Key Points
Regional groundwater model for North China Plain integrating most available data
Most comprehensive analyses to date of groundwater storage depletion in the NCP
Groundwater sustainability ...under complex hydrologic and socioeconomic conditions
The North China Plain (NCP) is one of the global hotspots of groundwater depletion. Currently, our understanding is limited on spatiotemporal variability in depletion and approaches toward more sustainable groundwater development in this region. This study was intended to simulate spatiotemporal variability in groundwater depletion across the entire NCP and explore approaches to reduce future depletion. Simulated predevelopment groundwater recharge (∼13 km3/yr) primarily discharged as base flow to rivers and evapotranspiration. Initial groundwater storage was estimated to be 1500 km3 of drainable storage in shallow aquifers and 40 km3 of compressive storage in deep aquifers. Simulated groundwater depletion from 1960s to 2008 averaged ∼4 km3/yr. Cumulative depletion was 50 km3 (∼20% of pumpage) in the piedmont district, 103 km3 (∼20%) in the central plain, and 5 km3 (12%) in the coastal plain. However, depletion varied with time: ∼2.5 km3/yr in the 1970s, ∼4.0 in the 1980s, ∼2.0 in 1990–1996; ∼7.0 in 1997–2001, and ∼4.0 in 2002–2008. Recharge also varied spatially, averaging ∼120 mm/yr and concentrated in the piedmont district (200–350 mm/yr) while lower in the central and coastal plains (50–100 mm/yr). Simulation of several alternatives, including managed aquifer recharge, increased water use efficiency, brackish water use, and interbasin water transfer, indicated that the combination of these strategies could be used to recover groundwater storage by 50 km3 over a 15‐year period. This study provides valuable insights for developing more sustainable groundwater management options for the NCP; the methods are useful for managing other depleted aquifers.
The concentrations and spatial occurrences of 17 legacy per- and polyfluoroalkyl substances (PFAS) and 4 emerging PFAS in the coastal water-dissolved phase, surface sediment phase and suspended ...particulate matter (SPM) in the coastal areas of Bohai Bay were investigated. In addition, the partition behaviors of PFAS in the water-SPM system and water-sediment system and the potential sources of PFAS in the marine environment were revealed. The total concentrations of PFAS (∑PFAS) in the water-dissolved phase, surface sediment and SPM were 20.5–684 ng/L, 2.69–25.0 ng/g dry weight (dw) and 4.39–527 ng/g dw, respectively. The level of PFAS contamination in the coastal areas of Shandong Province was higher than that in other areas. The average partition coefficients (log Kd) of PFAS in the water-SPM system and water-sediment system were 1.56–3.57 and 0.72–2.95, respectively. Long-chain PFAS and PFECHS (perfluoroethylcyclohexane sulfonate) have a higher log Kd than that of short-chain PFAS. PFAS with short carbon chains were mainly detected in the water-dissolved phase, but long-chain PFAS mainly occurred in the surface sediment and SPM phases. Source analysis based on the positive matrix factorization (PMF) model found that erosion inhibitor factories, aqueous film-forming foam factories, metal plating plants, fluoropolymer chemical manufacture and food contact materials were the main sources of PFAS in Bohai Bay. These results improved our understanding of the partitioning behavior and sources of PFAS in aquatic environments.
∑PFAS (ng/L) and composition profile in water dissolved phase in the coastal area of Bohai bay, China. Display omitted
•Occurrences and sources of PFAS in water, surface sediment and SPM of Bohai bay were investigated.•HFPO-DA and Cl-PFAESs were ubiquitous in water dissolved phase.•Short-chain PFAS were mostly presented in water, while long-chain PFAS prevailed in sediment and SPM.•AFFFs factories, metal plating plants, FP manufacture and food contact materials are the key contributing to PFAS.
The occurrence, partition behaviors and potential source of legacy and emerging PFAS in coastal areas were investigated.
Significant advances in regional groundwater flow modeling have been driven by the demand to predict regional impacts of human inferences on groundwater systems and associated environment. The wide ...availability of powerful computers, user friendly modeling systems and GIS stimulates an exponential growth of regional groundwater modeling. Large scale transient groundwater models have been built to analyze regional flow systems, to simulate water budget components changes, and to optimize groundwater develop- ment scenarios. This paper reviews the historical development of regional groundwater modeling. Examples of Death Valley and Great Artesian Basin transient groundwater models are introduced to show the application of large scale regional groundwater flow models. Specific methodologies for regional groundwater flow modeling are descried and special issues in regional groundwater flow modeling are discussed.
Deforestation and intensive land use have accelerated soil erosion, reshaped topography, and altered carbon reservoirs for thousands of years. The timing, scope, and magnitude of long‐term ...anthropogenic soil erosion across China are especially important to understand the global scale of this process. Here, sediment accumulation rates (SARs) from 191 sediment archives are found to be temporally correlated with monsoon intensity during 6–40 ka BP, indicating that hydroclimate was the main driver of soil erosion in this time interval. The rapid increase in SARs after ca. 5 ka BP is decoupled from persistently weakened hydroclimate but instead follows the trend of increasing population and related agricultural activities in China, implying a change in the primary controlling factor since then. Early human activities in China therefore appear to have had profound implications on Earth's surface at a continental scale.
Plain Language Summary
The key agency in modulating Earth's surface environment and carbon reservoirs includes the hydroclimate and anthropogenic factors. However, their effect on the magnitude and drivers of long‐term soil erosion across China is not well understood yet. Here changes in sediment accumulation rates were applied as a proxy for soil erosion. The results showed a direct linkage between soil erosion proxy and Chinese population for ca. 5,000 years, suggesting that hydroclimate controlled soil erosion before the mid‐Holocene, but human impacts overwhelmed afterward and started to control soil erosion ca. 5,000 years ago in China. The timing was about 1,000 years earlier than the global average, highlighting the inter‐continental differences and extending our view of long‐term human‐environment interactions.
Key Points
Hydroclimate controlled soil erosion before the mid‐Holocene in China
Direct linkages between sediment accumulation rates and Chinese population were detected across China
Human impacts started to control soil erosion in China 5,000 years ago, at least 1,000 years earlier than the global average
•An EnSRF is used for model parameter/state estimation in a real field case.•Localization and two covariance tuning alternatives are applied to improve filter performance.•Using a damping factor is ...superior to using an inflation factor.•A larger measurement error is less informative during assimilation in the real case.•From synthetic cases, no conclusion can be drawn for performance in the real case.
Data assimilation techniques are widely used in hydrology and water resources management to improve model forecast uncertainty by assimilating observations. The big challenge in practical applications is how to describe model uncertainties correctly to avoid the occurrence of spurious covariance during data assimilation. In this study, the ensemble square root filter (EnSRF) is used to estimate parameters and states of a groundwater model in Guantao, China, which updates ensemble means and perturbations separately and avoids the need to perturb observations. The uncertainty in parameters and states decreased with time while assimilating observations. However, incorrect updates of parameters and states were obtained, which could not be corrected by assimilating further observations improving the representation of the hydrological system. To compensate for this effect and reduce other sampling errors introduced during assimilation, localization and two covariance-tuning methods (inflation factor and damping factor) are explored in the study. The results show that alternative scenarios with proper localization length or a large inflation factor or a small damping factor produce better model estimates and improve the filter performance. The scenario with a damping factor of 0.05 shows a distinct gain in model predictive capability. The damping factor method is superior to the inflation factor method and preferable in real field applications. The scenario combining the damping factor with localization further improved the filter performance. The performance of the EnSRF with respect to different amounts of measurement error is also analysed. Even though the increase of observation error can increase the error covariance, a corresponding filter improvement is not observed as in that case, observations are less informative.
Land subsidence usually bears strong relationship to abstraction of underground fluid. Land subsidence occurs commonly in the North China Plain (NCP) and has become a major environmental factor ...hindering regional sustainable development. This paper focuses on issues associated with mechanism of land subsidence in the NCP. The analysis shows that multi-layer aquifer systems with deep confined aquifers and the thick normally consolidated or unconsolidated compressible clay layers are the key of geological and hydrogeological conditions favorable for the development of land subsidence in the NCP. Groundwater withdrawal results in an increase in the distribution of effective stress within the strata and the compression of the aquifers and the confining layers, and then triggers land subsidence. In the middle-east plain of the NCP, the land subsidence volume approximately represents the amount of water released from compression of deep aquifers and aquitards in that land subsidence is primarily caused by excessive groundwater withdrawal in deep aquifer system. The percentage of water released from compression of aquifers and aquitards in deep groundwater abstraction is significant but distinct in Cangzhou City and in the whole middle-east plain. This is due to the difference in local lithological structure and recharge and discharge conditions of deep groundwater system. The hysteresis of land subsidence is also discussed in typical areas and the results reveal that the time for completing the primary consolidation ranges from less than one year to tens of years, and that the rate of secondary compression tends to increase with the moisture content.
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•Sonication-assisted green, and one-step synthesis of PdPtCu PNDs in 20 min at 25 °C.•Various experiments were done to confirm the formation mechanism of PtPdCu PNDs.•The MOR activity ...of PtPdCu PNDs was higher than PtPd PNDs, PtCu PNDs, and Pt/C.•PtPdCu PNDs outperformed all previously reported PtPdCu nanostructures for MOR.•PtPdCu PNDs remain durable, maintained shape and composition after MOR durability.
The tailored design of tri-metallic Pt-based porous nanodendrites (PNDs) is crucial for green energy production technologies, ascribed to their fancy features, great surface areas, accessible active sites, and stability against aggregation. However, their aqueous-phase one-step synthesis at room temperature remains a daunting challenge. Herein, we present a facile, green, and template-free approach for the one-step synthesis of PtPdCu PNDs by ultrasonication of an aqueous solution of metal salts and Pluronic F127 at 25 ℃, based on natural isolation among nucleation and growth step driven by the disparate reduction kinetics of the metals and acoustic cavitation mechanism of ultrasonic waves. The resultant PtPdCu PNDs formed in a spatial nanodendritic shape with a dense array of branches, open corners, interconnected pores, high surface area (46.9 m2/g), and high Cu content (21 %). The methanol oxidation reaction (MOR) mass activity of PtPdCu PNDs (3.66 mA/µgPt) is 1.45, 2.73, and 2.83 times higher than those of PtPd PNDs, PtCu PNDs, and commercial Pt/C, respectively based on equivalent Pt mass, which is superior to previous PtPdCu catalysts reported elsewhere, besides a superior durability and CO-poisoning tolerance. This study may pave the way for the controlled fabrication of ternary Pt-based PNDs for various electrocatalytic applications.
For HVDC cables, the electric field distribution is determined by the conductivity of insulation material, which is a function of temperature and field. As the result, the conductivity-dependent ...field in the DC insulation is an electro-thermal coupled field. A modified 2D model is set up in this paper to simulate the thermal field distribution of a 320 kV DC cable, and based on that, the electric field distribution in the XLPE insulation is studied by the finite element method without consideration of space charge effect. Electric field distribution of steady state is computed under thermal equilibrium and rated DC voltage, and it is found to be a quasi-linear function of the radius, with the field strength remaining nearly unchanged in the central part of the insulation, whose value is approximately equal to the average field. The field reversal is determined by the thermal activation energy in XLPE conductivity expression, with a larger activation energy corresponding to a lower temperature difference across the insulation when the field reversal happens, and the increase of electric field coefficient is beneficial for improving the field distribution. Simulation of the time-varying states is performed under thermal equilibrium and three typical transient waveforms, including the continuous rising DC voltage, polarity reversal DC voltage and the DC superimposed switching impulse. It is shown that the rise speed of the continuous rising voltage is a key parameter for the maximum field strength, with a high speed leading to a high field at the inner border of insulation, and a time duration of 2r to 3r is recommended for the voltage rise edge. By the consideration of the transition relaxation progress from the initial capacitive field to the steady-state resistive field, a formula is set up to calculate the field strength of the insulation after the application of a time-varying voltage, and the calculated results are highly consistent with those obtained by numerical simulation.
The continual rise of the CO2 concentration in the Earth’s atmosphere is the foremost reason for environmental concerns such as global warming, ocean acidification, rising sea levels, and the ...extinction of various species. The electrochemical CO2 reduction (CO2RR) is a promising green and efficient approach for converting CO2 to high-value-added products such as alcohols, acids, and chemicals. Developing efficient and low-cost electrocatalysts is the main barrier to scaling up CO2RR for large-scale applications. Heteroatom-doped porous carbon-based (HA-PCs) catalysts are deemed as green, efficient, low-cost, and durable electrocatalysts for the CO2RR due to their great physiochemical and catalytic merits (i.e., great surface area, electrical conductivity, rich electrical density, active sites, inferior H2 evolution activity, tailorable structures, and chemical–physical–thermal stability). They are also easily synthesized in a high yield from inexpensive and earth-abundant resources that meet sustainability and large-scale requirements. This review emphasizes the rational synthesis of HA-PCs for the CO2RR rooting from the engineering methods of HA-PCs to the effect of mono, binary, and ternary dopants (i.e., N, S, F, or B) on the CO2RR activity and durability. The effect of CO2 on the environment and human health, in addition to the recent advances in CO2RR fundamental pathways and mechanisms, are also discussed. Finally, the evolving challenges and future perspectives on the development of heteroatom-doped porous carbon-based nanocatalysts for the CO2RR are underlined.
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