Improving multidimensional normal cloud model to evaluate groundwater quality with grey wolf optimization algorithm and projection pursuit method.

Groundwater quality is related to several uncertain factors. Using multidimensional normal cloud model to reduce the randomness and ambiguity of the integrated groundwater quality evaluation is important in environmental research. Previous optimizations of multidimensional normal cloud models have focused on improving the affiliation criteria of the evaluation results, neglecting the weighting scheme of multiple indicators. In this study, a new multidimensional normal cloud model was constructed for the existing one-dimensional normal cloud model (ONCM) by combining the projection-pursuit (PP) method and the Grey Wolf Optimization (GWO) algorithm. The effectiveness and robustness of the model were analyzed. The results showed that compared with ONCM, the new multidimensional normal cloud model (GWOPPC model) integrated multiple evaluation parameters, simplified the modeling process, and reduced the number of calculations for the affiliation degree. Compared with other metaheuristic optimization algorithms, the GWO algorithms converged within 20 iterations during 20 simulations showing faster convergence speed, and the convergence results of all objective functions satisfy the iteration accuracy of 0.001, which indicates that the algorithm is more stable. Compared to the traditional entropy weights (0.27, 0.23, 0.47, 0.44, 0.29, 0.59, 0.12) or principal component weights (0.38, 0.33, 0.42, 0.34, 0.47, 0.29, 0.38), the weight allocation scheme provided by the GWOPP method (0.50, 0.48, 0.05, 0.38, 0.02. 0.51 and 0.32) considers the density of the distribution of all samples in the data set space. Among all 55 groundwater samples, the GWOPPC model has 21 samples with lower evaluation ratings than the fuzzy evaluation method, and 28 samples lower than the Random Forest method or the WQI method, indicating that the GWOPPC model is more conservative under the conditions of considering fuzziness and randomness. This method can be used to evaluate groundwater quality in other areas to provide a basis for the planning and management of groundwater resources.

A new probabilistic assessment process for human health risk (HHR) in groundwater with extensive fluoride and nitrate optimized by non parametric estimation method.

Excessive amounts of fluoride (F-) and nitrate (NO3-) in groundwater pose a significant threat to human health. However, a quantitative approach to assessing the human health risks caused by these harmful substances is lacking. To optimize the probabilistic assessment process for human health risk (HHR), this study introduced kernel density estimation (KDE) into the stochastic simulation of F- and NO3- content in groundwater samples. The potential HHRs caused by F- and NO3- in Songyuan City were summarized by combining the probabilistic and deterministic assessments. This study found that the concentrations of F- and NO3- did not follow common probability density functions (PDFs), but the KDE method passed the Kolmogorov-Smirnov test with the critical value of 0.067 and 0.062, showing high fitting accuracy. Monte Carlo simulation indicated that the probability of NO3- for children and adult exceeding the standard is 21.95% and 15.14%, respectively, which is comparable with the results of the deterministic assessment, but the probabilistic assessment emphasized lower probability of HHRs in children caused by excess F-(4.14%). Global sensitivity analysis revealed that excessive NO3- in groundwater has the highest sensitivity of the HHR (>0.1), followed by other factors representing water use habits (>0.01). This study presents a refined probabilistic assessment method for HHR and provides a scientific reference for understanding the state of groundwater environments.

Spatial patterns of climate change and associated climate hazards in Northwest China.

Northwest China (NWC) is experiencing noticeable climate change accompanied with increasing impacts of climate hazards induced by changes in climate extremes. Towards developing climate adaptation strategies to mitigate the negative climatic impacts on both the ecosystem and socioeconomic system of the region, this study investigates systematically the spatial patterns of climate change and the associated climate hazards across NWC based on high resolution reanalysis climate dataset for the period 1979 to 2018. We find that NWC overall is under a warming and wetting transition in climate with change rate of temperature and precipitation around 0.49 °C/10a and 22.8 mm/10a respectively. Characteristics of climate change over the NWC however vary considerably in space. According to significance of long-term trends in both temperature and aridity index for each 0.1° × 0.1° grids, five types of climate change are identified across NWC, including warm-wetting, warm-drying, warm without wetting, wetting without warming and unchanging. The warm-wetting zone accounts for the largest proportion of the region (41%) and mainly locates in the arid or semi-arid northwestern NWC. Our findings show most region of NWC is under impacts of intensifying heatwave and rainstorm due to significant increases in high temperature extremes and precipitation extremes. The warming but without wetting zone is found under a more severe impact of heatwave, particularly for areas near northern Mount. Qinling and northern Loess Plateau. Areas with stronger wetting trend is suffering more from rainstorm.

Impact of land use and cover on shallow groundwater quality in Songyuan city, China: A multivariate statistical analysis.

The utilization and development of land resources is an important process in which human activities affect groundwater quality. However, the impact of land use on groundwater chemical composition has complex multiple relationships, and is affected by the scale of the buffer zone. Based on these problems, this study used correlation analysis (CA) and principal component analysis (PCA) to discuss the mechanism of the effect of land use/land cover (LULC) on the hydrochemical composition of groundwater in Songyuan City. Samples were divided into two groups, i.e., quaternary unconfined aquifer (0-30 m) and quaternary confined aquifer (30-100 m). By comparing the variation trends of the correlation coefficient and cumulative variance interpretation rate of PCA in different buffer ranges, it was found that the optimal buffer range was 3000 m. Cropland had the greatest impact on groundwater hydrochemistry in the city. The transformation of natural landscapes (such as saline‒alkaline alkali land and grassland) to cropland inhibited salt accumulation in groundwater. This finding is noteworthy since few studies have involved areas where saline‒alkaline land is widely distributed. Compared with CA results, PCA results emphasized the deterioration of groundwater quality by agricultural pollution. Moreover, agricultural pollutants such as NO3- and K+ were accumulated in areas where cropland transitioned to natural landscapes such as grassland and water bodies. Considering that wide lakes and rivers provide the drainage area for irrigation water in the study area, the groundwater quality in the surrounding area was affected by the contaminated surface water. The multiple interaction relationship between LULC and hydrochemistry was further confirmed by the combination of principal component scores.

Coastal upward discharge of deep basalt groundwater through developed faults: A case study of the Subei Basin, China.

The relationship between groundwater and seawater is sensitive to groundwater exploitation, thus, not a simple result of groundwater and seawater lateral flow. The upward recharge of deep groundwater leads to a more complex relationship between groundwater and seawater in coastal regions with developed faults. The Quaternary confined groundwater level is significantly decreased in the case of groundwater overexploitation in the coastal region of the Subei Basin, where active faults are developed. The water level and hydrochemistry data for confined groundwater during periods of groundwater overexploitation was analyzed in the Subei Basin. Results show that confined groundwater is negligibly affected by seawater intrusion, while groundwater desalination is apparent during this period. High confined groundwater levels have been observed for many years in the area with intense groundwater exploitation. Additionally, the chemical and stable isotopic characteristics of confined groundwater, phreatic water, and surface water in the study area were investigated to reveal the pathways and origin of deep groundwater. The hydrogeochemical results demonstrate that the confined groundwater originates from basalt groundwater and is related to deep circulation. The active faults in the study area serve as pathways for upward recharge of basalt groundwater. Our findings provide new insights into the relationship between groundwater and seawater, and indicate that the upward recharge of deep groundwater should be considered in coastal regions with developed faults.

Evolution of the hydro-ecological environment and its natural and anthropogenic causes during 1985-2019 in the Nenjiang River basin.

Lakes and vegetation are important components of the hydro-ecological environment and sensitive indicators of anthropogenic climate change and human activities. For the first time, the lake area, vegetation cover change (obtained from Landsat satellite images), terrestrial water storage (TWS; estimated from the gravity recovery and climate experiment), and hydrochemistry, stable isotopes of different waterbodies were combined to analyze the long-term evolution and controlling factors of lake area and vegetation cover in the Nenjiang River basin, China. Between 1985 and 1999, the lake area experienced natural shrinkage due to climatic and hydrological changes, whereas artificial shrinkage related to increased human activities dominated during 2000-2019. The normalized difference vegetation index (NDVI) increased during 1988-1999 and was affected by hydrometeorological factors in the same year and lake area in the previous year. The rate of increase in the NDVI accelerated during 2000-2012 owing to the impact of human activities which is reflected by GDP, and the related artificial shrinkage of the lake area. The main hydrochemical type of lake water changed from Ca-HCO3 before 2000, which was similar to that of river water, to Na-HCO3 after 2000, which was the main hydrochemical type of groundwater. In addition, most of the lake water and groundwater samples were rich in H2SiO3, and a strong correlation between the TWS and lake area for the period 2003-2019 indicated that lake water was strongly affected by groundwater, which was related to deep circulation. Therefore, the decreased river water recharge owing to human activities made groundwater contribute more to lake water. This study can substantially improve the decision-making support for environmental protection and water resource management in ecologically diverse areas, specifically in arid and semi-arid areas.

Study on the groundwater quality and its influencing factor in Songyuan City, Northeast China, using integrated hydrogeochemical method.

Clean groundwater resources are important for the health of human. In Songyuan City, Northeast China, anthropogenic activities have led to changes in groundwater circulation, thereby depleting the aquifer system and causing water quality deterioration. To evaluate the genesis of water quality, we analyzed the hydrochemical and stable isotope compositions of shallow and deep groundwater. According to drinking water quality standards, the concentrations of Ca2+, Mg2+, and NO3- in 23.0, 30.2 and 35.4% of the samples, respectively, exceeded the acceptable ranges. The groundwater chemistry in these samples was related to geochemical processes and agricultural pollution. The hydrochemical analysis explained the reaction mechanisms in each aquifer, showing that the main source of ions in both deep and shallow groundwater is the weathering of silicate rock. In addition, the dissolution of carbonate minerals and artificial pollutants is greater in the shallow groundwater. The stable isotope results showed that long-term extraction is the cause of the diffusion of pollutants in shallow aquifers. Moreover, because most of the well-drilling techniques are backward, the aquifer structure is destroyed, and the deep groundwater is mixed with the shallow groundwater during the process of artificial extraction. The study also analyzed the conditions of the water-rock reaction. Combined with the geological background, it was found that the deep CO2 gas reservoir could provide the necessary material source for the reactions. Owing to frequent tectonic activities, deep CO2 could be discharged to the surface through the fault zone, which promotes the water-rock reaction in this area.