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Being a famous hometown of vegetables in China, Shouguang City has a long history of vegetable cultivation and is a comprehensive national commodity base for vegetables and fruits. In recent decades, with the expansion of agricultural production, the use of pesticides is increasing. Although organochlorine pesticides (OCPs) have been banned, there are still some residues in soil, groundwater and other media. The study on the migration of the OCPs in soil and groundwater is of great importance for the maintenance of food security. Using methods of hydrogeological survey, laboratory testing and numerical simulation, the spatial distribution characteristics, sources and pollution degree of OCPs in soil and groundwater were analyzed, and the migration and transformation of OCPs in soil–groundwater was dynamically simulated and predicted. The study showed that there were many kinds of OCPs residual in the soil environment. The hexachlorocyclohexane (HCHs) in the topsoil of the study area were mainly due to the use of lindane, and the main source of dichlorodiphenyltrichloroethane (DDTs) in soil was the use of DDTs in history. The contents of HCHs, DDTs and hexachlorobenzene in the topsoil of the study area were at a low level, while the content of endosulfan metabolite endosulfan sulfate was comparatively higher. In recent years, the content of organochlorine pesticides in soil has generally decreased. The indexes of OCPs in groundwater can meet the Standards for Drinking Water quality of China. It was predicted that the HCH pollutants would mainly be distributed in Gucheng Street, Shangkou Town, and its south area where the concentration exceeds 3 ng/L exceeds that of 240 km2. DDT pollutants would mainly be distributed in the east and north of Shouguang City, where the concentration beyond 0.6 ng/L exceeds that of 200 km2. Endosulfan sulfate pollutants would mainly be distributed in the Gucheng Street Office, Shangkou Town, and its south area where the concentration exceeds 1.5 ng/L will exceed that of 150 km2. Hexachlorobenzene (HCB) pollutants would mainly be distributed in Fengcheng in the west of Shouguang City and Nancha River in the northeast, where the concentration exceeds 0.2 ng/L will exceed that of 200 km2. The study enriched the monitoring data of OCPs in agricultural planting areas and provided reference for source analysis, migration prediction, and pollution prevention of OCPs. [ABSTRACT FROM AUTHOR]

Uranium is an important strategic resource, and its safe and efficient development and utilization are of great significance to ensuring a nation's energy supply and strategic security. Sandstone-type uranium ore is commonly mined by CO2 + O2 in situ leaching, for which understanding the coupling mechanism between the hydrodynamic and chemical fields is key to predicting uranium leaching. This study focused on a coal–uranium ore deposit in China. A convection and dispersion model of the solute transport by in situ leaching was constructed in COMSOL, and a thermodynamic model of CO2 + O2 in situ leaching in sandstone-type uranium ore was constructed in PHREEQC. The two models were coupled to simulate the reactive transport and dynamic leaching processes of uranium by CO2 + O2 in situ leaching. A sensitivity analysis was performed to quantitatively analyze the effects of different model parameters on the uranium leaching efficiency and uranium contamination remediation. The results showed that the coupled model could simulate and predict the reaction and transport of uranium. The sensitivity analysis indicated that the production rate and the injected CO2 and O2 concentrations are the key parameters that control the uranium leaching efficiency, followed by the formation permeability and injection rate. The uranium leaching efficiency does not increase monotonically with the formation permeability and production rate. The results also indicated that natural dilution is insufficient for remediating uranium-contaminated groundwater, but the remediation efficiency can be improved by increasing solution extraction. The results of this study can be used to develop guidelines for the safe and efficient development and utilization of uranium ore while protecting the ecological environment. [ABSTRACT FROM AUTHOR]

The groundwater system is polluted by chlorinated hydrocarbon pollution in eastern Jinan, Shandong province, China, exceeding the limit of pollutants concentration in class III of Groundwater Quality Standards (GQS, GB/T 14848-2017). In order to improve the current situation of chlorinated hydrocarbon pollutants in groundwater system of eastern Jinan, the optimization study of the pollution control is carried out. In this paper, the pollutant of carbon tetrachloride in groundwater system is taken as the main research object, and the solute transport model is established by using GMS numerical simulation software. The simulation results illuminate that with the passage of time, the concentration of carbon tetrachloride decreases, but the acreage of pollution plume in groundwater still has little change, and it is hard to reach the limit standard of 2.0 μg/L in class III of GQS within a short time. Sequentially, on the basis of simulation model, the optimization of pumping and injection wells is conducted in the pollution control field of research region. The results turn out that the layout of 8 pumping and 5 injection wells has the best control effect of carbon tetrachloride in groundwater system, the pollutant concentration reached the limit standard of 2.0 μg/L in only 1187 d, and the acreage of pollution plume in control field reduced from 21.80 km2 to 12.21 km2. In summary, through the optimal pollution control scheme of carbon tetrachloride, the time for pollutant concentration to reach 2.0 μg/L has been reduced, and the acreage of pollution plume has been effectively controlled. [ABSTRACT FROM AUTHOR]

Existing models often face limitations in the understanding and prediction of nitrate nitrogen (NO 3 - -N concentration changes in the southwest karst wetland of China. Additionally, fluorescence spectroscopy was employed to measure dissolved organic matter (DOM) components in the groundwater, providing insights into their variation and influence on NO 3 - -N concentration changes in the southwest karst wetland of China. Additionally, fluorescence spectroscopy was employed to measure dissolved organic matter (DOM) components in the groundwater, providing insights into their variation and influence on NO 3 - -N dynamics. The results demonstrated that coupling the Gaussian curve fitting method with the GMS model accurately simulated NO 3 - -N concentration changes in the study area. The simulation revealed lower NO 3 - -N prediction in groundwater and the role of DOM, offering a reference for groundwater protection in the southwest China karst basin.3 - -N was primarily distributed in the southwestern region and upper Mudong Lake, exhibiting a diffusion trend from west to east. DOM analysis indicated significant autochthonous contributions, particularly microbial metabolic by-products. The total fluorescence intensity and DOM components increased downstream, with the lowest values at the source and the highest values at river confluences. The humification index (HIX) was correlated with NO 3 - -N concentrations, where lower NO 3 - -N levels corresponded to lower HIX values, and higher NO 3 - -N levels corresponded to higher HIX values. In conclusion, this study provides valuable insights into NO 3 - -N prediction in groundwater and the role of DOM, offering a reference for groundwater protection in the southwest China karst basin., Competing Interests: Declarations. Ethics approval: All authors have read, understood, and complied as applicable with the statement on the “Ethical responsibilities of Authors” as found in the Instructions for Authors. Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

In karst groundwater, a common phenomenon in the solute transport process is solute transient storage. The mechanism of transient solute storage between karst conduit and fissures are revealed using a constructed physical model of conduit-fissures. Quantitative tracer tests were conducted under concentrated recharge conditions, and the solute transport processes were simulated using the Dual Region Advection Dispersion model. With enhanced concentrated recharge hydrodynamic conditions, the quantity of transient water storage in fissures tends to increase linearly; and the breakthrough curves transform from single peak to double-peaks. A negative correlation between the average flow velocity in conduit and fissures was confirmed. Breakthrough curve shapes are defined by the difference between solute retention times in conduit and fissures. The overall findings are that solute transient storage induces a tailing effect and the phenomenon of double-peaks in breakthrough curves, significantly controlling solute transport processes in karst groundwater. [ABSTRACT FROM AUTHOR]

The release of metals from a mine tailings pond to groundwater is an important pathway to assess the environmental impact of mining residues and implications for wider environmental risk. We research the impact of manganese ore area in Heling Town, Xiangtan City, Hunan Province, central China. The focus is to assess the migration of manganese (Mn) using the Visual MODFLOW model of groundwater flow and the MT3DMS software platform to model solute transport. The modelling objective focuses on evaluating the migration of the pollution plume of manganese over a 20 year time period. The results show the sustained release and transport of Mn from the tailing pond. The concentration of Mn in the central pollution halo is 1.97 mg/L, and the maximum detectable range is at 2291 m, with the concentration range exceeding the third level of national groundwater standard is 1280 m. The result provides a basis for the development and utilization of the mining area and the pollution prediction and protection of the tailings pond. [ABSTRACT FROM AUTHOR]

• Characterizing the spray characteristics of casting nozzles. • Investigating the metallurgical transport under different nozzle configurations. • Morphological change process of the solidification profiles. • Revealing the formation of W-shape solidification and segregation. • Industrial trials, model validation, and prospects conducted for the dual nozzle. Solidification and segregation in a W-shape pattern are critical quality issues that have not been adequately addressed in the continuous casting of slabs. In this paper, we propose an innovative method for characterizing the spray characteristics of casting nozzles in terms of the heat transfer conditions of the width and narrow faces in the secondary cooling zone. Using a segmented numerical coupling model, we investigate the temperature transfer, solute transport, and solidification profile of liquid steel under three different nozzle configurations. Our results show that the distribution of carbon concentration in the turbulent zone is mainly influenced by the flow trajectory of the liquid steel, and that the initial positive and negative segregation caused by turbulent flow can be inherited into the final solidified slab. In the mushy zone, the distribution characteristics of carbon segregation are consistent with the solidification profiles in the natural convection zone. The solidified end zone does not solidify uniformly, and the morphology of the solidification profiles varies across different nozzle configurations. Specifically, from the eighth of the width direction of the slab to the center, the maximum temperature differences of case 1, case 2 and case 3 are 69.61, 27.60, and 63.83 K, respectively. Moreover, the carbon segregation standard deviations of case 1, case 2, and case 3 are 0.0028, 0.0013, and 0.0032, respectively. The findings suggest that the occurrence of W-shape solidification and segregation is a complex and lengthy process that depends on the metallurgical transport behavior in the secondary cooling zone, rather than the mold process parameters. Finally, we demonstrate that the proposed dual nozzle configuration (case 2) can effectively improve W-shape quality issues and enhance economic benefits, as it has been successfully implemented in the slab continuous casting caster of a state-owned steel enterprise in China. [ABSTRACT FROM AUTHOR]

Groundwater-fed agriculture has caused water table declines and groundwater quality degradation in the North China Plain. Based on sediment sampling in deep vadose zone (with a maximum depth of 11.0 m), groundwater recharge, seepage velocity, solute inventory and transport under four typical irrigated agricultural land-use types (winter wheat and summer maize, WM; pear orchards, PO; outdoor vegetables, VE; and cotton, CO) were investigated in this study. The results reveal that there are many solutes stored in the vadose zone. Nitrate storage per unit depth in the vadose zone is highest under PO (1703 kg/ha), followed by VE (970 kg/ha), WM (736 kg/ha) and CO (727 kg/ha). However, the amount of annual leached nitrate under the four land-use types results in a different order (VE, 404 kg/ha; WM, 108 kg/ha; PO, 23 kg/ha; CO, 13 kg/ha). The estimated average recharge rates are 180 mm/yr for WM, 27 mm/yr for CO, 320 mm/yr for VE and 49 mm/yr for PO. The seepage velocity under VE (2.22 m/yr) exceeds the values under the other three land-use types (WM, 0.85 m/yr; PO, 0.49 m/yr; CO, 0.09 m/yr). The highest seepage velocity under VE caused significant nitrate contamination in groundwater, whereas the other two land-use types (WM and PO) had no direct influence on groundwater quality. The results of this work could be used for groundwater resources management. [ABSTRACT FROM AUTHOR]

Understanding the dynamics and mechanisms of soil water movement and solute transport is essential for accurately estimating recharge rates and evaluating the impacts of agricultural activities on groundwater resources. In a thick vadose zone (0-15 m) under irrigated cropland in the piedmont region of the North China Plain, soil water content, matric potential, and solute concentrations were measured. Based on these data, the dynamics of soil water and solutes were analysed to investigate the mechanisms of soil water and solute transport. The study showed that the 0-15-m vadose zone can be divided into three layers: an infiltration and evaporation layer (0-2 m), an unsteady infiltration layer (2-6 m), and a quasi-steady infiltration layer (6-15 m). The chloride, nitrate, and sulphate concentrations all showed greater variations in the upper soil layer (0-1 m) compared to values in the deep vadose zone (below 2 m). The average concentrations of these three anions in the deep vadose zone varied insignificantly with depth and approached values of 125, 242, and 116 mg/L. The accumulated chloride, sulphate, and nitrate were 2,179 ± 113, 1,760 ± 383, and 4,074 ± 421 kg/ha, respectively. The soil water potential and solute concentrations indicated that uniform flow and preferential flow both occurred in the deep vadose zone, and uniform flow was the dominant mechanism of soil water movement in this study. The piston-like flow velocity of solute transport was 1.14 m per year, and the average value of calculated leached nitrate nitrogen was 107 kg/ha∙year below the root zone. The results can be used to better understand recharge processes and improve groundwater resources management. [ABSTRACT FROM AUTHOR]

Mine soils are often polluted and degraded. The objectives of this study were to assess the effects of soil properties and vegetation on soil solute transport in reclaimed soil at an opencast coal mine site on the Loess Plateau. Four reclaimed areas with different vegetation types were selected for the analysis of physical and chemical properties. The miscible displacement technique was used to obtain the breakthrough curves (BTCs) of NO 3 − ion transport in undisturbed soil columns, which were taken from the soil profiles of the different sites. The chemical properties, such as total N, P, K and SOM, exhibited low contents, and the soil physicochemical properties showed high heterogeneity between different depths and different reclaimed areas. The structural stability index was less than 5%. The initial and entire penetration times were longer in the deeper layers than in the top layer. The BTCs of NO 3 − were fitted well by the deterministic equilibrium convection dispersion equation (CDE) model. Preferential flow and transport were found in the soil columns. The reclaimed soil had poor structure, and planting vegetation improved the physiochemical properties of the soil. The soil solute transport parameters exhibited high heterogeneity between different samples and were significantly correlated with soil bulk density and soil texture, which were highly influenced by vegetation and human activities. In the process of land reclamation, increasing the bulk density and selecting fine-textured soils could reduce the average soil pore water velocity and the dispersivity coefficient, thereby extending the solute penetration time. [ABSTRACT FROM AUTHOR]

The quality of groundwater along rivers is greatly affected by long-term infiltration from surface water, especially reclaimed water-receiving rivers. To predict the degree of influence of contaminated river water on groundwater quality, the spatiotemporal distribution and migration evolution prediction of benzo[a]pyrene (B(a)P) was monitored and simulated by Hydrus-coupled Groundwater Modeling Systems (GMS) model in terms of reclaimed water-receiving Liangshui River. The prediction results indicated the goodness-of-fit of this coupled model, according to the model efficiency (E: 0.78–0.93), the mean absolute error (MAE: 0.01–0.32 m) and the root-mean-square error (RMSE: 0.06–0.35 m). The vertical infiltration rate of B(a)P in the vadose zone was 0.102 m-1, which was only 0.73% that of water. B(a)P penetrated the 16 m depth vadose zone for 63 years owing to the attenuation function of adsorption and biodegradation, with contribution ratios of 78.4% and 19.3%, respectively. However, once B(a)P intersects with groundwater, the migration of B(a)P is dominated by horizontal migration due to downward movement along the groundwater flow direction. The migration rate of B(a)P in groundwater was 6.65 m/y in the horizontal direction, which was 2.42 and 16.22 times higher than the dispersion rate in the longitudinal and vertical directions, respectively. The spatiotemporal distribution indicated that the B(a)P concentration decreased with the crow-fly distance from river with attenuation rate constants of 1.19 × 10−4, 3.05 × 10−4, and 3.67 × 10−3 m−1 over horizontal, longitudinal, and vertical direction, respectively, which were negatively correlated with migration rate. However, the B(a)P content increased over the extension of infiltration time with an accumulation rate of 7.3 × 10−2 d−1. The migration and accumulation of B(a)P induced potential health risks to groundwater-based drinking water safety, which resulted in the groundwater safety utilization range decreasing from 450 m, 283 m, and 20.1 m–583 m, 338 m, and 28.2 m far from the river over the horizontal, longitudinal, and vertical directions, respectively, 20 years later. This study provides a numerical modeling solution for the viable spatiotemporal evolution of B(a)P in groundwater and an effective decision-making tool for the safe utilization of groundwater as drinking water. [Display omitted] • The vertical infiltration rate of B(a)P in unsaturated zone was 0.73% of that in water. • The penetration time of B(a)P in the vadose zone is about 63 years. • The horizontal migration rate of B(a)P in groundwater was higher than longitudinal and vertical. • The carcinogenic risk level increased at a average rate constant of 2.9 × 10−7 d−1. • The groundwater safety utilization range increased far from the river over time. [ABSTRACT FROM AUTHOR]

Groundwater vulnerability is often regarded as the resistance of aquifers to pollutions, which is in fact the groundwater environment vulnerability. Similarly the renewable capacity of groundwater system can be regarded as the indicator for groundwater resources vulnerability. In this paper, the concept of groundwater vulnerability is extended to include both the groundwater environment vulnerability and groundwater resources vulnerability, and the extended overall groundwater vulnerability is assessed by examining the solute transport process from ground surface to the water table (for groundwater environment vulnerability), and evaluating the renewable capacity of groundwater system (for groundwater resources vulnerability). For this case study in Beijing Plain, a 1D-modeling, 2D-mapping model is constructed in HYDRUS to simulate the solute transport process through vadose zone. The transit times and solute concentrations at the water table are selected as the indicators for groundwater environment vulnerability. Meanwhile, a 3D groundwater age model in MODFLOW/MT3DMS is employed to model the age distribution in saturated zone, and the modeled ages are taken as the indicators for groundwater resources vulnerability. These two models are coupled together by exchanging their vertical infiltrations and water table elevations. Overall vulnerability is finally assessed by taking all the indicators into account. The result suggests the overall vulnerability can finely represent the synthetic impact of solute transport characteristics (groundwater environment vulnerability in vadose zone) and groundwater system renewability (groundwater resources vulnerability in saturated zone). The most vulnerable regions of Beijing Plain are mostly in agricultural areas, the medium vulnerable areas mostly appear at pumping sites, and the least vulnerable areas are mostly distributed in recharge regions. [ABSTRACT FROM AUTHOR]

Xikuangshan antimony mine in Lengshuijiang, China, has been developed for many years, and stormwater runoff contains high levels of potentially toxic elements (PTEs). The aims were to find the sources of PTEs by statistical analysis and local spatial distribution of industrial activity and simulate transport process of PTEs in the soil to evaluate pollution extent and health risk. The PTEs in this study were antimony, cadmium, zinc, nickel, lead, and copper. The result showed antimony and a minor portion of zinc were derived from the antimony processing activities, copper derived from agricultural activities, and most of the zinc came from the zinc industry. Nickel, lead, and cadmium came from a mixed source of atmospheric transportation, vehicle transport, and other local industrial activities. Besides, antimony was the most hazardous element in this mining area. In the fourth year, the groundwater in the whole area was uncontaminated by antimony, and there was no non-carcinogenic health risk. Except for the southern area of Lianxi River and the area enclosed by South mine, Zhumushan village, and Tailing Dam, there was a non-carcinogenic risk at year 5.4. These sources of PTEs found in the stormwater runoff are useful for locals to control of PTEs pollution. And the health risk assessment method helps evaluate the risk of PTEs caused by stormwater runoff., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Abstract: Near surface disposal of low- and intermediate-level radioactive wastes (LILW) requires evaluating the field conditions of the candidate site. However, assessment of the site conditions may be challenging due to the limited prior knowledge of some remote sites, and various multi-disciplinary data requirements at any given site. These situations arise in China as in the rest of the industrialized world, particularly since a regional strategy for LILW disposal has been implemented to protect humans and the environment. This paper presents a demonstration of the site assessment process through a case study focusing mainly on the geologic, hydrogeologic and geochemical characteristics of the candidate site. A joint on-site and laboratory investigation, supplemented by numerical modeling, was implemented in this assessment. Results indicate that no fault is present in the site area, although there are some minor joints and fractures, primarily showing a north–south trend. Most of the joints are filled with quartz deposits and would thus function hydraulically as impervious barriers. Investigation of local hydrologic boundaries has shown that the candidate site represents an essentially isolated hydrogeologic unit, and that little or no groundwater flow occurs across its boundaries on the north or east, or across the hilly areas to the south. Groundwater in the site area is recharged by precipitation and discharges primarily by evapo-transpiration and surface flow through a narrow outlet to the west. Groundwater flows slowly from the hilly area to the foot of the hills and discharges mainly into the inner brooks and marshes. Some groundwater circulates in deeper granite in a slower manner. The vadose zone in the site was investigated specially for their significant capability for restraining the transport of radionuclides. Results indicate that the vadose zone is up to 38m in thickness and is made up of alluvial clay soils and very highly weathered granite. The vadose zone has low saturated hydraulic conductivities on the order of 10-5 cm/s and in this respect is well-suited for the disposal of LILW. The saturated formations are primarily made up of silt and moderately-to-slightly weathered granite, which exhibit even lower hydraulic conductivities, on the order of 10−6 cm/s, also favorable for restraining the transport of radionuclides. Chemical analyses indicate that the groundwaters at the site are of the HCO3–Na·Ca and HCO3·SO4–Na·Ca types and are weakly corrosive to concrete and steel. Geochemical analyses indicate that the rock and soil materials (particularly weathered granite) at the site contain very small fractions of colloidal particles and exhibit low Cation Exchange Capacities (CEC), and would therefore have limited capacity for sorption of radionuclides. Groundwater flow and solute transport models of the candidate site have been developed using MODFLOW and MT3DMS, incorporating the data obtained during the assessment program. Calibration was based on the available measured groundwater level fluctuations and tracer concentrations from in situ dispersion tests. The longitudinal dispersion coefficient as determined in calibration is equal to 5.0×10−3 m2/d. Numerical sensitivity analyses indicate that the hydraulic conductivity and the longitudinal dispersion coefficient are the key parameters controlling the transport of radionuclides, while the numerical model is not sensitive to changes in the effective porosity and the specific yield. Preliminary predictions have been performed with the calibrated model both for the natural setting of the site and the graded site in which the valleys of the site are backfilled with low permeable materials. Results indicate that the proposed site grading increases the safety of the site for disposal of LILW by reducing both the groundwater level and the hydraulic gradient and that radionuclide transport would not likely be a problem or cause groundwater contamination. Although there are some problems remaining to be addressed in future work, the conclusion of the assessment is that the conditions at this site are appropriate for LILW disposal. This study provides an example of the procedures necessary in an assessment of site conditions relevant to the safe disposal of LILW. Such an assessment is crucial to the site selection process and to subsequent environmental impact assessment. [Copyright &y& Elsevier]

In the semi-arid loess region of northwestern China, use of stone and gravel as mulch has been an indigenous farming technique for improving crop production for over 300 years. However, systematic studies on the effects of stone covers on soil and water conservation have been rarely conducted, except for a few investigations and documentations on the stone cover effects on erosion and solute transport in such a highly erodible loess region. We experimentally examined the effects of surface stone cover on sediment erosion and solute transport using the water-scouring method on sloping land in a semi-arid region in China, which had been left fallow with alfalfa ( Medicago sativa) for 3 years. All covered stones rested on the soil surface, and none were partly or completely embedded in the soil surface layer. Stone cover percentages were classified into three groups: 0% (no stone cover, the control treatment), 5.1%, and 20.8%. Two sizes of stones, SCA (7.6 × 7.6 cm) and SCB (18.4 × 18.4 cm), were used in the treatment of 5.1% stone cover. A dye method was used to measure flow velocities in the experiments. Each stone treatment had one replicate. The surface cover by stones influenced soil erosion processes, runoff generation, and solute transport. Runoff rate and sediment yield decreased as stone cover percentages increased from zero (no stone cover) to 20.8%. The effect of stone sizes on the runoff was not significant, whereas stone size type SCA caused lower sediment yield than SCB at the same stone cover percentage of 5.1%. Likewise, water flow velocity and the Froude numbers also decreased with increasing stone cover percentage. The Manning roughness increased with increasing stone cover percentage, ranging from 0.0296 to 0.0579 m−1/3 s. But the Reynolds numbers among different stone cover percentages and sizes remained nearly the same with a small variation from 483 to 486. The study implied that stone cover percentage and size have important influences on sediment and solute concentration in runoff. Surface-covering stones reduced the velocity of runoff, increased surface roughness, decreased sediment yield in runoff, and consequently reduced the quantities of solute release from soil surface. [ABSTRACT FROM AUTHOR]

The article discusses a study which examined the effects of coal gangue contents on infiltration, saturated hydraulic conductivity and solute transport parameters of a Chinese Loess plateau soil. Gangue refers to a waste residue from coal mining and coal washing. Findings revealed a decline in infiltration rates and saturated hydraulic connectivity as gangue content increases. The solute transport processes have been described by the simplified convection-dispersion equation and a two-region model.

The article reports on the results of the research conducted to assess the impact of soil erosion, rainfall and runoff on loess plateau in China. Researchers found that rainfall intensity and scouring inflow rate played a major role in runoff formation, solute transport and soil erosion. Moreover, they discovered that solute transport affect rainfall intensity and scouring inflow rate, as well as decrease in bromide concentration in runoff soils.

Abstract: Calcium carbonate concretions are present in the soil of the Loess Plateau as a result of pedogenesis. The presence of these small rock fragments can have a great impact on soil bulk density, structure and water storage properties, as well as on soil water movement and solute transport processes. We studied the effects of different gravimetric rock fragment contents in a soil (R w) (0, 10, 20, 30, 40, 50, and 60%) on infiltration, saturated hydraulic conductivity (K s) and solute transport. Both infiltration rates and the saturated hydraulic conductivity initially decreased with increasing rock fragment content to minimum values for R w =40%, and then increased. The Peck–Watson and Bouwer–Rice equations predicted K s for low rock fragment contents but failed to forecast the observed trends. Cumulative infiltration over time was described well by a power function. Solute transport processes, determined using CaCl2 as a tracer, were accurately described by both the convection–dispersion equation (CDE) and the two-region model (T-R) although the T-R model fitted the experimental data a little better than the CDE, which is possibly more convenient to use. When R w was about 40% solute transport parameters indicated that relatively more advection occurred in this mixture where immobile regions occupied the greatest proportion of the columns. [Copyright &y& Elsevier]

The analysis of solute transport characteristics in soil is of great significance in understanding nutrient cycling and pollutant migration in the Earth's Critical Zone. The objective of this study was to investigate the transport characteristics and the influencing factors of Cl− in soils with different textures (sandy-S and loamy-L), and covered by different vegetation types (arbor-AR, shrub-SH and grass-GR) in the water–wind erosion crisscross region of the northern Loess Plateau of China. Results showed that the initial penetration time (TS: 12–80 min), entire penetration time (TE: 75–480 min), average flow velocity in the pore (V : 0.52–1.98 cm h−1) and the hydrodynamic diffusion coefficient (D : 0.75–2.55 cm2 h−1) of Cl− varied with different soil textures and vegetation types, and at different soil depths. The V and D associated with Cl− transport were highest in the 0–20 cm soil layer and decreased with increasing depth, while the opposite trend was observed for TS and TE. For the 0–1 m soil profile of the same texture but covered by different vegetation types, the average V and D followed the order of S-AR > S-GR > S-SH and L-AR > L-SH > L-GR, while the average TS and TE exhibited the exact opposite order. This behavior is caused by the varying distributions of root biomass under different vegetation types that affect the number of macropores, the connectivity density and the preferential flow paths in the soil. For the 0–1 m soil profiles of different textures covered by the same vegetation type, the average V and D followed the order of S-AR > L-AR; S-SH > L-SH; and S-GR > L-GR, while the average TS and TE showed the opposite trend. This is because the pore size and distribution in soil are significantly affected by soil mechanical composition. There are significant correlations between soil properties (e.g., bulk density, number of macropores, pore connectivity density, saturated hydraulic conductivity, soil organic carbon content and particle composition) and the transport parameters (e.g., V , TS, and TE). The pedotransfer functions using readily available soil properties can adequately predict V of Cl− transport under different conditions of soil texture and vegetation type. These results provide guidance for the rational configuration of artificial vegetation in different textural soils with respect to reduce nutrient loss and improve ecosystem functions in the northern Loess Plateau of China. • We studied Cl− transport under different soil textures and vegetation types. • Both soil texture and vegetation type greatly affect the behavior of Cl− transport. • Pedotransfer functions can adequately simulate and predict Cl− transport parameter. [ABSTRACT FROM AUTHOR]

Preferential flow has an important role as it strongly influences solute transport in forest soil. The quick passage of water and solutes through preferential flow paths without soil absorption results in considerable water loss and groundwater pollution. However, preferential flow and solute transport under different infiltration volumes in southwestern China remain unclear. Three plots, named P20, P40 and P60, were subjected to precipitation amounts of 20, 40 and 60 mm, respectively, to investigate preferential flow and solute transport characteristics via field multiple-tracer experiments. Stained soils were collected to measure Br− and NO3− concentrations. This study demonstrated that precipitation could promote dye tracer infiltration into deep soils. The dye tracer reached the maximum depth of 40 cm in P60. Dye coverage generally reduced with greater depth, and sharp reductions were observed at the boundary of matrix flow and preferential flow. Dye coverage peaked at the soil depth of 15 cm in P40. This result demonstrated that lateral infiltration was enhanced. The long and narrow dye coverage pattern observed in P60 indicated the occurrence of macropore flow. Br− and NO3− were found at each soil depth where preferential flow had moved. Increasing precipitation amounts increased Br− and NO3− concentration and promoted solute movement into deep soil layers. Solute concentration peaked at near the end of the preferential flow path and when preferential flow underwent lateral movement. These results indicated that the infiltration volume and transport capacity of preferential flow had important effects on the distribution of Br− and NO3− concentrations. The results of this study could help expand our understanding of the effects of preferential flow on solute transport and provide some suggestions for protection forest management in southwestern China. [ABSTRACT FROM AUTHOR]

Groundwater and artificial reservoirs are in a continuous dynamic interaction that can affect not only water quantity but the quality. In this paper, taking the DR (Doumen Reservoir) as an example, the level dynamic changes between the DRTS (Doumen Reservoir Test Section) and groundwater were discussed, and the water quality used by SFE (single-factor evaluation) and WQI (water quality index) method were analyzed. A coupling model is presented to quantify the leakage impact range and groundwater budget and regionalize the impact of surface water on regional groundwater quality. The results show that the level dynamics of the reservoir and groundwater are highly consistent, with a cross-correlation coefficient of 0.85 and a lag time of about 7 days. The reservoir recharges the groundwater with an increase-decrease-stationary wave dynamic potential. After 3 years of operation of the DR, the groundwater still is recharged, the groundwater level will rise obviously, with a maximum of 8.5 m. The amount of surface water recharged is always 0. NH3-N, and COD will have varying degrees of impact, both of which are mainly the pollution halo around North Lake. The results can provide support for water resources management and environmental protection of urban plain reservoirs. [ABSTRACT FROM AUTHOR]

• A mass balance model for agricultural salt accumulation and leaching is developed. • The model has looser restrictions on the discretization of space and time. • The calculated soil salt are about 20% better when considering the immobile region. Soil salinization has become a widespread problem that seriously affects the sustainable development of agriculture. To deal with the salt accumulation and leaching problems in practical agricultural systems, a new soil water and solute transport model adopting the mass balance scheme is developed in this study. The soil water movement module is based on a previously published soil water mass balance model, named as UBMOD. The mobile-immobile assumption has been adopted to develop the soil solute transport module, which can describe the obvious anomalous transport phenomenon in practice. The advection, chemical reactions of solute, solute transfer between the mobile and immobile regions, and dispersion in the mobile region are considered in the solute transport module, while only chemical reactions and solute transfer between the mobile and immobile regions are considered in the immobile region. Three cases were designed to evaluate the performance of the model by comparing the simulation results with those obtained by experimental results, HYDRUS-1D, and practical observations. The results demonstrate that the developed model can solve the homogeneous and heterogeneous soil water movement and solute transport effectively, and it has looser restrictions on the discretization of space and time than the numerical solution of Richards' equation and can keep the mass balance well, which make it more suitable for practical conditions. Moreover, the real-world application of salt accumulation and leaching problems in Hetao Irrigation District, Inner Mongolia, China shows that the RMSE of the simulated soil salt content with the immobile present region is about 20% better than that when ignoring the immobile present region. Therefore, it is necessary to take the significant anomalous transport into account when studying the salt accumulation and leaching processes in practical agricultural systems. [ABSTRACT FROM AUTHOR]

Solute storage and release in groundwater are key processes in solute transport for groundwater remediation and protection. In karst areas where concentrated recharge conditions exist, pollution incidents can easily occur in springs that are hydraulically connected to densely inhabited karst depressions. The intrinsic heterogeneity common in karst media makes modeling solute transport very difficult with great uncertainty. Meanwhile, it is noteworthy that solute storage and release within subsurface conduits and fissures exhibit strong controlling function on pollutant attenuation during underground floods. Consequently, in this paper, we identified and estimated the solute storage and release processes in karst water systems under concentrated recharge conditions. The methodology uses the advection-dispersion method and field tracer tests to characterize solute transport in different flow paths. Two solute transport pathways were established (i.e., linear pathway (direct transport through karst conduits) and dynamic pathway (flow through fissures)). Advection-dispersion equations were used to fit the breakthrough curves in conduit flow, while the volume of solute storage in fissures were calculated by segmenting the best fitting curves from the total breakthrough curves. The results show that, greater recharge flow or stronger dynamic conditions leads to lower solute storage rate, with the storage rate values less than 10% at high water level conditions. In addition, longer residence time was recorded for solute exchange between conduits and fissures at the low water level condition, thereby contributing to a higher solute storage rate of 26% in the dynamic pathway., Competing Interests: The authors declare no conflicts of interest.

In karst areas, rock dissolution often results in the development of underground networks, which act as subterranean pathways for rapid water and nutrient (and possibly soil) loss during precipitation events. Loss of soluble nutrients degrades surface soils and decreases net primary productivity, so it is important to establish flow pathways and quantify nutrient loss during rainfall events of different magnitudes. We conducted a simulated rainfall experiment in karst and nonkarst areas to compare the concentration of nutrients in surface and subsurface flow water and effects on soil alkalinity in three lithologic soil formations under five different rainfall intensity treatments. Compared with the nonkarst area, the runoff in subsurface flows and the proportion of nutrient loss in the subsurface flow are larger in the karst area and less affected by rain intensity. The maximum loss loads of calcium (Ca 2+ ) and magnesium (Mg 2+ ) ions were 32.9 and 19.8 kg ha -1 , respectively. With the estimate of base cation loss loads in the China southern karst area under the rainfall intensity of 45 mm h -1 , more than 80% of the base cation loss load occurred in the limestone karst area. Although the alkalinity leaching value in nonkarst was similar to that in the karst area under simulated rainfall conditions, its impact on the ecological environment was quite different.