trend of P also has the above characteristics, but the difference is that the lag period in central China is the longest.

Hydrochemical assessments and driving forces of groundwater quality and potential health risks of sulfate in a coalfield, northern Ordos Basin, China.

Groundwater is the primary water source in coalfields under arid and semiarid climates. However, the problem of excessive concentrations of sulfate, which is a constant component in coalfields, and its potential health risks are often neglected in Northwest, China. To determine the groundwater quality, health threats, and driving forces of sulfate in coal mine groundwater, this study performed hydrochemical and isotopic analyses of 61 groundwater samples from a typical coalfield in northwestern China. We found that phreatic groundwater had lower total dissolved solid (TDS) and freshwater hydrochemical types (mainly Ca-HCO3 and Ca-Na + K-HCO3 types). In contrast, confined groundwater showed saline affinity (Na + K-SO4 type) and high TDS values, and the quality was unacceptable for drinking, with EWQI values larger than 100, which could be attributed to its high SO42- concentration. In addition, confined groundwater was also unsuitable for irrigation with high values of electric conductivity (EC), sodium absorption ratio (SAR), and Na%. Combining with isotopic analysis (δD, δ18Owater, δ34S and δ18Osulfate), the sulfate of confined and phreatic groundwater was controlled by gypsum dissolution and irrigation activities. As for public human health, SO42- poses potential non-carcinogenic risks to various populations, especially children. Therefore, the impact of geogenic and anthropogenic factors should be paid attention to, including the reduction of the use of sulfur-containing fertilizers and discharge of sulfur-containing sewage; and the water treatment should be carried out. Importantly, there is a need to adopt a strategy of water supply from multiple sources to ensure human health.

A comparative study of three stomatal conductance models for estimating evapotranspiration in a dune ecosystem in a semi-arid region.

The accurate simulation of stomatal conductance is crucial for not only revealing the carbon and water cycle processes of an ecosystem, but also to improve the accuracy of simulations of evapotranspiration (ET). This study coupled three stomatal conductance models, i.e. the Stannard (ST), Jarvis-Stewart (JS), and Ball-Berry (BB) models, with the Shuttleworth-Wallace (SW) model to estimate ET for a mobile dune ecosystem in the Horqin Sandy Land, North China. These models were calibrated and validated using eddy covariance (EC) measurements taken during the growing season between 2013 and 2018. The results indicated that the SW-BB model showed better performance in comparison to the SW-JS and SW-ST models at half-hourly and daily timescales. The stomatal conductance models incorporating soil moisture (SM) content generally showed better performance during the extreme drought period, with the rank of the three models according to performance being: SW-BB > SW-JS > SW-ST. The models showed the highest sensitivity to SM when incorporating the effect of SM on stomatal conductance, indicating that SM has an important effect on stomatal conductance and ET. The results of this study indicate that of the models assessed, the Ball-Berry stomatal conductance model coupled with the SW model is optimal for estimating ET in dune ecosystems with sparse vegetation.