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Mine integrated energy system (MIES) can promote the utilization of derived energy and achieve multi-energy complementation and ecological protection. Now it gradually becomes an important focus for scientific carbon reduction and carbon neutrality. To reduce the impact of uncertain prediction differences on the system during the process of using mine derived energy, a low-carbon economic operation strategy of MIES considering energy supply uncertainty is developed in this paper. Firstly, based on the basic structure of energy flow in MIES, the energy-carbon flow framework of MIES is established for the low-carbon operation requirements. Secondly, considering carbon emission constraints, the low-carbon economic operation optimization model (LEOOM) is built for MIES to minimize operation cost and carbon emission. Finally, multiple uncertainties of the system are modeled and analyzed by using the robust model under the risk aversion strategy of information gap decision theory (IGDT), and a model conversion method is designed to optimize the low-carbon economic operation model. The simulation results under three scenarios demonstrate that compared to the existed economic dispatching models, the proposed model achieves a 30% reduction in carbon emission while the operational cost of MIES only is increased by 2.1%. The model efficiently mitigates the carbon emission of the system, and the proposed uncertain treatment strategy can significantly improve the robustness of obtained operation plans.

Objective The permeability of coral sand is the key factor determining the groundwater reserves of coral islands. For a long time, the research on the influence of different salinity filtrates on the permeability of coral sand during the formation of freshwater lenses is quiet few. Methods In this study, three kinds of solutions with different salinities were designed to represent freshwater, transition zone water and seawater to conduct dissolution and permeation tests on coral sand. Based on X-ray diffraction analysis and PHREEQC reverse simulation, the possible causes of water-rock interactions and permeability changes in coral sand in different salinity solutions were discussed. Results Results showed that the permeability of coral sand was highly related to its dissolution in water bodies. The higher the salinity of the solution, the stronger the dissolution and the greater the permeability coefficient of the coral sand. The permeability coefficient of coral sand was almost unchanged in pure water. In saltwater, coral sand has undergone water-rock interactions, including carbonate dissolution and Na+-Ca2+ ion exchange, and the water-rock interaction is stronger with increasing salinity. After 360 hours of reaction under NaCl solutions with concentrations of 0.2 mol/L and 0.4 mol/L, the coral sand permeability coefficient changed from 0.58 m/d to 0.64 m/d and 0.74 m/d, respectively. It was inferred that dissolution could increase the overall porosity and thus the permeability coefficient by changing the sand particle size. Conclusion The results provide a scientific reference for the accurate assessment of freshwater reserves and the sustainable development of water resources on coral islands.

Groundwater pollution risk assessment is an effective tool for preventing and controlling groundwater pollution. The study on groundwater pollution risk assessment can serve as a basis for the management of groundwater contaminated sites. The present risk assessments often ignore the spatial variability of pollution within the site and the susceptibility of receptor. This paper proposes a new site groundwater pollution risk index system that can be used for pollution sites with a variety of features. The index system considers the spatial distribution of pollutant at the site and nearby receptors. Based on the four aspects of pollution load, vadose zone vulnerability, aquifer vulnerability, and receptor susceptibility, this paper conducted index screening and weight calculation using the analytical hierarchy process. A site groundwater pollution risk assessment index system was constructed, and the risk was divided into four levels: low, medium, higher, and high. Using the constructed risk index system, the spatial risk distribution of a hexavalent chromium site in Henan Province was studied. The results show that the site was at a medium risk level, with the highest risk at the chrome slag heaps and the southeastern of the buried chrome slag. The potential loss of surrounding receptors and the pollution load are the main causes of groundwater contamination risk at the site. Single parameter sensitivity analysis shows that the effective weights of each index are in line with the theoretical weights, indicating the rationality of the constructed site groundwater pollution risk assessment system, which can be applied to other sites with characteristic pollutants.

Fresh groundwater lenses are important resources for local inhabitants and ecosystems in coral islands. In view of the complexity of the coral islands, it is necessary to seek the measures of low-cost, effective and less impact on the stability and the ecosystem to increase freshwater reserves. Based on the sandbox experiments and numerical simulations, this study proposes an engineering measure to increase freshwater reserves by laying impermeable materials on the slope of an island. The effects of the measure on fresh groundwater lenses formation and different factors on increasing freshwater reserves in slope seepage prevention are evaluated. The practical feasibility of this measure is also discussed in case of the Yongxing Island. The results show that the slope seepage control increases the freshwater reserves by changing the groundwater flow field to increase the freshwater head. The stabilization time of the freshwater lens is also increased. After laying impermeable materials on slope of the sandbox (with the length, width and height of 50 cm, 5 cm and 35 cm, respectively), the maximum thickness of freshwater lens increases from 13.7 cm to 24.9 cm, the freshwater reserves increases from 561.8 cm3 to 1592.3 cm3, and stabilization time increases from 120 min to 150 min, respectively. The increased freshwater reserves develop with the increasing rainfall intensity and slope impermeable depth, and also extend with the decreasing permeability of coral sand and impermeable materials. The Yongxing Island is taken as an example, and laying impermeable materials with a depth of 2 m on the slope will increase the freshwater reserves from 3.4×106 m3 to 4.4×106 m3 in the next 30 years, increasing the original reserve by 1/4. This study can provide theoretical support and practical guidance for sustainable groundwater management and water resources security in island areas of China.

The hydrogeological settings of bedrock islands in northern China are unique. Climate change and human activities can affect the interaction between groundwater and seawater around the islands to varying degrees, but there is a lack of quantitative understanding of such hydrological processes, including seawater intrusion (SWI) and submarine groundwater discharge (SGD). In this study, we analyzed the precipitation, groundwater levels, and water quality data (2012-2016) for identifying the characteristics and controlling factors of the interaction between groundwater and seawater in bedrock islands by using mathematical statistics, spatial interpolation, and hydraulics methods. The results show that precipitation and groundwater pumping are the main factors affecting the groundwater-seawater interaction. The variations of groundwater levels lag behind the rainfall events by about 10 days. There occurred no SWI in most areas on the northeastern and southern coasts of the South Island, with relative stable marine groundwater discharge. The average SGD velocity was 0.2 m/d, and the average NO3-N flux to the sea was 81.8 mmol/(m2·d). The southeast area of the North Island has been seriously threatened by SWI, and the groundwater levels have been below sea level for a long time and falling year by year. The average SWI rate is 0.3 m/d, and the average NO3-N flux towards the land is 69.6 mmol/(m2·d). The SGD rates of the South and NorthIslands were estimated for dry season (April 2014) and wet season (September 2013), respectively. It was 3.5×104−4.5×104 m3/d for the North Island, and 0.4×104−1.1×104 m3/d for the South Island. The results can provide important reference for coastal groundwater resource management and ecological environment protection in bedrock islands.

Reclaimed water has been widely used to recharge river channels in Beijing, with 2.3×108 m3 of reclaimed water recharge to the Shunyi section of the Chaobai River from the end of 2007 to 2017. It has a high background value of pollutants (Cl− concentration ranging from 62 to 122 mg/L) and recharges the ambient aquifers, which has an impact on the ambient groundwater through riverbank filtration, particularly on the shallow groundwater. Based on 10-year series groundwater monitoring data (2007−2017), we conducte a 3D groundwater flow and solute transport model to simulate the variations of the shallow groundwater table and chloride concentrations, and analyze the variations in groundwater storage, Cl− loads, and NO3-N loads in the shallow aquifers near the Chaobai River receiving reclaimed water. The results demonstrate that the ambient groundwater table swiftly rose by about 3−4 m following the reclaimed water replenishment from 2007 to 2009, and stayed steady under the condition of continuous replenishment of reclaimed water. However, affected by the exploitation of deep groundwater, the groundwater storage in the unconfined aquifer still decreased overall from 2007 to 2014. After reducing the groundwater extraction since 2014, the shallow groundwater storage recovered from 3.76×108 m3 at the end of 2014 to 3.85×108 m3 at the end of 2017. Cl− concentrations in the ambient shallow groundwater changed from a range of 5−75 mg/L before the recharge to 50−130 mg/L after the recharge (2007−2009), and then remained stable. The areas of shallow groundwater quality affected by reclaimed water infiltration expanded from 11.7 km2 in 2008 to 26.7 km2 in 2017. The Cl− loads in the affected areas increased from 1.8×103 t in 2008 to 3.8×103 t in 2017. The NO3-N loads decreased from 29.8 t in 2008 to 11.9 t in 2017. Although the results show that the shallow groundwater quality outside the affected area is not significantly affected by the reclaimed water, the potential salinization and pollution cannot be ignored and need to be further clarified in the subsequent studies.

Evaluating actual crop evapotranspiration (ETc) variations and their determining factors under changing climates is crucial for agricultural irrigation management and crop productivity improvement in non-humid regions. This study analyzed the spatiotemporal characteristics and detected the determining factors of ETc for winter wheat and summer maize rotation system from 2000 to 2017 in the North China Plain (NCP), by combining the FAO-56 dual crop coefficient approach with remotely sensed vegetation indices (VIs). The results indicated that daily air temperature increased in varying degrees while wind speed and sunshine hours decreased slightly during the growing season of winter wheat and summer maize over the study period. The trends of relative humidity and effective precipitation varied in crop growing seasons. Based on the validated relationship of dual crop coefficients and VIs, the estimated multi-year average ETc of winter wheat (370.29 ± 31.28 mm) was much higher than summer maize (281.85 ± 20.14 mm), and the rotation cycle was 652.43 ± 27.67 mm. Annual ETc of winter wheat and the rotation cycle increased by 2.96 mm a−1 and 1.77 mm a−1, respectively. However, the ETc of summer maize decreased with distinct spatial variation. Spatially, winter wheat ETc increased significantly in the northeast NCP, covering the Beijing-Tianjin-Hebei areas. Meanwhile, significant increases in summer maize ETc were detected in the southwest NCP. The sensitivity and contribution analysis showed that ETc of winter wheat and summer maize was positively sensitive to temperature, wind speed, and sunshine hours while negatively to relative humidity. Moreover, wind speed and sunshine hours contributed most to changes in ETc (around 20%–40%).

Reclaimed water has demonstrated its broad applications in social construction to alleviate the contradiction of water shortage in Beijing, China. Using multivariate statistical analysis, the current study investigated the spatial variations of water quality in the Chaobai River restored by reclaimed water during the high-flow period. Hierarchical cluster analysis (CA) classified the 11 sampling sites into four clusters, namely most polluted, highly polluted, moderately polluted, and lowly polluted sections. The Kruskal-Wallis test showed that pH, TDS, EC, Ca2+, Mg2+, Cl−, SO42−, NO3−-N, and TN had significant spatial differences among four clusters (p < 0.05). Mean value of total nitrogen (TN) in the most polluted site exceeded the guideline (15 mg/L) of the Water Quality Standard for Scenic Environment Use, reaching 22.3 mg/L. Principal component analysis (PCA) extracted three principal components (PCs) accounting for 81.5% of the total variance in the data set of water quality. The three PCs reflected the chemical characteristics of reclaimed water, mineral pollution, and nutrient pollution, respectively. With the ordination biplot of sampling sites defined by the first and second PCs, PCA provided a classification of sampling sites based on the similarity of pollution sources, which supported the results of CA. The results revealed that water quality of the Chaobai River restored by reclaimed water was affected by untreated domestic and agricultural sewage with nitrogen and minerals being the main pollutants along the river basin. This study showed rivers restored by reclaimed water had significant spatial variations of water quality, demonstrating effectiveness of multivariate statistical methods on water quality analysis. HIGHLIGHTS Water quality of the river restored by reclaimed water showed significant spatial variations.; Nitrogen pollution was severe compared to standard values.; CA and PCA indicated similar spatial patterns of water quality variations.; Besides reclaimed water, untreated domestic and agricultural sewage were also pollution sources.; The effectiveness of multivariate statistical methods on water quality analysis was demonstrated.;

This paper develops a sliding-mode control with an improved nonlinear extended state observer (SMC-INESO) for the rotation system of a hydraulic roofbolter with dead-zones, uncertain gain, and disturbances, with the purpose of improving tracking performance. Firstly, the rotation system is modeled to compensate for dead-zone nonlinearity. Then, we present an improved nonlinear extended state observer to estimate disturbances of the rotation system in real time. Moreover, a proportional-integral-differential sliding-mode surface is introduced and an improved sliding-mode reaching law is designed. Based on this, a sliding-mode control law is developed. In order to eliminate the influence of estimation error and uncertain gain, we design two adaptation laws based on the sliding-mode surface and the estimated states. Finally, the effectiveness of the proposed SMC-INESO is verified through comparative simulation studies.

Studies of evapotranspiration on remote tropical coral islands are important to explore and sustain scarce freshwater resources. However, there is a significant knowledge gap between research to evaluate evapotranspiration based on remote sensing methods and the influences of different land use types on water dynamics on reclaimed coral islands. This study applied the remote-sensing-based Vegetation Interfaces Processes (VIP-RS) model to estimate actual evapotranspiration (ETa) on Zhaoshu Island, Yongxing Island, and Yongshu Island in the South China Sea from 2016 to 2019. The results showed that the average annual ETa of Zhaoshu Island, Yongxing Island, and Yongshu Island was 685 mm, 530 mm, and 210 mm, respectively. Annual transpiration (Ec) and soil evaporation (Es) exhibited similar patterns on the natural islands; however, Es controlled the water consumption on the reclaimed islands. Water dynamics exhibited seasonal fluctuations due to the uneven distribution of precipitation (PRP). However, ETa of the natural islands was higher than PRP in the dry season, indicating vegetation has to absorb water from the groundwater to sustain growth. The results also agreed with the analysis of dominant driving factors based on partial correlation analysis, which demonstrated that the Normalized Difference Vegetation Index (NDVI) is the most important factor that influences ETa, while relative humidity (RH) controlled the bare land or sparsely vegetated areas on the reclaimed islands. The setting of different land use types showed that vegetation and built-up or hardened roads took control of evapotranspiration and rainwater collection, respectively, which play important roles in water dynamics on corals islands. The evaluation of ETa based on a remote-sensing-based model overcame the difficulty in fieldwork observation, which improves the certainty and accuracy at a spatial scale. In addition, it gave us a new reference to protect and manage scarce freshwater resources properly.

During the mid-1980s, there were 31 stations in China that successfully participated in the Global Network of Isotopes in Precipitation. However, most observations were suspended after the mid-1990s. The discontinuous data hindered the application of precipitation isotopes, which are strongly affected in China by the Asian monsoon and are thus of intrinsic interest for palaeoclimatologists. Therefore, to continuously observe precipitation isotopes nationwide, the Chinese Network of Isotopes in Precipitation was established in 2004. The current study reviewed the major characteristics of the 928 samples that were collected from 2005 to 2010. The ranges of δD and δ18O values generally followed the pattern NE>NW>TP>NC>SC, and the amount-weighted δ-values followed the pattern SC>NW>NC>TP>NE. Temporal variations presented a ‘V’-shaped pattern at the SC region and reverse ‘V’-shaped patterns at the NE and NW regions. Decreasing trends with the advent of the rainy season were found at the NC and TP regions. The Chinese Meteoric Water Line has been established as δD=7.48δ18O+1.01. The distributions of scattering along the line demonstrated different water vapour origins and characteristics. The values of δ18O showed strong temperature dependence at the NE (0.27‰/°C) and NW stations (0.37‰/°C), and this dependent variable switched to water vapour pressure and vapour pressure at the SC stations. The geographical controls of δ18O were −0.22‰/° and −0.13‰/100 m for latitude and altitude, respectively. The δ18O/Latitude gradient increased from south to north at the Eastern Monsoon Region, and the δ18O/Altitude gradient (−0.30‰/100 m) was especially significant for the TP region. The results of this study could provide basic isotopic information for on-going investigations in hydrology, meteorology, palaeoclimatology and ecology at different regions of China.

River water plays a critical role in riparian plant water use and riparian ecosystem restoration along losing rivers (rivers losing flow into underlying groundwater) under climate warming. How to quantify the contributions of river water to riparian plants under different water tables and the related responses of plant water use efficiency is a great challenge. In this study, experiments of stable isotopes (d²H, d18O and 222Rn) in different waters and leaf d13C were conducted for riparian deep-rooted Salix babylonica (L.) during dry year (2019) and wet year (2021) along the Chaobai River in Beijing, China. The MixSIAR model in combination with an iteration method were proposed to quantify the proportional river water contribution (RWC) to riparian S. babylonica and its correlations with the depth of water table (WTD) as well as leaf d13C. Results showed that riparian S. babylonica took up deep water (in 80-170 cm soil layer and groundwater) by 56.5 ± 10.8%. River water that recharged riparian deep water was an indirect water source and contributed 20.3% of water to riparian trees nearby the losing river. Significantly increasing river water acquisitions (by 7.0%) but decreasing leaf d13C (by -2.0‰) of riparian trees were observed as the WTD changed from 2.7 m in 2019 to 1.7 m in 2021 (p < 0.05). A short residence time (no more than 0.28 days) of groundwater indicated that there was rapid and frequent river recharge to riparian groundwater in 2021. It was found that the RWC to riparian S. babylonica was negatively correlated with the WTD but positively related to the leaf d13C in linear functions (p = 0.000). The rising water table would stimulate riparian trees to maximize transpiration water consumptions and show a profligate water use strategy with increasing water extraction from the losing river. This study provides critical insights into understanding the mechanism of water cycle in Groundwater-Soil-Plant-Atmosphere Continuum, managing water resources and riparian afforestation along losing rivers. [ABSTRACT FROM AUTHOR]