Study of experimental and numerical simulation on the influence of gravel on the interflow of slope land.

The formation of interflow is of great significance for the stability of mountain slopes and soil erosion. Hillsides are often covered with a certain amount of gravel, and research on interflow of slope land with different gravel ratios needs to be carried out. This article is based on indoor experiments and numerical models to study the formation law of interflow in hillside soil under different gravel coverage ratios. It was found that the interflow in the soil rapidly increased in the early stage and began to decrease after briefly reaching equilibrium. The formation of interflow is a complex process that is related to slope, soil characteristics, and rainfall intensity, but the correlation is not high when viewed separately. The lattice Boltzmann model can effectively simulate such problems and achieve high simulation accuracy. The [Formula: see text] of the simulated data and measured data ranged from 0.5217 to 0.7403, and [Formula: see text] of the simulated data and measured data ranged from 0.4051 to 0.5711.

Effects of sewage sludge application methods on the transport of heavy metals with runoff and their mechanisms.

Woodland utilization is a promising disposal method for sewage sludge (SS). However, the potential risk of heavy metals (HMs) transport with runoff must be considered. Among the various factors influencing HMs loss, SS application methods (Holing application, HA; Broadcasting and mixing application, BM; Broadcasting application, BA) are likely to cause significant effects by altering soil erosion and soil aggregates. This study aimed to determine how SS application methods affect HMs loss, soil aggregates erosion, and how they are related. Accordingly, the losses of HMs in surface runoff, interflow, and sediment were quantified during six simulated rainfalls. The results demonstrated that all methods reduced surface runoff, but BA was the most effective. Additionally, BA significantly reduced the total sediment yield and the total proportion of the <0.05 mm fraction aggregates. Moreover, BA had the smallest cumulative losses of Pb and Cd through surface runoff and Cu, Pb, and Cd through sediment. Sediment was the most important pathway for HMs loss, through which over 76.56 % of HMs were lost. In BA, the <0.05 mm fraction aggregates had the lowest HMs load, whereas in other treatments had the highest (54.33 %-80.33 %). The potential ecological risk coefficient of Cd was beyond "moderate" in all the pathways of BM and "high" in the interflow of each SS treatment. Nonetheless, when the multi-elements were evaluated collectively, the potential ecological risk index for each SS treatment was categorized as "low". Overall, BA not only reduced soil erosion but also posed no risk of HMs pollution. It should be noted that the loss of Cd in the interflow had a great impact, while the <0.05 mm fraction aggregates played a significant role in the HMs load. Thus, the current study not only provides an effective approach for the environmentally safe disposal of SS but also proposes a scientific method for the application of SS in woodlands.

Nitrogen removal from low COD/N interflow using a hybrid activated sludge membrane-aerated biofilm reactor (H-MABR).

A hybrid activated sludge membrane-aerated biofilm reactor based on a two-stage simultaneous nitrification-denitrification (SND) process was built, and its utility for treating interflow with low chemical oxygen demand (COD)/total nitrogen (TN) (COD/N) was explored. The operating performance, functional microbial communities, and functional genes for nitrogen metabolism were evaluated at low COD/N (4-1.3). The reactor could achieve stable operation at COD/N = 4-1.5, and the removal efficiency of COD, TN, and ammonia nitrogen was stable at 90.30 ± 2.36 %, 85.69 ± 2.22 %, and 89.52 ± 6.06 %, respectively. The SND rates were 70.89 % and 50.75 % when influent COD/N was 2.0 and 1.7, respectively, indicating that SND makes an important contribution to nitrogen removal under these two COD/N conditions. Microbial analysis revealed that the sampling sites with a high abundance of denitrification genes in the outer ring experienced aerobic conditions, inferring that aerobic denitrification also plays an important role in denitrification.

Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May-October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%-90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

Pollution in the interflow from a simple landfill in a mountainous and hilly area in Southwest China.

Simple landfills lack pollution prevention measures and therefore continuously release pollutants into the surrounding environment. There are a large number of simple landfills in the mountainous and hilly areas in China, and the interflow accounts for a large proportion of runoff. However, the pollution in the interflow stemming from the simple landfill has not been extensively studied. Here, the pollution of the interflow caused by the simple landfill near the Yunxi Town Landfill in the mountainous and hilly region in Southwest China was studied. The composition and pollution release potential of aged refuse in the landfill were determined, and the water quality of interflow around the landfill was monitored for five months. Seasonal changes in water quality of the interflow were observed, and the concentration of pollutants in the interflow around the simple landfill greatly exceeded the water quality standard for the local water function zoning throughout the sampling period. Specifically, the chemical oxygen demand concentrations of the interflow were 247.90 ± 81.57 mg/L, and more than 50 types of refractory organics were detected, with as many as 10 types of polycyclic aromatic hydrocarbons and Environmental Protection Agency priority pollutants. The total nitrogen concentration of the interflow was 132.45 ± 108.68 mg/L; organic nitrogen (53.27%) was the main component, followed by nitrate nitrogen (32.28%) and nitrous nitrogen and ammonia nitrogen (14.45%). The results highlight the need for the remediation of interflow around simple landfills in mountainous and hilly areas. Generally, the basic data could be used to aid the development of remediation technology.

[Characteristics of Dissolved Organic Carbon Loss in Purple Soil Sloping Fields with Different Fertilization Treatments].

The characteristics of dissolved organic carbon loss with different fertilization treatments were examined to derive the best nutrient management method for sloping farmland in the Three Gorges Reservoir area where maintaining the soil carbon balance and reducing environmental pollution caused by carbon loss is crucial. Experimental runoff plots were set up at the Experimental Station for Soil and Water Conservation and Environmental Research in the Three Gorges Reservoir Region, Chinese Academy of Sciences, involving the following five treatments:No fertilization (CK), conventional fertilization (conventional), optimum fertilization (optimum), biochar combined with 85% optimum fertilizer (biochar), and straw combined with 85% optimum fertilizer (straw). The effects of the five treatments on runoff flux, sediment yield, and soil organic carbon flux were monitored and evaluated. Results show that:①Subsurface flow accounted for 52.84%-92.23% of the runoff (both surface and subsurface flow) and the loss flux of dissolved organic carbon (DOC) in the subsurface accounted for 43.64%-87.35% of the total loss flux. Thus, in this sloping farmland, subsurface flow was the main pathway of runoff and dominated dissolved organic carbon transport. ②Compared with the optimum treatment, straw treatment reduced the surface runoff flux, sediment yield, surface loss flux of DOC, and loss flux of organic carbon in the sediment by 30.39%, 39.41%, 28.71%, and 23.97%, respectively, but increased the subsurface runoff flux and loss flux of DOC. Compared with the optimum treatment, the biochar treatment significantly increased the surface and subsurface runoff flux, sediment yield, loss flux of DOC in the surface and subsurface, and the loss flux of organic carbon in the sediment. ③The loss flux of DOC accounted for 99.31%-99.94% of the loss flux of soil organic carbon, and DOC was the major species of organic carbon in the organic carbon loss in this type of sloping farmland. The loss flux of DOC under the different fertilization treatments was ranked biochar > optimum > straw > conventional > CK. ④Compared to the optimum treatment, the straw treatment and biochar treatment increased the soil organic carbon (SOC) content by 95.79% and 32.16%, respectively. Based on these results, straw combined with 85% of optimum fertilizer is the best nutrient management method for this sloping farmland as it can reduce surface runoff flux, sediment yield, and the loss flux of soil organic carbon while increasing the soil organic carbon content.

[Response of Nitrogen Loss Flux in Purple Soil Sloping Field to Reduced Fertilizer and Combining Straw].

The purple soil sloping field is considered as the main source of sediment and non-point source pollution in the Three Gorges Reservoir area. To prevent and control the non-point source pollution, it is indispensable to explore the characteristics of nitrogen loss in the overland flow and interflow of purple soil sloping field in Three Gorges Reservoir area. The purple soil sloping runoff plots, located in the Shibaozhai Experimental Station of Chengdu Institute of Chinese Academy of Sciences in Zhongxian County, Chongqing, were studied. The experiment included no fertilization treatment (CK), traditional fertilization treatment (T1), amended fertilization treatment (T2), and reduced fertilizer with straw treatment (T3). According to the data of volume of the interflow and runoff and the leach concentration and flux of nitrogen forms under rapeseed-maize rotation system, the response of nitrogen leaching flux to reduce fertilizer with straw application can be definite in purple soil sloping plots. The results show that the ratio of interflow to total runoff is 60.14%-88.56%, and the flux of nitrogen leaching in the interflow accounts for 72.88%-92.35% of total nitrogen loss flux. Ammonium was mainly leached by the overland flow. In addition, nitrate was mainly leached by the interflow and was the main form of nitrogen leaching. The fluxes of ammonium and nitrate under different treatments followed the order T1 > T2 > T3 > CK. The total nitrogen flux of T3 was 20.07 kg·(hm2·a)-1, which was 43.59% and 39.55% lower than that of T1 and T2, respectively. The reduced fertilizer with straw application significantly decreased the leaching flux of ammonium, nitrate, and total nitrogen, and weakened the effect on runoff nitrogen leaching in the purple soil sloping plots.

Arbuscular mycorrhizal fungi reduce cadmium leaching from polluted soils under simulated heavy rainfall.

Cadmium (Cd)-polluted soils were collected from wasteland, farmland, and slopeland surrounding a lead-zinc mine in Yunnan Province, Southwest China. Maize plants (the host) were inoculated with arbuscular mycorrhizal fungi (AMF) in a dual-compartment cultivation system that included mycorrhizal and hyphal compartments as part of an AMF inoculation treatment and root and soil compartments as part of a the non-inoculation treatment. The effects of AMF on maize biomass and Cd uptake, soil aggregate composition, and Cd concentration in the interflow within two soil layers (0-20 and 20-40 cm) as well as the Cd leaching from these three Cd-polluted soils under simulated heavy rainfall (40 and 80 mm/h) were investigated. The results demonstrated that AMF led to increased maize biomass and Cd uptake. There were greater contents of total glomalin-related soil protein (T-GRSP) and >2.0 mm aggregates and lower Cd concentrations in the interflow and lower dissolved Cd leaching in the mycorrhizal and hyphal compartments than in the soil compartment. A two-way analysis of variance revealed that AMF significantly increased the contents of T-GRSP and >2.0 mm aggregates and reduced both Cd concentrations in the interflow and dissolved Cd leaching. Moreover, AMF interacted extensively with the roots and affected soil aggregate composition and Cd concentrations in the interflow. Under 40 mm/h of rainfall, the contents of T-GRSP and >2.0 mm aggregates were significantly negatively correlated with both Cd concentrations in the interflow and dissolved Cd leaching. In addition, the Cd concentrations in the interflow were significantly positively correlated with the amount of dissolved Cd leaching. Therefore, both AMF-reduced Cd concentrations in the interflow and Cd leaching from Cd-polluted soils were closely related to increased T-GRSP contents and macroaggregate proportion in the soils.

Effects of rainfall intensity and slope gradient on runoff and sediment yield from hillslopes with weathered granite.

The method of indoor artificial rainfall simulations was applied to compare the characteristics of runoff and sediment yield under different slope gradients (5°, 8°, 15°, and 25°) and rainfall intensities (30, 60, 90, 120, and 150 mm/h) for two kinds of different hillslopes with weathered granite and with exposed soils respectively from the laterite layer (L-soil) and sand layer (S-soil). The results show that the distribution of runoff yield significantly varied with soil types as the surface flow was predominant for L-soil while interflow was the main runoff form for S-soil. Both surface flow and sediment yield of L-soil was more than that of S-soil, and the changing trends for L-soil were more regular. The relationships between surface flow, sediment yield, and rainfall intensity can be expressed by power functions (R2 > 0.68). Interflow was positively related to slope gradient and displayed a single peak curve with the prolongation of runoff time. For S-soil, the surface flow increased with increasing slope gradient under light rainfall intensities but showed a decreasing trend under heavy rainfall intensities. Surface flow for L-soil showed a decreasing trend with increasing slope gradient under all rainfall intensities. The combined effects of slope gradient and rainfall intensity on runoff and sediment yield could be accurately described by linear correlation equations (R2 > 0.59). The impact of rainfall intensity on surface flow and sediment yield was much greater than that of slope gradient. Slope gradient presented a more significant effect on interflow. The eroded sediment consisted of a relatively higher content of clay, silt, and fine sand, which was approximately 1.26 times greater than the original soils. There was a grading limit of particle size (0.25 mm) for sediment transport. These results not only demonstrate the effects of rainfall intensity and slope gradient on sloping runoff and sediment yield but also provide valuable information for loss prediction and conservation of soil and water.

[Characteristics of Phosphorus Output Through Runoff on a Red Soil Slope Under Natural Rainfall Conditions].

The development of agriculture in the red soil sloping uplands has been increasingly restricted by low water availability, high temperatures, and low fertilizer use efficiency. Subsurface flow has a significant influence on runoff generation, nutrient loss, and soil erosion. The rainfall-runoff process makes it easy for nutrients on the sloping land to enter water bodies through subsurface flow mainly in the liquid phase, which may lead to environmental problems such as eutrophication and groundwater pollution. Phosphorus as one of the common nutrients causing eutrophication is immobile in the soil because it is easily absorbed and fixed by soil particles. Thus, the principal pathway of phosphorus release from the soil is the surface flow. In some regions, sufficient and concentrated rainfall results in the surface-subsurface flow that enhances phosphorus migration. Recently, researchers have studied the migration patterns of red soil phosphorus through surface flow and the impact factors arising from these migrations, as well as the generation of subsurface flow and its influence on phosphorus outputs. However, there are relatively few investigations that have comprehensively considered the influence of both surface flow and subsurface flow on the migration of red soil phosphorus. In order to investigate the characteristics of phosphorus loss through runoff under natural rainfall, a large-scale field lysimeter experiment was conducted with three treatments i.e., grass cover (GC), litter mulch (LM), and bare land (BL) on a red soil slope land in southeast China. Phosphorus loss through surface flow, interflow at different soil layers (30 cm and 60 cm), and groundwater flow (at 105 cm depth) was observed under each natural precipitation event over a one-year period. The results showed that:① The concentrations of total P (TP) and dissoluble P (DP) in surface flow were slightly higher than those in interflow and groundwater flow; the concentrations of TP and DP showed a gradual downward trend with the increase in soil depth. The total amount of TP runoff loss was ordered as BL (1.61 kg·hm-2) > LM (1.33 kg·hm-2) > GC(0.82 kg·hm-2). ② Surface flow, interflow, and groundwater contributed to 57%, 6%, and 37%, respectively, of the phosphorus runoff loss on BL plot; surface runoff was the main pathway of phosphorus loss. Groundwater flow was the crucial route of phosphorus runoff loss once a vegetation cover was in place; groundwater flow contributed to more than 71% of the phosphorus runoff loss while the surface flow contributed less than 14%. ③ Particulate phosphorus was the primary pattern of phosphorus transport which accounted for 64%-97% of the total amount of phosphorus runoff loss. The effect of phosphorus loss through groundwater flow cannot be neglected on the red soil slope land. The loss load of phosphorus through runoff can be controlled by grass cover and litter mulch treatments, whereas the concentrations of phosphorus in runoff do not significantly reduce.

[Hydrological characteristics of calcareous soil with contrasting architecture on dolomite slope of Northwest Guangxi]. / æ¡‚è¥¿åŒ—ç™½äº‘å²©å¡åœ°å ¸åž‹åœŸä½“æž„åž‹çŸ³ç°åœŸæ°´æ–‡ç‰¹å¾.

The traditional hydrology method, stable hydrogen and oxygen isotope technology, and rainfall simulation method were combined to investigate the hydrological function of small experimental plots (2 m×1.2 m) of contrasting architecture in Northwest Guangxi dolomite area. There were four typical catenary soils along the dolomite peak-cluster slope, which were the whole-sand, up-loam and down-sand, the whole loam, up-clay and down-sand soil types, respectively. All the experimental plots generated little amounts of overland runoff and had a high surface infiltration rate, ranging from 41 to 48 mm·h-1, and the interflow and deep percolation were the dominant hydrological progress. The interflow was classified into interflow in soil clay A and C according to soil genetic layers. For interflow in soil clay A, matrix flow was generated from the whole-sand, up-loam and down-sand, up-clay and down-sand soil types, but preferential flow dominated in the whole-loam soil type. As for interflow in soil clay C, preferential flow dominated in the whole-loam, up-clay and down-sand, up-loam and down-sand soil types. The soils were shallow yet continuously distributed along the dolomite slope. The difference of hydrological characteristics in soil types with different architectures mainly existed in the runoff generation progress of each interface underground. It proved that the a 3-D perspective was needed to study the soil hydrological functions on dolomite slope of Northwest Guangxi, and a new way paying more attention on underground hydrological progress should be explored to fully reveal the near-surface hydrological processes on karst slope.

[Reduction Effect of Reduced Phosphorus Fertilizer and Combining Organic Fertilizers on Phosphorus Loss of Purple Soil Sloping Field].

In order to better understand the effect of reduced phosphorus fertilizer and combining organic fertilizers on phosphorus loss of purple soil sloping field, three rainfall-runoff events were monitored using field runoff observation method in the purple soil sloping field in 2014. There were six treatments in this research, including optimized fertilization (P), optimized fertilization+pig manure application (MP), optimized fertilization+straw return (SP), optimized fertilization which was reduced by 20%+pig manure application (MDP), optimized fertilization which was reduced by 20%+straw return (SDP), without phosphate (P0). The results indicated that the interflow was the main pathway of runoff for purple soil sloping field. The average contents of total phosphorus (TP) and the phosphorus loss load of overland flow were all much higher than those of the interflow. The overland flow was the main pathway of the phosphorus loss load for purple soil sloping field. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of purple soil sloping field. Compared with the treatment P, the average content of total phosphorus on SDP was reduced by 57% and that on MDP was reduced by 48% in the storm rainfall. Combining straw was better than pig manure. The average contents of the phosphorus loss load of typical rainfall changed between 0.01 and 0.26 kg·hm-2. In different fertilization treatments, the average contents of the phosphorus loss load followed the order of P > MP > SP > MDP > SDP > P0. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of overland flow, but increased soil phosphorus leaching for purple soil sloping field.