The Yanxi karst groundwater system in northern China. By analyzing long timeseries monitoring data of the groundwater level, groundwater quality, and groundwater withdrawal over the past 30 years, this paper aims to evaluate the regime characteristics of the karst groundwater in the Yanxi fault block and guide the rational exploitation and utilization of groundwater. Using groundwater regime analysis, hydrogeochemical analysis, and isotope analysis, the evolution of the karst groundwater regime under large-scale exploitation conditions is analyzed. The results reveal that before and after large-scale exploitation, the karst groundwater cycle conditions changed fundamentally, the karst groundwater level continued to fall below the sea table for a long time, and the main discharged changed from lateral runoff to centralized exploitation in the groundwater source field. The spatial distribution of the karst groundwater quality is closely related to the distribution of the surface water quality and coal measure strata. The hydrochemical components are mainly controlled by the dissolution of the minerals in the Ordovician limestone and, to a certain extent, by the dissolution of silicate-rock minerals. The mineral precipitation and concentration caused by evaporation are relatively weak. It is urgent to take a series of management and protection measures for groundwater resources to curb the evolution trend of the groundwater environment.

Microplastics-derived dissolved organic matter (MPs-DOM), as a novel and non-negligible of DOM, significantly influences the photoaging of coexisting microplastics (MPs), but their interactions remain underexplored. In this study, we investigated the effects of different MPs-DOM (aromatic polystyrene DOM (PS-DOM), aliphatic polyethylene DOM (PE-DOM), and biodegradable poly(butylene adipate-co-terephthalate) DOM (PBAT-DOM)) on the aging behavior of PS-MPs and their transformations characteristics within 96 d of UVA irradiation. Result demonstrated that MPs-DOM notably accelerated the PS-MP aging (especially PBAT-DOM), and the aging rate was closely correlated with MP-DOM evolution. Notably, PS-MP exhibited significant and rapid increase in aging within the first 6h, which was attributed to the presence of highly unsaturated and phenolic compounds in MPs-DOM that promote the generation of reactive oxygen species (ROS). Throughout this process, these compounds were transformed into the saturated and low-aromatic compounds via the carboxylic acid and dealkylation reactions. As the reaction proceeded, PS-DOM released from PS-MP gradually became the dominant component in MP-DOM. The highly unsaturated components of PS-DOM have higher ability to produce ROS, thereby further accelerating PS-MPs aging. These findings provide valuable insights into the interactions between MPs and MPs-DOM and contribute to a better understanding of their environmental implications and risks.

This study aimed to analyze the spatiotemporal trends of the non-agriculturalization of cultivated land (NACL) and evaluate the effectiveness of land management strategies in Shaanxi Province, China. First, geostatistical analysis was conducted to examine NACL dynamics, revealing that most areas remained in a mild early warning state from 2000 to 2010. However, warning levels escalated to severe or extreme in northern Shaanxi, parts of Guanzhong, and southern Shaanxi between 2010 and 2020. Subsequently, the Patch-Generated Land Use Simulation Model (PLUS) was employed to simulate NACL under different land management scenarios, using 2020 as the baseline and 2035 as the target year. The scenarios include natural growth (NG), cultivated land protection (CP), and ecological protection (EP), which were designed based on national and provincial land use planning objectives for 2035. The results indicated that, under the NG scenario, the overall NACL area is projected to decline by 2035, although northern and southern Shaanxi will remain highly susceptible to NACL. The CP scenario effectively mitigated NACL, reducing warning levels to moderate or mild in parts of Guanzhong and northern Shaanxi. Spatial clustering analysis further revealed that NACL in northern Shaanxi consistently exhibited high–high clustering in both historical periods and across different management scenarios. These findings establish a research framework for identifying and forecasting NACL while providing a scientific basis for optimizing land resource allocation and informing policy decisions.

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To deeply investigate the impact of closed coal mines on groundwater sulfate contamination in the Panlong River basin, Zaozhuang, Shandong Province, China, the hydrochemical characteristics and controlling factors of groundwater were analyzed based on 64 surface water and groundwater samples. The sources of sulfate contamination were identified by sulfur and oxygen isotope analysis. The results indicate that the sulfate content in the pore groundwater exceeds the Standard for Groundwater Quality (China) Category III (250 mg/L), with a maximum content of 666.2 mg/L. Specifically, the exceedance rate of sulfate in pore water near the western boundary of the Taozao coal field is directly related to mine water. The exceedance rate of sulfate in karst groundwater is 28%, peaking at 1131 mg/L, and is mainly distributed outside the western boundary of the Taozao coalfield and near the Dingzhuang water source in the southeast of the coalfield, indicating a significant influence from high-sulfate mine water in the coal-bearing strata. The sulfur and oxygen isotope differences are significant between surface water, mine water, karst water, and pore water. Through Bayesian end-member analysis, it was determined that 40–83% of sulfate in the downstream pore water of the Taozao coal field originated from mine water, while 48–86% of the sulfate in the karst water originated from mine water, which greatly affects the groundwater in the western and southeastern parts of the Taozao coalfield. Therefore, measures should be taken as soon as possible to control the risk of sulfate pollution of neighboring groundwater, especially karst groundwater, by mine water from closed coal mines.

Microplastics (MPs)-derived dissolved organic matter (MPs-DOM) is becoming a non-negligible source of DOM pools in aquatic systems, but there is limited understanding about the photoreactivity of different MPs-DOM. Herein, MPs-DOM from polystyrene (PS), polyethylene terephthalate (PET), poly(butylene adipate-co-terephthalate) (PBAT), PE, and polypropylene (PP), representing aromatic, biodegradable, and aliphatic plastics, were prepared to examine their photoreactivity. Spectral and high-resolution mass spectrometry analyses revealed that PS/PET/PBAT-DOM contained more unsaturated aromatic components, whereas PE/PP-DOM was richer in saturated aliphatic components. Photodegradation experiments observed that unsaturated aromatic molecules were prone to be degraded compared to saturated aliphatic molecules, leading to a higher degradation of PS/PET/PBAT-DOM than PE/PP-DOM. PS/PET/PBAT-DOM was mainly degraded by hydroxyl (•OH) via attacking unsaturated aromatic structures, whereas PE/PP-DOM by singlet oxygen (1O2) through oxidizing aliphatic side chains. The [•OH]ss was 1.21-1.60 × 10-4 M in PS/PET/PBAT-DOM and 0.97-1.14 × 10-4 M in PE/PP-DOM, while the [1O2]ss was 0.90-1.35 × 10-12 and 0.33-0.44 × 10-12 M, respectively. This contributes to the stronger photoreactivity of PS/PET/PBAT-DOM with a higher unsaturated aromatic degree than PE/PP-DOM. The photodegradation of MPs-DOM reflected a decreasing tendency from aromatic-unsaturated molecules to aliphatic-saturated molecules. Special attention should be paid to the photoreactivity and environmental impacts associated with MPs-DOM containing highly unsaturated aromatic compounds.

A comprehensive understanding of the role of natural and anthropogenic factors in groundwater pollution is essential for sustainable groundwater resource management, especially in alluvial plains with intensive anthropogenic activities. Numerous studies have focused on the contribution of individual factors on groundwater pollution in alluvial aquifers, but distinguishing the effects of natural and anthropogenic factors is limited. In this study, 64 wells were sampled in different seasons from the Yellow River alluvial plain in China for hydrochemical and isotopic analysis to investigate the spatiotemporal distribution, sources and health risks of fluoride and nitrate in alluvial aquifers. Results showed that fluoride contamination was widely distributed without significant seasonal variation, and 78.1 % of the dry season samples and 65.6 % of the wet season samples showed fluoride concentrations above the permissible limit (1.5 mg/L). High-F- groundwater was generally accompanied by Na-HCO3 and Na-HCO3·SO4 water types. Fluoride was from a natural origin mainly associated with mineral dissolution, competitive adsorption, cation exchange, and evaporation. Groundwater nitrate contamination was spatially sporadic and showed significant seasonal differences. Only 13.6 % of the dry season samples and 3.2 % of the wet season samples had NO3- concentrations exceeded the permissible limit of 50 mg/L. The hydrochemical phase evolved from bicarbonate or sulfate type to chloride type with increasing nitrate concentration. Manure and sewage attributed to agricultural activities contributed the most nitrogen to groundwater, followed by soil organic nitrogen and chemical fertilizers, revealing the anthropogenic origin of nitrate. Nitrification was the dominant nitrogen transformation process in the wet season, and denitrification was prevalent in the dry season. Oral ingestion of high fluoride groundwater was a major threat to human health, especially for infants. This study provided a significant reference for water resources management in alluvial aquifers.

Petroleum spills and land contamination are becoming increasingly common around the world. Polycyclic aromatic hydrocarbons (PAHs) and other pollutants found in petroleum are constantly migrating underground, making their migration in soil a hot research topic. Therefore, it is of great significance to evaluate the migratory process of petroleum hydrocarbons in petroleum-polluted soil to clarify its ecological and environmental risks. In this study, Phenanthrene (PHE) was used as a typical pollutant of PAHs. The soil was gathered from three typical oilfields in China, and a soil column apparatus was built to simulate the vertical migration of PHE in the soil. The migration law and penetration effect of PHE in various environmental conditions of soil were investigated by varying the ionic strength (IS), pH, particle size, and type of soil. According to the literature, pH has no discernible effect on the migration of PHE. The migration of PHE was adversely and positively linked with changes in IS and soil particle size, respectively. The influence of soil type was mainly manifested in the difference of organic matter and clay content. In the Yanchang Oilfield (YC) soil with the largest soil particle size and the least clay content, the mobility of PHE was the highest. This study may reveal the migration law of PAHs in soils around typical oilfields, establish a new foundation for PAH migration in the soil, and also provide new ideas for the management and control of petroleum pollution in the soil and groundwater.

Groundwater is an important water source for domestic, industrial, and agricultural use in the western part of Zoucheng, China. Understanding its hydrochemical characteristics and formation mechanisms is important for the sustainable development and utilization of groundwater. In this study, 36 water samples were collected during the wet and dry seasons, respectively, and the hydrochemical components such as K+, Na+, Ca2+, Mg2+, Cl−, SO42−, HCO3−, NO3−, F−, TH, and TDS were analyzed. A graphical method, correlation analysis, and principal component analysis were applied to explore the hydrochemical characteristics and evolution mechanisms of groundwater in the study area. The results show that the orders of the anion and cation concentrations of karst groundwater and pore groundwater are Ca2+  > Na+  > Mg2+  > K+ and HCO3−  > SO42−  > Cl−  > NO3−  > F−, respectively. On the whole, the karst groundwater quality is better than the pore groundwater quality, which in turn is better than the surface water quality. In addition, water quality in the dry season is better than water quality in the wet season for all the three water sources. The hydrochemical types of groundwater are complex and changeable. Compared with dry seasons, HCO3 and SO4 type water increase during the wet seasons, while the Cl type and Mg type water decrease. Na type is significantly more prevalent in pore groundwater than in karst groundwater. The chemical formations of karst groundwater and pore groundwater in the dry and wet seasons are mainly affected by water–rock interactions and human activities.

Modelling soil detachment capacity by rill flow with hydraulic variables is essential to understanding the rill erosion process and developing physically based rill erosion models. A rill flume experiment with non-erodible flume bed and small soil samples was conducted. Seven flow discharges and six steep slope gradients were combined to produce various flow hydraulics. The soil detachment capacity increases with the increase in slope gradient and flow discharge. The critical slope gradients of 21.26 and 26.79% cause the detachment capacity to increase at a slow pace. The soil detachment capacity can be defined by a power function of flow discharges and slopes. The contribution rates of slope gradient and flow discharge to soil detachment capacity are 42 and 54%, respectively. The soil detachment capacity increases with shear stress, stream power and unit stream power; the increase rates of these parameters are greater under gentle slopes than steep slopes. Stream power is the superior hydrodynamic parameter describing soil detachment capacity. The linear model equation of stream power is stable and reliable, which can accurately predict soil detachment capacity by rill flow on steep loessial hillslopes. This study can help to sufficiently clarify the dynamic mechanism of soil detachment and accurately predict soil detachment capacity for steep loessial hillslopes.

The Loess Plateau has been experiencing large‐scale land use and cover changes (LUCCs) over the past 50 years. It is well known about the significant decreasing trend of annual streamflow and sediment load in the catchments in this area. However, how surface run‐off and sediment load behaved in response to LUCC at flood events remained a research question. We investigated 371 flood events from 1963 to 2011 in a typical medium‐sized catchment within the Plateau in order to understand how LUCC affected the surface run‐off generation and sediment load and their behaviours based on the analysis of return periods. The results showed that the mean annual surface run‐off and sediment load from flood events accounted for 49.6% and 91.8% of their mean annual totals. The reduction of surface run‐off and associated sediment yield in floods explained about 85.0% and 89.2% of declines in the total annual streamflow and sediment load, respectively. The occurrences of flood events and peak sediment concentrations greater than 500 kg/m 3 showed a significantly downward trend, yet the counterclockwise loop events still dominated the flood event processes in the catchment. The results suggest that LUCC over the past 50 years resulted in significant changes in the water balance components and associated soil erosion and sediment transportation in the catchment. This was achieved mainly by reducing surface run‐off and sediment yield during floods with return period of less than 5 years. Run‐off–sediment load behaviour during the extreme events with greater than 10‐year return periods has not changed. Outcomes from this study are useful in understanding the eco‐hydrological processes and assisting the sustainable catchment management and land use planning on the Loess Plateau, and the methodologies are general and applicable to similar areas worldwide.

The vegetation restoration project, named the Grain to Green Program, has been operating for more than ten years in the upper reaches of the Beiluo River basin, located in the Loess Plateau of China. It is significant to be able to estimate the success of preventing soil erosion. In this study, the Revised Universal Soil Loss Equation (RUSLE) and the Sediment Distributed Delivery (SEDD) model were used to assess the annual soil loss derived from water erosion. The results showed that the study area suffered from primary land use changes, with increasing grassland and forest and decreasing farmland from 1990 to 2010. Based on that, the average soil erosion modulus decreased from 18,189.72 t/(km2 a) in 1990–7408.93 t/(km2 a) in 2000 and 2857.76 t/(km2 a) in 2010. Compared with 1990, the average soil erosion modulus decreased by 59.0% and 84.3% for 2000 and 2010, respectively. Benefiting from the increased vegetation coverage and improved ecological environment, the soil erosion in this study area clearly declined. This research also found that the distribution of the three years of soil erosion was similarly based on topographic factors. The soil erosion modulus varied with different land use types and decreased in the order of residential area>farmland>grassland>forest. The average soil erosion modulus gradually increased with the increase of the slope gradient, and 76.08% of the total soil erosion was concentrated in the region with a gradient more than 15 degrees. The soil erosion modulus also varied with slope aspects in the order of sunny slope>half-sunny slope>half-shady slope>shady slope. This research provides useful reference for soil and water conservation and utilization in this area and offers a technical basis for using the RUSLE to estimate soil erosion in the Loess Plateau of China.

Accurate assessment of soil loss caused by rainfall is essential for natural and agricultural resources management. Soil erosion directly affects the environment and human sustainability. In this work, the empirical and contemporary model of revised universal soil loss equation (RUSLE) was applied for simulating the soil erosion rate in a karst catchment using remote sensing data and geographical information systems. A scheme of alterative sub-models was adopted to calculate the rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C) and conservation practice (P) factors in the geographic information system (GIS) environment. A map showing the potential of soil erosion rate was produced by the RUSLE and it indicated the severe soil erosion in the study area. Six classes of erosion rate are distinguished from the map: 1) minimal, 2) low, 3) medium, 4) high, 5) very high, and 6) extremely high. The RUSLE gave a mean annual erosion rate of 30.24 Mg ha−1 yr−1 from the 1980s to 2000s. The mean annual erosion rate obtained using RUSLE is consistent with the result of previous research based on in situ measurement from 1980 to 2009. The high performance of the RUSLE model indicates the reliability of the sub-models and possibility of applying the RUSLE on quantitative estimation. The result of the RUSLE model is sensitive to the slope steepness, slope length, vegetation factors and digital elevation model (DEM) resolution. The study suggests that attention should be given to the topographic factors and DEM resolution when applying the RUSLE on quantitative estimation of soil loss.

Under the background of the "Grain for Green" program to control severe soil loss from human activities,the soil erosion and sediment yield were estimated based on the sediment delivery distributed model (SEDD) and the revised universal soil loss equation (RUSLE) in the upper reaches of the Beiluo River on China's Loess Plateau.The model was used to simulated the spatial vatiations of soil erosion intensity and sediment yield in 1990,2000 and 2010.The results show that the average soil erosion modulus were 18 189.72 t/ (km2 · a),7 408.93 t/(km2 · a) and 2 857.76 t/(km2 · a),respectively,and the average annual sediment yield were 14 093.31 t/(km2 · a),5 997.65 t/(km2 · a) and 2 394.37 t/(km2 · a),respectively in 1990,2000 and 2010.Besides,the average soil erosion modulus gradually decreased with the increasing vegetation coverage.The results also showed that both the soil erosion modulus and sediment yield were the highest in the altitude of 1 475～1 575 m.The average soil erosion modulus gradually increased with the increasing slope gradient,and with 75％ of soil erosion was ascribed to the region with slope ＞15°.Moreover,the ranking of the average soil erosion modulus from high to low was:sunny slope＞half-sunny slope＞half-shady slope＞shady slope.This results provide an useful reference for the rational utilization of water and soil resources and offer a technical basis for using RUSLE to estimate the soil erosion on the Loess Plateau of China.

The Loess Plateau of China has been experiencing great land use and land cover changes under the "Grain for Green" program to control severe soil loss from human activities. Over the past 30 years, annual streamflow and sediment delivery have also reduced in most areas of Loess Plateau. In consequence, a physically based model of Soil and Water Assessment Tool (SWAT) has been employed to simulate the responses of surface hydrology to human activities in a typical catchment in the upper reaches of the Beiluo River on China's Loess Plateau. As a result of using various sources of information, including remote sensing, it has been shown that farmland in the catchment decreased by 22.8% in 2000 and 35.0% in 2010 compared to the area in 1990. Meanwhile, forestland increased by 22.6% in 2000 and 119.8% in 2010. The area of shrubland increased by a factor of 3.3 in 2000 and 5.5 in 2010. The vegetation coverage greatly increased in the catchment during this period. Using the SWAT model, it was found that the average ET at the sub-basin scale increased by 7.4 mm in 2000 and 44.0 mm in 2010 as the vegetation coverage improved compared to that in 1990. Meanwhile, the soil water content decreased by 8.1 mm and 14.9 mm and the surface runoff decreased by 6.1 mm and 16.2 mm by these two years. The trends in the evapotranspiration, surface runoff and soil water content were closely associated with alterations in the land use and cover categories at the sub-basin scale. Generally, the higher the increasing rate of forest and grassland, the more that evapotranspiration transferred and the less surface runoff and soil water content that was generated. Spatially, the ET, surface runoff and soil water content showed the same changing gradient with land use and cover from the northern and northwestern to the southern and southeastern areas of the catchment during these periods. The scenarios simulation showed that the streamflow were more sensitive to variability in the precipitation than temperature. These results are expected to be helpful to the sustainable watershed management and provide useful information regarding land use planning and ecosystem construction strategies in the future on the Loess Plateau.

The relationship between soil detachment capacity (Dc) by rill flow and hydraulic parameters (e.g., flow velocity, shear stress, unit stream power, stream power, and unit energy) at low flow rates is investigated to establish an accurate experimental model. Experiments are conducted using a 4 x 0.1 m rill hydraulic flume with a constant artificial roughness on the flume bed. The flow rates range from 0.22 x 10(-3) m(2) s(-1) to 0.67 x 10(-3) m(2) s(-1), and the slope gradients vary from 15.8% to 38.4%. Regression analysis indicates that the Dc by rill flow can be predicted using the linear equations of flow velocity, stream power, unit stream power, and unit energy. Dc by rill flow that is fitted to shear stress can be predicted with a power function equation. Predictions based on flow velocity, unit energy, and stream power are powerful, but those based on shear stress, especially on unit stream power, are relatively poor. The prediction based on flow velocity provides the best estimates of Dc by rill flow because of the simplicity and availability of its measurements. Owing to error in measuring flow velocity at low flow rates, the predictive abilities of Dc by rill flow using all hydraulic parameters are relatively lower in this study compared with the results of previous research. The measuring accuracy of experiments for flow velocity should be improved in future research. (C) 2016 Elsevier B.V. All rights reserved.

细沟侵蚀是黄土坡面重要的侵蚀过程和形式,细沟水流分离是细沟侵蚀的初始阶段,而水流分离能力的大小直接决定水流带走土壤的多少和产生侵蚀的强烈程度.阐明细沟水流分离能力随坡度和流量的变化特征可以深入揭示细沟侵蚀过程机理,为建立黄土坡面细沟侵蚀过程模型奠定重要基础.采用细沟水槽试验方法对黄土坡面细沟水流分离能力变化特征进行研究.结果表明:不同坡度或不同流量下,细沟水流分离能力随流量或坡度的增加而增大,可用线性方程和幂函数方程很好地描述;细沟水流分离能力随流量及坡度变化的因子模型为二元幂函数方程:Dc=61551.72S0.762741-136.248/S2Q1.850263-0.000003/Q,试验条件下流量对细沟水流分离能力的影响大于坡度的影响.

As the limit by natural and economic factors and the lack of historical data,remote sensing images collected in different periods were used to reveal the development process of karst rocky desertification landscape in Mawoshan basin of Weining county,Guizhou Province.GIS and statistics analysis methods were used to analyze a karst rocky desertification distribution over the past 33 years based on remote sensing images(MSS,ETM+ and AVNIR-2) obtained in different periods.The temporal and spatial distribution characteristics of rocky desertification,vegetation degradation features and soil erosion were evaluated based on the analysis and previous research achievements.The results showed that,with expanding trend of the scale,the formation and development of rocky desertification of the Mawoshan watershed was greatly controlled by human activities.Early(1977—2002) and late(2002—2010) periods of rocky desertification presented rapid expanding and slow increase,respectively.The increase of rocky desertification areas of these two periods were 0.42 km2 and 0.12 km2,respectively.From 1980 to 2010,the human controlled erosion modulus reached 3 983.15 t/(km2·a) because of soil erosion resulted from intensive human activities.