Spatial variability of source contributions to nitrate in regional groundwater based on the positive matrix factorization and Bayesian model.

Groundwater nitrate (NO3-) pollution has attracted widespread attention; however, accurately evaluating the sources of NO3- and their contribution patterns in regional groundwater is difficult in areas with multiple sources and complex hydrogeological conditions. In this study, 161 groundwater samples were collected from the Poyang Lake Basin for hydrochemical and dual NO3- isotope analyses to explore the sources of NO3- and their spatial contribution using the Positive Matrix Factorization (PMF) and Bayesian stable isotope mixing (MixSIAR) models. The results revealed that the enrichment of NO3- in groundwater was primarily attributed to sewage/manure (SM), which accounted for more than 50 %. The contributions of nitrogen fertilizer and soil organic nitrogen should also be considered. Groundwater NO3- sources showed obvious spatial differences in contributions. Regions with large contributions of SM (>90 %) were located in the southeastern part of the study area and downstream of Nanchang, which are areas with relatively high population density. Nitrogen fertilizer and soil organic nitrogen showed concentrated contributions in paddy soil in the lower reaches of the Gan and Rao Rivers, and these accumulations were mainly driven by the soil type, land use type, and topography. This study provides insight into groundwater NO3- contamination on a regional scale.

Source and evolution of sulfate in the multi-layer groundwater system in an abandoned mine-Insight from stable isotopes and Bayesian isotope mixing model.

The source and evolution of sulfate (SO42-) in groundwater from abandoned mines are widely concerned environmental issues. Herein, major dissolved ions, multi-isotopes (δ34S, δ18Osulfate, δ2H and δ18Owater), machine learning (Self-organizing maps) and Bayesian isotope mixing model were used to identify the source and evolution of SO42- in an abandoned mine (Fengfeng mine, northern China) with a multi-layer groundwater system. Groundwater in the study area was mainly divided into three clusters (Cluster I, Cluster II and Cluster III), dominated by Na-SO4, Ca-SO4 and Ca-HCO3 types, respectively. According to δ2H and δ18Owater, groundwater in the study area mainly originated from atmospheric precipitation. δ34S, δ18Osulfate and SO42- suggested that bacterial sulfate reduction did not affect the SO42- isotopic composition. Dual SO42- isotopes, and MixSIAR model revealed that the main source of SO42- in the study area was pyrite oxidation/gypsum dissolution, accounting for an average of 57.4 % (gypsum), 71.24 % (pyrite oxidation) and 52.93 % (pyrite oxidation) of SO42- in the samples of Clusters I-III, respectively. Combined with the hydrochemical diagrams, the evolution of SO42- in different clusters of samples was derived. Cluster I was mainly gypsum dissolution; In contrast, Clusters II and III were mainly pyrite oxidation accompanied by carbonate dissolution, and Cluster II was also influenced by cation exchange. These findings will help in developing management strategies for protecting groundwater quality, which will provide a reference for the study of solute sources and S cycling in abandoned mines.

Geochemical fingerprint and spatial pattern of mine water quality in the Shaanxi-Inner Mongolia Coal Mine Base, Northwest China.

The spatial distribution of mine water quality and geochemical controls must be investigated for water safety and ecosystem protection in Shaanxi-Inner Mongolian Coal Mine Base (SICMB). Based on 122 mine water samples collected from 14 mining areas, self-organizing maps (SOM) combining with principal component analysis (PCA) derived that the mine water samples were classified into seven clusters. Clusters 1 and 3 (C1 and C3) samples were dominant by HCO3-Ca and mixed types, which were distributed in the recharge area of the middle SICMB. In this area, the active groundwater circulation contributed to the good water quality. Cluster 2 (C2) samples were characterized by HCO3-Na type, mainly distributed in the discharge area of the middle SICMB. These samples were threatened by heavy fluorine contamination and high residual sodium carbonate (RSC) because of slow groundwater flow in this area. Clusters 4 and 5 (C4 and C5) samples, distributed in the northeast and middle SICMB, were characterized by high Cl- concentration and light fluorine contamination. They were influenced by anthropogenic input through faults or underground mining. In contrast, Clusters 6 and 7 (C6 and C7) samples with high salinity and sulfate were distributed in the southwest SICMB. The deep groundwater circulation enhanced water-rock interaction and contributed to poor water quality. These findings are beneficial to the management of mine water resources in the SICMB and provide an insight to investigate the mine water quality in large spatial scale.

Preparation of hollow-fiber nanofiltration membranes of high performance for effective removal of PFOA and high resistance to BSA fouling.

Nanofiltration (NF) process has become one of the most promising technologies to remove micro-organic combined water pollution. Developing a NF membrane material with efficient separation for perfluorooctanoic acid (PFOA) combined pollution is highly desired, this manuscript targets this unmet need specifically. In this work, hydrophilic SiO2 nanoparticles with various contents blended with carboxylic multiwalled carbon nanotube were used to modify poly (m-phenylene isophthal amide) (SiO2/CMWCNT/PMIA) hollow fiber NF membrane. The modified membrane with 0.1 wt% SiO2 doping exhibits way better fouling resistance with irreversible fouling ratio decreased dramatically from 18.7% to 2.3%, and the recovery rate of water flux increases significantly from 81.2% to 97.7%. The separation experiment results had confirmed that the modified membrane could improve the rejection from 97.2% to 98.6% for perfluorooctanoic acid (PFOA) and its combined pollution with bovine serum albumin (BSA). It is clear that this reported SiO2/CMWCNT/PMIA hollow fiber NF membrane potentially could be applied in water treatment. This research also provides a theoretical basis for efficiently removal of PFOA and its combined pollution by NF membrane.

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.

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.

Identifying locations and sources of groundwater discharge into Poyang Lake (eastern China) using radium and stable isotopes (deuterium and oxygen-18).

Knowledge of groundwater discharge (location and sources) into Poyang Lake is needed for water resources management and ecological security. In this study, hydrochemical and stable (δD and δ18O) and radium (223Ra, 224Ra, 226Ra, and 228Ra) isotopic approaches were employed to study the hydrochemical and isotopic characteristics of groundwater and surface water (river water and lake water) to identify the places where groundwater discharged into Poyang Lake and the groundwater discharge sources. The results showed that the groundwater discharge area was extensive during the dry season. The locations of predominant groundwater discharge were indicated by the evolution of radium and stable isotopes in lake water along two water flow profiles. At the confluence of Ganjiang and Xiushui rivers, groundwater with more negative δ18O value than that of the lake water discharged into this area, and the estimated groundwater discharge proportion in this area was close to that of the river water input. The main sources of groundwater input for Poyang Lake were inferred to originate from clastic rock pore-fissure aquifer and bedrock fissured aquifer around this lake. This study also found that groundwater affected by the anthropogenic activities may have discharged into Poyang Lake. Future studies are required to focus on groundwater discharge into Poyang Lake for its management and protection.

Temperature governs the distribution of hot spring microbial community in three hydrothermal fields, Eastern Tibetan Plateau Geothermal Belt, Western China.

The eastern Tibetan Plateau geothermal belt in the southwest of China hosts a number of hot springs with a wide range of temperature and hydrogeochemical conditions, which may harbor different niches for the distribution of microbial communities. In this study, we investigated hydrochemical characteristics and microbial community composition in 16 hot springs with a temperature range of 34.6 to 88.2 °C within and across three typical hydrothermal fields (Kangding, Litang, and Batang). According to aquifer lithologic and tectonic differences, the hydrochemical compositions of hot springs displayed an apparent regional-specific pattern with distinct distributions of major and trace elements (e.g., Ca2+, Mg2+, F-/B) and were primarily formed by water-rock interaction across the three hydrothermal fields. Nonetheless, microbial communities significantly assembled with the temperature rather than the geographic locations with distinct hydrogeological features. Low temperature (<45 °C), moderate temperature (55-70 °C) and high temperature (>70 °C) groups were identified based on their community compositions. Proteobacteria and Nitrospirae were the predominant phyla in low-temperature hot springs, while in moderate to high-temperature springs they were mainly composed of Aquificae, Deinococcus-Thermus, Thermodesulfobacteria, Thermotogae and Cyanobacteria. Variation partition analysis suggested a higher explanation of temperature (29.6%) than spatial variable (1.8%) and other geochemical variables (2.5%) on the microbial distribution. Microbial co-occurrence network showed >80% negative associations hinting a low co-existence pattern and highlighted the driving force of temperature as well as F- or total organic carbon (TOC) for microbial interactions. Microbial dissimilarity displayed significant linear correlations with environmental (temperature) and geographic distance in Batang but only with temperature in Kangding area, which might be attributed to the regional-specific hydrogeochemistry. This study may help us to better understand the distribution of the microbial community in hot spring across different hydrothermal fields.

Groundwater microbial communities and their connection to hydrochemical environment in Golmud, Northwest China.

Groundwater microbial community normally co-varies with the associated geochemical transect in some hydrogeological sections along flowpath. However, in hydrogeological section with similar geochemical transect (e.g., salinity, ion compositions) how microbial community in groundwater varies are poorly understood. In this study, groundwater samples were collected at six boreholes vertically and horizontally along a generalized groundwater flowpath in the Golmud area, Qaidam Basin, northwest China. High-throughput sequencing and multivariate statistical analysis were applied to explore the underlying relationships between microbial community structure and hydrogeochemical environment. The result showed that microbial communities changed considerably at both horizontal and vertical scales, although the groundwater samples were of relatively stable ionic compositions and hydrochemical types. The dominant bacterial phyla in groundwater varied from Alphaproteobacteria, Betaproteobacteria and Flavobacteriia in 'phreatic and phreatic-like' groundwater in the recharge area to Gammaproteobacteria in the confined groundwater in the lacustrine plain. At both vertical and horizontal scale, Gammaproteobacteria increased while Alpha- and Betaproteobacteria decreased as the function of distance. Genera Roseateles, Aquabacterium, Sphingomonas, Acinetobacter, Acidovorax and Flavobacterium presented in phreatic groundwater, while Pseudomonas, Hydrogenophaga and Perlucidibaca presented in confined groundwater. Spatial distribution of microbial community was highly affected by the pH (for 'phreatic and phreatic-like' groundwater) and ORP (for confined groundwater) of groundwater that had similar salinity or ion compositions. This research extends our knowledge about microbial communities' variation along groundwater flowpath in studied area and similar arid or semi-arid areas.

Isotopes in groundwater (2H, 18O, 14C) revealed the climate and groundwater recharge in the Northern China.

We collected 3275 sets of δD and δ18O and 1451 14C data of groundwater in 14 basins or plains in the Northern China from the published sources in an attempt to investigate the isotopic characteristics of groundwater and their possible link with groundwater recharge and modern and past climate conditions in regional scales. The results showed that the deuterium excess of groundwater in the Monsoon regions were generally lower than that in the Westerly regions in the Northern China, reflecting the influences of different vapor sources and transmission modes. The δD and δ18O in groundwater lied closely to the Asian summer monsoon limit (ASML) were affected by both the Asian monsoon and Westerlies. The δD and δ18O of groundwater exhibited obvious latitude effect in the monsoon region, while it seemed to be dominated by the continental and elevation effects in the Westerly region both in the late Pleistocene and the Holocene. Based on the isotopic proxy records of climates, the depletion in 18O and D of the groundwater recharged in last glacial period in the late Pleistocene was observed which indicated that it was cooler especially in the Last Glacial Maximum (LGM), while the 18O and D were enriched in groundwater recharged in the Holocene. The transition from the late Pleistocene to Holocene was characterized by higher frequency fluctuation of δ18O in the groundwater, probably suggesting that the climatic conditions were unstable. The groundwater recharge could be roughly divided into three main periods under relative warm and humid climates. The variation of regional climate was one of the driving forces for the recharge and regeneration of groundwater. Our results may enhance the understanding of groundwater recharge and its connection with the climate changes in the regional scales.